Rhodopsin mutation G90D and a molecular mechanism for congenital night blindness

Mutations in the gene for the visual pigment rhodopsin cause retinitis pigmentosa (RP) and congenital night blindness. Inheritance of the diseases is generally autosomal dominant and about 40 different rhodopsin mutations have been documented. Although the cell death and retinal degeneration associated with RP have been suggested to result from improper folding and accumulation of the mutant proteins in rod photoreceptor cells, this may not account for the disease in all cases. For example, RP mutations at Lys 296, site of Schiff base linkage to the retinal chromophore, result in constitutive activation of the protein in vitro; that is, the mutants can catalytically activate the G protein transducin in the absence of chromophore and in the absence of light. Similarly, mutation of Ala 292-->Glu activates opsin in vitro and causes night blindness. We show here that the mutation Gly 90-->Asp (G90D) in the second transmembrane segment of rhodopsin, which causes congenital night blindness, also constitutively activates opsin. Furthermore, we show that Asp 90 can substitute for the Schiff base counterion, Glu 113, which is located in the third transmembrane segment of the protein. This demonstrates the proximity of Asp 90 and Lys 296 in the three-dimensional structure of rhodopsin and suggests that the constitutively activating mutations operate by a common molecular mechanism, disrupting a salt bridge between Lys 296 and the Schiff base counterion, Glu 113.

Gene for autosomal dominant congenital stationary night blindness maps to the same region as the gene for the beta-subunit of the rod photoreceptor cGMP phosphodiesterase (PDEB) in chromosome 4p16.3

We studied a large multigeneration Danish family with autosomal dominant congenital stationary night blindness. Both electrophysiological and psychophysical findings in affected family members were identical to those reported in patients from the 'Nougaret family'. The disease locus in the Danish family has now been mapped by demonstrating close linkage without recombination (Q = 0.00 at Zmax = 14.4) to the locus for alpha-L-iduronidase assigned to chromosome 4p16.3. Interestingly the gene for the beta-subunit of the rod photoreceptor cGMP-specific phosphodiesterase maps to the very same chromosomal region.

Genetic mapping of a cone and rod dysfunction (Aland Island eye disease) to the proximal short arm of the human X chromosome

A five generation family with an X linked ocular disorder has been investigated. The major clinical features were reduced visual acuity, nystagmus, and myopia. Although impaired night vision was not a symptom, using psychophysical and electrophysiological testing both rod and cone function were found to be abnormal in all affected males. No abnormality was detected in carrier females. Gene location studies showed X linked transmission of a gene that maps to proximal Xp11. The findings observed in this cohort are similar to those previously reported in both congenital stationary night blindness type 2 (CSNB2) and Aland Island eye disease (AIED). This study addresses whether CSNB2 and AIED are a single entity or whether the latter is a subset of the former.

Manifestations of X-linked congenital stationary night blindness in three daughters of an affected male: demonstration of homozygosity

X-linked congenital stationary night blindness (CSNB1) is a hereditary retinal disorder in which clinical features in affected males usually include myopia, nystagmus, and impaired visual acuity. Electroretinography demonstrates a marked reduction in b-wave amplitude. In the study of a large Mennonite family with CSNB1, three of five sisters in one sibship were found to have manifestations of CSNB1. All the sons of these three sisters were affected. Each of the two nonmanifesting sisters had at least one unaffected son. Analysis of Xp markers in the region Xp21.1-Xp11.22 showed that the two sisters who were unaffected had inherited the same maternal X chromosome (i.e., M2). Two of the daughters who manifested with CSNB had inherited the other maternal X chromosome (M1). The third manifesting sister inherited a recombinant X chromosome with a crossover between TIMP and DXS255, which suggests that the CSNB1 locus lies proximal to TIMP. One of the affected daughters' sons had inherited the maternal M1 X chromosome, a finding consistent with that chromosome carrying a mutant CSNB gene; the other affected sons inherited the grandfather's X chromosome (i.e., P). Molecular analysis of DNA from three sisters with manifestations of CSNB is consistent with their being homozygous at the CSNB1 locus and with their mother being a carrier of CSNB1.

A Japanese pedigree of autosomal dominant congenital stationary night blindness with variable expressivity

Three cases in three successive generations of one family with autosomal dominant congenital stationary night blindness are presented. Case 1, the proband, and Case 3, his grandfather had the same electroretinographic responses: nonrecordable scotopic electroretinogram (ERG), normal but slightly diminished flicker ERG, and negative-shaped single bright-flash ERG. Their dark adaptation curves were monophasic with no rod segment. However, Case 2, the proband's father, showed different ERG findings; a moderately diminished scotopic ERG, a normal flicker ERG, and a biphasic dark adaptation curve with an elevated final rod threshold. The authors believe that these differences reflect variations in the expressivity of a single gene mutation with the lowest expressivity being seen in Case 2.

