赤錐体一色型色覚の所見を呈した1例

A case of deutan type of achromatopsia with normal visual acuity

　等色実験の結果，一種類の原刺激であらゆる検査色光と完全等色が成立し，その分光感度が赤錐体の特性を示したことから，赤錐体一色型色覚と診断された1例について報告した．

　本症例は先天性赤緑異常と診断されていたが，視力良好にもかかわらず，各種検査表に応答不能が多く，青黄異常検出表も判読不能であった．さらに，色相配列検査における色相混同軸が第2異常からややscotopic軸寄りに存在し，通常の赤緑異常とは性質を異にしていた．また，視野検査において内部イソプターの著しい狭窄が示され，周辺部における杆体系の機能異常も示唆された．さらに，中心部における暗順応曲線は2相性であり，2種類のメカニズムの存在が示され，これらの回復速度から本症例では網膜中心部に赤錐体系とともに杆体系の反応を有しているものと推察した．

A 17-year-old male presented with deutan type of achromatopsia. His visual acuity was 1.2 in both eyes. Slitlamp and funduscopic findings were un-eventful. Goldmann perimetry showed severe con-traction of visual fields for test targets I-4 to I-1 in both eyes. He failed to read any plate of Ishihara' s, AO-HRR, Okuma's or TMC plates. Panel D-15 test showed a trend toward the scotopic axis from the deutan axis. The orientation axis of hue errors for 100-Hue test fell close to the deutan axis with a slight trend toward the scotopic axis.

He could make an exact match for every spectral light against a 560 nm primary of 100 trolands by merely adjusting the intensity of test light. The action spectrum was similar to that of normal photopic or deuteranopic function. Dark adatation curve for 480 nm test light at the fovea showed two branches. The time constants for the upper and lower branch were similar to that of cone and rod mechanisms respectively.

It was concluded that this subject, though a monochromat, has two functioning mechanism at the fovea : one as red cone and the other as rod.

Rinsho Ganka (Jpn J Clin Ophthalmol) 42(7) : 797-799, 1988