The nature of refractive surgery is that of rapid change and development. Mainstays such as laser in situ keratomileusis (LASIK) and photorefractive keratectomy (PRK) are now being augmented with algorithms incorporating advanced wavefront measurements and topography-guided treatments. Data regarding comparative outcomes also help refine our understanding of corneal refractive surgery, corneal collagen cross-linking (CXL) has expanded indications for treatment, and new research adds to our understanding of common refractive surgery complications such as corneal ectasia, deep lamellar keratitis, and ocular surface disease. Finally, new frontiers are also being forged, with reports on new procedures, such as the small-incision lenticule extraction (SMILE), corneal presbyopic treatments and inlays, femtosecond laser intrastromal astigmatic keratotomy, and phakic intraocular lenses (IOLs).
In the field of refractive surgery, detection of keratoconus and subclinical keratoconus (forme fruste keratoconus [FFKC]) is crucial. Subclinical keratoconus is still considered the most important risk factor for developing post-LASIK ectasia. Recent studies evaluated the role of keratoconus or subclinical keratoconus detection using (1) Placido-based anterior corneal topography, (2) Scheimpflug camera combined with Placido corneal topography, (3) corneal biomechanics, (4) wavefront technology, and (5) optical coherence tomography (OCT).
Placido-Based Anterior Corneal Topography
Placido-based anterior corneal topography is an affordable and valuable tool for screening for keratoconus. A variety of indices, such as the Rabinowitz and Rabinowitz-McDonnell indices (K, I-S, KISA%) and the Klyce/Maeda indices (KPI, KCI%), have been proposed. These keratoconus indices derived from the Placido-based systems are based on the corneal curvature data converted from the image of the rings in the keratographic picture by a variety of sophisticated algorithms.
Using the CSO topography system (CSO, Firenze, Italy), Ramos-López and colleagues1 introduced a set of new irregularity indices, which directly use digitized Placido images and bypass the conversion to corneal curvature. The advantages of these corneal indices over the standard approaches are (1) their independence from the proprietary algorithms of conversion of the raw ring images into curvature and corneal power, and (2) these indices can be easily adapted to any particular commercially available Placido disk topographer.
In a group of normal (50 eyes), keratoconic (50 eyes), and keratoconus suspect (50 eyes), Ramos-López et al2 assessed the performance of the new topographic indices computed directly from the digitized images of the Placido rings. They reported that significant differences were found on the values of the indices among groups (all P < 0.05), and the results confirmed the capability of the indices to discriminate between the 3 groups. They concluded that the analysis of the digitized images of the Placido disks projected on the cornea is a valid and effective tool for the keratoconus and subclinical keratoconus screening that can be used in the screening process. At this stage of their work, they recommend them as a complementary screening tool designed to alert the clinician especially in the borderline cases of irregular corneas for which a more exhaustive examination is recommended.
Scheimpflug Camera Combined With Placido Corneal Topography
Devices based on Scheimpflug technology provide data from both anterior and posterior corneal surfaces. Arbelaez and colleagues3 investigated the use of a support vector machine, a machine learning technique, for keratoconus and subclinical keratoconus detection by topographic and tomographic data provided by a Scheimpflug camera combined with Placido disc corneal topography (Sirius; CSO, Florence, Italy).
This study included 877 eyes with keratoconus, 426 eyes with subclinical keratoconus, 940 eyes with a history of corneal surgery (defined as abnormal), and 1259 healthy control eyes. The accuracy of the classifier was excellent both with and without the data generated from the posterior corneal surface and corneal thickness, with the number of true predictions of greater than 95% and 93%, respectively, in all groups. In contrast, the sensitivity improved markedly when posterior corneal surface and thickness parameters were included, especially in the diagnosis of subclinical keratoconus. Using the data from both anterior and posterior corneal surfaces and pachymetry allowed the support vector machine to increase its sensitivity from 89.3% to 96.0% in abnormal eyes, 92.8% to 95.0% in eyes with keratoconus, 75.2% to 92.0% in eyes with subclinical keratoconus, and 93.1% to 97.2% in normal eyes.
The Ocular Response Analyzer (ORA; Reichert Ophthalmic Instruments, Depew, NY) is a device for in vivo evaluation of corneal biomechanical properties. Lower biomechanical parameters have been reported in patients with keratoconus.
Using the ORA, Kara and colleagues4 compared the biomechanical properties of the cornea between topographically normal relatives of patients with keratoconus and age-matched controls. In 30 healthy individuals (control group) and 30 topographically normal relatives of patients with keratoconus, they found that the corneal hysteresis and corneal resistance factor values were significantly lower in the relatives of patients with keratoconus than in the controls.
Wolffsohn et al5 investigated the air pressure–corneal deformation relationship of 37 patients with keratoconus and 37 age- and sex-matched control subjects with healthy corneas using the ORA. Four repeated air pressure–corneal deformation profiles were averaged, and 42 separate parameters relating to each element of the profiles were extracted. Most of the biomechanical characteristics of keratoconic eyes were significantly different from normal eyes (P < 0.001), especially during the initial corneal applanation. Characteristics of the air pressure–corneal deformation profile are more affected by keratoconus than the traditionally extracted corneal hysteresis and corneal resistance factor. Using the corneal biomechanical data to assist in the detection of keratoconus, 5% higher sensitivity was achieved compared with keratometry combined with pachymetry obtained from the Orbscan II (Bausch & Lomb, Rochester, NY).
Studies have shown that wavefront technology may also be a useful adjunct to topography for diagnosing keratoconus. Saad and Gatinel6 investigated the application of total and corneal wavefront high-order aberrations for the detection of FFKC. Using the NIDEK Corneal Navigator System automated corneal classification software in the OPD Scan (NIDEK Co Ltd, Gamagori, Japan), 220 eyes were separated into 3 groups: normal (n = 123), FFKC (normal topography with contralateral keratoconus) (n = 34), and keratoconus (n = 63). Anterior corneal and ocular aberrations were obtained with the OPD Scan. Corneal and ocular tilt, vertical coma, and trefoil were significantly different in the FFKC as compared with the normal group. The discriminant functions between the FFKC and the normal group and between the keratoconus and the normal group reached an area under the receiver operating characteristic curve of 0.98 and 0.96, respectively.
Optical Coherence Tomography
Optical coherence tomography is a noncontact technique that is based on the principles of low-coherence interferometry. The high axial resolution of OCT allows excellent delineation of corneal surfaces.
