The negative ERG is not synonymous with nightblindness

PURPOSE

To provide electroretinographic differentiation between 4 genetically distinct conditions associated with a negative. Schubert Bornschein type electroretinogram (ERG): Complete congenital stationary night blindness (cCSNB), incomplete CSNB (incCSNB), Duchenne muscular dystrophy, and a family with an autosomal dominantly inherited negative ERG.

METHODS

ERGs were recorded in all subjects according to the ISCEV standards. Additionally, a long-duration flash was used under photopic testing conditions to separate depolarizing (ON) and hyperpolarizing (OFF) bipolar cell contributions. Dark adaptometry was obtained in cooperative adult subjects.

RESULTS

We were unable to differentiate between these 4 genetically distinct conditions using the scotopic ERG response to the bright white flash only. The photopic, cone-derived ERG to both short- and long-duration flashes was more informative in making distinctions between these 4 disorders and understanding the possible mechanisms behind the abnormal ERG.

CONCLUSION

None of these disorders are progressive or a result of abnormal photoreceptor phototransduction. We suggest that they each represent a signal transmission error at the photoreceptor to depolarizing bipolar cell synapse that affects both rod and cone output. We propose that vision is spared in the latter 2 conditions because of timing errors in transmission as opposed to a complete signaling block, as seen in cCSNB.

A new, simple, inexpensive means of testing functional vitamin A status: the night vision threshold test (NVTT). A preliminary field-test report

Vitamin A deficiency is the leading cause of preventable childhood blindness in developing countries. Each year, an estimated 13.5 million children world-wide are unable to adapt to the dark and half a million children progress to complete blindness annually from lack of vitamin A. Most of the currently available methods for assessing vitamin A status are expensive, require sophisticated instrumentation and are not efficacious in field conditions. A simple, inexpensive method was developed to identify children with defective dark-adaptability, thereby providing a reflection of marginal vitamin A stores. The purpose of this preliminary study was to test the field-efficacy of the Night Vision Threshold Tester (NVTT). Thirty-nine middle-school children with a mean age of 13.5 +/- 1.37 years were initially tested for their ability to adapt to the dark using the

Molecular genetics of Oguchi disease, fundus albipunctatus, and other forms of stationary night blindness: LVII Edward Jackson Memorial Lecture

PURPOSE

To compare the clinical findings of the various forms of stationary night blindness caused by mutations in identified genes encoding proteins of photoreceptors or the retinal pigment epithelium.

METHODS

Review of the visual acuities, visual fields, fundi, dark-adaptation curves, and electroretinograms from patients with stationary night blindness caused by mutations in the genes RHO, GNAT1, PDE6B, RHOK, SAG, RDH5, and CACNA1F, respectively encoding rhodopsin, the alpha subunit of rod transducin, the beta subunit of rod cGMP-phosphodiesterase, rhodopsin kinase, arrestin, 11-cis retinol dehydrogenase, and a retinal L-type calcium channel.

RESULTS

In the evaluated forms of stationary night blindness, the time course of dark adaptation and the characteristics of the electroretinogram indicate that rod photoreceptors are present and that they function, although abnormally. In night blindness resulting from defects in rhodopsin, the alpha subunit of rod transducin, or the beta subunit of rod cGMP phosphodiesterase, rod photoreceptors respond only to light intensities far brighter than normal, and the sensitivity of rods to light is similar to that of normal individuals who are not dark adapted. In fundus albipunctatus and in Oguchi disease, the rod photoreceptors can achieve normal sensitivity to dim light but only after 2 or more hours of dark adaptation, compared with approximately 0.5 hours for normal individuals. In each of these forms of stationary night blindness, the poor rod sensitivity and the time course of dark adaptation correlate with the known or presumed physiologic abnormalities caused by the identified gene defects. Patients with some forms of stationary night blindness, such as fundus albipunctatus and Oguchi disease, may develop degeneration of the retina leading to severe loss of vision in later life.