Ultrastructural changes of the retina and the retinal pigment epithelium in Briard dogs with hereditary congenital night blindness and partial day blindness

The offspring of two Briard dogs (brother and sister) with congenital, clinically stationary night blindness showed an aggravation of the disease with severe impairment of day vision in addition to night blindness. This ultrastructural study was performed on four such second generation puppies at the age of 4 months. The neuroretina and retinal pigment epithelium (RPE) from four locations were studied: the central area (immediately temporal to the optic disc); the centre of the tapetal area; the upper periphery (border of tapetal area); and the lower periphery (non-tapetal area). The RPE showed large inclusions, seemingly lipid in nature, mainly in the central and tapetal areas of the retina. Small, membrane bound, electron-dense inclusions were scattered in the RPE cytoplasm in all areas examined. The small inclusions were found to be less numerous in normal than in affected dogs and may be lysosomal in nature. Forty to fifty percent of the rod outer segments in the tapetal area showed disorientation of the disc membranes, whereas the corresponding figures were 20-40% in the central and lower peripheral areas and 6-25% in the upper peripheral area. No structural abnormalities were found in the rod inner segments or synaptic bodies. The cones were better preserved. The inner retina appeared normal. These electron microscopic findings seem to correspond to a previously published electrophysiologic evaluation, indicating a defective and delayed rod function (virtually no scotopic a- and b-waves), a better preserved cone function (photopic flicker responses present, although reduced) and impaired RPE activity (a prominent, slow negative potential of long latency at the site of the c-wave). It appears that these Briard dogs, showing structural changes of the rod outer segments in addition to pigment epithelial inclusions, mainly located in the posterior pole, comprise a pigment epitheliopathy and retinopathy morphologically different from other hereditary canine retinopathies that have been described earlier in the literature and different from animal models of congenital night blindness.

Congenital ocular anomalies

This discussion provides an idea of the diversity and relative prevalence of certain congenital ocular conditions of horses. Many are not difficult to diagnose, yet curative treatment may be impossible. When dealing with owners of horses affected with unusual anomalies, responsible client service requires veterinarians to provide accurate information and to know where answers to unusual questions can be found. Again, most veterinarians never encounter all of the diverse congenital defects. As a result, the horse owner frequently receives misinformation. Hopefully, this brief coverage of congenital ocular anomalies will provide useful information and assist in appropriate communication to concerned parties.

Linkage analysis in X-linked congenital stationary night blindness

X-linked congenital stationary night blindness (XL-CSNB) is a nonprogressive disorder of the retina, characterized by night blindness, reduced visual acuity, and myopia. Previous studies have localized the CSNB1 locus to the region between OTC and TIMP on the short arm of the X chromosome. We have carried out linkage studies in three XL-CSNB families that could not be classified as either complete or incomplete CSNB on the criteria suggested by Miyake et al. (1986. Arch. Ophthalmol. 104: 1013-1020). We used markers for the DXS538, DMD, OTC, MAOA, DXS426, and TIMP loci. Two-point analyses show that there is close linkage between CSNB and MAOA (theta max = 0.05, Zmax = 3.39), DXS426 (theta max = 0.06, Zmax = 2.42), and TIMP (theta max = 0.07, Zmax = 2.04). Two multiply informative crossovers are consistent with CSNB lying proximal to MAOA and distal to DXS426, respectively. Multipoint analysis supports this localization, giving the most likely order as DMD-17 cM-MAOA-7.5 cM-CSNB-7.5 cM-DXS426/TIMP-cen, and thus refines the localization of CSNB.

Affected females in X-linked congenital stationary night blindness

Most heterozygous (carrier) females in families with X-linked congenital stationary night blindness are asymptomatic. Several anecdotal cases of manifesting females in X-linked congenital stationary night blindness have been reported, but few clinical details are available. The authors report clinical, electroretinographic, and dark adaptation studies of four affected females from a five-generation family with X-linked congenital stationary night blindness. Each of the manifesting females was the daughter of a different, asymptomatic, carrier mother. None of the 14 daughters of the 9 affected males showed signs or symptoms of congenital stationary night blindness. Uneven X-chromosomal lyonization is the most likely reason for these females manifesting this X-linked disorder.