Li and colleagues7 mapped the corneal epithelial thickness with Fourier-domain OCT (RTVue; Optovue, Inc, Fremont, Calif) and developed epithelial thickness–based variables for keratoconus detection. Compared with normal eyes, keratoconic eyes had significantly lower inferior (P = 0.03) and minimum (P < 0.0001) corneal epithelial thickness, greater S-I (P < 0.013), more negative min-max (P < 0.0001), greater map SD (P < 0.0001), and larger pattern SD (PSD) (P < 0.0001). Among all epithelial thickness–based variables investigated, PSD provided the best diagnostic power. A PSD cutoff value of 0.057 resulted in 100% specificity and 100% sensitivity. Keratoconus was characterized by apical epithelial thinning. The resulting deviation from the normal epithelial pattern may be detected with very high accuracy using the PSD variable.
EXCIMER LASER CORNEAL ABLATION
Advances in LASIK and PRK continue to dominate the refractive surgery literature. There has been much interest in several areas: (1) surface ablation versus LASIK, (2) integration of CXL, (3) topography-guided treatments, (4) wavefront analysis and treatment, (5) use of femtosecond lasers for flap creation, and (6) enhanced understanding and prevention of complications.
Surface Ablation Versus LASIK
Shortt and Allan8 reviewed 13 randomized controlled trials between 1997 and 2012 comparing the effectiveness and safety of LASIK and PRK for correction of myopia. All LASIK procedures were done with a femtosecond laser flap creation, augmenting a prior review of LASIK performed with microkeratomes. Unfortunately, the overall quality of evidence was considered low for most outcomes because of the risk of bias in the included trials. Nonetheless, although their review concluded that LASIK provides faster visual recovery than PRK and is less painful, patients appear to have similar outcomes 1 year after surgery.9
A prospective, randomized, contralateral-eye study published in Ophthalmology evaluated long-held beliefs that LASIK is more likely than PRK to cause dry eye symptoms. Sixty-eight patients were treated with femtosecond LASIK in 1 eye and PRK in the other, and symptoms were evaluated using surveys of dry eye and visual fluctuation. Dry eye symptoms were increased in both LASIK and PRK eyes at 1 month (both P < 0.05) but were not different between eyes (P = 0.50). By 3 months, both groups had returned to baseline. Visual fluctuation was greater in PRK eyes at 1 month (P = 0.003) but was similar at 3, 6, and 12 months. Despite a small sample size, this study challenges assumptions that LASIK is more likely to cause dry eyes and adds further evidence that although LASIK leads to more consistent refractive outcomes in the first several months after surgery, long-term results are similar.10
Several studies have reinforced the viability of epipolis-LASIK (epi-LASIK) as an alternative to PRK or LASIK. Tran11 treated 83 patients with epi-LASIK with discarded flap in 1 eye (off-flap) and LASIK in the other; he found no differences in uncorrected visual acuity (UCVA) or contrast sensitivity (CS) at 1 year; transient decrease in corneal sensitivity at 6 months was seen in LASIK eyes (P < 0.05), and 2.5% of epi-LASIK eyes had mild haze that resolved at 6 months. Magone et al12 evaluated pain and re-epithelialization times with off-flap epi-LASIK versus PRK using the automated epithelial brush; 60 patients were treated with flap-off epi-LASIK in 1 eye and PRK in the other. They found that although pain scores were statistically significantly decreased in the epi-LASIK group at days 1, 2, 3, and 4 (all P < 0.01), the average difference was only 0.33 points out of 6, unlikely to be clinically significant, and there was no difference in re-epithelialization times between groups (P = 0.97). Finally, although it was hoped that replacing the epi-LASIK flap would lead to improved comfort and diminished inflammation, a recent study by Zhang et al13 suggests an etiology for opposite results. Eighteen patients underwent off-flap epi-LASIK in 1 eye and on-flap epi-LASIK in the other, with mitomycin C used in both groups. The off-flap group had better uncorrected distance visual acuity (UDVA), higher percentages of healed epithelium at 5 days, lower pain scores at 5 days (although higher on day 1), and lower levels of haze (all P < 0.05). Tear levels of proinflammatory cytokines, including basic fibroblast growth factor, platelet-derived growth factor BB, interleukin 8 (IL-8), and tumor necrosis factor α, were all significantly higher in the on-flap group (all P < 0.05) at 2 hours. These results implicate higher proinflammatory cytokines in the early postoperative period in the decreased healing and increased pain, inflammation, and haze see in on-flap epi-LASIK.
Corneal Collagen Cross-linking
Although its application in the prevention of keratoconus progression is beyond the scope of this article, and the addition of CXL to corneal ablative surgery has now been well established since 2009,14 several new reports have added to existing evidence and introduced new applications.
Adding to the evidence supporting the combination of PRK to CXL for keratoconus, Alessio et al15 compared CXL alone versus CXL combined with topography-guided PRK for 34 patients with keratoconus; the worse eye received the combined treatment. After 2 years’ follow-up, compared with baseline, the combined treatment group had significantly better uncorrected and best-corrected visual acuity (BCVA), manifest spherical equivalent (SE), cylinder, keratometry measurements, and coma-like aberrations (all P < 0.05). The CXL-alone group showed no difference in uncorrected or BCVA, manifest SE or cylinder, and coma-like aberrations, although there was a statistically significant reduction in spherical power and some keratometry measurements.
Helping to confirm the beneficial effect attributed to combined CXL and PRK, a study reported in Cornea showed improved quality-of-life surveys (National Eye Institute Visual Function Questionnaire [NEI-VFQ 25]) in keratoconus patients with BCVA 20/20 vision before treatment.16 When the patient’s worse eye was treated with either CXL or CXL with PRK, despite initially good BCVA, patients receiving CXL and PRK reported significantly improved scores in near activities, mental health, role limitations, dependency, and driving (all P < 0.05) as assessed at 1 year after surgery. The CXL-alone group reported significant improvement in dependency and near activities only. This study suggests that it may be beneficial to treat patients in earlier stages of keratoconus with CXL and PRK; however, the study is limited by the nonrandomized nature of treatment and the fact that patients eligible for combined CXL and PRK generally had better keratoconus indices allowing for combined treatment; long-term follow-up beyond 1 year would also be informative.