CONCLUSIONS

The identification of the mutant genes causing forms of stationary night blindness refines the classification of these diseases and enhances our understanding of the underlying physiologic defects. Ophthalmologists must be aware that although these diseases are traditionally categorized as "stationary," some of them lead to reduced visual acuity or constricted visual fields, especially in older patients. Efforts to develop therapies for these diseases should concentrate on these more severe forms.

A case of a combination of Oguchi's disease and congenital retinoschisis

We report here a rare case of a combination of Oguchi's disease and congenital retinoschisis. A 36-year-old male patient presented with a decrease in vision in both eyes and night blindness. Indirect ophthalmoscopy revealed bilateral macular stellate striations and golden-gray discoloration of the retina outside the vascular arcades. This discoloration turned to a normal retina after complete adaptation to darkness (Mizuo-Nakamura phenomenon).

Node way out

A 47-year-old woman without a history of melanoma experienced visual hallucinations, abnormal visual field, and an ERG suggestive of melanoma-associated retinopathy (MAR). A lymph node biopsy showed malignant melanoma. Appropriate evaluation, management, and treatment of MAR is discussed.

Comparison of the Goldmann-Weekers dark adaptometer and LKC Technologies Scotopic Sensitivity tester-1

The standard for dark adaptation has long been the Goldmann-Weekers Dark Adaptometer(Haag-Streit). More recently, portable, relatively inexpensive LED-based dark adaptometers have become commercially available. These devices have potential use in areas with limited resources to screen for night-blindness, commonly caused worldwide by vitamin A deficiency. In order to determine the sensitivity to detecting changes in night vision, this study compared one such device, LKC Technologies Scotopic Sensitivity Tester-1 (SST-1) to the Goldmann-Weekers in patients with hereditary retinal degeneration and loss of rod function. Dark-adapted final thresholds and rod full-field ERG responses were obtained from 87 patients and 24 normal subjects. Linear regression analysis, discrepancy analysis, and receiver operator characteristic curves for both devices show that the SST-1 quantifies psychophysical rod function nearly as well as the Goldmann-Weekers, within some limitations. We conclude, therefore, that the SST-1 is a viable alternative to the Goldmann-Weekers for the screening of night-blinding retinal disorders.

Retrobulbar optic neuritis and rhegmatogenous retinal detachment in a fourteen-year-old girl with retinitis pigmentosa sine pigmento

A 14-year-old girl complained of a sudden decrease in right visual acuity. The patient had night blindness, a mottled retina but no pigments, extinguished scotopic electroretinographic response, central scotoma in the right eye and rhegmatogenous retinal detachment. She had initially received laser photocoagulation around the retinal tear and then corticosteroid therapy, cryoretinopexy and segmental buckling. Her right visual acuity increased to 1.0. The association of retinitis pigmentosa sine pigmento, retrobulbar optic neuritis and rhegmatogenous retinal detachment, as demonstrated in our patient, may be uncommon.

[An automated and spectral differentiating dark adaptometer--initial results of a clinical study]

BACKGROUND

Routine measurement of dark adaptation is a lengthy process and the presence of a qualified operator is required.

MATERIALS AND METHODS

Our dark adaptometer uses either a red or a green light-emitting diode to produce the threshold stimulus. Through an electronic circuit arrangement the dark adaptation curve is automatically measured. A computer stores the resulting data and renders the statistical analysis possible. To obtain the normal adaptation curve, 33 healthy volunteers were tested. We subsequently examined 32 patients in the clinical assay.

RESULTS

The adaptation for the green test light results in an overlapping photopic/scotopic graph and is used as an analogy for the curve resulting from a white test light. The red LED produces the scotopic graph later on with a more elevated threshold. Of the patients examined, 14 with night blindness show the expected pathological results. Correlating to the type of disease, the other 18 patients without night blindness show normal dark adaptation.