[Family investigation and clinical genetic analysis of a large pedigree with congenital stationary night blindness]

A large pedigree of congenital stationary night blindness (CSNB) was investigated by both the family method and the family history method, and the diagnosis was confirmed by dark adaptation and full-field electroretinogram tests. There were 57 affected members of 7 successive generations in the pedigree which showed typical autosomal dominant inheritance with a complete gene penetrance. Based on this study and other sources, the genetic aspect and the clinical manifestations of CSNB, especially the characteristics of dark adaptation and electroretinogram, were discussed.

Changes in the DC electroretinogram in Briard dogs with hereditary congenital night blindness and partial day blindness

Five Briard dogs, 7-12 months old, with congenital night blindness and severely reduced day vision (offspring of a sister and brother with congenital and supposedly stationary night blindness but with normal or nearly normal day vision) and three normal control dogs were studied by means of direct current (DC) electroretinography in order to analyse fast and slow retinal and pigment epithelial (RPE) potentials. No definite a- and b-waves were seen in the affected dogs in the dark-adapted state, which indicates severely impaired rod function. All affected dogs responded to 30 Hz flickering light in the light-adapted state, although with an amplitude reduced by 50-70%. Thus, cone function was better preserved than rod function. The control dogs showed a small c-wave and a deep negative trough between the b- and c-waves, indicating that slow PIII from the Müller cells, as well as the photoreceptor potential, are very prominent. In the affected dogs, there was no c-wave, but from a stimulus intensity of 3 log U above the normal b-wave threshold, a slow negative potential appeared, the latency and peak time of which were very long, 5-7 and 11-15 sec, respectively. With increasing stimulus intensities, both parameters decreased substantially, whereas the amplitude increased to a maximum of 2400 microV. In the light-adapted state, the dog with the best day vision showed a negative potential of short duration (peak time about 0.2 sec), followed by a positive potential (peak time about 1.2 sec).(ABSTRACT TRUNCATED AT 250 WORDS)

Autosomal dominant stationary night-blindness. A large family rediscovered

In 1909, 2 years after the famous publication by Nettleship, a large family with congenital stationary night-blindness of the 'Nougaret type' was published by the Danish district surgeon, Sigurd Rambusch. In 1990 the 'Rambusch family', still resident in the original area, was sought out and rediscovered, at which time the reconstructed part of the pedigree comprised more than 200 affected persons in 11 generations. Dark adaptometry and electroretinography were performed on a few affected family members, including a descendant with a uniocular affection. The pedigree is presented and recordings of dark adaptation courses and electroretinographical responses from a few family members are demonstrated.

Genetic heterogeneity of Oguchi's disease

An analysis of the cases reported in Punjab, India, indicates the presence of genetic heterogeneity of Oguchi's disease, for which autosomal recessive inheritance has been documented earlier. The autosomal dominant inheritance pattern of this disease is associated with incomplete penetrance and a distinct sex bias towards females. This recognition is important for genetic counselling.

ERG characteristics of congenital stationary night blindness

The ERGs of 9 cases (18 eyes) of congenital stationary night blindness with normal fundi or myopia were tested. All eyes showed nonrecordable rod ERG and cone ERG with normal a-wave. Scotopic mixed ERGs were of the negative type in 7 eyes and of the subnormal type in 11 eyes. The b/a ratio was reduced in all eyes. The ERG characteristics are useful for the classification, estimation of the probable location of the lesion, and differential diagnosis of the disease.

Aland eye disease (Forsius-Eriksson-Miyake syndrome) with probability established in a Danish family

A reinvestigation of a Danish family with X-linked inherited congenital nystagmus through 6 generations revealed a congenital stationary retinal dysfunction syndrome with characteristics of both incomplete congenital stationary night blindness and Aland Eye Disease. In spite of rather uniform electrophysiological findings in our patients, this retinal disorder which affects both cones and rods demonstrated considerable intrafamilial diversity with respect to visual acuity, nystagmus, refractive state and fundus pigmentation.

A locus for X-linked congenital stationary night blindness is located on the proximal portion of the short arm of the X chromosome

Linkage between X-linked congenital stationary night blindness (CSNB1) and seven markers on the X chromosome was investigated in a large four-generation Albertan kindred. We detected significant linkage between the CSNB1 locus and the locus DXS255 (maximum lod score = 6.73 at a recombination fraction of 6%; confidence interval of 1% to 18%), which anchors the CSNB1 locus to the proximal region near p11.22 on the short arm of the X chromosome.

Long-term follow-up of the physiologic abnormalities and fundus changes in fundus albipunctatus

Fundus albipunctatus (FA) is considered to be a congenital stationary night-blinding disorder, but there has been no electrophysiologic or photographic documentation of long stability or change. This documentation is presented for two cases followed for 13 to 14 years. The physiologic (functional) deficits appeared to be stable, in support of the concept that FA is not a progressive dystrophy. However, the fundus lesions evolved in appearance from flecks in childhood to relatively permanent punctate dots that increase in number over the years.

