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Case report

Wavefront analysis and Scheimpflug imagery in diagnosis of anterior lenticonus

Xu, Yinfei; Hersh, Peter S. MD; Chu, David S. MD

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Journal of Cataract & Refractive Surgery: May 2010 - Volume 36 - Issue 5 - p 850-853
doi: 10.1016/j.jcrs.2009.09.043
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Abstract

Anterior lenticonus is a rare condition in which a portion of the crystalline lens capsule and underlying cortex bulge anteriorly. The conical protrusion results from a genetic defect in synthesis of type IV collagen, a major component of the lenticular basement membrane.1 Anterior lenticonus develops progressively and bilaterally, possibly manifesting as severe myopia and lenticular irregular astigmatism.2 Although sometimes isolated, anterior lenticonus may present as a pathognomonic feature of Alport syndrome, a hereditary nephritis accompanied by sensorineural hearing loss as well as other ocular abnormalities.3 Anterior lenticonus occurs in approximately 25% of patients with X-linked Alport syndrome.4 Posterior lenticonus is not usually associated with a systematic disease.5

Several articles have reported success in treatment of anterior lenticonus. Liu et al.5 recommend phacoemulsification with foldable intraocular lens (IOL) implantation as a safe and efficient procedure. However, the disorder must be diagnosed before it can be treated, a process that may prove difficult. Because the change in lens contour is often very subtle, anterior lenticonus can remain undetected throughout ocular examinations. New imaging technology, such as wavefront analysis and Scheimpflug imaging, can help in the early diagnosis of such optical disorders.

To demonstrate these technologies as important tools in diagnosing anterior lenticonus and other optical disorders, we present an Alport syndrome patient whose subtle lenticular abnormalities were first detected by wavefront analysis and then confirmed by Scheimpflug quantitative imaging.

CASE REPORT

A 44-year-old man with Alport syndrome was referred to our clinic to be considered for refractive surgery. His chief complaint was a progressive reduction of vision in both eyes, and he sought the procedure in hopes of improving his vision. Ocular symptoms were managed by wearing prescription glasses, but corrected distance visual acuity (CDVA) remained unsatisfactory. Ocular history was otherwise unremarkable. The patient had a history of renal failure and kidney transplantation 21 years previously. His medications included prednisone, cyclosporine, magnesium oxide, acitretin, esomeprazole magnesium, amlodipine besylate, atorvastatin calcium, warfarin sodium, colchicines, iron polysaccharide, atenolol, doxercalciferol, fenofibrate, folic acid, duloxetine hydrochloride, methotrexate, allopurinol, and digoxin.

On examination, the uncorrected distance visual acuity was 20/50−1 in the right eye and 20/70 in the left eye. The CDVA and subjective manifest refraction were 20/30−1 with −6.25 –1.00 × 155 in the right eye and 20/40−2 with −7.25 –2.50 × 170 in the left eye. Slitlamp biomicroscopy revealed a clear, compact cornea with normal intraocular pressure and fundi. No significant cataract or other obvious anomalies of the lens and anterior segment were observed. Corneal topographic and elevation maps computed by Pentacam software (Oculus) were normal. Sagittal curvature and elevation maps of the front of the cornea are shown in Figure 1.

Figure 1
Figure 1:
Corneal topographic maps showing sagittal curvature and elevation in the normal left eye.

Wavefront analysis was performed with the LADARWave aberrometer (Alcon, Inc.), which uses Hartmann-Shack principles to detect, measure, and display higher-order aberrations (HOAs). Total-eye wavefront analysis revealed high negative spherical aberration in both eyes with root mean square (RMS) values of −1.08 μm and −1.43 μm in the right eye and left eye, respectively. Preoperative wavefront maps with Zernike modes and aberration values are shown in Figure 2 and other HOAs and lower-order aberrations, in Table 1. Given normal corneal maps and abnormal total-eye wavefront analysis, the internal optics of the eye was likely the main source of vision deficits.

Figure 2
Figure 2:
Preoperative wavefront maps of right (A) and left (B) eyes showing dominant spherical aberrations in both eyes, represented by a highly negative center with a positive ring. Zernike modes, including coma and spherical, with the patient's total-eye aberration values are shown below the wavefront maps.
Figure 2
Figure 2:
(continued)
Table 1
Table 1:
Preoperative wavefront aberrations in right and left eyes of anterior lenticonus patient and postoperative results in the left eye.

The Oculus Pentacam is able to define the anterior curvature of the lens. Rotating Scheimpflug imaging with the Pentacam captured 25 image slices from the anterior surface of the cornea to the posterior surface of the lens. These images detailed the contour of the protrusion in the patient's dilated lens over a 360-degree circle. Scheimpflug images in Figure 3 display the anterior lenticonus in the patient against that of a normal lens.

Figure 3
Figure 3:
Scheimpflug images showing the dilated lens contour of anterior lenticonus (left) and of a normal lens (right); 4.0 mm chord and lens protrusion values are indicated.

