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Straylight before and after phacoemulsification in eyes with preoperative corrected distance visual acuity better than 0.1 logMAR

Lapid-Gortzak, Ruth MD, PhD*; van der Meulen, Ivanka J.E. MD, PhD; van der Linden, Jan Willem BOpt; Mourits, Maarten P. MD, PhD; van den Berg, Thomas J.T.P. PhD

Author Information
Journal of Cataract & Refractive Surgery: May 2014 - Volume 40 - Issue 5 - p 748-755
doi: 10.1016/j.jcrs.2013.10.030
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Abstract

The diagnosis of cataract is routine for clinicians. They use a combination of visual acuity, lens opacity, and patient-reported symptoms to determine whether cataract surgery should be performed. However, there are no universal guidelines on when a cataract should be removed.1,2 There is ongoing discussion about which criteria to use.3 The indications and frequencies of cataract surgery vary among geographic regions.4 Variation is caused by differences in supply and demand,3,5 the availability of hospitals and surgeons to perform the surgery,3 reimbursement for the surgery,5 and the difference in the true incidence of cataract in different countries and regions.3

In most studies, the criteria for evaluating the appropriateness of cataract surgery are visual acuity, lens opacification seen on slitlamp examination, and sometimes the results of visual function questionnaires.4,6 Quintana et al.2 suggest that the expected visual acuity be the predominant factor in deciding when to perform surgery and that preoperative indicators of visual acuity and visual function also be considered. The question is whether parameters other than visual function should be included in the decision.

In refractive lens exchange (RLE), ametropia and sometimes presbyopia are corrected by performing a cataract procedure in an eye without cataract. When the patient’s preoperative corrected distance visual acuity (CDVA) is excellent, little lenticular opacification is seen, and no visual disability except the refractive error is noted in the patient’s history or on visual function questionnaires, the indication for a refractive lens procedure is straightforward. Often, patients with a refractive error can be corrected to achieve a high level of visual acuity on acuity charts. However, these patients may report problems with visual quality even though there is little evidence of lenticular changes on slitlamp examination.

Amesbury et al.7 assessed visual outcomes based on questionnaire results in patients with a preoperative CDVA of 20/20 (0 logMAR) and concluded that visual acuity is not always a good indicator of visual function. Frost and Sparrow6 have shown that it is not unusual for a cataract surgeon to remove a cataract even when visual acuity is relatively good. They also found that the use of ancillary testing varies greatly. Rubin et al.8 found that contrast, glare sensitivity, visual acuity, visual fields, and stereoacuity are independent risk factors in self-reported visual disability in the elderly. This indicates that many cataract surgeons are aware that the results of visual acuity, the physical examination, and visual function questionnaires do not fully answer the question of whether there is an indication for cataract surgery. Most guidelines now suggest testing for visual functional disability when determining whether cataract surgery is appropriate and when evaluating outcomes.9,10 In most cases, the primary determination of fitness to drive a car is based on visual acuity and the visual field; however, it has been shown that determining straylight values enhances the assessment.11,12

As early as 1993, disability glare scores were found to be useful in detecting early cataract.13 Current guidelines of the Royal College of Ophthalmologists state that tests such as contrast sensitivity, glare, laser interferometry, and specular microscopy are valid in determining the need for cataract surgery.9 In 2005, an instrument to measure disability glare, the C-Quant (Oculus Optikgeräte GmbH), was introduced on the market. It has proved to be valid and practical in a clinical setting.1,14,15

Disability glare is defined by international standards as straylight.16 Straylight is the light that enters the eye but does not come into focus because of imperfections in the optical system; rather, the light is scattered in the eye.14,17,18 The point-spread function (PSF) is a parameter that describes the quality of a point source on the retina. The PSF has a small-angle domain, which influences visual acuity, and a large-angle domain, which is objectively and physiologically measured by measuring straylight.1,11,14,18 This is why visual acuity alone is not enough to evaluate all aspects of quality of vision and why measuring straylight can give additional information.1,11,14,18 van den Berg et al.19 published an extensive survey on the history of straylight measurements.