Variable expressivity in X-linked congenital stationary night blindness

X-linked congenital stationary night blindness (CSNB) is a well-documented disorder in which the most striking clinical features are impaired night vision, nystagmus and myopia. Recent reports have highlighted differing features between families, and it has been suggested that these discrepancies may be the result of two loci on the X chromosome or of two mutant alleles. We outline the clinical and visual function findings in 42 affected members from 10 families and 1 adopted person. There was a relative unawareness of the disorder in clinical practice. At least one of the main features of CSNB was absent in 75% of the patients. The visual function values varied widely, both between and within families (visual acuity 20/30 to 20/400, refractive error +1.50 to -22.50 and rod segment elevation 1.5 to 3.0 log units). The findings are consistent with a single allele exhibiting a wide variation in clinical expression.

A form of congenital stationary night blindness with apparent defect of rod phototransduction

We report findings obtained from an individual with an unusual form of congenital stationary night blindness (CSNB). Although the rhodopsin density difference of this subject was normal, there was no evidence of rod-mediated visual function. Dark-adapted thresholds were cone-mediated, and dark-adapted electroretinograms (ERGs) represented activity of the cone system exclusively. ERG a- and b-waves obtained under light-adapted conditions were normal. The absence of a rod a-wave but the presence of normal rhodopsin density, in combination with normal cone function, indicates that this form of CSNB likely involves a defect of phototransduction that is limited to the rods. In addition, light-adapted b-wave responses to high luminance flashes were larger than dark-adapted responses, whereas a-wave amplitudes were reduced by light adaptation. These ERG results address proposed mechanisms by which light adaptation might enhance cone system responses.

Autosomal dominant congenital stationary night blindness and normal fundus with an electronegative electroretinogram

We studied three members of three successive generations of a family with autosomal dominant congenital stationary night blindness and normal fundi. Psychophysical studies on two members showed normal final cone thresholds and mildly increased rod thresholds. Full-field electroretinograms on all three members showed normal photopic b-wave amplitudes and implicit times. Under scotopic conditions, the rod response was absent, and with a bright flash stimulus, there was a normal a-wave with no b-wave. This electronegative dark-adapted electroretinogram resembled the Schubert-Bornschein type seen in congenital stationary blindness, which has been seen only in autosomal and X-linked recessive pedigrees.

Models of the normal and abnormal rod system

A framework is presented for using threshold data to test hypotheses about the action of a disease, a chemical agent, or a developmental process. A model of the normal rod system, based on models from the physiological and psychophysical literature, is presented. Hypotheses about the alteration of the rod system are specified in this model. The approach is illustrated with a class of hypotheses that places the decrease in sensitivity with retinal disease at the rod receptors and with data from patients with retinitis pigmentosa and congenital stationary night blindness. The implications for models of the normal rod system are considered.

Assignment of the gene for complete X-linked congenital stationary night blindness (CSNB1) to Xp11.3

X-linked congenital stationary night blindness (CSNB) is a nonprogressive retinal disorder characterized by a presumptive defect of neurotransmission between the photoreceptor and bipolar cells. Carriers are not clinically detectable. A new classification for CSNB includes a complete type, which lacks rod function by electroretinography and dark adaptometry, and an incomplete type, which shows some rod function on scotopic testing. The refraction in the complete CSNB patients ranges from mild to severe myopia; the incomplete ranges from moderate hyperopia to moderate myopia. To map the gene responsible for this disease, we studied eight multigeneration families, seven with complete CSNB (CSNB1) and one with incomplete CSNB, by linkage analysis using 17 polymorphic X-chromosome markers. We found tight genetic linkage between CSNB1 and an Xp11.3 DNA polymorphic site, DXS7, in seven families with CSNB1 (LOD 7.35 at theta = 0). No recombinations to CSNB1 were found with marker loci DXS7 and DXS14. The result with DXS14 may be due to the small number of scored meioses (10). No linkage could be shown with Xq loci PGK, DXYS1, DXS52, and DXS15. Pairwise linkage analysis maps the gene for CSNB1 at Xp11.3 and suggests that the CSNB1 locus is distal to another Xp11 marker, TIMP, and proximal to the OTC locus. Five-point analysis on the eight families supported the order DXS7-CSNB1-TIMP-DXS225-DXS14. The odds in favor of this order were 9863:1. Removal of the family with incomplete CSNB (F21) revealed two most favored orders, DXS7-CSNB1-TIMP-DXS255-DXS14 and CSNB1-DXS7-TIMP-DXS255-DXS14. Heterogeneity testing using the CSNB1-M27 beta and CSNB1-TIMP linkage data (DXS7 was not informative in F21) was not significant to support evidence of genetic heterogeneity (P = 0.155 and 0.160, respectively).

