History of present illness
We present a case of a 31-year-old male patient who is HIV positive and has had nyctalopia for several years. Patient denies any flashes of light or color deficiencies.
Ocular examination findings
Visual acuity was 20/20 in the right eye and 20/25 in the left eye. Intraocular pressure was normal. Dilated fundus examination exhibited bilateral optic disc drusen but otherwise normal macula and peripheral retinal examination.
Imaging
Fundus examination had no visually significant abnormalities ( Fig. 24.1 ). Optical coherence tomography (OCT) showed normal foveal contour with mild attenuation of the ellipsoid zone (EZ) in both eyes ( Figs. 24.2–24.4 ).
Questions to ask
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Is the nyctalopia progressive? When was it first noticed? Patients with congenital stationary night blindness (CSNB) usually have these symptoms from birth with limited progression over time. Because of this, some patients may not be aware of their difficulty with night vision as it seems “normal” to them.
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No
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What is the patient’s refractive error? Patients with CSNB may present with minimal fundus findings, but this condition has been associated with myopia, strabismus, and even nystagmus.
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This patient is emmetropic with normal motility.
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Does the patient have any vitamin or nutritional deficiencies? It is important to check for acquired causes of nyctalopia that can mimic nonreversible causes of night blindness. Additionally, it is important to recognize that several medications employed in the treatment of patients who are HIV positive may impair vitamin A absorption.
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Vitamin A levels were decreased in this patient but were adequately supplemented with limited to no improvement in symptoms.
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Assessment
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This is a case of a 31-year-old male patient who is HIV positive with nonprogressive nyctalopia, a normal fundus examination, and an electronegative electroretinogram (ERG).
Differential diagnosis
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Congenital Stationary Night blindness (CSNB)
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Retinitis pigmentosa
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Vitamin A deficiency
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Zinc deficiency
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Oguchi disease
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Fundus albipunctatus
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Rod-cone dystrophy
Working diagnosis
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CSNB
Multimodal testing and results
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Fundus photographs. The fundus examination in these patients is usually normal, although there are two variants with abnormal fundi.
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Fundus albipunctatus: These patients have multiple white dots throughout the fundus sparing the central fovea.
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Oguchi disease: The fundus examinations have a yellow “metallic” sheen in the light-adapted state, but with 2 to 3 hours of dark adaptation this will go away, and the fundus will appear normal.
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OCT
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Our patient showed some attenuation diffuse attenuation of the EZ, but classically CSNB patients with normal fundi have an unremarkable OCT.
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Patients with the fundus albipunctatus variant show hyperreflective deposits at the layer of the outer retina.
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Electroretinogram (ERG). The ERG findings of CSNB can be divided into several subtypes:
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Riggs type (type I): The scotopic ERG shows no a- or b-wave with a dim flash and a decreased b:a ratio with a bright flash. The photopic response is normal.
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Schubert-Bornschein (type II): This is characterized by the electronegative ERG with a normal a-wave but reduced b-wave. This diagnosis is also further classified as complete or incomplete form. ,
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Complete (dysfunction of the ON bipolar cells): The photopic ERG shows an almost a-wave with a broadened trough and a sharply increasing b-wave with loss of oscillatory potentials.
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Incomplete (dysfunction of the ON and OFF bipolar cells): The photopic ERG is more affected, specifically the 30-Hz flicker, which is delayed and often shows a bifid peak due to some residual rod function. ,
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Genetic testing A number of genetic mutations have been identified based upon the subtype and inheritance pattern of the disease ( Table 24.1 ).