To determine which hard-to-detect aspects of early cataract influence visual function and quality, we assessed the changes in straylight in patients with a preoperative CDVA of 0.1 or better who were scheduled for cataract surgery or RLE.

Patients and methods

All patients having cataract surgery or RLE at a private refractive surgery clinic were consecutively included. The study adhered to the tenets of the Declaration of Helsinki. All patients provided consent.

Patients were included if they had a preoperative CDVA of 0.1 logMAR or better. Patients were excluded if they had other ocular disease (eg, corneal opacity, endothelial dysfunction), previous refractive surgery, glaucoma, traumatic eye disease, or retinal pathology (eg, macular degeneration).

Surgical Technique

All patients had standard phacoemulsification through a 2.2 mm incision with implantation of an intraocular lens (IOL). The IOL type depended on shared decision making between the patient and the eye surgeon.

Patient Examinations

A full ophthalmic examination was performed preoperatively and 1 week and 1 and 3 months postoperatively and included uncorrected distance visual acuity (UDVA), CDVA, refraction, slitlamp biomicroscopy, tonometry, dilated fundoscopy, and straylight measurements. Topography (Orbscan) and wavefront aberrometry (Zywave) (both Technolas Perfect Vision GmbH) were performed preoperatively only.

Straylight Measurements

Straylight was measured using the C-Quant straylight meter and expressed as log(s).20–22 For measurements with this device, patients perform a forced-choice task on a visual test in which the center of the field is divided into 2 flickering half fields surrounded by a flickering ring. The patient perceives the flickering of 1 central half field because the ring of light is projected partly on the retinal image of the central test field by intraocular scattering. A counter-phase compensation light stops the flickering and causes a difference in modulation between the 2 central test fields. The patient chooses the half with the strongest flicker. The response is charted and computed on a psychometric response curve. The reference database was established previously and determined to be reproducible. The instrument supplies the estimated standard deviation (SD), which is the reliability index for each measurement. Only reliable measurements with an estimated SD less than 0.1 were included. Trained personnel measured each eye twice before surgery and twice 3 months after surgery. The mean of the 2 measurements was calculated. The repeated-measures SD for the straylight measurements (derived from the differences between the 2 repeated measures) was 0.09 preoperatively and 0.10 postoperatively.

Statistical Analysis

Data were analyzed using statistical functions in Excel 2003 software (Microsoft Corp.). Correlations were calculated using normal regression analysis. Regression lines plotted in the figures are the major axis regression lines. All postoperative data reported here are from the 3-month visit.

Results

The study enrolled 160 eyes of 89 patients with complete data sets. The mean age of the 38 men and 51 women was 59.4 years ± 8.1 (SD) (range 44.5 to 83.8 years). The surgery was cataract extraction in 96 eyes and RLE in 64 eyes.

The IOL distribution was as follows: 52 SN6AD1 (Alcon Laboratories, Inc.), 38 Seelens MF (Hanita Lenses), 35 LS-312 MF30 (Oculentis GmbH), 24 Acri.Lisa toric (Carl Zeiss Meditec AG), and 9 Acrysof SN60WF and 2 toric Acrysof SN6AT aspheric monofocal IOLs (both Alcon Laboratories, Inc.).

Overall Visual Acuity

Postoperatively, the mean UDVA improved by 0.38 logMAR and the mean CDVA by 0.02 logMAR (Table 1). The mean preoperative spherical equivalent (SE) refraction was +1.01 ± 2.74 diopters (D) (range −8.88 to +10.13 D), which decreased to a mean of +0.02 ± 0.40 D (range −1.38 to +1.50 D) postoperatively.

Table 1
Table 1:
Uncorrected and corrected distance visual acuities.

