Donders first described high myopia associated with night blindness in a family with x-linked inheritance.1 The complete syndrome of x-linked recessive congenital stationary night blindness (CSNB) is characterized by decreased visual acuity, nystagmus, strabismus, and night blindness.2-7 Three monogenic inheritance modes, autosomal recessive, x-linked recessive, and autosomal dominant, have been described.4,5,8,9 Because the fundus usually appears normal, the diagnosis depends on the characteristic electroretinogram (ERG) findings as described by Schubert and Bornschein10 and Riggs.11 When evaluating males with decreased vision, high myopia (with or without a tilted disc), nystagmus, and perhaps strabismus, x-linked recessive CSNB may be overlooked unless nyctalopia is reported or specific inquiry is made in this regard.
We report eight patients from three families (Figure 1A-C) who were followed for decreased visual acuity, myopia, nystagmus, and strabismus. Seven of the eight patients failed to report night blindness, emphasizing the need for electrodiagnostic testing in these patients. The hereditary pattern in all three families with CSNB was x-linked recessive. In two patients, the pupils behaved paradoxically, showing an initial constriction to darkness followed by normal dilation.12,13 In patients with poor vision and nystagmus, this suggests retinal dysfunction.
METHODS AND PATIENTS
Each patient underwent a complete ophthalmic examination. Additional studies included fundus photography, Farnsworth Munsell 100-hue testing, Lanthony color testing, dark adaptometry, and photopic, scotopic, and flicker ERG.
Pupillary examination was performed with hand-held illumination. Pupillary constriction to darkness was demonstrated consistently each time the lights were extinguished. Each patient was then evaluated using infrared cameras. The diameter of the pupil was measured directly from the video monitor using frame by frame analysis.13
FIGURE 1A-C; The pedigrees of the three families with CSNB. Those patients examined by the authors are indicated with an X. The inheritance mode in all three families appears to be x-linked.
The results of clinical and electrophysiologic testing are summarized in the Table. Seven of the eight patients with CSNB had no complaints of nyctalopia. Five patients were over 10 years old when they were first evaluated for decreased visual acuity. Patient III2 (Family A) was first examined at age 24 because a brother (Case III10) had decreased acuity. Similarly, Case III2 (Family B) was evaluated at age 12 because a first cousin (Case IVl) was having problems with night vision.
The patients' Snellen acuity ranged from 20/30 to 20/400. The majority of eyes were 20/70 or better. The patients tended to be highly myopic, ranging from - 3.00 to - 15.50 diopters with a mean of - 7.00. Three of the patients had jerk nystagmus; one was pendular. Six of the patients had strabismus, four with esotropia and two with exotropia. One patient (II2, Family C) had tilted discs. Otherwise, the fundus appearance was normal except for myopic peripapillary changes.
Final dark adaptation thresholds in all the patients were elevated by at least 2 log units. Although the photopic fawave amplitude was reduced, the implicit times were normal. Patients showed either the Schubert-Bornschein10 ERG or the Riggs11 ERG. The photopic flicker ERG was normal in all patients.
Patients with CSNB initially may show nystagmus and decreased acuity without specific complaints of night blindness. Pinckers et al described two patients with no symptoms of night blindness.3 One of these patients was followed with decreased visual acuity without a specific diagnosis prior to electrodiagnostic testing. Therefore, as in seven of our eight patients, the subjective complaints may not be present to help in making the diagnosis. Haim described seven cases of CSNB.14 Only one of the patients had a clinical diagnosis made prior to ERG testing. In addition, three were diagnosed as having congenital nystagmus and two of these as having optic atrophy. Thus, the importance of ruling out CSNB in young patients, especially males, who present with cryptogenic nystagmus and decreased visual acuity cannot be overemphasized.
The family of a child with decreased acuity and nystagmus is concerned with the genetic implications for future offspring, the natural history of the disease, and the child's future vocational needs. The electrodiagnostic (ERG) and psychophysical (dark adaptation) tests occasionally help to identify sporadic cases of nystagmus as being heritable. A child with CSNB should have a non-progressive disease confirmed by serial ERG testing. Carriers of the x-linked disorder would for the most part be unaffected. Miyake and Kowasi,15 however, report an abnormally reduced oscillatory potential amplitude of the scotopic b-wave in 17 of 22 eyes of female carriers.
Other possible clinical indicators of the syndrome of CSNB include: positive family history, decreased acuity, pupillary constriction to darkness,12,13 high myopia (- 4.00 to - 14.50 diopters),5 dysplastic discs,3,16 and strabismus. In a very young child with decreased acuity and nystagmus, pupillary constriction to darkness suggests hereditary retinal disease.12,13 Two of the six patients evaluated in our clinic demonstrated this unusual darkness reaction. It is clinically evident with the use of a handlight and is present each time the lights are turned out. Accommodation and direct light responses are normal. It can be found at any age and is not limited to CSNB, but also has been described in congenital achromatopsia.12,13 The optic discs in CSNB have been described as tilted, pale, or simply dysplastic.
Summary of Cases
The concentration and rate of regeneration of rhodopsin appears to be normal in CSNB.9 Two different ERG patterns have been described. First, there is the so-called "negative ERG" in which there is a reduction mainly in the scotopic b-waves. The a-wave typically increases in amplitude with progressive dark adaptation. Therefore, the awave is normal. The second type of ERG shows a subnormal a- and b-wave that remain essentially unchanged without significant increment with dark adaptation. Further recent analysis of the reduction in the photopic ERG has demonstrated an absence of the two oscillations normally present on the ascending part of the b-wave.17 Members of the same family afflicted with CSNB generally show the same ERG pattern, but there are exceptions.18 This was confirmed further by Miyake et al19 who reported on 64 patients with CSNB. Their patients were divided into complete and incomplete forms depending on the presence of some rod function. But no family appeared to have both a complete and an incomplete type.
Beneficial genetic counseling demands accurate diagnoses. CSNB is not a progressive disease. Our patients presented with decreased acuity and nystagmus. When a darkness constriction of the pupils was seen, CSNB was strongly suspected, but it was the electrodiagnostic testing that confirmed the diagnosis.
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