Cone and rod function in vitamin A deficiency with chronic alcoholism and in retinitis pigmentosa

Potential therapeutic strategies for photoreceptor degeneration: the path to restore vision

Photoreceptors (PRs), as the most abundant and light-sensing cells of the neuroretina, are responsible for converting light into electrical signals that can be interpreted by the brain. PR degeneration, including morphological and functional impairment of these cells, causes significant diminution of the retina's ability to detect light, with consequent loss of vision. Recent findings in ocular regenerative medicine have opened promising avenues to apply neuroprotective therapy, gene therapy, cell replacement therapy, and visual prostheses to the challenge of restoring vision. However, successful visual restoration in the clinical setting requires application of these therapeutic approaches at the appropriate stage of the retinal degeneration. In this review, firstly, we discuss the mechanisms of PR degeneration by focusing on the molecular mechanisms underlying cell death. Subsequently, innovations, recent developments, and promising treatments based on the stage of disorder progression are further explored. Then, the challenges to be addressed before implementation of these therapies in clinical practice are considered. Finally, potential solutions to overcome the current limitations of this growing research area are suggested. Overall, the majority of current treatment modalities are still at an early stage of development and require extensive additional studies, both pre-clinical and clinical, before full restoration of visual function in PR degeneration diseases can be realized.

Serial ERG monitoring of response to therapy in vitamin A deficiency related night blindness

Two male patients with known systemic disorders who presented with complaints of nyctalopia underwent a complete ophthalmic examination including electrophysiological evaluation and serum vitamin A (retinol) levels. A significant vitamin A deficiency was detected, supplementation started and repeat electroretinogram (ERG) testing was carried out to monitor the timeline of recovery. Restoration of rod and generalised cone function was rapid within the first week of receiving treatment and near normal recovery was seen after 1 month of supplementation. Serial monitoring of ERG changes in vitamin A deficiency (VAD) associated night blindness plays an important role to demonstrate functional recovery post-treatment. The different effects of VAD on rod and cone function, and their rate of recovery, may reflect differences in the visual cycle between the two photoreceptors. We report the serial ERG changes in VAD related night blindness secondary to intestinal lipofuscinosis and liver cirrhosis in two patients.

REVERSIBLE NYCTALOPIA ASSOCIATED WITH VITAMIN A DEFICIENCY AFTER RESECTED MALIGNANT ILEAL CARCINOID AND PANCREATIC ADENOCARCINOMA

PURPOSE

To describe the rapid time course of visual and electroretinographic recovery from vitamin A deficiency in a patient with a history of multiple resected abdominal tumors, including ileal carcinoid and pancreatic adenocarcinoma.

METHODS

A 61-year-old white man with a history of resected malignant ileal carcinoid and Stage III pancreatic adenocarcinoma referred with complaints of 6 weeks of difficulty with night vision.

RESULTS

Initial testing showed significantly reduced scotopic rod responses in both eyes and decreased vitamin A levels and a normal cancer-associated retinopathy laboratory panel. He had complete recovery of both his symptoms and full-field electroretinography within 5 days of starting intramuscular vitamin A.

CONCLUSION

Vitamin A deficiency-related retinopathy after abdominal surgery may be an underreported complication. This case provides a unique clinical perspective in our patient with a history of ileal carcinoid and Stage III pancreatic adenocarcinoma and confirms that rapid symptomatic and electroretinographic recovery is possible with appropriate treatment.

Treatment of vitamin A deficiency retinopathy with sublingual vitamin A palmitate

PURPOSE

To report treatment of vitamin A deficiency retinopathy with sublingual vitamin A drops.

METHODS

Case report with review of the literature.