Straylight Measurements

Figure 1 shows the straylight results. The mean straylight value was 1.21 ± 0.20 log(s) (range 0.80 to 1.74 log[s]) preoperatively and 1.11 ± 0.16 log(s) (range 0.76 to 1.63 log[s]) postoperatively. The mean improvement was 0.09 log(s), which is comparable to a 1-line improvement on the reading chart. Of the 160 eyes, all 44 (27.5%) with a preoperative CDVA of better than 0.1 logMAR had an improvement of more than 0.2 log(s), which is comparable to a 2-line improvement on the reading chart. Analysis of the overall dataset in Figure 1 gave a Pearson correlation coefficient of 0.67 (P<.0005).

Figure 1
Figure 1:
Change in preoperative to postoperative straylight (160 eyes). A higher straylight value preoperatively correlates with a greater improvement in straylight postoperatively (cat = cataract surgery; rle = refractive lens exchange).

Figure 2 compares the eyes in the current study with those in a previous study. Eyes in the current study had a CDVA of 0.1 logMAR or better; however, most had an increase in straylight, indicating worsening of quality of vision. In the figure, the current study population is shown as having relatively good visual acuity with increased (impaired) straylight compared with the normal cataract population, which is shown as having decreased visual acuity with increased straylight.

Figure 2
Figure 2:
The study population, eyes with good logMAR visual acuity, together with a previous study population of a cataract center.1 The red lines represent the limit for acceptable levels and indicative of functional cataract. Quadrant I shows eyes with normal logMAR visual acuity and straylight scores (below and to the left of the red lines). Quadrant II shows eyes with normal logMAR visual acuity and increased straylight (above and to the left of the red lines). Quadrant III shows eyes with insufficient visual acuity and normal straylight levels (right and below the red lines). Quadrant IV shows eyes with insufficient visual acuity and increased straylight (EDTRS = Early Treatment Diabetic Retinopathy Study; SL = straylight; VA = corrected distance visual acuity).

At a preoperative straylight value of 1.117 log(s), the chance of straylight improving postoperatively was greater than 50% (Figure 1). The mean age for achieving this log(s) value in normal (best) eyes was 58.3 years (Figure 3).

Figure 3
Figure 3:
Preoperative and postoperative straylight are plotted on the phakic norm graph. The regression line shows that the older patients had reduced straylight (ie, improvement) compared with their phakic peers. The point at which the pseudophakic eyes show better straylight function than their age-matched peers was 51 years.

Between-Group Comparisons

Table 2 compares parameters between the cataract group and the RLE group. The difference in age, preoperative CDVA, and preoperative SE refraction was statistically significant between the cataract group and the RLE group. The cataract group was statistically significantly older and had statistically significantly worse CDVA preoperatively. The postoperative difference in CDVA and SE between the cataract group and the RLE group was not statistically significant.

Table 2
Table 2:
Comparison between the cataract group and the RLE group.

The improvement in straylight was greater in the cataract group than in the RLE group. More eyes in the cataract group (34 of 96 eyes [35.4%]) had an improvement in straylight by more than 0.2 log(s); 10 (15.6%) of 64 eyes in the RLE group had this level of improvement. In the cataract group, the mean improvement in CDVA was 1 letter on the visual acuity chart. The CDVA remained unchanged in the RLE group.

Discussion

In this study, we found that after standard phacoemulsification and IOL implantation, eyes with good preoperative CDVA (0.1 logMAR or better) achieved a mean improvement of 0.1 log(s) in straylight measurements. In 35.4% of eyes in which a cataract was diagnosed preoperatively, the improvement was more than 0.2 log(s). This significant improvement in straylight, a parameter of visual acuity, was achieved even though these patients had very good CDVA preoperatively. In the RLE group, this level of improvement occurred in 10 (15.6%) of 64 eyes. This result shows that visual acuity as a sole parameter is not a good indicator of the necessity for surgery or of the possibility of improving the patient’s vision. In this study, 27.5% of all eyes (44 of 160) had an improvement in straylight of more than 0.2 log(s), which is equivalent to a 2-line improvement on the visual acuity chart. However, there was little or no improvement in CDVA in the cataract group or in the RLE group. These results show that visual acuity alone is not enough to establish an indication for cataract surgery and that straylight measurements complement visual acuity measurements.