CONCLUSIONS

In 150 examinations the dark adaptometer proved to be easy to handle, yielding valid and reliable results. The automatic recording allows operator-independent measurements. The dark adaptation rate for red and green and the final cone and rod threshold can be evaluated. The computer control provides statistical analysis and the possibility to delegate the examination.

The Night Vision Threshold Test (NVTT): a simple instrument for testing dark adaptation in young children

It is estimated that 41 per cent of the population aged under 5 in the developing world has an inadequate vitamin A dietary intake resulting in increased morbidity and mortality. Half a million children go blind each year as a result of vitamin A deficiency. Thirteen and a half million have night blindness, the first sign of vitamin A deficiency. Unfortunately, there is no simple, sensitive and inexpensive means to identify the child who has marginal levels of vitamin A and thus institute means to prevent their development of severe deficiency. A low cost, simple, easy-to-use instrument designed to detect a young child's ability to adapt to darkness was tested in children admitted to the Mwanamugimu Nutrition Unit at Makerere Medical School in Kampala, Uganda. Despite the severe degree of malnutrition found in these children, Night Vision Threshold Test results and serum retinol levels were related (r = 0.41, p < 0.05). Further efficacy trials for this instrument are planned at community sites in Nepal.

Blue-on-yellow perimetry in the complete type of congenital stationary night blindness

PURPOSE

To resolve the discrepancy between nonrecordable full-field short wavelength cone electroretinograms (S-cone ERGs) and the presence of normal color vision in patients with the complete type of congenital stationary night blindness (CSNB1).

METHODS

Conventional white-on-white (W-W) perimetry, blue-on-yellow (B-Y) perimetry, and the Farnsworth-Munsell 100-hue test were performed in five patients with CSNB1. Diagnosis of CSNB1 was made by clinical and electrophysiological examinations. Twelve normal, age-matched control subjects and an additional 7 normal, highly myopic subjects were tested.

RESULTS

Color vision was normal in all the CSNB1 patients by the Farnsworth-Munsell 100-hue test. B-Y perimetry demonstrated that blue cone sensitivity in CSNB1 was normal in the fixation area, but the mean sensitivities of the entire 60 degrees field, the central 0 degrees-to-15 degrees, and 15 degrees-to-30 degrees ring were significantly decreased compared with the normal and myopic subjects. The sensitivity difference between 15 degrees-to-30 degrees and 0 degrees-to-15 degrees in B-Y perimetry increased significantly in CSNB1 compared with both normal and myopic control subjects.

CONCLUSIONS

Our perimetric results demonstrated that the S-cone function in CSNB1 is preserved only in the fovea and becomes abnormal toward the peripheral retina. This accounts for the normal color vision that tests mainly foveal function and the nonrecordable S-cone ERGs that arise mainly from peripheral retina.

Electroretinograms and visual evoked potentials elicited by spectral stimuli in a patient with enhanced S-cone syndrome

PURPOSE

To evaluate the properties of the retina of a Japanese patient with enhanced S-cone syndrome by analyzing electroretinograms (ERGs) and visual evoked potentials (VEPs) elicited by different spectral stimuli.

METHODS

Ganzfeld spectral flashes in the presence of strong white adapting background illumination were used to elicit cone ERGs and VEPs.

RESULTS

The cone ERG elicited in the patient by short wavelength stimuli was distinctly different from the normal S-cone ERG. The action spectrum of the cone ERG confirmed its relative hypersensitivity to short wavelengths. The action spectrum of the VEP for the patient showed a similar relative hypersensitivity to short wavelengths. The response of the VEPs to short wavelength stimuli was different in waveform from the VEP response to longer wavelength stimuli observed in a normal subject.

CONCLUSIONS

These results indicate that the hypersensitivity to short wavelengths is transmitted to the central nervous system and that there is a short wavelength transducing photopigment in many of the photoreceptors, either abnormal S-cones or photopic rods.

Fundus albipunctatus and other flecked retina syndromes

BACKGROUND

Several ophthalmic conditions manifest a flecked retina. Developing an understanding of their clinical presentations will enable the practitioner to most appropriately manage these conditions.

