Corrrection of exotropia by implantable collamer lens.

Sir,

Exotropia associated with myopia is a common presentation in strabismus practice. Usually, the deviation is corrected by appropriate refractive correction.[1] However, patients presenting late, having high myopia or significant anisometropia, have limited binocularity and the deviation remains unchanged with use of glasses.[1] Refractive correction by phakic intraocular lenses (IOLs) has been known to significantly improve the quality of vision, enhance binocular functions, and also has a positive impact on ocular deviations.[23]

A 21-year-old lady presented in our strabismus clinic for cosmetic correction. She was using a refractive correction of −4.5 D sphere in right eye (RE) and plain glass in left eye (LE) for 2 years. Her logMAR visual acuity (VA) with glasses was 0.0 (20/20) RE and 1.5 (20/640) LE. She had left ET of 25PD with no variability or incomitance. Her correction was appropriate in RE; however, but LE improved to 1.1 (20/250) with −20.0 D Sphere. Both eyes had myopic degeneration with no staphyloma or treatable lesions. RE amblyopia therapy trial for 3 months caused no change in VA or ocular deviation. Simultaneous macular perception without fusion was present. Refractive correction followed by ocular alignment was planned. After appropriate evaluation and peripheral iridotomies, the patient underwent implantable collamer lens (Visian Implantable collamer lens (ICL) − Staar Surgical, California) implantation simultaneously in both eyes (−6.5 D RE, −23.0 D LE). 3 days postoperatively, the uncorrected VA improved to −0.1 (20/16) in the RE. The corrected VA in LE was 0.6 (20/80) with −0.75 D Sph. She was orthophoric for distance and near with fusion with a limited range.

The following factors played a role in satisfactory outcome of our patient:

Contact lenses are known to increase the accommodative effort in myopes compared to spectacles with the increase being proportional to the refractive error.[4] The phakic IOLs have a greater effect on the accommodative effort.[23]

An exotrope, when wearing minus spectacle lenses, looks through a base out prism which apparently increases the magnitude of an exodeviation. The prismatic effect is proportional to the refractive correction. When contact lenses (or phakic IOLs) are used, this effect is eliminated, revealing the true angle of deviation.[5]

A large portion of the stimulus to fuse is elicited through the peripheral field of vision. For highly myopic patients, glasses create significant peripheral distortion. With phakic IOLs, peripheral distortions are eliminated making fusion easier.[6]

A clearer, lesser minified, and aniseiokonic image stimulates and enhances binocularity. Myopic refractive correction closer to the nodal point is well-known to improve VA.[7]

The observations of (i) restoration of ocular alignment, (ii) elimination of need for spectacles, (iii) improvement in best corrected VA, and (iv) improvement in binocularity prove the optical and functional superiority of ICL over spectacle lenses. But for the ICL, this patient may have been subjected to strabismus surgery. This demonstrates that patients with ocular deviations associated with high refractive errors should undergo an appropriate procedure to eliminate spectacles before squint surgery.