Further analysis of the results showed that the cutoff for a chance of obtaining more than a 50% improvement in straylight was 1.117 log(s). In the normal phakic population, the cutoff for such improvement was an age of 58.3 years.

Because guidelines for cataract surgery are not universal, the indication for surgery can depend on different criteria. For example, poor countries must divide their resources when serving the most needy populations. Richer countries may also consider societal needs, such as the ability to perform difficult motor and visual tasks (eg, driving).

Most guidelines take into account the “fudge” factors of visual acuity, patient complaints, and the ophthalmic surgeon’s assessment of whether changes in the lens affect visual acuity. Contrast sensitivity has been proposed as a parameter to use in such decisions. However, studies13,23,24 found this to be an erratic approach that is sensitive to the testing environment, is not easily standardized, and is often not reproducible. These factors undermine the reliability of contrast sensitivity as a test to determine the need for cataract surgery.

Straylight assessment directly measures disability glare according to Commission Internationale de l’Éclairage definition. In a large population-based study, van den Berg et al.14 found that straylight increased with age and that the major cause for the increase was opacification and age-related changes in the lens (ie, cataract formation). Van der Meulen et al.1 have shown that visual acuity and straylight measure different aspects of visual acuity and that the 2 methods complement each other. The addition of straylight to preoperative assessment rendered the postoperative results more predictable.

Van der Meulen et al.1 found preoperative breakeven points of 0.06 logMAR and 1.29 log(s) to be indicators of a 50% chance of postoperative improvement in visual function. Our findings agree; all our patients had a preoperative CDVA of 0.10 logMAR or better, close to van der Meulen et al.’s preoperative visual acuity breakeven point. However, our study found improvement in straylight (mean 0.09 log[s]) and a lower straylight breakeven point of approximately 1.117 log(s). The difference between the 2 studies might be due to a difference in patient age.

The population in our study differed from the general cataract patient population. Patients come to the clinic because of early visual complaints. Many ophthalmologists would not perform surgery in such patients precisely because of the good preoperative CDVA. Our population was significantly younger than the general cataract patient population (mean 59.4 years in our study and 72 years in van der Meulen et al.’s study1). Our patient population is interested in having a refractive lens procedure, is well informed, and has clear and high expectations about the postoperative results. Screening in refractive lens surgery involves selecting which patients should receive monofocal IOLs because of ocular surface, glaucoma, or retinal disorders and which patients are eligible for multifocal IOL implantation because they have no ocular risk factors. Preoperative screening has to discern, on an ethically sound basis, between patients who have visual complaints that are not the result of a refractive error and thus are likely candidates for a cataract procedure and patients whose sole motivation is to improve their refraction. As long as cataract surgery is reimbursed, this distinction is important, even though it is sometimes difficult to make. On the other hand, unless refractive procedures become part of mainstream treatments reimbursed by insurance or health care organizations, most refractive surgeries for ametropia or surgery for early cataract will be considered unnecessary and will be paid for out of pocket by patients.

It is no surprise that the preoperative straylight value breakeven point for a 50% chance of a postoperative improvement was 1.117 log(s) in our normal population and 1.29 log(s) in the elderly, and often more complex, cataract population. The log(s) value of 1.117 extrapolates to a mean age in the population of 58.3 years old, nearly 14 years younger than the average cataract patient in the other study.1 In our study, the RLE group was significantly younger (mean 54.2 ± 6.33 years) than the cataract group (mean 63.3 ± 6.8 years). The breakeven point was well centered between the 2 mean ages.

Visual acuity alone is insufficient to assess subjective disability from vision disturbances.8 That patients with a good preoperative visual acuity benefit from cataract surgery in terms of visual function has been shown.7 In a study by Amesbury et al.,7 the basis for assessing visual function was glare measurements obtained in a nonstandardized manner and results on the VF-14 questionnaire.25 The use of questionnaires to assess visual function has been validated and has even been proposed as a way to determine eligibility for cataract surgery; however, questionnaire results can be confusing and controversial.4,8,25,26

A weakness of our study is that we did not use a visual function questionnaire. Previous studies have used questionnaires to assess the effect of straylight and visual acuity on visual quality.1 The study found that straylight and visual acuity taken separately had more or less the same influence on visual quality.1 Our dataset of eyes with good preoperative acuity and our lack of exclusion of any level of preoperative straylight complements the previous dataset,1 in which the effects of straylight and visual acuity on visual quality were assessed separately in a population of cataract patients.