RESULTS

A 69-year-old Caucasian woman with a history of small bowel resection presented with progressive symptoms of bilateral nyctalopia and decreased visual acuity. Ophthalmic examination revealed bilateral conjunctival xerosis and fine white granular deposits in the midperipheral retina suggestive of vitamin A deficiency. Full-field electroretinogram (ERG), multifocal ERG (mfERG), and two-color dark adaptometry revealed significant impairment of rod and cone photoreceptor function. Kinetic perimetry demonstrated depressed macular sensitivity with constriction of the finer isopters. After 5 months of treatment with sublingual vitamin A drops, the patient's vision, ERG, mfERG, dark adaptometry, and perimetry normalized. A review of the literature summarizing the electrophysiologic testing in vitamin A deficiency is also discussed.

CONCLUSIONS

This case highlights novel observations on the effects of sublingual vitamin A supplementation for acquired vitamin A deficiency retinopathy. Sublingual vitamin A may represent a viable and efficacious treatment modality for vitamin A deficiency.

Fundus white spots and acquired night blindness due to vitamin A deficiency

To report a successfully treated case of acquired night blindness associated with fundus white spots secondary to vitamin A deficiency. An ocular examination, electrophysiologic testing, as well as visual field and OCT examinations were obtained on a 61-year-old man with vitamin A deficiency who had previously undergone gastric bypass surgery. The patient had a re-evaluation after treatment with high doses of oral vitamin A. The patient was observed to have numerous white spots in the retina of each eye. Best-corrected visual acuity was initially 20/80 in each eye, which improved to 20/40-1 OU after oral vitamin A therapy for 2 months. Full field electroretinogram (ERG) testing, showed non-detectable rod function and a 34 and 41% reduction for 32-Hz flicker and single flash cone responses, respectively, below the lower limits of normal. Both rod and cone functions markedly improved after initiation of vitamin A therapy. Vitamin A deficiency needs to be considered in a patient with white spots of the retina in the presence of poor night vision.

Functional observations in vitamin A deficiency: diagnosis and time course of recovery

AIMS

To describe the effects of vitamin A deficiency (VAD) on retinal function and the subsequent recovery following treatment in three patients with systemic conditions (two with Crohn disease; one secondary to IgE syndrome).

METHODS

Electrophysiological testing (including pattern electroretinogram, PERG; electroretinogram, ERG; visual-evoked potential) established the diagnosis of VAD. Repeat testing was carried out in two patients to monitor the time course of recovery following intramuscular vitamin A injection. The third patient had repeat recordings following 13 months of oral supplementation.

RESULTS

All three patients initially displayed a characteristic absence of rod function associated with VAD. In addition, delayed and reduced amplitude cone ERGs, loss of short wavelength cone (S-cone) function and subnormal macular function were observed in two patients. Restoration of rod and generalised cone function was rapid in the two patients who received intramuscular injection, with normalisation of some electrophysiological responses after only 3 days. Normal S-cone amplitudes and cone latencies were reached within 12 days of vitamin A injection. Macular function returned to within normal limits by 12 days postinjection in one patient, but remained mildly subnormal in the second patient. Full recovery was present after 13 months oral supplementation in the third patient.

CONCLUSIONS

Novel observations regarding dark-adapted cone function, S-cone function, and PERG are presented. The differences between the effects of VAD on rod and cone function, and their rate of recovery, may reflect differences in the visual cycle between the two photoreceptor classes. The importance of rapidly and accurately diagnosing VAD, a treatable condition, is noted.

Retinal toxicity during pegylated alpha-interferon therapy for chronic hepatitis C: a multifocal electroretinogram investigation

BACKGROUND

Ocular side-effects in the form of retinal ischaemia and haemorrhages have been reported in patients undergoing standard alpha-interferon therapy.

AIM

To assess the ocular impact of therapy with sustained release pegylated alpha-2a interferon (Pegasys) for chronic hepatitis C.

METHODS

Ten patients receiving Pegasys and ribavirin and 10 healthy volunteers were recruited. Patients underwent full ophthalmic investigations and multifocal electroretinogram testing at baseline, at regular intervals during treatment and post-treatment. The multifocal electroretinogram maps retinal function. Responses were compared with sequential recordings from healthy volunteers.