Two similar studies reported outcomes of combined topography-guided PRK and CXL in keratoconus patients after implantation of intracorneal ring segments (ICRSs). Al-Tuwairqi and Sinjab17 treated 13 eyes, and Coskunseven et al18 treated 10 eyes; compared with pre-ICRS baseline, there was significant improvement (P < 0.05) in UDVA, corrected distance visual acuity (CDVA), steep and flat Ks, and SE in both studies. Al-Tuwairqi and Sinjab also reported significant improvement in topographic and manifest astigmatism, as well as coma. In a related study, Kremer et al19 reported 45 eyes with significant improvement in UCVA, BCVA, cylinder, and decreased mean apex keratometry values (all P < 0.05) after wavefront-guided PRK and CXL following ICRS placement. Epithelial hyperplasia required scraping in 1 patient, and 11% had mild haze persistent after 1 year.
There may also be a role for CXL in routine hyperopic ablation, in which hyperopic regression is commonly encountered.20 Kanellopoulos and Kahn21 conducted a study of 34 patients undergoing hyperopic topography-guided LASIK; 1 eye was treated with LASIK alone, and the other received 3 minutes of high-irradiance CXL. After 2 years, there was significantly less hyperopic regression in the CXL-treated eyes (+0.22 diopters [D]) versus those without (+0.72 D). However, the non-CXL group was intentionally overcorrected by +0.50 D, which may in part explain the higher regression rate.
A controversial topic has been that of “prophylactic” CXL during routine LASIK as a means to prevent ectasia. Celik et al22 reported a pilot study in which they performed myopic LASIK on 4 patients; each patient received LASIK in 1 eye and LASIK with accelerated CXL in the other. After 12 months, the LASIK + CXL eyes had equal or better UDVA and CDVA compared with the LASIK-only group. Early mild haze in the CXL group resolved by 1 month, and no other complications were seen in either group. The authors suggest that positive early results warrant further investigation.
Topography-guided treatment may offer advantages over traditional or wavefront-guided treatment in irregular and highly aberrated corneas. Lin et al23 treated a series of eyes with decentered prior ablations, small optical zones, asymmetric astigmatism, postoperative radial keratotomy, postoperative keratoplasty, keratoconus combined with CXL, and postoperative LASIK ectasia combined with CXL, using an algorithm that combined a topographic and refractive treatment. They reported generally effective results in all of the above categories, with significant improvement in UCVA, BCVA, and visual symptoms. Treatment was generally safe, although 2 of 217 eyes in the keratoconus + CXL group required penetrating keratoplasty due to corneal haze.23
Tan et al24 reported their outcomes using topography-guided LASIK on 2051 eyes with myopia and myopic astigmatism. They found that 86.1% of eyes were within 0.50 of targeted refraction, 97.9% had 0.50 D of cylinder or less, and 73.5% were 20/20 or better. Higher myopic treatments showed a trend toward overcorrection.
Wavefront Measurements and Treatments
Corneal pseudoaccommodation has been used to explain the unexpected depth of focus sometimes observed in pseudophakic patients with monofocal IOLs. Yeu et al25 demonstrated the theoretical contribution of corneal wavefront aberrations to the phenomenon of pseudoaccommodation in normal corneas and corneas with prior myopic PRK or hyperopic LASIK/PRK. Although depth of focus was widely variable, especially in post–refractive surgery eyes, for 6-mm pupils, both postmyopic and hyperopic LASIK/PRK eyes had higher depth of focus than normal eyes, and for a 4-mm pupil, posthyperopic LASIK/PRK eyes had higher depth of focus than normal and postmyopic PRK eyes. In normal eyes, spherical aberration was the best predictor of pseudoaccommodation, and in post–refractive surgery eyes, coma showed the highest correlation with pseudoaccommodation.
Wavefront-optimized ablation profiles are intended to reduce the induction of higher-order aberrations (HOAs) of the total eye incurred during refractive surgery; Smadja et al26 described the effect of myopic LASIK specifically on the induced corneal HOAs after wavefront-optimized treatments. Dividing 64 eyes into low (<−3.00 D), moderate (−3.00 to −6.00), and high (>−6.00) myopia, they found that whereas there was no significant induction of corneal HOAs or positive spherical aberration in the low-myopia group, the moderate- and high-myopia groups had significant induction of corneal HOAs and spherical aberration (both P < 0.001). Corneal coma was increased only in the high-myopia group (P = 0.01). The amount of myopic correction was highly correlated with the induction of corneal HOAs (Spearman coefficient = 0.6) and spherical aberration (Spearman coefficient = 0.88). The authors caution that, although wavefront-optimized profiles did induce some corneal HOAs, they are not a reflection of total eye HOAs or visual quality; in fact, previous studies have not demonstrated significant induction of total HOAs even at higher myopic treatments,27 which may be due to compensation of internal aberrations as suggested by ray tracing analysis.28
Corroborating this is a study performed at the same institution, in which the authors separated 100 eyes again into low (<−3.00 D), moderate (−3.00 to −6.00), and high (>−6.00) myopia treated with wavefront-optimized LASIK using a femtosecond laser for flap creation.29 Analyzing total HOAs, and specifically spherical aberration and coma, they found that although there was no statistically significant change in total HOAs or spherical aberration in the low-myopia group, there was a 0.04 μm (P = 0.01) and 0.11 (P = 0.01) increase in total HOAs in the moderate- and high-myopic groups, respectively. Coma was unchanged in the low-myopic group and increased by 0.04 μm (P = 0.01) and 0.11 (P = 0.01) in the moderate- and high-myopic groups. Spherical aberration was unchanged in all groups. The authors conclude that wavefront-optimized LASIK is effective at treating spherical aberration but may increase coma.
The femtosecond laser has made huge inroads in refractive surgery since its introduction in 2001 and is now the instrument most frequently used for LASIK flap creation.30 Several studies have expounded on the use of the femtosecond laser in LASIK flap creation.
A report released by the American Academy of Ophthalmology31 reviewed femtosecond lasers for the use of flap creation in LASIK; safety and efficacy of multiple femtosecond platforms were analyzed and compared with mechanical microkeratome outcomes. They found that available evidence supports its safety and efficacy, and most studies have concluded it is equal to or superior than the mechanical microkeratome in terms of repeatability, safety, and visual outcomes. Complications, mostly mild and manageable, include transient light-sensitivity syndrome, rainbow glare, opaque bubble layer, epithelial breakthrough of gas bubbles, and gas bubbles within the anterior chamber. However, the majority of studies included only 1 particular platform (IntraLase; Abbott Medical Optics, Inc, Santa Ana, Calif), and long-term results are limited, suggesting that future studies evaluating multiple platforms and with longer-term results are indicated.
