2013 Volume 32 Pages 29-33
In recent years, attention has been focused on glaucoma animal models due to increase in the development of therapeutic agents for glaucoma. Cynomolgus monkeys have ocular structure close to that of humans and have been frequently used as a model for laser-induced ocular hypertension. Although diagnosis of glaucoma has been based on intraocular tension, large variations in measurement values have become a problem. In addition, recent studies have shown that patients with glaucoma do not always exhibit high intraocular pressure. Therefore, detecting methods using indices other than intraocular pressure are required for glaucoma. The "Guideline for Detecting Glaucomatous Abnormalities in Optic Disc and Retinal Nerve Fiber Layer"1) (hereafter referred to as "Guideline"), in which evaluation methods independent of intraocular pressure are used, was issued by the Japan Glaucoma Society for humans. In addition, since it takes a long time to condition non-anesthetized cynomolgus monkeys to the intraocular pressure measurement2), an alternative method of detection using numerical indices, which is simpler and not easily affected by the measurement environment, is considered to be effective. Under these circumstances, as the first step of investigation for possible application of the Guideline to cynomolgus monkeys, digital fundus photographs of 97 untreated cynomolgus monkeys (48 males and 49 females, total of 194 eyes) were taken for qualitative evaluation and determination of the vertical cup-to-disc ratio (VCDR) (calculated by dividing the maximum vertical diameter of the cup by the maximum vertical diameter of the disc)3), which are thought to be effective for diagnosis of glaucoma. The purpose of this study was to evaluate glaucoma using the VCDR in fundus photographs, therefore convexo-concaves around the optic papilla were not observed with a slit light lamp. The optic disc of cynomolgus monkeys has a slightly vertically oval form. The optic cup, which is located near the center of the optic disc, also has a slightly vertically oval form. The width of the neuroretinal rim was nearly the same in all areas, except for the upper and lower parts of the optic disc which were slightly wider than the other parts. The mean vertical C/D ratios were 0.56 ± 0.08 (left eye) and 0.55 ± 0.08 (right eye) in males and 0.59 ± 0.08 (left eye) and 0.60 ± 0.08 (right eye) in females. The differences in the VCDR between the right and left eyes were 0.00 to 0.07 in all animals and the mean was 0.02. These values indicated the development of glaucoma was not evident in any animal.
Based on the results for determination of VCDR, it was considered feasible to apply the Guideline to score glaucomatous changes in cynomolgus monkeys.