CASE REPORT

A 27-year-old Middle Eastern woman manifested flecked retinas and nyctalopia. She had been given a diagnosis of retinitis punctata albescens, an inherited, progressive, night blindness; however, the medical history and clinical findings were not consistent with this disorder. Rather, they were consistent with fundus albipunctatus, an autosomal recessive, stationary, night blindness. The clinical presentation of fundus albipunctatus is characterized by discrete, white dots at the level of the retinal pigment epithelium and stable night blindness. A prolonged time for dark adaptation is required to produce normal amplitude electroretinograms in fundus albipunctatus as the result of a delay in the regeneration of rhodopsin. An electroretinogram administered after a prolonged dark adaptation time confirmed the diagnosis of stationary night blindness.

CONCLUSION

In order to ensure an accurate diagnosis for fundus albipunctatus, it is important to be aware of the clinical characteristics and appropriate electroretinogram protocol for this disorder.

Clinical features of Goldmann-Favre syndrome

A 21-year-old woman complained of progressive loss of visual acuity. She had also had night blindness since she was ten years old. At the eye examination, the vitreous was found to be degenerated in both eyes. The fundus findings were a large retinoschisis in the right macula, edema resembling retinoschisis in the left macula and annular degenerative changes in the midperiphery. ERG and dark adaption were abnormal. This vitreoretinal degeneration was diagnosed as Goldmann-Favre syndrome.

[From the symptom to electroretinography diagnosis]

Retinal function can be documented noninvasively and objectively by electroretinography, complementing clinical examinations. Symptoms of nightblindness and of dayblindness with photoaversion, nystagmus, poor vision in infants or unclear visual field defects are meaningful indications for ERG testing. We use standardized (ISCEV) full-field single flash ERGs to evaluate the function of the rod- and of the cone-system. In infants, general anesthesia is useful to combine an abbreviated ERG protocol with ophthalmoscopy and fundus photography. ERG testing facilitates to distinguish between functional deficits in the rod- and cone-system, between congenital-stationary retinal dysfunction and progressive retinal heredo-degenerations. Frequently a functional deficit of the retina without ophthalmoscopic changes can be assessed. These entities include achromatopsia, congenital stationary night blindness, early stages of retinitis pigmentosa (RP) or progressive cone dystrophy, as well as toxic retinal changes. Congenital amaurosis Leber (LCA), infantile RP, Usher's syndrome and retinal involvement in other neuropediatric or metabolic syndromes can be diagnosed or excluded by ERG recording early-on. Synoptic evaluation of the full-field ERG, pattern-ERG and VEP completes neuro-ophthalmological screening.

Retinal degeneration in retinitis pigmentosa and neuronal ceroid lipofuscinosis: An overview

Retinal degeneration is an early consequence of the group of lysosomal storage diseases collectively referred to as the neuronal ceroid lipofuscinoses (NCLs). This review details specialized techniques that have evolved for retinal assessment in patients with hereditary retinal degeneration. A standard ERG protocol is described for assessing rod- and cone-mediated function. Standardization will be crucial for planning and implementing multicenter trials as rational therapeutic intervention becomes available. In recent years, there has been a dramatic increase in knowledge of the molecular biological bases of retinitis pigmentosa and allied retinal degenerations. Rather than attempting a comprehensive summary, this review stresses the concepts of genetic, allelic, and clinical heterogeneity, which have obvious parallels in the NCLs. Many of the mutations that cause retinal degeneration are in genes that encode photoreceptor cascade proteins; others are in genes that encode photoreceptor structural proteins. Recent advances in linking the retinal degeneration slow (RDS) and ATP-binding cassette transporter retina (ABCR) genes to a variety of disease phenotypes will be summarized. Clinical heterogeneity even among family members with the same mutation raises the possibility that modifying factors, either genetic or environmental, could influence the severity of the disease. Here, we focus on vitamin A and docosahexaenoic acid, two potential nutritional modifiers that have received considerable attention in recent years.