Outcomes and recovery after LASIK surgery have improved to the degree that patients are beginning to expect the convenience of almost immediate recovery of functional uncorrected vision. Durrie et al32 studied the immediate postoperative visual and functional trends after femtosecond-assisted LASIK in 20 patients. They found that all patients were at least 20/32 by 30 minutes and 20/20 at 4 hours. The majority of patients reported the ability to send text messages immediately after surgery and to drive by 2 hours after surgery.
The previous year brought new insight regarding the pathogenesis and management of corneal ablative complications, including epithelial ingrowth, diffuse lamellar keratitis (DLK), ectasia, dry eye syndrome, and a newly described complication dubbed “peripheral toxic keratopathy.”
Henry et al33 conducted a review of 45 patients over 8 years who underwent flap lift for epithelial ingrowth. Although they found a recurrence rate of 31% after 3 months, 78% maintained 20/25 or better best-corrected vision at that time point, and 18% required at least 1 more flap lift. They found hyperopia (P = 0.06), microkeratome usage for original flap creation (P = 0.04), and traumatic etiology of ingrowth (P = 0.04) were risk factors for recurrence.
Santhiago et al34 conducted a review of all LASIK flap lifts for enhancements, separated into those in which flap lift was successful versus not possible. Time to flap lift was a significant risk factor for unsuccessful lift, with an average of 5.3 months for successful versus 10.3 months for unsuccessful flap lifts (P < 0.001). There was a steady decline from 100% success at 3 months to 91% success at 12 months. No other factors, including age, ablation depth, side cut, or bed energies, were found.
Diffuse Lamellar Keratitis
de Paula et al35 attempted to identify risk factors for DLK. Of 801 eyes included after femtosecond LASIK, 99 (12.4%) had some degree of DLK. Most cases were mild, with only 1% progressing to stage II, and although patients with DLK were less likely to have UCVA of 20/20 or better on day 1 (P = 0.0453), by 1 week there was no difference seen. Significant correlations were seen with larger flap diameter (P = 0.0171), higher side-cut energy (P = 0.0037), and higher raster energy (P = 0.0033). However, because most cases of DLK were mild and without long-term visual significance, the authors did not recommend altering flap parameters to minimize DLK incidence.
Despite improved screening methodologies, ectasia remains a feared consequence of corneal refractive surgery. Several studies have enhanced our understanding of the risk factors for postrefractive ectasia.
Randleman et al36 compared measured flap thickness with anticipated flap thickness in 50 eyes with post-LASIK ectasia. They found that the mean measured flap thickness (138 μm) was not significantly different than the anticipated thickness (125 μm), suggesting that excessively thick flaps were not likely to be a significant factor in post-LASIK ectasia. However, they did find incidents of unexpectedly thick flaps, even with femtosecond flap creation, and recommend that the anticipated flap thickness plus 2 SDs be used to estimate residual stromal bed thickness, particularly in eyes with borderline thickness.
A recent study analyzed outcomes in patients with automated “keratoconus-suspect” indices treated with PRK. Guedj et al37 treated 62 eyes with PRK; initially selected as appropriate for PRK based on topographic and refractive indices, presurgical topography using the Corneal Navigator OPD system algorithm (Nidek Co, Gamagori, Aichi, Japan Ltd) revealed in a retrospective analysis that the percentage of similarity to keratoconus suspects or keratoconus was 50% or greater in all eyes. After a mean 5 years of follow-up, no patient had ectasia, although 3 patients were wearing spectacles for myopic regression. However, the authors urge careful selection of patients for PRK when automated systems indicated keratonus suspicion despite normal topographic indices.
A study by Kymionis et al38 evaluated refractive surgery in patients with superior topographic steepening. While inferior corneal steepening may be harbinger for ectasia, superior corneal steepening is very rarely an indication of ectatic conditions such as atypical marginal pellucid degeneration or superior keratoconus and is more frequently associated with blepharitis, ptosis, or vernal conjunctivitis. Laser in situ keratomileusis was performed on 7 eyes and PRK on 22 eyes in patients with superior > inferior steepening of greater than 1 D, but with otherwise normal topographies and corneal thickness. After 24-month follow-up, they reported predictable refractive results and no incidence of ectasia, indicating that corneal refractive surgery may be safely performed in carefully selected patients with superior corneal steepening.
Although a thin cornea is an established risk factor for post-LASIK ectasia, Djodeyre et al39 reviewed 5-year outcomes after LASIK or surface ablation in 128 eyes with preoperative corneal thickness of less than 470 μm and normal topography and a residual stromal bed of at least 250 μm. Flaps were generally thin (mean, 73.8 μm) and were created with a mechanical microkeratome. Both LASIK and surface ablation groups showed equal and good efficacy (0.99 and 0.93, respectively) and predictability (0.93 and 0.92, respectively). There were no complications; specifically, no cases of ectasia were reported.
Finally, Brenner et al40 have proposed a grading system of post-LASIK ectasia based on visual limitations, including CDVA, CDVA loss, SE, and the corneal bulge (delta K); they then correlated the degree of ectasia to preoperative risk factors such as residual stromal bed, ablation depth, ablation ratio (ablation depth:pachymetry), corneal depth (flap + ablation depth), and corneal ratio (corneal depth:pachymetry). They found that the ablation ratio was the best predictive factor for CDVA loss (P = 0.049) and postoperative CDVA (P < 0.001), whereas the corneal ratio best predicted SE and delta K (P < 0.001). These results suggest that the amount of tissue included in the flap plus ablation may be a better predictor of postablative structural instability than the residual stromal bed and should be considered when screening high-risk patients.
Dry eyes are the most frequently reported complication of LASIK.41 Several new studies have attempted to add clarity to the etiology and treatment of post-LASIK dry eyes.
The first study to compare dry eye signs and symptoms with nasal versus superior femtosecond-created LASIK flaps was reported by Huang et al42; 43 patients received a nasal hinge in 1 eye and a superior hinge in the other. At week 1, both eyes had decreased corneal sensation and increased corneal staining (both P < 0.05), which returned to baseline by 3 and 6 months, respectively. Increased basic Schirmer secretion testing and Ocular Surface Disease Index scores were seen throughout the 6-month study period (all P < 0.05). No differences were seen between eyes, suggesting that flap hinge location does not play a role in post-LASIK ocular surface disease.