RESULTS

All patients had normal clinical ophthalmic investigations at baseline. During therapy a single patient experienced central visual disturbance lasting 24 h with no prolonged ill effect. No other patient was aware of any change in vision. Fundal abnormalities appeared in five patients during treatment. The multifocal electroretinogram showed reductions in retinal function in five patients. Nine of 10 patients exhibited abnormalities on at least one multifocal electroretinogram or fundoscopic investigation.

CONCLUSIONS

Subclinical retinal toxicity during anti-viral therapy with pegylated alpha-interferon and ribavirin was frequent in this study and it suggests that patients should be warned of this risk and monitored during therapy.

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.

Electrophysiology in the investigation of acquired retinal disorders

Electrophysiological research on acquired retinal disorders, both common and rare, is reviewed. Age is a major factor influencing electroretinogram (ERG) and electro-oculogram (EOG) findings. Bipolar or Müller cell death in the aging retina could account for much of the amplitude decline that is observed with age. In diabetic retinopathy, the oscillatory potentials can monitor the progression of the disease and indicate neuronal alterations rather than diabetic angiopathy of the retina. Human ERG studies on glaucoma concentrated on ERG measures that are dominated by inner retinal contributions. It has been shown that the pattern ERG can serve as a predictor of ocular hypertension's progression to glaucoma. In retinal disorders caused by endogenous intoxication, such as hepatic retinopathy, or exogenous intoxication from chronic lead exposure, ERG changes give an objective measure of the damage and allow to study the pathophysiological mechanisms that are involved. Inflammations of the choroid and the retina affect the standard ERG when they are diffuse. In central serous chorioretinopathy, functional disturbances can be revealed not only in the photoreceptors but also in the middle and inner retinal layers with the use of focal stimuli. Choroidal melanoma leads to large reductions of the EOG light peak-to-dark trough ratio through its influence on the transepithelial potential of the retinal pigment epithelium (RPE). In cancer-associated retinopathy, both the rod and cone ERGs are reduced. However, selective cone dysfunction has been described. In melanoma-associated retinopathy, the long flash ERG may reveal a specific pathophysiological mechanism, namely the affection of the ON-pathway with preservation of the OFF-pathway. ERG measurements can reveal vitamin A deficiency and are altered in cases with a mutation in the gene for the retinol binding protein in which other organs are not affected. Photochemical damage to the retina from light emission by the operating microscope can be assessed by electrophysiological methods.

Vitamin A status in relation to electroretinographic and electrooculographic findings in HIV infection

OBJECTIVES

To investigate the electrooculogram (EOG) and an expanded battery of electroretinograms (ERGs) in HIV-infected subjects without retinopathy at two different levels of immunosuppression. Consideration was given to the possible effects of serum levels of vitamin A.

METHODS

Two groups of neurologically normal HIV-positive subjects with CD4+ cell counts of <200 (n=17) or >400 (n=19) were contrasted with 20 HIV-negative controls. Rod ERGs, oscillatory potentials and cone ERGs were obtained using ganzfeld stimulation. A sequence of dark- and light-adapted EOG recordings was analyzed to obtain light/dark ratios. The HIV-positive subjects underwent a comprehensive ophthalmologic examination.

RESULTS

Intergroup comparisons failed to reveal any significant intergroup differences. Abnormal ERG findings, those exceeding the 98% confidence limits, occurred in 11% (4/36) of the HIV-positive subjects. One of these subjects was hyporetinemic and another had a subnormal retinol level. No subjects had abnormal EOGs.

CONCLUSIONS

HIV infection influenced retinal function in 11% of a group of neurologically normal subjects without clinical signs of retinopathy. The profile of electrophysiological findings suggested predominant functional deficits involving middle or inner retinal layers. Vitamin A deficiency and possible vascular changes could account for the observed ERG abnormalities.