Case report of Usher's syndrome in two sisters--first reported case in Singapore

A 28-year-old Chinese woman presented with poor night vision since childhood. Ocular examination showed pigmentary retinopathy and systemic examination revealed sensorineural hearing loss. Family history showed a similar condition in her youngest sister. Ocular and systemic examination of her sister showed similar findings. This is presented as the first case report of Usher's syndrome in Singapore. A general discussion of Usher's syndrome is also presented.

[Melanoma-associated retinopathy with night blindness. Case report]

BACKGROUND

Night blindness is usually symptomatic of retinal dysfunction. However, apart from congenital forms of night blindness such as congenital stationary night blindness (CSNB) and pigmentary retinopathy without clumping of pigment, the acquired forms of night blindness present a particular diagnostic challenge to the ophthalmologist.

CASE REPORT

A 51-year-old patient with formerly healthy eyes presented with malignant skin melanoma and sudden night blindness. Along with reduced acuity, concentric visual field limitation, and a marked decrease in sensitivity of the retinal rods and cones in adaptometrical tests, significantly reduced b waves and intact a waves were registered in the flash-ERG of both eyes with otherwise inconspicuous morphologic findings. Furthermore, serum levels of antibodies (IgG) against retinal bipolar cells were found to be increased.

CONCLUSION

Results indicate the presence of melanoma-associated retinopathy (MAR), which-like carcinoma-associated retinopathy (CAR)-ranks among the tumor-associated diseases of the retina. CAR, MAR, and CSNB can be differentiated immunohistochemically by serum autoantibody determination and electrophysiologically by flash-ERG. As opposed to CAR, the immune response in the case of MAR is not to antigens of photoreceptors and ganglion cells, but to retinal so-called ON-depolarizing bipolar cells mainly connected in series to the rods. In addition, a waves are intact and b waves extinct, resembling the situation of CSNB.

[Congenital stationary night blindness]

The clinical and electrophysiological data in 48 cases of congenital stationary night blindness (CSNB) are analysed. The existence of the complete (with only the cone part of the dark adaptation curve) and incomplete (some rod activity also present) form of this anomaly has been confirmed. The Schubert-Bornschein's type of ERG responses corresponds to the complete CSNB. After 12 years of observation period in some patients the diminution of both the a and b potential of the ERG curves but not the extinction of the ERG potentials has been found. PERG curves and PVEP responses in CSNB are normal. Two pedigrees of CSNB are presented. The first reflects the autosomal dominant mode of heredity in 4 generations, in the second pedigree (5 generations) it is not possible to estimate the mode of heredity.

Night Vision Testing in Unoperated Eyes

BACKGROUND

We previously described a simple test which evaluates image degradation in post-excimer laser (PRK) patients under scotopic conditions. After refractive surgery, corneal haze, ablation zone decentration, ablation zone/pupillary diameter disparity, and under-correction each result in a characteristic pattern on the Night Vision Recording Chart.

METHODS

Using the same method, further studies evaluated night vision image degradation in 118 un-operated emmetropic, myopic, hyperopic, and astigmatic eyes and in 26 contact lens wearers.

RESULTS

Scotopic image degradation increases with myopic refractive error, image displacement increases with astigmatism, and contact lens wearers have more image degradation that with spectacle correction.

CONCLUSION

Our Night Vision Recording Chart offers a simple, reproducible method to characterize image degradation under scotopic conditions.

[Incomplete congenital stationary night blindness (CSNB). An important differential diagnosis of congenital nystagmus]

BACKGROUND

Classifying congenital nystagmus in the absence of biomicroscopically detectable abnormalities of the eye, and in an otherwise healthy child is difficult, especially early in life. At that age, nystagmus and visual loss may be the predominant symptoms of congenital stationary night-blindness. Unless night-blindness is specifically asked for or an ERG performed the correct diagnosis may be missed.