Cyclosporine A (CSA) 0.05% emulsion (Restasis) is frequently used for the treatment and prevention of post–refractive surgery dry eyes and to hasten visual recovery after LASIK and PRK, particularly in patients with preexisting dry-eye signs or symptoms. The evidence for its prophylactic use in normal eyes, however, is lacking. Hessert et al43 selected 124 patients without preexisting ocular surface disease undergoing LASIK or PRK; patients were randomized to standard treatment or standard treatment with CSA for 3 months postoperatively. There were no statistically significant differences in subjective symptoms, target refraction, final UDVA, rate of visual recovery, or tear-film composition, including matrix metalloproteinase 9, IL-6, or IL-8 (all P > 0.05). The authors conclude that routine prophylactic CSA use in PRK or LASIK in young, healthy patients without ocular surface disease may not be indicated, although they do not question its use in patients with indications of dry eyes preoperatively or postoperatively.
Peripheral Toxic Keratopathy
Liu et al44 describe 5 eyes of 4 patients with a condition they name “peripheral toxic keratopathy”; analogous to central toxic keratopathy, within 1 week of LASIK or PRK, all 4 patients had peripheral, arcuate-shaped, well-defined noninflammatory opacification with thinning and induced astigmatism, leading to reduced visual acuity. Some were associated with the “cracked-mud” appearance seen with central toxic keratopathy. All cases resolved spontaneously over a period of months, with at least partial improvement in thinning. Although sometimes occurring in the setting of DLK, it is a distinct entity with a different time course and clinical appearance.
Two studies have added to the evidence that patient age may have an influence on refractive outcomes. A study by Luger et al45 evaluated 612 eyes undergoing myopic LASIK, with an average age of 38 years. They found that increasing age had a significant correlation with postoperative SE and residual astigmatism at 1 year (both P < 0.05), indicating overcorrection of sphere and higher residual astigmatism in older patients. Based on these results, the authors suggest adjusting nomograms, adding 3% to SE treatment for patients younger than 30 years, −1% for those 31 to 49 years, and −7% for those older than 50 years. They recommend adding 4% adjustment to cylinder for all patients. A second study by Patel et al46 evaluated the effect of age and refractive index on postoperative refractive error after LASIK; they found a positive correlation between age and the refractive index of the cornea (r = 0.239), as well as undercorrection in patients younger than 33 years and overcorrection in those older than 33 years. However, when recalculating ablation plans taking into account individual corneal refractive index, they found better correlation between calculated and actual postoperative SE (P < 0.05 for 1, 3, and 6 months). In the future, adding age and individual refractive index to nomograms may help improve refractive accuracy.
Two studies also evaluated the anatomic response of the cornea to corneal ablation. Smadja et al47 divided 80 eyes undergoing myopic LASIK into groups of greater than 100-μm ablation depth (group 1), 50 to 99 μm (group 2), and less than 50 μm (group 3). They measured posterior surface steepening by dual rotating Scheimpflug [DRS imaging (Galilei; Ziemer Ophthalmic Systems AG, Port, Switzerland)] and found significant increases in posterior corneal curvature in group 1, which was greatest on day 1 (−0.106 D, P = 0.03), and significantly greater than groups 2 and 3 (both P < 0.05). By month 3, posterior corneal curvature returned to baseline. A related article by Sy et al48 urges caution, however, when choosing which instrument to image the posterior cornea after myopic ablation. When analyzing premyopic and postmyopic LASIK posterior corneal curvature in 78 eyes, they found no change in posterior corneal curvature at 6 weeks based on DRS imaging (P = 0.953), but a significant increase when measured by scanning slit beam imaging (Orbscan IIz; Bausch & Lomb) (P < 0.001). This difference as measured by a scanning slit beam system is attributed to artifact based on changes in the anterior corneal surface.
Finally, based on previous studies linking Google searches to regional infectious epidemics such as influenza and chickenpox, Stein et al49 utilized “Google trends” to gauge public interest in LASIK from 2007 to 2011 in the United States, United Kingdom, India, and Canada. Google searches for “LASIK” showed a steady downward trend, mirroring American and International refractive society surveys showing a 31% decline in LASIK volumes during a similar time span (Duffey RJ, Leaming D. “Trends in Refractive Surgery in the United States: The 2010 ISRS Survey.” Presented at the Annual Meeting of the American Academy of Ophthalmology, October 15, 2010, Chicago, Ill; and “US Surgery: 2010 ASCRS Survey.” Presented at the American Society of Cataract and Refractive Surgery (ASCRS) Annual Meeting, March 24, 2011, San Diego, Calif. Available at www.duffeylaser.com/physicians_resources.php). This trend may be a result of the economic downturn or a Food and Drug Administration report on refractive surgery complications.
SMALL-INCISION LENTICULE EXTRACTION
An exciting new frontier in corneal refractive surgery, the SMILE technique has generated significant interest. A flapless intrastromal lenticule is created using the femtosecond laser and extracted through a small peripheral corneal tunnel, ideally providing predictable refractive outcomes while maintaining structural integrity and avoiding the complications of LASIK flaps, including dry eyes, epithelial ingrowth, ectasia, and flap dislocation. Preliminary studies have shown results with efficacy and safety similar to reported LASIK outcomes.50,51
Hjortdal et al52 reported their outcomes on 670 eyes of 335 patients undergoing the SMILE procedure. At 3 months after surgery, 80.1% of eyes were within 0.50 D, and 94.2% were within 1.00 D of the attempted correction; the safety index (BCVA preoperative:BCVA postoperative) was 1.07, and efficacy index (BCVA preoperative:UCVA postoperative) was 0.90. Bivariate analysis showed significant influence of patient age, sex, and corneal power on the error in SE refraction at 3 months. There was a trend toward undercorrection of 0.012 D per increasing year of age, undercorrection of 0.041 D per diopter of corneal steepening, and an average undercorrection of 0.085 D for females (all P < 0.01). Of the treated eyes, 2.4% (16 eyes) lost 2 or more lines of CDVA. The amount of attempted spherical correction did not correlate with safety or efficacy (P > 0.05).
The best way to perform a refractive enhancement after SMILE remains an unanswered question. Several strategies have been proposed, including LASIK, PRK, or SMILE anterior to the initial treatment, a phakic IOL (pIOL), or conversion of the SMILE cap to a full flap with subsequent excimer laser enhancement. An animal study by Riau et al53 investigated this last option by attempting 4 different circular ring femtosecond laser patterns to facilitate conversion of the original SMILE cap to a flap. They then graded the ease of flap lift, smoothness of the stromal bed, and area available for ablation. Pattern D, in which the circular cut is at the same depth as the original cap, provided the best combination of flap-lift ease, smoothness, and appropriate retreatment area.