The infant with nystagmus, normal appearing fundi, but an abnormal ERG

Many retinal disorders present during infancy with nystagmus, decreased vision, and normal-appearing fundi, but an abnormal ERG. The most common of these disorders are Leber's congenital amaurosis, achromatopsia, and congenital stationary night-blindness. Other disorders with similar ocular manifestations may be associated with a variety of life-threatening systemic abnormalities. This review describes the clinical, electrophysiological, and laboratory findings that can be used to distinguish among these conditions.

The Briard dog: a new animal model of congenital stationary night blindness

Congenital stationary night blindness (CSNB), apparently inherited in an autosomal recessive manner, was observed in a litter of Briard dogs in Sweden. Of nine litter mates five had nyctalopia. The results of different clinical tests, including electroretinography (ERG), were compared with the results found in four human cases of CSNB, three of which were most probably associated with autosomal recessive inheritance and one with X-linked inheritance. The congenital and stationary nature of the disease, ophthalmoscopically normal appearing fundi, and recordable but reduced photopic flicker responses were some of the similarities found between canine and human cases. The single-flash ERG response was abnormal in the humans as well as in the affected Briards. However, the human cases showed a "negative' ERG, whereas in the Briards both the a and b waves were extremely reduced and present only at a photopic level. Cases similar to these Briards have been described also in man, where rhodopsin concentration and regeneration were found to be normal, suggesting a disturbed transduction mechanism. It thus appears that the Briard dog may become a valuable model of human CSNB.

Aland Island eye disease (Forsius-Eriksson syndrome) associated with contiguous deletion syndrome at Xp21. Similarity to incomplete congenital stationary night blindness

We report the ophthalmological findings of a 6-year-old boy who has features of both Aland Island eye disease (also called Forsius-Eriksson ocular albinism) and incomplete congenital stationary night blindness, as defined by Miyake, leading us to suspect that they are the same entity. This child has a deletion of part of band 21 of the short arm of the X chromosome (Xp21) and three other X-linked disorders: congenital adrenal hypoplasia, glycerol kinase deficiency, and Duchenne type muscular dystrophy. The electroretinogram showed negative scotopic and abnormal photopic waveforms that were similar, if not identical, to the electroretinographic findings in both Aland Island eye disease and X-linked incomplete congenital stationary night blindness. Because of this similarity and the defective dark adaptometry that has been reported in patients with this disorder, we believe that Aland Island eye disease is more appropriately classified as a form of congenital night blindness than as a form of ocular albinism. From our case and review of the literature, Aland Island eye disease and incomplete congenital stationary night blindness appear indistinguishable. If further studies confirm that the disorders are the same, we recommend use of the term Aland Island eye disease or Forsius-Eriksson-Miyake syndrome. We also recommend that the gene symbols CSNB1 and CSNB2 be used for complete congenital stationary night blindness and Aland disease, respectively.

[ERG characteristics of congenital stationary night blindness]

The ERG of 9 cases (18 eyes) of congenital stationary night blindness with normal fundi or myopia were tested. All eyes showed absence of rod ERG and cone ERG with normal a-wave. Scotopic mixed ERG were of the negative type in 7 eyes and the subnormal type in 11 eyes. The b/a ratio was reduced in all eyes. The ERG characteristics are useful for the classification, estimation of the probable location of the lesion, and differential diagnosis of the disease.

Oscillatory potentials of X-linked carriers of congenital stationary night blindness

ERG oscillatory potentials (OPs) were recorded from obligate carriers of CSNB and from age-matched normal subjects. The OPs were recorded under four stimulus conditions and were analyzed in the time and frequency domains. The results, first of all, provide confirmation of the previous report that the OP amplitude is reduced in carriers. Second, the results show that, of four stimulus conditions examined, the best condition for discriminating the carriers and normal subjects was when the flash was blue and the eye was dark-adapted. Third, the results show that, in the frequency domain, optimal discrimination occurs when examining the power content of the OP at a center frequency of about 130 Hz using a 70 Hz bandwidth window. In the time domain, optimal discrimination occurs when examining the amplitude of the third peak of the response.

