Case report

Aberrometry changes following surgical management of isolated typical lens coloboma

Kaweri, Luci MD*; Kurian, Mathew MS, DNB; Madhu, Sumukh DNB; Das, Sudeep DO, DNB; Shetty, Rohit FRCS, PhD; Shetty, Bhujang MS

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Journal of Cataract and Refractive Surgery Online Case Reports: April 2016 - Volume 4 - Issue 2 - p 19-22
doi: 10.1016/j.jcro.2016.02.001
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Abstract

A typical ocular coloboma results from the failure of the embryonic fissure of the optic cup to fuse along the line extending from the optic disc to the inferonasal border of the pupillary margin.1 The colobomatous defects usually occur in association with several other ocular or systemic pathologies.2 An isolated lens coloboma is a rare entity.3 It occurs because embryonic fissure fails to fuse during the fifth to seventh weeks of fetal life.4 Absence or weakening of zonular fibers in the area of the coloboma induces flattening, concavity, notching, and segmental contraction in that area.5 This results in high lenticular astigmatism.6

Outcomes of cataract surgery in cases of typical lens coloboma have been reported.5,7 We report the aberrometric changes following surgical management by lens extraction with intraocular lens (IOL) and capsular tension ring (CTR) implantation for visual rehabilitation in typical isolated lens coloboma.

CASE REPORT

A 23-year-old woman presented to us with complaints of decreased vision in the right eye since childhood. The uncorrected distance visual acuity (UDVA) was 20/200 in the right eye and 20/40 in the left eye, with near vision of N12 and N6, respectively. The acuity improved to 20/30 and N8 with −1.0 −6.5 × 20 in the right eye and 20/20 and N6 with 0.75 −1.75 × 180 in the left eye. Dilated slitlamp examination showed the presence of a lenticular coloboma of about 2 clock hours in the inferonasal quadrant in the right eye (Figure 1, A and B). The rest of the ocular examination was within normal limits in both eyes.

Figure 1.
Figure 1.:
Preoperative evaluation. A: Slitlamp photograph of pharmacologically dilated right eye showing clear lens with inferonasal lenticular coloboma from 4 o'clock to 6 o'clock (2 clock hours). B: Slitlamp photograph of pharmacologically dilated left eye showing clear crystalline lens. C: Ray-tracing aberrometry showing increased internal and total defocus (white arrows) in the right eye. D: Ray-tracing aberrometry showing normal ocular aberrations in the left eye.

Ray-tracing aberrometry (iTrace, Tracey Technologies) performed in natural light conditions (<1 lux) to achieve mesopic pupillary dilation (3.0 mm) with an internal light-emitting diode target showed high internal defocus of 1.098 μm, high internal astigmatism of 1.156 μm, and increased total ocular aberrations of 1.543 μm (Figure 1, C and D). The area under the curve (AUC) of the modulation transfer function (MTF) was 3.308 from the poor internal optics caused by the lenticular colobomatous changes. Visual simulation using the Snellen equivalent showed gross distortion in the right eye.

Based on the patient's symptoms and clinical examination, lens extraction with CTR and IOL implantation was planned in the right eye. Keratometry (K) measured using the Pentacam HR (Optikgeräte GmbH) showed astigmatism of 2.7 diopters (D) on the corneal plane (flat K 40.2 D @ 20.4; steep K 42.9 D). The option of a toric IOL was explained to the patient, but because of the additional costs involved, she opted for a monofocal IOL. Implantation of a negative aspheric (corneal spherical aberration +249 μm) monofocal IOL (Acrysof IQ SN60WF) was planned.

Under topical anesthesia, two 1.0 mm side-port incisions and a 2.2 mm clear corneal incision were made. A large molecular weight ophthalmic viscosurgical device (sodium chondroitin sulfate 4.0%–sodium hyaluronate 3.0%, Viscoat) was used as a tamponade to prevent vitreous from entering the anterior chamber in the area of the coloboma. A continuous curvilinear capsulorhexis was made using a 26-gauge bent cystotome needle centered on the lens. Lens aspiration and implantation of a single-piece monofocal IOL with CTR insertion were performed without disturbing the vitreous (Figure 2) (Video 1).