CORNEAL TREATMENT FOR PRESBYOPIA
There are several corneal surgical treatment modalities for presbyopia, including presbyopic LASIK, monovision LASIK or PRK, intrastromal femtosecond laser presbyopia treatment (INTRACOR procedure), and intracorneal inlays.
Previous studies have assessed the outcomes of the INTRACOR procedure during the first year after surgery.54,55 In this procedure, 5 corneal intrastromal ring cuts are done using a femtosecond laser, causing an increase in central corneal steepness and leading to a multifocal cornea. These studies showed that the patients had an improvement in uncorrected near visual acuity (UNVA) with minimal or no change in UDVA, and their CDVA continued to improve over time.54,55 Recently, Menassa et al56 reported the visual outcomes and corneal changes during an 18-month follow-up period of 25 eyes (Table 1). They also observed a significant gain in UNVA at all postoperative visits when compared with preoperative data. No significant loss of UDVA was observed. However, differently from the study by Ruiz et al,54 there was a slight, but significant, decrease in the final CDVA, which the authors attributed to changes in vision quality related to modifications in the depth of focus induced by the treatment and possibly changes in CS.3 Nine patients (25%) reported mild halos.56
Similarly to the literature,55 a slight myopic shift of −0.50 D occurred after surgery.56 This myopic shift prevents the use of the standard INTRACOR procedure in plano emmetropic or myopic patients. Recently, Thomas et al57 investigated the use of a modified INTRACOR procedure in plano emmetropes. This modified version adds 8 intrastromal midperipheral radial cuts to the 5 standard central ring cuts. One year after surgery, median UNVA in the operated eye had significantly improved from 20/80 to 20/25, whereas the median CDVA had significantly decreased from 20/16 to 20/20. Subjective SE refraction was not affected by surgery and remained unchanged during the 1-year follow-up.57
Regarding corneal changes, after the standard INTRACOR procedure, there was significant corneal steepening in the treated area, which is the aim of the intrastromal cuts, and the steepening was stable over the 18-month follow-up period.56 After the modified INTRACOR procedure, central corneal steepening and midperipheral flattening occurred.4 None of the eyes developed keratectasia.56,57 Similarly to prior reports in the literature,54 endothelial cell density (ECD) remained stable after both types of surgery, and corneal pachymetry was stable in the first postoperative year.56,57 However, 18 months after the standard INTRACOR procedure, a statistically significant, but clinically insignificant, corneal thickening occurred when compared with the preoperative measurement.56 The studies suggest that the INTRACOR procedure provides a stable gain in UNVA, with stable corneal steepening and minimum or no effect on corneal endothelium and thickness in up to 18 months after surgery.54–57 In addition, the results suggest that the modified INTRACOR procedure may be an option to treat presbyopia in plano emmetropic patients, although longer follow-ups are necessary to determine if the effect remains stable over a longer period.57
Recently, studies evaluated the visual outcomes and the safety profile of corneal inlays with femtosecond laser–created pockets (Table 1).58–60 Seyeddain et al58 reported data regarding the Kamra corneal inlay (ACI7000PDT; Acufocus, Inc, Irvine, Calif) in 24 patients. The Kamra corneal inlay is a 5-μm-thin microperforated artificial aperture made of polyvinylidene fluoride with nanoparticles of carbon. It has an inner and outer diameter of 1.6 and 3.8 mm, respectively. Based on the pinhole effect, it increases the depth of focus.58 The mean CS values significantly reduced postoperatively,58 although they remained within the reference range.61 The UNVA and the uncorrected intermediate visual acuity improved in the surgical eye after surgery and remained stable during the 2-year follow-up. Although there was a small reduction in mean UDVA and CDVA in the surgical eye, binocular mean UDVA and CDVA remained stable throughout the study. These results regarding UNVA, UDVA, and CDVA agree with other studies.59,60
Dexl et al59,60 reported the 1- and 2-year reading performance of 24 patients with the Kamra. There was a statistically significant postoperative improvement in mean reading distance, mean reading acuity at best distance, and smallest readable print size in both follow-up periods. Although there was also an increase in mean and maximum reading speed, this was statistically significant only in the first year after surgery.59,60 When comparing their results to that of another study assessing the 6-month reading performance after bilateral implantation of a monofocal, a refractive multifocal, or a multifocal IOL with a diffractive component,62 patients with the Kamra achieved a better mean reading speed and mean reading distance 1 and 2 years after surgery.59,60 The mean maximum reading speed was also better 1 year after the Kamra implantation.60 However, the 2-year Kamra mean maximum reading speed was similar to that achieved with the IOLs.59–62
Similarly to the findings of Dexl et al,59,60 no inlays in the study of Seyeddain et al58 had to be explanted or recentered; thus, the authors believe the pocket technique is better for inlay centration than the flap technique as it allows exact and clear visualization of the first Purkinje reflex during surgery as a reference point. One eye (4.2%) developed epithelial ingrowth at the temporal pocket entrance 1 month after the procedure; this remained stable over the follow-up period. Another eye (4.2%) developed brown iron deposits in the epithelium parallel to the outer margin of the inlay 18 months after surgery, contrasting to 56% of 32 eyes that developed iron deposits after 3 years of implantation of the first-generation Kamra design.63 In addition, there was no visual fields defect, and the ECD and central corneal thickness did not change significantly after surgery.58
Another study assessed the 1-year outcomes of the Flexivue Micro-Lens (Presbia Coöperatief U.A., Amsterdam, the Netherlands) with femtosecond laser–created pockets in 47 patients.64 This device is a transparent, hydrophilic disc composed of a copolymer of hydroxyethylmethacrylate and methylmethacrylate. It has a thickness of 15 to 20 μm and a 3-mm diameter. The central 1.8-mm diameter is plano in power, and the peripheral zone has the addition power. Similarly to the results with the Kamra,58 the mean UNVA significantly improved, and the mean CDVA significantly decreased in the surgical eye, whereas binocular CDVA did not change. However, although 81.25% of the patients perceived their UDVA in the operated eye as being good, this parameter significantly decreased in the operated eye, whereas it did not change when tested binocularly. The authors hypothesized that the significant increase in total higher-order aberrations and mean spherical aberration at 3- and 4-mm pupil diameter may have negatively influenced the distance visual performance, while also positively contributing to near vision by increasing ocular depth of focus. One year after surgery, 12.5% of patients experienced halos and glare, which decreased in intensity during follow-up and did not interfere in the patients’ activities.64 The preoperative and postoperative ECD and central corneal thickness were similar,64 in agreement with a previous study assessing outcomes with the Kamra.58 In addition, normal corneal characteristics were seen using confocal microscopy at depths below and above the inlay, which supports the Flexivue Micro-Lens safety in the first postoperative year.64
Garza et al65 have investigated the safety and efficacy of the Raindrop corneal inlay (ReVision Optics, Inc, Lake Forest, Calif) with a femtosecond laser–created flap. The Raindrop corneal inlay is made of a clear, permeable hydrogel material. It has a 2-mm diameter and a central thickness of 32 μm. The inlay has the same index of refraction as the cornea and has no intrinsic power. Thus, it alters the eye’s refractive power by increasing the central radius of curvature of the cornea overlying the implant. The UNVA significantly improved after surgery and was stable from the 1-week evaluation until the final follow-up visit, 1 year after the procedure. Similarly to the results with Kamra58 and Flexivue Micro-Lens,64 the mean CDVA significantly decreased after surgery in the operated eye: the eyes lost a mean of 0.02 logarithm of the minimum angle of resolution.65 The postoperative mean CS values were within the reference range,61 although reduced when compared with preoperative data. Regarding adverse events, 1 of the 19 studied patients referred severe halos 6 months after surgery, which was reported as being mild on the 12-month follow-up visit. Another patient had a decentered inlay that was repositioned 1 month after the initial surgery. In addition, a third patient underwent corneal inlay explantation due to a dissatisfaction with postoperative distance vision. Thus, the device was retained in 18 of the 19 implanted corneas with good results.
