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Marsha L. Kisilak, Kaitlin Bunghardt, Melanie C. Campbell, Elizabeth L. Irving, Sally A. McFadden, V; Optical Properties and Accommodation in the Guinea Pig Eye. Invest. Ophthalmol. Vis. Sci. 2011;52(14):845.
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Generally, the guinea pig eye shows emmetropization and accommodation and is a model of myopia. Some animals have been reported to be spontaneously myopic and lack accommodation. We studied the retinal image quality in the guinea pig eye as a function of any accommodation.
Three male guinea pigs aged 5.5 weeks were acquired from a Canadian pet supplier. Retinoscopy and Hartmann-Shack (H-S) measurements were attempted in each awake animal with natural pupils and in two animals after cycloplegia (1% cyclopentolate). Keratometry was performed on all eyes. Eye length was measured in one animal. H-S measurements were analyzed for refractive errors and higher order aberrations (HOA) and their co-dependence was assessed. Values of astigmatism and HOA’s are reported for the first time.
Noncycloplegic retinoscopy gave variable refractions across and within eyes, from hyperopic to myopic. One eye with 6D of myopia by retinoscopy prior to cycloplegia became emmetropic after cycloplegia. For many of the H-S frames, spots could not be analyzed due to poor tear film and optical quality issues. Average H-S refractions varied from -1.2D to +3.1 D in different eyes. Under cycloplegia, the quality of the H-S patterns worsened. Refraction, eye length and keratometry values were consistent with published values. Cylinder values ranged between 1.5 and 2 D. HOA’s could be analyzed over pupil sizes up to 3 mm diameter, smaller than the full pupil, giving root mean square values of 0.08 microns. Spherical aberration (SA) was highly variable, even across frames within an eye. SA was increasingly negative with increasingly negative mean ocular refraction (MOR), significant when data were combined across all eyes (p<0.0001). HOA also depended significantly on MOR in some eyes and across all eyes with a minimum close to emmetropia.
The optical quality of these guinea pig eyes was poorer than chick eyes (a diurnal species) and more similar to our previously reported results in rat eyes, another non-diurnal species. Optical quality worsened with tear film degradation and cycloplegia. Unlike other rodents, these animals appear to accommodate. The dependence of SA on MOR also suggests varying accommodation during H-S measurements, similar to that seen in humans with accommodation. As in other species, SA, astigmatism and accommodation could provide signals to emmetropization. Although accommodation appears to increase the variability of HOA’s, cycloplegia impairs optical quality.
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