Visual function questionnaires are problematic in the sense that the results can be erratic and influenced by psychological or circumstantial factors.27–30 Correlations with other measures, such as visual acuity, are low. Also, each question on these visual function questionnaires results in an answer on 1 dimension of vision; thus, the summation and averaging of the results of a set of these questions will lead to generalization of different parameters in 1 dimension.31 Even so, visual function questionnaires are considered useful in assessing functional visual outcomes of cataract surgery in the public health setting.4

In the pseudophakic population, straylight levels vary.32–36 There is no consensus on the effect of multifocality of an IOL on straylight. Dick et al.37 found no difference between eyes with a monofocal IOL and eyes with a multifocal IOL. One study32 found that when adjusted for age, straylight was higher by a mean of 0.078 log(s) with an apodized diffractive IOL than with a monofocal IOL of the same material. Ehmer et al.34 found a larger increase in straylight in cases of multifocal pseudophakia. Other studies35,38 found no increase in straylight with multifocal IOLs compared with monofocal IOLs. The type of addition (add)33 or type of multifocal IOL (eg, sectorial-add multifocal IOL36) made no difference. De Vries et al.32 found that in a patient population younger than 70 years, the mean straylight in the multifocal IOL group was 1.113 log(s), which compares well with our results. In the study by van der Meulen et al.1 of straylight in cataract surgery, the mean postoperative straylight was 1.29 log(s) and the mean age was significantly higher than in our study. In our study, we did not differentiate between the types of multifocal IOLs, a matter that requires further study. Also, it has been shown that in pseudophakic eyes, straylight increases with age because of posterior capsule opacification, vitreous turbidity, or reasons that have not been elucidated.14 The size of the capsulorhexis,39 the use of anterior capsule polishing during surgery, and the biocompatibility of the IOL material with the capsule may play a role.39,40 The effect of a specific operative technique on postoperative straylight levels is difficult to elucidate. What is clear is that early cataract extraction or RLE in eyes with higher preoperative straylight levels, even in the presence of a good corrected visual acuity, leads to a significant decrease in straylight to levels in younger phakic eyes. Preoperative increased straylight levels may justify surgery under the definition of a medically indicated cataract procedure, even in cases with good visual acuity. In eyes with low preoperative straylight values, straylight may increase postoperatively as a result of 1 or a combination of the above-mentioned known causes.

In conclusion, straylight improved considerably in eyes with higher preoperative levels of straylight, despite a good corrected preoperative visual acuity, in eyes in which lens extraction performed for a cataract or a refractive purpose. The addition of straylight preoperatively helps predict which patients will benefit from lens extraction for either reason.

What Was Known

  • Straylight measurements may predict which patients will benefit from cataract extraction, independent of visual acuity measurements.

What This Paper Adds

  • Straylight improved after phacoemulsification in eyes with good visual acuity.
  • Straylight measurements may help detect patients with an increase in disability glare that may benefit from phacoemulsification, despite having good visual acuity and thus justifying the performance of cataract surgery.

References

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Financial Disclosures

The Royal Dutch Academy of Arts and Sciences has a proprietary interest in the C-Quant Straylight meter. Dr. Lapid-Gortzak has received speaker fees from Alcon Laboratories, Inc., Hanita Lenses, Merck Sharp & Dohme Corp. and Thea Pharma GmbH and is a clinical investigator for Alcon Laboratories, Inc. Dr. van der Meulen has received speaker fees from Merck Sharp & Dohme Corp. No other author has a financial or proprietary interest in any material or method mentioned.

© 2014 by Lippincott Williams & Wilkins, Inc.