FEMTOSECOND LASER-ASSISTED ASTIGMATIC KERATOTOMY
Femtosecond laser technology has been used to perform astigmatic keratotomy for the correction of astigmatism. It has the ability to create precise corneal dissections at a variety of depths and orientations. Several prior studies have reported the use of a femtosecond laser system for the correction of astigmatism using incisions that penetrate Bowman membrane and the epithelium. In this past year, 2 articles reported results of nonpenetrating incisions.
Rückl and colleagues66 evaluated the feasibility and safety of purely intrastromal arcuate keratotomy procedures performed using the 150-kHz Intralase iFS femtosecond laser system (Abbott Medical Optics, Inc). The intrastromal incisions were planned to be placed 100 μm from the epithelium and the endothelium, without penetrating the Bowman layer or Descemet membrane, to avoid the risks associated with incisions that break the protective epithelial and endothelial surfaces. The angular arc length of all incisions was 90 degrees with a 30-degree cut angle, and the optical zone diameter was set at 7.5 mm.
In 16 patients with corneal astigmatism (naturally occurring or after cataract surgery),66 paired stromal arcuate incisions were performed on the steep meridian. Postoperative examination showed that no penetration of Bowman or Descemet membrane occurred and that all incisions were placed at the planned locations. At the 6-month follow-up, the mean refractive cylinder and mean topographic astigmatism had significantly reduced from preoperatively 1.41 ± 0.66 D to 0.33 ± 0.42 D and from 1.50 ± 0.47 D to 0.63 ± 0.34 D, respectively. The mean UDVA improved significantly with a mean gain of 2.8 ± 1.47 lines, and no patient lost any lines of UDVA. The mean CDVA remained fairly stable from preoperatively to 6 months postoperatively. Six eyes (37.5%) had an improvement of 1 to 2 lines, 4 eyes (25.0%) had a stable CDVA, and 6 eyes (37.5%) had a loss of CDVA (1 eye, 3 lines; 3 eyes, 2 lines; 2 eyes, 1 line). This loss of CDVA was considered to be associated with an increase in lens opacities based on slit-lamp evaluation. There was no statistically significant loss of endothelial cells in the treated eyes. This small initial case series shows that a predictable stable effect can be achieved with femtosecond laser intrastromal arcuate incisions.
Another study by Venter et al67 performed nonpenetrating femtosecond laser intrastromal astigmatic keratotomy in patients with mixed astigmatism after previous refractive surgery. This study included 112 eyes that had low mixed astigmatism after excimer laser surgery, refractive lens exchange, or pIOL implantation. The intrastromal astigmatic keratotomy was performed with the iFS femtosecond laser. Paired symmetrical arcuate incisions ranging from 40 to 60 angular degrees based on the magnitude of preoperative refractive cylinder were created. The incisions extended from 60 μm below the corneal surface to 80% depth at 7-mm diameter. The mean UDVA significantly improved from 0.18 ± 0.14 to 0.02 ± 0.12 logarithm of the minimum angle of resolution. The mean absolute subjective cylinder significantly decreased from 1.20 ± 0.47 D preoperatively to 0.55 ± 0.40 D postoperatively. No surgical complications occurred.
These studies suggest that femtosecond laser–assisted intrastromal astigmatic keratotomy is a potentially effective and safe method and could be used to fine-tune low astigmatism in patients after refractive and cataract surgeries. Advantages of the intrastromal approach could include better accuracy, faster visual recovery, improved comfort, greater stability, and fewer complications. Large randomized studies of intrastromal arcuate keratotomy are desirable to refine nomograms, validate the merits of this approach, and possibly adapt it for higher levels of astigmatic correction.
PHAKIC INTRAOCULAR LENS
Phakic IOL implantation is an evolving surgical option to correct the ammetropia, typically in patients who are not good candidates for corneal refractive surgery. The main advantages of the pIOL are the refractive stability that does not depend on corneal healing, a wide range of correction, removability, and, compared with refractive lens exchange, preservation of accommodation.68 Regarding this treatment modality, there has been much interest in several areas: (1) sulcus diameter-based sizing for posterior chamber pIOL, (2) implantation of toric pIOL, (3) visual and aberrometric outcomes in normal and keratoconic eyes with pIOL, and (4) complications of pIOLs.