To characterize this Scheimpflug image of lenticonus and compare it with the anterior surface of eyes in the normal population, measurements were taken from the apex of the bulge to a 4.0 mm chord length for 15 refractive surgery candidates with normal lenses. Variability was minimized by including only dilated lenses and candidates within 6 years of age of our patient. Measurements yielded a 400 μm protrusion in the lenticonus eye compared with a mean of 255.7 μm ± 27.2 (SD) in eyes without lenticular abnormalities (Table 2, Figure 3).

Table 2
Table 2:
Anterior protrusion values of normal lenses from 15 refractive surgery candidates within 6 years of age of patient.

Since ocular symptoms were most severe in the left eye, cataract extraction and IOL implantation were performed first in that eye. Following lens removal with phacoemulsification, an AcrySof IOL (Alcon, Inc.) was inserted in the eye.

Table 1 shows the improved wavefront parameters in the operated eye 1 week after IOL implantation. Left eye HOAs, which preoperatively contributed 63% of total aberrations, were reduced to 40%. Improvements included a reduction of coma RMS from −0.64 μm to −0.06 μm and spherical RMS from −1.43 μm to 0.09 μm. Lower-order aberrations were also reduced; eg, defocus from 1.58 μm to 0.16 μm. No marked improvements in astigmatism or other aberrations were found.

The CDVA and subjective manifest refraction was 20/25 with −0.25 –100 × 5 at the 2-month follow-up. The patient was satisfied with the amount of improvement in his vision.

DISCUSSION

This case highlights the role of wavefront analysis and Scheimpflug imaging technology in detecting lenticular abnormalities that were undetected by other ophthalmic examinations, including anterior segment slitlamp. Eye aberrations can result from lenticular and corneal imperfections since the cornea and lens contribute approximately two-thirds and one-third of the total focusing power of the eye, respectively. The subtlety of the lenticular abnormality made it difficult to detect and was observed only after wavefront analysis pointed to it as a contributing factor in the patient's vision loss.

Wavefront maps define the deviation of an aberrated wavefront from the ideal reference wavefront. The reference shape used for comparison is a flat circular plane, which represents an emmetropic, or theoretically perfect, eye. The RMS values correspond to decreases in optical quality and are represented by deviations from the emmetropic plane as cooler or warmer colors. Evaluation of HOAs in our patient revealed predominant spherical aberration in both eyes (Figure 2), suggesting that reflection patterns were produced by an anterior lens surface bulge. In a study evaluating irregular astigmatism, Ninomiya et al.6 found that astigmatism induced by anterior lenticonus produced such spherical-like aberrations. On the other hand, predominance of coma-like aberrations would have indicated keratoconus-induced irregular astigmatism.

Further examination with the Scheimpflug camera captured a complete picture of the anterior segment and provided visual confirmation of anterior lenticonus. Measurements and calculations performed on the images supported the diagnosis with quantitative results. Lenticular protrusion at 400 μm from a 4.0 mm chord was more than 3 standard deviations away from the mean of 255.7 μm in 15 normal patients. Given the patient's medical history of Alport syndrome and wavefront analysis results, Scheimpflug imaging was sufficient to confirm the diagnosis.

After cataract extraction and IOL implantation, total-eye aberrations were reduced from 2.64 μm to 1.38 μm. The improvements in optical quality are reflected in the postoperative wavefront map and aberration values (Figure 4), which show a much greater resemblance to a flat circular plane, representing the emmetropic eye. As most of the aberrations were due to lenticonus, surgical treatment dramatically restored the visual acuity in the patient's left eye from 20/40−2 to a CDVA of 20/25.

Figure 4
Figure 4:
Postoperative wavefront maps (above) and Zernike modes (below) of the left eye showing significant reduction of spherical and other aberrations, resulting in a greater resemblance to the emmetropic eye.

Advanced imaging technologies are useful for diagnosing a variety of optical disorders, including anterior lenticonus. Since optical disorders can have various origins, such as lenticular, corneal, retinal, and or neurological, a long differential process of elimination may be required. However, wavefront analysis can assist the diagnostic process by identifying subtle abnormalities through characteristic clues such as spherical and coma aberrations. Finally, when correlated with medical history and wavefront analysis, Scheimpflug imaging can provide visual confirmation of treatable pathology.

REFERENCES

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2. Liu YB, Tan SJ, Sun ZY, Li X, Huang BY, Hu QM. Clear lens phacoemulsification with continuous curvilinear capsulorhexis and foldable intraocular lens implantation for the treatment of a patient with bilateral anterior lenticonus due to Alport syndrome. J Int Med Res. 36. 2008. 1440-1444. Available at. http://www.jimronline.net/content/full/2008/88/1062.pdf. Accessed January 13, 2010.
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© 2010 by Lippincott Williams & Wilkins, Inc.