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MC Howlett, SA McFadden; A Fast and Effective Mammalian Model to Study the Visual Regulation of Eye Growth . Invest. Ophthalmol. Vis. Sci. 2002;43(13):2928.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: To develop the pigmented guinea pig (GP) as a mammalian model of eye growth control, that has the advantages of the chick including rapid changes in eye growth in response to visual manipulations, a non-surgical method of lens & diffuser attachment, ready access and easy animal care. Methods: Lenses or diffusers were attached over the GP eye using Velcro®. Refractive errors (RE) were assessed by streak retinoscopy under cycloplegia in awake animals. Axial measures were made with high frequency A-scan ultrasound while GPs were anaesthetised with halothane. Three major paradigms were tested. 1. Form deprivation (FD): From 5 days of age, GPs wore monocular diffusers for 6, 11 or 16 days (n= 19,19 & 15 resp) (Also see McFadden SA, ARVO, 2002). 2. Recovery from FD: 18 GPs wore diffusers for 11 days and then had unrestricted vision for 1, 2 or 3 days. 3. Lens wear: Lenses (+ 4, +2, -2, -4 D or plano, n=6 for each) were worn monocularly for 10 days from 2-3 days of age. Fellow control eyes were untreated. A binocular group (n=6) wore +4 D lenses over one eye and plano over the fellow control eye from age 2-7 days. All data are presented as the difference between the experimental and control eyes at the end of the experiment. Results: 1. FD: All 3 occlusion periods led to longer axial lengths (p<0.001 in each case) and myopic RE (p<0.0001) compared to the fellow eyes. Most of the axial and RE change occurred within the first 6 days (79% & 69% resp). 2. Restoring unrestricted vision rapidly reduced the myopic RE and axial length differences (p<0.05 in each case), the majority of change occurring in the first 24hrs. 3. GPs wearing plano lenses developed -2.2±.5 D (mean ± se) of myopia and slightly longer eyes (.01±.01mm). Compared to the plano group, animals wearing either +4 or +2 D were more hyperopic (-.44±.4 & -1.1±.5 D resp) and had shorter axial lengths (-.04±.1 & -.03±.01 mm resp) while GPs wearing -2 or -4 D lenses were more myopic (-3.66±.7 & -5.31±.5 D resp) and had longer axial lengths (.04±.01 & .06±.02 mm resp). The hyperopic response was confirmed: in subjects wearing both +4 and plano lenses, the experimental eyes were 2.7±.04 D more hyperopic and .05±.02 mm shorter in axial length. Conclusion: Altering the visual environment of the GP with either lenses or diffusers produces rapid changes in the physical and optical properties of the eye. The GP therefore presents a useful model to study the visual regulation of eye growth conferring many of the benefits of the popular chick model, while offering the potential to quickly assess genetic and biochemical regulators of eye growth in a mammalian retinal and vascular ocular system (See Mertz JR et al, ARVO, 2002).
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