A 5-year-old Syrian female was born with Oguchi disease: a rare case report

Introduction:

Oguchi disease is a rare autosomal recessive disease that causes congenital stationary blindness, which is distinguished by the Mizuo–Nakamura phenomenon and caused by mutations of rhodopsin kinase gene or the arrestin gene.

Case presentation:

A 5-year-old Syrian female complains of stationary night blindness, investigated by fundus photo and optical coherence photograph and diagnosed as Oguchi disease.

Discussion:

Oguchi disease is an autosomal recessive retinal disorder causing stationary nyctalopia. It is characterized by Mizuo–Nakamura phenomenon, which is the alteration of fundus reflex color from golden-yellow to normal with dark adaptation. Literature reports suggest that mutations in rhodopsin kinase or arrestin genes may cause Oguchi’s disease.

Conclusions:

Optical coherence tomography is of great importance in Oguchi’s disease. Optical coherence tomography usually shows an absence of the inner and outer segments line in the extrafoveal area during a partly dark-adaptation phase.

Introduction

HIGHLIGHTS

• Oguchi disorder is a rare autosomal recessive disease that causes stationary nyctalopia.

• The abnormal genetic function in Oguchi’s disease causes continuous activation of transduction.

• In Oguchi disease, optical coherence tomography usually shows an absence of the inner and outer segments line.

• We can assess the functional status of the rods through the presence of the inner and outer segments line in FD-OCT (spectral domain optical coherence tomography) images.

Oguchi disorder is a rare autosomal recessive disease that causes stationary nyctalopia. Patients usually complain of stationary night blindness, which resolves after a delayed period of darkness. The disease is characterized by a distinct bright golden sheen on fundus examination. However, the sheen disappears after a long dark adaptation (the Mizuo–Nakamura phenomenon)1. Mutations of the rhodopsin kinase gene or the arrestin gene are known to cause the Oguchi disease2. Optical coherence tomography (OCT) can be very helpful in diagnosing. Here we report a case of 5-year-old female with Oguchi disease3.

We report a rare case of a 5-year-old female with Oguchi disease. This case has been reported in line with the SCARE (Surgical CAse REport) criteria4.

Case presentation

A 5-year-old female presented with difficulty in night vision. Medical and family history was unremarkable.

Best-corrected visual acuity was 1.0 with +1.5 sphere. Intraocular pressure, color vision, visual field, and anterior segment examination were in both eyes normal. Fundus examination of both eyes revealed a distinct bright golden sheen, and the sheen disappeared after 2 h of dark adaptation, which indicates the Mizuo–Nakamura phenomenon (Fig. 1).

Figure 1.

(A, B) Fundus photograph of the right and left eye shows golden-yellow reflex (the Mizuo–Nakamura phenomenon). (C, D) Fundus photograph of the right and left eye shows normal fundus color, after 2 h of dark adaptation.

In both eyes, spectral domain OCT showed increased reflectivity of the outer retinal layer [inner and outer segments (IS/OS) line and RPE/Bruch (Retinal Pigment Epithelium-Brunch) band] (Fig. 2).

Figure 2.

(A, B) Optical coherence tomography cross-sectional of the right and left eye shows high-intensity regions in the outer segment. (C, D) Optical coherence tomography cross-sectional shows the disappearance of these deposits and normal intensity.

Based on its clinical and imaging findings, Oguchi’s disease was diagnosed.

Discussion

Oguchi disease is an autosomal recessive retinal disorder that leads to stationary nyctalopia. Patients mainly present with congenital stationary night blindness while their vision in bright light is preserved. They also show a characteristic golden-yellow fundus reflex which returns to normal after a long dark adaptation. This alteration of fundus reflex color with dark adaptation is known as the Mizuo–Nakamura phenomenon2,3.

Arrestin (SAG) and rhodopsin kinase (GRK1) are two genes that work in sequence to deactivate rhodopsin in order to stop the phototransduction cascade. Mutations in both of those genes may cause Oguchi’s disease. Rhodopsin kinase recognizes photoactivated rhodopsin and then phosphorylates serine and threonine residues near rhodopsin’s carboxy terminus. Next comes the arrestin, which creates a complex with phosphorylated rhodopsin and blocks any further interaction of the activated rhodopsin with transducing. However, the abnormal genetic function in Oguchi’s disease causes continuous activation of transducin by photoactivated rhodopsin, which results in desensitizing the rods2.

It is also worthy of notice that some mutations in the SAG gene may cause retinitis pigmentosa in addition to Oguchi disease in the same family5.