PATIENTS AND METHODS

We present the clinical data of two families with X-linked incomplete CSNB previously undiagnosed. ERG recordings in both families were suggestive of CSNB. The ERG of the obligate carrier was normal. In an attempt to distinguish between the complete and the incomplete type, and to identify further carrier signs, scotopic perimetry and dark adaptation were performed in both affected males and carriers. Scotopic perimetry allows to test the rod-mediated visual pathway in its spatial distribution.

RESULTS

In affected males with non-recordable ERGs scotopic perimetry and dark adaptation disclosed residual rod function indicating an incomplete type. In carriers, there was a sensitivity loss at 600 nm, which may be a new carrier sign.

CONCLUSIONS

The correct diagnosis of the different forms of CSNB together with the identification of carriers is important for (1) genetic counselling and (2) linkage studies to identify the gene(s) for CSNB.

[Electrophysiologic tests for diagnosis of congenital night blindness]

Electrophysiological study in diagnosis of congenital stationary night blindness.

MATERIAL AND METHODS

The goal of this study was to describe a family with X-linked congenital stationary night blindness (CSNB) in which 3 brothers had similar symptoms: night blindness, reduced visual acuity and "negative" type of Flash ERG.

RESULTS

Electrophysiological study permitted to differentiate CSNB from generalized progressive retinal degeneration, what has a prognostic value for these patients.

The electroretinographic diagnosis of the incomplete form of congenital stationary night blindness

Fifteen patients with the incomplete form of congenital stationary night blindness (iCSNB) were reviewed to better characterize their electroretinographic (ERG) findings in view of differential diagnosis with other retinal conditions also presenting with negative bright-flash ERG responses. In all 15 patients, in dark-adapted conditions, the bright-flash ERG response had a normal a-wave followed by a subnormal b-wave. Oscillatory potentials (OPs) observed on the ascending limb of the b-wave, although delayed in implicit time, were of large amplitude. The response to a long-wavelength stimulus showed cone-related components and some well-delineated OPs. On the other hand, the photopically elicited cone responses were strongly abnormal, with a subnormal a-wave followed by a barely recordable b-wave. No OPs could be elicited under photopic conditions. The cone related components and the OP characteristics clearly distinguish iCSNB from the complete form of CSNB and other retinal conditions presenting with minimal fundus abnormalities but with negative bright-flash ERG responses, such as found in Duchenne muscular dystrophy and Aland Island eye disease. The severely abnormal post-synaptic components in the photopic recordings contrast with the well-differentiated cone activity evoked in scotopic conditions. We propose a cone system that does not respond optimally under the normal operating range (photopic) but rather under mesopic or scotopic conditions. In spite of the severe cone-ERG deficits, visual acuity was only slightly reduced. We propose that the defect, which interferes marginally with the neuronal flow of information, lies in the structures responsible for the building of the b-wave.

Diagnosis of night blindness and serum vitamin A level: a population-based study

In a cross-sectional survey of 5420 children in northern Bangladesh, 124 were reported to have night blindness by their parents. Of these, 105 cases along with controls matched for age, sex, and neighbourhood had their scotopic vision examined under standard condition using a luxometer, underwent an ophthalmological examination, and had their serum vitamin A level determined. The mean serum vitamin A level was lowest among children identified as night blind by both their parents and the investigators (16.3 micrograms/dl; 95% confidence interval (CI), 13.9-18.7) and highest among those identified as not night blind by both their parents and the investigators (23.6 micrograms/dl; 95% CI, 21.3-25.9). The results show that parents' report of their children's night blindness had low sensitivity compared with diagnosis using standard observations of scotopic vision with a luxometer.

[Congenital non-progressing night blindness--report of cases]

The authors present 5 cases of nonprogressing congenital disturbances of adaptation. Electroretinogram, typical of this entity can be useful in the differential diagnosis of disorders of scotopic adaptation in other diseases.