眼球電図にてArden比の減弱を伴った網膜および網膜色素上皮過誤腫の1例

A case of combined hamartoma of the retina and retinal pigment epithelium with a lower Arden ratio on electrooculogram

要約　目的：眼球電図は眼球運動を利用して暗所および明所における常在電位を測定する検査で，網膜色素上皮の機能評価に有用である。網膜および網膜色素上皮過誤腫（CHRRPE）は比較的稀な良性腫瘍で，病理組織学的な構成成分の割合により臨床像が異なる。今回，眼球電図にてlight peak：dark trough比（Arden比）の減弱を伴ったCHRRPEの1例を経験したので報告する。

症例：67歳，男性。再生不良性貧血および移植後リンパ増殖性疾患のため，名古屋大学医学部附属病院（以下，当院）血液内科にて化学療法後の経過観察中に視力低下の訴えがあり，白内障の手術加療のため当院眼科に紹介となった。

所見：初診時視力は右（0.8），左（0.2）で，両白内障手術後の視力は右（1.0），左（0.5）となった。両眼の前眼部および中間透光体，右眼の眼底には特記すべき異常を認めなかったが，左眼の眼底には，乳頭近傍から上耳側に広がる，表面に白色の線維性肥厚を伴う境界明瞭な約1乳頭径の隆起性病変を認めた。網膜光干渉断層計では，網膜内層に網膜神経線維層との境界が一部不明瞭な充実性の肥厚性病変を認め，全層性の網膜ひだも伴っており，CHRRPEと一致した臨床像を呈していた。網膜電図では錐体・杆体反応ともに明らかな左右差を認めなかったが，眼球電図ではArden比は右眼1.90，左眼1.37であった。

結論：眼球電図は，CHRRPEにおける発生異常に起因すると考えられる網膜色素上皮の変化を評価できる可能性があり，中高年ではArden比の低下を示すことがある。

Abstract　Purpose：Electrooculography（EOG）is a diagnostic tool used to evaluate retinal pigment epithelium（RPE）function by measuring the standing potential of the eye under varying light and dark conditions using eye movement. Combined hamartoma of the retina and retinal pigment epithelium（CHRRPE）is a relatively rare benign tumor with a variable clinical presentation based on its histopathological composition. In this report, we present a case of CHRRPE characterized by a reduced Arden ratio on EOG.

Case：A 67-year-old man presented with decreased vision while undergoing follow-up after chemotherapy for aplastic anemia and posttransplant lymphoproliferative disease at the Department of Hematology, Nagoya University Hospital. He was referred to our Ophthalmology department with a suspected cataract. Following bilateral cataract surgery, the patient's best-corrected visual acuity was 1.0 in the right eye and 0.5 in the left eye. No significant abnormalities were noted in the anterior segment or intermediate media of either eye, and the fundus of the right eye appeared within normal limits. However, a well-demarcated, elevated lesion measuring approximately one optic disc diameter was observed in the fundus of the left eye. This lesion extended from the peripapillary area to the superior temporal region with white fibrous thickening on its surface. Optical coherence tomography revealed a solid, thickened lesion in the inner retina, partially connecting the retinal nerve fiber layer. Additionally, it showed full-thickness retinal folds, presenting a clinical appearance consistent with CHRRPE. Electroretinography showed no significant differences between the right and left eyes in both cone and rod responses. However, the EOG demonstrated an Arden ratio of 1.90 in the right eye and 1.37 in the left eye.

Conclusion：EOG may be a valuable tool for assessing retinal RPE changes associated with developmental abnormalities in patients with CHRRPE, with a reduced Arden's ratio in middle-aged patients.