Figure 2.
Figure 2.:
Surgical management showing intraoperative image of an inferonasal lenticular coloboma (A), a continuous curvilinear capsulorhexis centered on the lens (B), clear lens aspiration (C), irrigation/aspiration (D), insertion of a CTR (E), and a well-centered IOL (F).

One week after surgery, the UDVA in the right eye was 20/60, improving to 20/30 with pinhole. Anterior segment examination showed a well-centered posterior chamber IOL. One month after surgery, the CDVA was 20/30 with a manifest refraction of −0.75 +1.75 × 110. Ray-tracing aberrometry showed a decrease in internal defocus (0.154 μm, 85.97% decrease) and total higher-order aberrations (HOAs) (0.137 μm, 91.12% decrease). The AUC of the MTF improved from 3.308 to 8.913 (169.4% increase). The Snellen letter display showed considerable improvement in letter morphology (Figure 3).

Figure 3.
Figure 3.:
Preoperative and 1-month postoperative internal ocular aberrations. A: A decrease in internal defocus and internal astigmatism (white arrows). B: Total mean MTF curve shows an increase in height for each spatial frequency after surgery. C: Visual acuity simulation using the Snellen equivalent E chart shows significant improvement in distortion after the procedure.

DISCUSSION

Congenital coloboma of the lens results from the failure of embryonic fissure to close and is characterized by the lack of inferior lens equator with zonular dialysis or weakness.8 None of the ocular or systemic associations of lenticular coloboma mentioned in the literature was seen in our patient.2,3 Unilateral isolated lens coloboma is rare; when cases occur, they usually present with dense anisometropic amblyopia.5 Amblyopia was not pronounced in our case despite the high spherocylindrical error that could have resulted in distorted vision and monocular diplopia.9

Our patient did not complain about diplopia or distorted vision, but ray-tracing aberrometry showed significant distortion in the simulated Snellen visual acuity chart and helped us counsel the patient for surgery. Ray-tracing aberrometry can distinguish between the aberrations arising from the cornea and those arising from the total ocular aberrations.10 The lens is the major contributor to internal aberration.11 Aberrometry objectively confirmed that visual disturbances were lenticular in origin, and therefore we proceeded with our clinical decision of lens extraction and IOL implantation. Lens aspiration was completed using low phaco parameters, and a CTR was inserted after IOL implantation for better centration and long-term stability as the coloboma was less than 3 clock hours.12

Postoperatively, the CDVA improved and there was a significant decrease in manifest cylinder. The residual cylindrical values can be attributed to astigmatism on the corneal plane. Aberrometry was also repeated after the procedure. There was significant decrease in internal defocus (86%) and total ocular aberrations (91%) with a centered IOL, confirming that the earlier aberrations were predominantly lenticular in origin. Image quality metrics like MTF display the ratio of image contrast to object contrast for ocular optics as a function of the spatial frequency of a sinusoidal grating.13 The imaging capability of the human optical system can be analyzed using MTF, and the imaging quality of the visual image can be better explained by the MTF.14 In our case, the MTF curve showed an increase in values for each spatial frequency, with the AUC of the MTF showing an increase of 169%, suggesting significant improvement in functional vision.

Our report documents the improvement in the aberration profile in a case of noncataractous unilateral isolated lenticular coloboma after lens extraction with IOL and CTR implantation. Detailed analysis of HOAs and lower-order aberrations along with MTF showed that not only quantity but also quality of vision were significantly impaired in a case of lenticular coloboma and that vision improved significantly with treatment. Thus, we believe that aberrometry is a useful tool for objective assessment and patient counseling.

REFERENCES

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SUPPLEMENTARY DATA

Video 1
Video 1:
Intraoperative surgery of a case of isolated typical lens coloboma of 2 clock hours (from 4 to 6 o'clock position) in which clear lens extraction was done with implantation of a monofocal intraocular lens and a capsular tension ring.
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