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Management of Extended-Wear Contact Lenses in Infant Rhesus Monkeys

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Management of Extended-Wear Contact Lenses in Infant Rhesus Monkeys Behavior Research Methods, Instruments, & Computers 1988, 20 (I), 11-17 Management of extended-wear contact lenses in infant rhesus monkeys ALCIDES FERNANDES, MARGARETE TIGGES, JOHANNES TIGGES, J. ALLEN GAMMON, and CHARLES CHANDLER Emory University, Atlanta, Georgia Infant rhesus monkeys were fitted with extended-wear contact lenses (EWCLs) to correct sur­ gically induced aphakia. The protocol that produced the most favorable experimental outcome, including goodlens-wear compliance, involved: (1) custom-made EWCLs with parameters adjusted for each animal, (2) selection for study of neonates who seemed to tolerate EWCLs most natur­ ally, (3)individual housing of monkeys, (4)lens check at 2-h intervals around the clock by trained personnel, (5) a large inventory of EWCLs for each animal, (6) periodic ophthalmologic examina­ tions, and (7)darkroom housing of monkeys during treatment oflens-wear-related incidents. The EWCL is a new tool for studies of the visual system and is a useful complement to existing ex­ perimental techniques. The visual system of infant rhesus monkeys has been they provide a wide range of possibilities for manipulat­ studied extensively to determine the effects of visual ex­ ing the visual input under various deprivation conditions. perience on the development ofnormal visual functions. For example, lenses can be designed to produce focused In particular, experiments using monocular deprivation images on the retina of objects at known distances, near have proven the importance of equal patterned inputs to to the monkey or far from it. Lenses can be dyed black both eyes for the development of binocular vision. For and used as occluders to reduce stimulation of the retina. example, the technique of suturing the lids of one eye It is possible with EWCLs to provide a totally different deprives that eye of contour vision and results in severe visual experience for each eye. For example, an aphakic functional and anatomical deficits in the visual system eye (i.e., an eye without its natural lens) can be provided (Wiesel, 1982). Other tools and techniques have also been with a corrective lens, and an occluder lens can be used devised to modify normal visual experience, including hel­ on the fellow eye of the same infant monkey. In fact, this mets designed to hold optical prisms in front of the eyes experimental situation is a close simulation of the treat­ (Crawford & Von Noorden, 1979) and daily unilateral ment of a congenital monocular cataract in human infants. atropinization to cause monocular blurred images of the Weare concentrating our experimental efforts on this visual world (Kiorpes et al., 1987; Von Noorden, 1981). monkey model of a specific human condition (Fernandes We have introduced the use of extended-wear contact et al., 1986; Gammon et al., 1985). lenses (EWCLs) to manipulate visual experience in ne­ After the removal of monocular cataracts from human onate rhesus monkeys (Fernandes et al., 1986; Gammon, infants, those fitted with EWCLs to correct aphakia de­ Boothe, Chandler, Tigges, & Wilson, 1985). EWCLs are veloped good vision (Beller, Hoyt, Marg, & Odom, convenient to use because they can be easily inserted in 1981). However, it has not been resolved whether an the monkey's eyes and removed from them. Moreover, aphakic eye should be overcorrected, undercorrected, or corrected to plano to achieve optimal vision. Also, the Some of the ophthalmic surgery was performed by consultant optimal duration of patching (occlusion) of the fellow eye ophthalmologists H. M. Eggers and J. P. Wilmeth. Special thanks are is still undetermined. Therefore, the data resulting from due the veterinarians of the Yerkes Regional Primate Research Center our monkey experiments have clinical relevance for the (YRPRC) and their stafffor providing expert care to the monkeys. Ex­ treatment and management of monocular congenital pert technical services were provided by C. L. D'Amato, C. D. O'Dell, cataracts in children. K. L. Hipps, M. W. Quick, and D. J. Torbit. We are especially in­ debted to Kevin L. Vaughan for his dedication and expertise in lens The purpose of this paper is to describe the methods manufacturing. R. G. Boothe, J. G. Herndon, and J. R. Wilson ren­ and procedures that we found essential for the successful dered helpful suggestions during the preparation of the manuscript. This application of EWCLs in monkeys. Lens-wear compli­ investigation was supported in part by NIH Grant RR-00165 from the ance and tolerance are also reported. Division of Research Resources to the YRPRC, by Grants EY-0536l and EY·05975 to J. Allen Gammon, and by Grant EY..Q6001 to Mar­ garete Tigges. Support was also received from VisionTech, American METHOD Medical Optics, the National Children's Eye Care Foundation, and The Subjects National Society for the Prevention of Blindness. The YRPRC is fully All 34 rhesus monkeys (Macaca mulatta) of this study accredited by the American Association for Accreditation of Labora­ were born in the breeding colony of the Yerkes Regional tory Animal Care. Address correspondence to Margarete Tigges, Yerkes Regional Pri­ Primate Research Center (YRPRC). In 11 neonatal mon­ mate Research Center, Emory University, Atlanta, GA 30322. keys, one normal eye was continuously occluded to pre- 11 Copyright 1988 Psychonomic Society, Inc. 12 FERNANDES, TIGGES, TIGGES, GAMMON, AND CHANDLER vent stimulation of the retina. To simulate the condition growth of the eye and to select the appropriate contact oflens removal as a treatment of monocular cataract, 23 lens diameter. In addition, retinoscopy and refraction monkeys underwent unilateral lensectomy during the first served to determine the power of the correct lens accord­ or second week of life; during this procedure an Ocutome ing to experimental requirements. Keratometry (Varidot) was used. Surgeries were performed under ketamine and measurements were used to determine the refractive pentobarbitol anesthesia administered by a staff veterinar­ powers of the corneas, which, in conjunction with the axial ian. The monkeys were closely monitored after surgery lengths ofthe eyes, supplied the data necessary to calcu­ to prevent postsurgical discomfort and complications. All late the refractive powers of the contact lenses. surgical and clinical procedures were performed in strict compliance with the NIH "Guide for the Care and Use Lens Manufacturing of Laboratory Animals." All EWCLs were produced in our laboratory, because The infants were housed in the nursery of the YRPRC. the eyes of neonatal monkeys require lenses that are They were reared initially in isolettes and at 6-8 weeks smaller than commercially available lenses. The material of age were transferred to individual cages. This rearing used was lidofilcon B, a hydrophilic plastic that hydrates procedure facilitated supervision with respect to lens-wear to 79% water when immersed in 0.9% saline. compliance and early detection of lens-wear-related Lathes (Nissel, Robertson) were used for the produc­ problems. tion ofcontact lenses ofvarious diameters, base curves, For this report, we selected lilensectornized and 4 oc­ and corrective powers. Details of mathematical calcula­ cluded monkeys from the total of 34 animals. These mon­ tions for our lens-cutting specifications and of other tech­ keys were chosen because they had been in the study for nical aspects involved in lens manufacturing will be the longest time and served as examples of the full spec­ provided in a separate publication. Quality controls (con­ trum of lens-wear compliance and tolerance. firmation of diameters and base curves, inspection of These monkeys belonged to the following experimen­ edges and optical surfaces) were performed at appropri­ tal groups: Group I-Optical overcorrection of the ate steps during the lens-manufacturing process. We made aphakic eye to a near point; full-time occlusion of the non­ occluders from plano lenses that were dyed black and used operated fellow eye (monkeys RPK-I, RQK-I, RSK-I, as "patches." After dying, each occluder was inspected and RTK-1). Group 2-0ptical undercorrection of the to ensure opaqueness. The lens manufacturing process is aphakic eye; full-time occlusion of the non-operated fel­ labor-intensive. It takes a trained lens maker about 2 h low eye (monkeys RAP-22, RAP-23, and RAP-24). to produce one edged lens from a plastic button. Group 3-0ptical overcorrection of the aphakic eye to a near point as in Group I; no manipulation of the normal Lens Fitting fellow eye (monkeys RAP-20, RJN-I, RNN-I, and Monkeys were fitted with EWCLs based on the follow­ ROQ-I). Group 4-Continuous occlusion of one normal ing ocular measurements: Keratometry measurements eye; no manipulation of the normal fellow eye (monkeys served to determine the base curve; these curves for new­ RCI-I, RGI-I, RHR-I, and RYK-I). born monkeys varied from 6.8 to 7.0 mm. Lens diameter We will also briefly describe the lens history of the only was based on measurements of horizontal corneal di­ 2 monkeys (N-897 and RAP-IS) of the total of 34 animals ameters; the lens diameters for the neonatal eyes ranged that did not comply with the experimental protocol be­ from 11.0 to 1l.S mm. cause of lens-wear-related problems. These monkeys are The initial lens fitting for each monkey was done on not listed in Table 1. a trial basis, beginning with a lens closely corresponding to the monkey's corneal diameter. Ideally, the contact lens Eye Examinations should remain centrally positioned on the cornea with Formal ophthalmologic examinations were performed slight vertical movements during each blink. A steeper before surgery to assure that the monkeys did not have base curve should be selected if lens movement is exces­ congenital eye disorders and after surgery to detect pos­ sive. A lens with a flatter base curve should be chosen sible postoperative complications. Thereafter, monthly if little or no movement of the lens is observed.
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