Description
Congenital stationary night blindness is a broad term that covers several different conditions:
- Normal appearing fundus: this form of congenital stationary night blindness may be inherited as an autosomal dominant, autosomal recessive or Xlinked recessive trait. Establishing a correct diagnosis is important because confusion with progressive disorders involving nyctalopia (night blindness) such as retinitis pigmentosa is avoided.
- Abnormal fundus appearance comprising Oguchi disease, fundus
albipunctatus and Kandori’s flecked retina. These conditions are rare and characterized by stationary (nonprogressive) night blindness, normal visual acuity and an autosomal recessive inheritance pattern, although autosomal dominance has occasionally been demonstrated in fundus albipunctatus. Their fundal appearances are quite different and distinctive.
Symptoms
In all types of congenital stationary night blindness there is a characteristic difficulty seeing at night of early onset. Visual acuity under photopic conditions is usually normal, especially in autosomal dominant cases where a significant degree of myopia is generally not a complicating factor. In autosomal recessive and X-linked recessive forms of the disease, vision may be compromised by nystagmus and high myopia. Patients do not complain of
a restricted visual field as they may, for example, in advancing retinitis pigmentosa. Vision and the visual field are also normal in Oguchi disease, fundus albipunctatus and Kandori’s flecked retina.
Signs
- Normal appearing fundus form: visual acuity, visual fields, color discrimination
and the appearance of the fundus are typically normal in the first type of
congenital stationary night blindness, although, as noted above, some
recessive cases may show nystagmus and high myopia. When inherited as an X-linked recessive trait, a pigmentary mottling of the fundus has been observed in some patients.
2. Abnormal fundus appearances:
- In Oguchi disease,a condition rarely seen in other than Japanese people, the fundus has a typical yellow sheen against which the retinal blood vessels stand out with great clarity. Remarkably, after a few hours under dark adaptation conditions, the fundus color becomes normal. This is known as Mizuo’s phenomenon
- Fundus albipunctatus, as the name suggests, is characterized by a plethora of small discrete punctate white spots that litter the fundus. They extend from the posterior pole, sparing the macula, well into the far periphery. In the periphery they become more linear in nature.
- In Kandori’s flecked retina, yellowgrey well-defined spots are found in
the equatorial fundus.
Prevalence
All of these conditions are very uncommon.
Differential diagnosis
Retinitis pigmentosa; choroideremia; gyrate atrophy of the choroid; vitamin
A and zinc deficiencies; uncorrected myopia.
Management
Additional Investigations Characteristically, the dark adaptation curve shows no rod adaptation. Electrophysiological testing is usually also helpful to the diagnosis. The autosomal recessive and X-linked
Fig. 42.1
Fundus albipunctatus deposits in the right fundus of a young Indian female. There were no symptoms of nyctalopia and vision was normal. The dark adaptation curve was slightly reduced. The left fundus had a similar appearance and images from 4 years earlier were virtually identical.
recessive forms manifest an electronegative electroretinogram (ERG) finding, whereas, in autosomal dominant cases, a normal photopic waveform of reduced amplitude has been described. Both ERG responses have also been noted within a single inheritance trait.
Advice No treatment is available for any of the forms of congenital stationary night blindness. Patients need to be reassured
as to the stationary (non-progressive) nature of the disease.
Genetics Genetic counselling may be appropriate and patient education is important regarding any limitations that nyctalopia may impose.
Review Any potential ocular ramifications of high myopia, if present, must be considered. Otherwise, the patient should be reviewed on a routine basis.