Large rod-like photopic signals in a possible new form of congenital night blindness

A 10-year-old Persian girl has symptoms of congenital stationary night blindness and some drusen-like lesions in the region of the vascular arcades. Her electroretinogram shows no rod response to a weak stimulus, but a large (475 microV) slow scotopic response to a strong stimulus that is unchanged by photopic conditions (15 Fl background illumination). However, the response to flicker had the typical (smaller) amplitude of a cone signal. They may represent a new form of night blindness in which rod sensitivity is reduced so that there is no vision under dim conditions but rod function still persists under photopic conditions.

X-linked congenital stationary night blindness. Review and report of a family with hyperopia

X-linked congenital stationary night blindness is almost always associated with myopia. We have reviewed all previously reported pedigrees and have found only two with patients without myopia. A recently proposed classification of night blindness includes a complete type associated with myopia and an incomplete type in which both hyperopia and myopia were found. Complete and incomplete types did not occur within the same pedigree. We report on a family in which three of the five affected members had hyperopia and could be classified as the incomplete type and in which a fourth member with myopia was more consistent with the complete type. The lack of myopia in three members of our pedigree can be explained by two hypotheses: crossing over of the night blindness and myopic genes on the X-chromosome, or an autosomal dominant hyperopic gene that masks the myopic gene. The data from our family support the first of these two hypotheses.

Incomplete congenital stationary night blindness: electroretinogram c-wave and electrooculogram light rise

Three cases of congenital stationary night blindness are reported. In all patients a negative electroretinogram was recorded by single bright flash stimulation and changed to positive on sequential reduction of the stimulus intensities. Oscillatory potentials were recognized. Biphasic dark adaptation curves and moderate elevation of the relative logarithmic final threshold of dark adaptation were also found. Values of critical flicker fusion frequency were reduced to a mild or moderate extent. VEP latency was prolonged beyond the normal range in two cases. In all three the electroretinogram c-wave was extinguished despite a normal electrooculogram light-dark ratio. It is hypothesized that in congenital stationary night blindness some disorder may exist in the apical membrane of the retinal pigment epithelium but not in the basal membrane in view of dissociation between the c-wave response and the light rise in the electrooculogram.

Rod densitometry in night blindness: a review and two puzzling cases. Rod densitometry in night blindness

Since the non-invasive technque of retinal densitometry became available in 1955, rhodopsin kinetics could be studied in vivo. It was obvious that with this new tool investigators focussed attention on the aetiology of night blindness in various diseases. A brief review about the clinical developments in the past two decades is given. Also three case-reports are presented, which suggest that in some cases of congenital stationary night blindness (CSNB) the night blindness might arise from the absence of rhodopsin. This is contrary to the standing opinion and present problems regarding the integrity of the retina.

X-linked congenital stationary night blindness with myopia and nystagmus without clinical complaints of nyctalopia

Seven of eight patients presented initially or were followed for decreased acuity and nystagmus without complaints of night blindness. The diagnosis of congenital stationary night blindness was established with electroretinogram and dark adaptation testing. Careful electrodiagnostic testing is needed to provide accurate genetic counseling. Two patients showed pupillary constriction to darkness which is a sign of retinal disease in young patients.

Mechanisms of rod-cone interaction: evidence from congenital stationary nightblindness

The dark-adapted rod system can elevate cone-mediated thresholds for flicker detection as well as thresholds for the detection of hue. We examined these two types of rod-cone interactions in two individuals with congenital stationary nightblindness (CSNB), a retinal disorder in which rod outer segment function is intact, but in which a defect occurs in the transmission of rod signals within the retina. The two types of rod-cone interaction were differentially affected by the retinal pathology; the rod-cone flicker interaction was normal, but the rod-cone hue interaction was absent. These results provide evidence that, despite similarities in the adaptational properties of these two types of rod-cone interaction, they are mediated by different visual mechanisms.

Characteristic ERG-flicker anomaly in incomplete congenital stationary night blindness

Ten patients with the incomplete type of congenital stationary night blindness (CSNB) were examined with a 30 Hz flicker electroretinogram (ERG). After 30 min of dark adaptation, 30 Hz flicker ERG was recorded continuously for 12-15 min under white background illumination. All patients showed an exaggerated increase of amplitude and a universal characteristic change of wave shape as the light adaptation progressed. Thirty normal subjects also showed increased amplitude during light adaptation, but the increase in amplitude was significantly less than in incomplete-type CSNB, and there was little change in wave shape. The same procedure was applied to patients with complete-type CSNB, retinitis pigmentosa, congenital retinoschisis, cone dystrophy, and Oguchi's disease; neither the exaggerated increase of amplitude nor the wave change was seen. Our results indicate that incomplete-type CSNB is a newly identified cone-rod dysfunction syndrome with a special functional property.