Patients with Oguchi’s disease show a noticeably prolonged dark-adaptation curve, whereas the early cone branch of the curve is normal. This prolonged dark adaptation occurs over a period ranging from 3 to 4 h. For the first 1–2 h, we can notice a plateau of sensitivity at the cone level, then a rod-cone break arises. During the last 1–2 h, a full recovery of rod sensitivity occurs. This recovery of light sensitivity in Oguchi’s disease is correlated to the time needed for rhodopsin regeneration. This phenomenon affects the typical findings of this disease on the Electroretinogram, as they may return to normal amplitude and timing after a prolonged period of dark adaptation5.

Literature reports have proposed that mutations in the rhodopsin kinase gene lead to Oguchi’s disease with no signs of photoreceptor degeneration, whereas arrestin mutations include some characteristics of Oguchi’s disease, such as the Mizuo–Nakamura phenomenon2,6.

Mizuo–Nakamura phenomenon involves that the color of the fundus is normal following prolonged dark adaptation, but this color alters to a dark or golden hue after a few minutes in the light. There are still some unclear aspects or causes of this disease, among which the biochemical causes of this phenomenon are unknown until now. It is presumed that the cause of this phenomenon is high extracellular potassium levels accumulated in the retina in response to uncontrolled and excessive stimulation of rod photoreceptors. Another aspect that is unclear also is the cause of why some patients with Oguchi’s disease develop retinitis pigmentosa7.

OCT is an extremely crucial investigation for assessing the fine structures of the retina. There are four highly reflective lines in OCT imaging which are the external limiting membrane, the connection between the photoreceptor IS/OS line, and the intermediate line8.

In Oguchi disease, OCT usually shows an absence of the IS/OS line in the extrafoveal area during the partly dark-adaptation phase. Research suggests that the cause of this finding may be the integration of the IS/OS line into the RPE/Bruch band during this state of adaptation8.

The absence of the IS/OS line occurs simultaneously with the phase when the visual threshold is high, and the rods are most likely nonfunctional. Then happens the prolonged dark adaptation. Following this prolonged phase comes the recovery of the visual threshold and normal coloration of the fundus. In some cases, this has been linked to the appearance of the IS/OS line, which suggests a causative relationship in those cases. However, in other cases of Oguchi’s disease, IS/OS line is clearly found at the foveal area, where there are no rods or very few of them. This suggests that the correlation between the presence of the IS/OS line with the normal function of rods may not be consistent in all cases8.

Normal eyes have a higher density of rods in the extrafoveal area compared to the cones, and the IS/OS line is detectable in this area. The correlation of the reappearance of the IS/OS line with the visual threshold going back to normal levels suggests that the physiological function of the rods should be normal in order to have a visible IS/OS line8.

This absence of the IS/OS line in the extrafoveal area may be the morphological representation of the functional alteration that the rods undergo during elevated visual threshold. This finding suggests that we can assess the functional status of the rods through the presence of the IS/OS line in FD-OCT (spectral domain optical coherence tomography) images8.

No specific treatment has been established in the literature, although there have been reports suggesting the possible role of zinc in treating Oguchi’s disease as it is required for vitamin A metabolism, and its deficiency may cause abnormal dark adaptation9.

Conclusions

To conclude, although Oguchi’s disease includes characteristic clinical presentations, they are more likely to be missed if they are not accompanied by thorough history taking and electrophysiological testing. Findings including normal cone function delayed rod Electroretinogram dark adaptation and marked rod desensitization to a bright flash are distinctive for Oguchi’s disease.

Ethical approval

The research was conducted ethically in accordance with the World Medical Association Declaration of Helsinki.

Patient consent

Written informed consent was obtained from the patient for the publication of this case report and accompanying images. A copy of the written consent is available for review by the Editor-in-Chief of this journal on request.

Sources of funding

There are no sources of funding.

Author contribution

R.H.: analyzed and drafted the manuscript; M.B. and B.B.: drafted the manuscript; A.Z.: analyzed and interpreted the research manuscript; A.M.: designed and drafted the manuscript. All authors approved the final version of the manuscript to be submitted.

Conflicts of interest disclosure

The authors declare that there are no conflicts of interest.

Research registration unique identifying number (UIN)

Not applicable.

Guarantor

Dr Ameen Marashi.

Patient perspective

The patient participated in the treatment decision and she was satisfied with the results of the treatment.

Provenance and peer review

Not commissioned, externally peer-reviewed.