ACUITY AND CONTRAST SENSITIVITY IN MONKEYS AFTER NEONATAL INTRAOCULAR-LENS IMPLANTATION WITH AND WITHOUT PARTTIME OCCLUSION OF THE FELLOW EYE

Purpose. The authors used a monkey model to evaluate intraocular lense s (IOLs) for the treatment of infantile cataract in humans. Specifical ly, they sought to assess the effectiveness of IOLs, with and without occlusion therapy, in preventing amblyopia. Methods. A diffuser contac t lens was placed on one eye each of 11 neonatal monkeys to simulate a n infantile cataract. A unilateral lensectomy, combined with the impla ntation of an IOL, was performed on the same eye 1 to 2 weeks after bi rth. Clear contact lenses were used to adjust the optical correction o f tile pseudophakic eyes to a near point, and opaque lenses were used to maintain daily parttime (70%) occlusion of tile fellow eyes of half tile subjects. Behavioral methods were used to assess grating acuity, optotype acuity (Landolt C), and contrast sensitivity. Results. In fi ve of the animals, complications that developed in the eye with the im plant were severe enough to interfere with visual function. The author s present only behavioral outcomes obtained before or in the absence o f surgical complications. In monkeys that underwent daily 70% occlusio n, grating acuity in the pseudophakic eyes eventually matured to norma l adult levels. Grating acuity was significantly poorer in animals wit h no occlusion therapy. Even in animals with normal grating acuity, as sessments of optotype acuity revealed amblyopic deficits; contrast sen sitivity was impaired as well at middle and low spatial frequencies. C onclusions. The current study demonstrates that if there are no compli cations secondary to surgery, normal grating acuity can be obtained in neonatal monkey eyes that undergo IOL implantation, optical correctio n of the pseudophakic eye to a near point, and 70% occlusion of the fe llow eye. However, these good outcomes for grating acuity cannot be at tained without occlusion therapy. In addition, optotype acuity and sen sitivity to contrast always are impaired.