Cone function in congenital nyctalopia

A patient with congenital stationary night blindness (CSNB) (Schubert-Bornschein type) transmitted as an autosomal recessive trait was studied with several tests of electrical function as well as a variety of psychophysical procedures. Comparison of the patient's present findings with those obtained 23 years earlier showed that while rod thresholds have remained the same, cone sensitivity has decreased. Subjective flicker thresholds obtained following a bleach were unchanged during the course of dark adaptation. The absence of rod-cone interaction, together with an absent scotopic b-wave, implies that the defect is in the mid-retinal layers. Further, the absence of oscillatory potentials in the photopic electroretinogram (ERG) suggests that the interplexiform cell may be implicated in some manner. The focal ERG of the CSNB patient showed normal amplitude and normal phase delays, supporting the idea that the focal ERG samples primarily cone photoreceptor activity.

Congenital stationary night blindness presenting as Leber's congenital amaurosis

Two siblings with autosomal-recessive congenital stationary night blindness were clinically blind in infancy. Both had markedly abnormal electroretinograms that, in the first child, led consultants at two university centers to make the diagnosis of Leber's congenital amaurosis. The patients had intermittent nystagmus and esotropia, but good photopic vision developed eventually. Scotopic vision was clearly defective in each child. Refractive error in both patients was close to emetropic in early infancy but became myopic by 1 year of age. Congenital stationary night blindness must be considered in the differential diagnosis of the blind infant.

Congenital stationary night blindness with negative electroretinogram. A new classification

An analysis of 64 patients with congenital stationary night blindness showed that all had essentially normal fundi. Electroretinography (ERG) showed a normal a wave with extremely reduced b wave (negative type) when recorded with a single bright white stimulus in the dark. We classified these patients into two groups based on the evaluation of rod ERG and/or psychophysical dark adaptation measured with an 11 degree test target at 15 degrees in the upper part of the retina. One group (35 patients) lacked rod function (complete type). Nine patients could not be classified. No pedigree showed a complete and incomplete type in one family. Differences between the two groups in refractive error, photopic function, and oscillatory potentials in the ERG suggest a different pathogenesis. Our analysis may provide a new classification of congenital stationary night blindness with a negative ERG.

Congenital stationary night blindness with myopia: a clinico-pathologic study

The left eye of a 77 year old male patient was enucleated because of absolute glaucoma. This eye showed subnormal electroretinogram (ERG) and oscillatory potentials preoperatively, but the other eye showed Schubert-Bornschein type ERG and monophasic dark adaptation curve. Light and electron microscopic studies of the left eye showed a normal arrangement of discs of rod outer segments, normal synaptic ends of the photoreceptors, and complete loss of ganglion cells. From the subnormal ERG in the left eye we assumed it was originally Schubert-Bornschein type ERG but inverted to subnormal type ERG following the loss of inhibitory mechanisms. Thus we propose that the cause of night blindness in congenital stationary cases with Schubert-Bornschein type ERG may be related to the mechanisms inhibitory to cells of the bipolar layer.

Congenital stationary night blindness

Congenital stationary night blindness (CSNB) seems to be a very rare condition in Scandinavia. From Denmark a 7-generation family with the dominant form was published in 1909, and one family with the X-linked recessive form was reported from Norway. On going through the files of the National Eye Clinic for Visually Impaired, 7 patients were found (1 dominant, 4 X-linked recessive, 1 simplex case and 1 autosomal recessive). Including anamnestic information on relatives, 17 patients had a diagnosis of CSNB. The clinical findings in these cases are reported with stress on alteration in ERG, dark adaptation and the optic discs. The loss of oscillatory potentials in a carrier of CSNB is described. The provisional findings seem to indicate that 3 genetic variants are present in the Danish population. The real prevalence is estimated considerably higher than 17 out of 5 million.

Paradoxic pupillary constriction in a patient with congenital stationary night blindness

Paradoxic pupillary constriction to an "off-step" of light was studied in a 35-year-old woman with congenital stationary night blindness. ERG was of the Schubert-Bornschein type (scotopic B-wave absent); fundi were normal for a high myope. Paradoxic constrictions were larger in response to full field and peripheral off-steps from low photopic levels than from higher photopic levels. The patient's "on response" was smaller in magnitude and slower in both latency and dynamics than the on-response of normal subjects. Pupillary hippus was larger in magnitude and more peaked in the patient than in normal subjects. Steady-state (tonic) pupil size increased paradoxically with increased light level over the range 1-2 log fL.

