Oguchi's disease - Clinical image

A 21-year-old male was referred to our retina clinic as a part of refractive surgery workup. The best corrected visual acuity in both eyes was 6/6 with a correction of − 4.50 Dsph in the right eye and − 3.00 Dsph in the left eye. The anterior segment examination of both eyes was normal. Fundus examination revealed a normal-appearing disc, vessels, and macula. A golden yellow sheen was noticed over the posterior pole in both eyes [Figure 1]. Optical coherence tomography of the macula was normal. Family history was only significant for myopia with no history of night blindness or any other ocular illness. On further probing, the patient complained of difficulty in dimly illuminated surroundings since childhood. He was dark adapted for an hour and his fundus was reexamined, which showed the disappearance of the golden sheen with a normal retinal reflex suggestive of the Mizuo–Nakamura phenomenon [Figure 2]. Full-field electroretinogram (ERG) adhering to the International Society of Clinical Electrophysiology of Vision guidelines revealed negative ERG in scotopic ERG – with normal appearing A waves and absent B waveforms with reduced oscillatory potentials. Single-flash cone and 30 Hz flicker responses were also diminished [Figure 3]. Multifocal ERG was done which showed blunting of waveforms in a trace array with preserved foveal peaks in both eyes [Figure 3]. Based on the above findings, a diagnosis of Oguchi's disease was made and the patient was prescribed glasses. He was advised genetic testing which was to be followed by genetic counseling, but the patient was not willing to do the same.

Figure 1.

(a and b) The presence of parafoveal golden yellow sheen in the light-adapted state. There was no evidence of any vascular or macular changes or chorioretinal atrophy

Figure 2.

(a and b) Normalization of the background retinal sheen with 45 min of dark adaptation

Figure 3.

A full field scotopic ERG showing the absence of b waves (indicated by red arrow) suggestive of negative ERG and multifocal ERG showing reduced foveal, perifoveal and parafoveal ring responses. ERG: Electroretinogram

Congenital stationary night blindness (CSNB) is a group of genetically diverse nonprogressive retinal dystrophies characterized by categorized by rod dysfunction or abnormality in signal transduction between rods and bipolar cells.[1] Oguchi's disease is an autosomal recessive condition which presents as stationary night blindness from childhood and it is due to disruption in the steps of inactivation of rod phototransduction in light-adapted states. Patients often complain of nyctalopia which is nonprogressive since childhood and can rarely be asymptomatic. Typically, the disc, vessels, and peripheral retina appear normal and there is no evidence of bony spicules in these patients.[2] Mutations in the SAG gene coding for Arrestin located on chromosome 2q37 which causes type 1 Oguchi's disease and mutation in GRK 1 gene coding for rhodopsin kinase located on chromosome 13q34 causes type 2 Oguchi's disease. Arrestin and rhodopsin kinase plays a key role in the deactivation of rhodopsin to stop the phototransduction cascade as a part of dark adaptation.[3] Genotyping is essential to distinguish between these gene mutations. A distinctive feature of this disease is the Mizuo–Nakamura phenomenon, where the fundus has a golden yellow hue in light-adapted states which disappears with prolonged dark adaptation, with the golden hue reappearing within a few minutes of exposure to light or repeated light flashes.[4] The biochemical basis is postulated to be an increase in extracellular potassium levels in the retina following the overstimulation of rod photoreceptors.[5] This phenomenon has also been documented in patients with juvenile X-linked retinoschisis and cone-rod dystrophy. ERG is essential to differentiate between the different types of CSNB and establish the diagnosis. In Oguchi's disease, the light-adapted cone responses are normal, whereas the rod responses vary depending on whether the eye is light or dark-adapted – with reduced or extinguished responses in light-adapted states which recover with an increase in amplitude with prolonged dark adaptation.[6] It can also display a negative electrogram showing absent B waves, whereas the A waves are preserved. Oguchi's disease does not have any specific treatment and management includes family screening, genetic testing, and counseling as it is autosomal recessively inherited and tends to present in siblings.

In conclusion, Oguchi's disease is a rare form of inherited CSNB which can be missed on routine examination because of its subtle clinical features. The prognosis of the condition is usually good and may rarely cause constriction of visual fields in later stages.

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The authors certify that they have obtained all appropriate patient consent forms. In the form, the patient has given his consent for his images and other clinical information to be reported in the journal. The patient understands that his name and initials will not be published and due efforts will be made to conceal his identity, but anonymity cannot be guaranteed.

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