Sizing for Phakic Intraocular Lens
The implantable collamer lens (ICL) current standard white-to-white diameter-based sizing has previously been shown less accurate than the sulcus diameter-based sizing using ultrasound biomicroscopy.69 Recently, Reinstein et al70 assessed the inclusion of a direct sulcus diameter measurement obtained using the Artemis 2 very-high-frequency digital ultrasound arc scanner (ArcScan Inc, Morrison, Colo) in the ICL-sizing formula. The sulcus diameter-based sizing using data from the Artemis 2 very-high-frequency had a significantly better predictability of postoperative vault height than the white-to-white diameter-based sizing formula. This supports the results seen when using ultrasound biomicroscopy measurements and suggests that the inclusion of a direct sulcus diameter measurement can improve the ICL-sizing accuracy, reflecting on safety of ICL implantation.70
Toric Phakic Intraocular Lens
Recently, studies were published reporting the efficacy, predictability, safety, and stability of the foldable toric Artiflex pIOL (Ophtec BV, Groningen, the Netherlands).68,71 This pIOL is a 3-piece lens that consists of a flexible silicone optic and 2 rigid polymethylmethacrylate haptics. It can be inserted through a 3.2-mm incision, in contrast to the rigid Artisan pIOL that requires a 5.3- to 6.2-mm incision; the reduced incision size decreases surgically induced astigmatism and induced HOAs and hastens visual recovery.72 In a study by Muñoz et al,68 the proportion of eyes with an UDVA of 20/25 or better 1 year after surgery was the same as the proportion of eyes with a CDVA) of 20/25 or better preoperatively (78.6%). Seventy percent of eyes had an SE correction within the range ±0.50 D of the preoperative target, and 92.9% had an SE correction within the range ±1.00 D. Postoperatively, the mean manifest cylinder was of −0.39 D. Similarly to the study of Doors et al,71 there was excellent rotational stability, which the authors hypothesize as being due to the iris IOL fixation. There was transient pigment deposit in only 16.7% of the eyes, and the postoperative corneal endothelial cell loss was similar to previous studies investigating the Artisan IOL.73 However, another study reported mild halos in 4.3% of eyes after 6 months of toric Artiflex pIOL implantation.71 In addition, although this pIOL has a vault of 0.20 mm between the optic-haptic junction and the iris plane, some patients developed posterior synechiae of unknown cause.71
Visual and Aberrometric Outcomes With Phakic Intraocular Lens
The posterior chamber Visian implantable collamer lens (ICL) (STAAR Surgical, Nidau, Switzerland) is a 1-piece plate-haptic pIOL partly made of collamer, a flexible and hydrophilic material. The ICL’s optic is 6 mm in diameter, and its overall diameter ranges from 11 to 13 mm.7 A recent study used an adaptive optics simulator to assess the optical and visual quality attained by different powers of ICL and by small versus large incisions.74 Visian ICL provided good optical and visual quality, which was even better with −3 and −6 D ICLs implanted through an incision smaller than 3.2 mm, when compared with −15 D ICLs and incisions ranging from 3.2 to 4.5 mm. The outcomes decreased with larger surgical incisions due to an increase in aberrations. Thus, the authors suggest that myopic eyes with astigmatism might benefit more from a toric ICL implanted through a small incision than from a spherical ICL implanted through a large incision.74
Previous studies have demonstrated that the ICL is superior to LASIK for the correction of myopia ranging from −4 to −12 D, regarding safety, efficacy, predictability, and stability.75,76 In eyes with high myopia, ICL implantation has also been shown to induce significantly fewer ocular HOA than wavefront-guided LASIK.77 The CS significantly increased after ICL implantation and decreased after wavefront-guided LASIK.10 Recently, Kamiya et al78 assessed these 2 outcome measures of visual performance in eyes with low and moderate myopia that had undergone ICL implantation or wavefront-guided LASIK. Although this latter treatment modality did not significantly alter the CS, the other results were similar to those described in eyes with high myopia: the ICL implantation induced significantly fewer HOA than wavefront-guided LASIK, and ICL implantation significantly increased CS.77,78 Therefore, the studies suggest that ICL implantation may provide superior visual performance compared with standard and wavefront-guided LASIK in the correction of all degrees of myopia, although the differences in visual outcomes become smaller in lower grades of ammetropia.75,78 In addition, long-term studies of complications are needed.
Considering eyes with stable or stabilized keratoconus, Kurian et al79 assessed the visual and aberrometric outcomes after 6 months of ICL implantation. There was a statistically significant improvement in mean UDVA after surgery, and 80% of eyes maintained or gained multiple lines of CDVA. After the procedure, 3 eyes (30%) had an SE within the range ±0.50 D of the preoperative target, and 7 eyes (70%) had an SE correction within the range ±1.00 D.79 These later results were not as good as reported elsewhere.80 The authors hypothesized that this difference could be due to the greater difficulty in obtaining accurate and repeatable refractions in patients with keratoconus because of the scissors reflex in early keratoconus and to the irregular reflex movement in advanced keratoconus, especially in eyes with intrastromal corneal ring segments. Stability was good, indicating both the stability of the underlying keratoconus and the device: only 1 eye (10%) had a change in the manifest refraction SE greater than 0.50 D over the 6 months, although longer follow-up is obviously required. However, despite acceptable refractive outcomes, there was poor visual quality due to the aberrations associated with corneal changes induced by the keratoconus.79
Complications of Phakic Intraocular Lens
Regarding complications after pIOL implantation, a case report described a severe endothelial cell loss in a highly myopic patient following implantation of the Acrysof Cachet (Alcon Laboratories, Inc, Fort Worth, Tex) and the GBR/Vivarte (IOL Tech-Zeiss, Göttingen, Germany).81 Ten years after the Cachet implantation, the endothelial cell count density had decreased from 2481 cells/mm2 to 680 cells/mm2, and 8 years after GBR/Vivarte implantation, the endothelial cell count density had decreased from 2240 cells/mm2 to 570 cells/mm2.81 This later lens has been withdrawn from the market because of endothelial cell loss. Although previous articles reported the safety profile and effectiveness of the Cachet up to 3 years after its implantation,82,83 this recent report highlights the importance of close long-term follow-up of these patients.81
During the past 12 months, many studies have evaluated the improvements and progress in the field of refractive surgery. In the detection of keratoconus and subclinical keratoconus, new indices have been proposed based on the digitized Placido images of traditional Placido-based topographer and OCT. Advances in LASIK and PRK include integration of CXL, refinement of techniques, and enhanced understanding and prevention of complications. The SMILE technique has gained significant interest. In the area of corneal treatments for presbyopia, studies have reported the visual outcomes and corneal changes in eyes that underwent intrastromal femtosecond laser presbyopia treatment and intracorneal inlays. Femtosecond laser–assisted intrastromal astigmatic keratotomy has been reported to be a potentially effective and safe method for correction of low astigmatism. Phakic IOL implantation is an alternative surgical procedure to correct ammetropia. Studies have focused on the evaluation of efficacy, predictability, safety, and stability of the toric pIOL; visual and aberrometric outcomes; and complications of pIOL. With advances in technology, the field of refractive surgery will continue to provide exciting developments with increasing quality of outcomes.
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