Spontaneously Myopic Guinea Pig: Model of Early Pathologic Myopia

PURPOSE: To evaluate whether pigmented guinea pigs with spontaneous myopia present characteristic changes of pathologic myopia. METHODS: The fundus images of guinea pigs (3 weeks old) were graded according to fundus tessellation (FT) degree. Biometric parameters, including refraction, vitreous chamber depth (VCD), and axial length (AL), were measured at ages 21 and 43 days. Some of these animals were divided into three groups: hyperopic without FT (H w/o FT), myopic without FT (M w/o FT), and myopic with FT (M w/ FT). The horizontal and vertical radii of curvature of posterior sclera (R(P-H) and R(P-V), respectively) and the radii of curvature and arc lengths of superior sclera (R(S) and L(S), respectively), inferior sclera (R(I) and L(I), respectively), nasal sclera (R(N) and L(N), respectively), and temporal sclera (R(T) and L(T)) were evaluated by Fuji. RESULTS: The fundi were graded as type A or type B (both without FT), type C (mild FT), or type D (severe FT). The prevalence of FT was correlated with myopic refraction, longer VCD, and longer AL. Eyes of M w/FT animals had shorter R(P-H) and R(P-V), longer R(S) and R(T), and longer L(S) and L(T) than eyes of H w/o FT or M w/o FT animals. Refractions shifted toward hyperopia in eyes lacking FT, but not in eyes having FT. The changes in VCD were consistent with the changes in refraction. This relatively myopic shift in refraction and shortening of VCD were found only in myopic eyes with FT, but not in myopic eyes without FT. CONCLUSIONS: Spontaneously myopic guinea pig eyes have a high prevalence of FT. Myopic eyes with FT presented characteristic signs of pathologic myopia.