Pupillary constriction to darkness

Patients with congenital achromatopsia and congenital stationary night blindness have been known to show a transient pupillary constriction to darkness. We examined 50 normal subjects and 108 patients with retinal and optic nerve dysfunction to see if any had an initial pupillary constriction to darkness. We used a new infrared television apparatus. Four patients with congenital stationary night blindness, four with achromatopsia, two with bilateral optic neuritis, and one with dominant optic atrophy showed the phenomenon. In the patients who showed this unusual pupillary response to darkness it was the first observable event every time the lights were turned off. The constriction could usually be seen with a handlight, and it was similar in latency to the normal pupillary dilatation to darkness. Pupillary constriction to darkness is a clinically valuable sign that can be used in the detection of congenital retinal disease in children with poor vision.

Reduced amplitude of oscillatory potentials in female carriers of X-linked recessive congenital stationary night blindness

We studied the electroretinograms of 12 female carriers in eight families with X-linked recessive congenital stationary night blindness. Forty-two normal eyes served as controls. The age and refractive error of the normal eyes were matched to those of the female carriers. We found the amplitude of the oscillatory potentials (01 + 02 + 03 + 04) in carriers was statistically smaller than in normal eyes. Seventeen of 22 eyes of carriers were more than +/- 2 S.D. away from normal, and the mean value was statistically lower than normal (P less than .001). The peak time of oscillatory potentials, and the amplitude of the a-, b-, scotopic b-, and photopic b-waves were all within the normal range. The selective abnormality of the amplitude of the oscillatory potentials is a new finding in female carriers in X-linked recessive congenital stationary night blindness.

Loss of electroretinographic oscillatory potentials, optic atrophy, and dysplasia in congenital stationary night blindness

New criteria for diagnosing congenital stationary night blindness include loss of the oscillatory potentials in the photopic and bright-flash dark-adapted electroretinogram, and atrophy or dysplastic changes, or both, in the optic nerve head. Ten patients (seven male and three female, ranging in age from 6 to 19 years) had typical findings of congenital stationary night blindness including congenital nonprogressive nyctalopia, no pigmentary retinopathy, and full visual fields consistent with myopia. Visual acuities ranged from 20/30 to 20/60, though one patient had a visual acuity of 20/200. Most patients had histories of strabismus. The photopic electroretinograms were subnormal. Of the male patients, five had tilted optic disks with temporal portions of the nerve missing, and two had misshapen nerve heads. The three female patients had pallor of the optic disk without evidence of tilt.

The photopic electroretinogram in congenital stationary night blindness with myopia

Previous studies have reported that subjects affected with congenital stationary night blindness and myopia demonstrated some photopic (cone) abnormalities in their electroretinogram (ERG). By comparing the photopic ERG elicited with a threshold and a suprathreshold stimulus it was found that, at threshold, no significant differences were noted both in the peak time and in the amplitude of ERGs evoked from CSNB and normal subjects. However, a more powerful stimulus (16 times the threshold) yields a significant difference in the ERGs recorded from the two groups. ERGs recorded from CSNB patients are decreased in amplitude with a b-wave peak time that remains normal. First derivative analysis of the ERG wave along with a selective recording of the oscillatory components of the ERG suggest that the only visible anomaly in the suprathreshold photopic ERG of CSNB patients is an absence of the two oscillations normally seen on the ascending portion of the b-wave. Data obtained on normal subjects are also reported that try to explain the functional significance of these two oscillatory potentials.

Vitreous fluorophotometry in congenital stationary nightblindness

Vitreous fluorophotometry was performed on eyes with three kinds of congenital stationary nightblindness: Oguchi's disease (two cases), X-linked congenital stationary nightblindness (two cases), and fundus albipunctatus (one case). The results were compared with the electroretinogram (ERG) and the electro-oculogram (EOG). In spite of the variable degree of abnormality of the ERG and EOG, all eyes showed normal values on vitreous fluorophotometry. These results strongly suggest that the blood-retinal barrier in congenital stationary nightblindness is intact and that the electrophysiological results and the functioning of the blood-retinal barrier do not correlate in these diseases.

The Eisdell pedigree. Congenital stationary night-blindness with myopia

A pedigree of X-linked congenital stationary night-blindness, originally published by Nettleship, is presented with abstracts from his private correspondence. An affected descendant has supplied letters and the original working pedigree which led to the publication of the extended pedigree in 1912.

X-linked recessive congenital stationary night blindness, myopia, and tilted discs

A family with X-linked recessive congenital stationary night blindness, myopia, and tilted discs has been identified. All affected members have decreased vision, nystagmus, strabismus with decreased binocular function, visual field defects, abnormal fundus appearance with typical fluorescein angiographic findings of tilted disc syndrome, abnormal electroretinograms, and abnormal visual evoked responses to patterned stimuli. Similar clinical evaluation of an obligate carrier revealed no ocular abnormalities.