Hepatic retinopathia. Changes in retinal function

In patients suffering from hepatic failure, the brain is subject to defined morphological and functional changes known as hepatic encephalopathia (HE). The morphological changes are dominated by glial cells (Alzheimer-type II astrocytes). It has recently been possible to demonstrate, that the retinal glia (Müller) cells undergo similar morphological changes. The present study was carried out in order to reveal if these Müller cell changes cause any characteristic functional deficits. We examined 11 patients with different stages of HE due to liver cirrhosis. Six patients were at stage 0 or 1 (group I) and five at stage 2 or 3 (group II). They underwent ophthalmological routine examination, colour vision testing and standard ERG recording. None of the patients reported impaired vision, in daylight or at night. There were no fundus abnormalities except very mild changes of the pigment epithelium and abnormal reflexes of the inner limiting membrane, especially in the higher HE stages. The number of confusions in the colour arrangement test increased with the higher stages of HE, preferably in the tritan axis. The scotopic a- and b-waves of the electroretinogram (ERG) were almost unchanged in group I and significantly decreased and delayed in group II. The photopic ERG b-wave amplitudes were changed in a similar fashion. Oscillatory potentials proved to be most sensitive to hepatotoxic changes. Their latencies were significantly delayed even in group I. Amplitudes were decreased significantly only in group II. Patients suffering from hepatic failure and accompanying HE display functional abnormalities of the retina. These are best demonstrated by the ERG, and correlate well with the degree of HE. A hypothesis is presented that relates the observed functional changes to altered neurotransmitter levels and impaired retinal glial-neuronal interaction, due to Müller cell damage caused by elevated ammonia levels.

Night blindness in Sorsby's fundus dystrophy reversed by vitamin A

Sorsby's fundus dystrophy (SFD) is an autosomal dominant retinal degeneration caused by mutations in the tissue inhibitor of metalloproteinases-3 (TIMP3) gene. Mechanisms of the visual loss in SFD, however, remain unknown. In a SFD family with a novel TIMP3 point mutation, we tested a hypothesis that their night blindness is due to a chronic deprivation of vitamin A at the level of the photoreceptors caused by a thickened membrane barrier between the photoreceptor layer and its blood supply. Vitamin A at 50,000 IU/d was administered orally. Within a week, the night blindness disappeared in patients at early stages of disease. Nutritional night blindness is thus part of the pathophysiology of this genetic disease and vitamin A supplementation can lead to dramatic restoration of photoreceptor function.

Clinical and subclinical ophthalmic findings with retinol deficiency

BACKGROUND

Patients at risk for retinol deficiency in developed countries include those with hepatic dysfunction and malabsorption states. Symptoms of retinol deficiency may go unrecognized or unreported.

METHODS

The authors describe 15 patients with hepatic dysfunction, two of whom had procedures that would predispose to malabsorption and were ophthalmologically symptomatic of retinol depletion. The other 13 patients were ophthalmologically asymptomatic liver transplant candidates examined prospectively for subclinical evidence of retinol deficiency. Combined laboratory analysis, Schirmer's testing, conjunctival impression cytology, and electroretinography were performed.

RESULTS

Twelve of 15 patients had serum retinol levels below the lower limit of normal. Aqueous tear production was reduced in 7 of 14 patients. Abnormal conjunctival morphology was noted in 6 of 12 patients. Electroretinograms were abnormal in the two patients who were visually symptomatic and in seven of nine patients who were ophthalmologically asymptomatic.

CONCLUSION

Subclinical, physiologically significant retinol deficiency may be a frequent and unrecognized problem among patients with hepatic dysfunction.

Electro-oculogram in vitamin A deficiency associated with cystic fibrosis. Short communication

Electro-oculograms (EOGs) were recorded in a patient with cystic fibrosis and vitamin A deficiency before and during vitamin A supplementation (25,000 IU/day). Before vitamin A supplementation the EOG Arden light/dark ratio was 1.27. After seven months of vitamin A supplementation the Arden ratio increased to 3.0. These results reveal that vitamin A deficiency can cause an abnormal EOG.

A long term follow up of ocular siderosis: quantitative assessment of the electroretinogram

Siderosis oculi is a severe sequel of retained, iron made, intraocular foreign body. Iron atoms or ions, dissolved from the foreign body, may diffuse to the retina and produce irreversible cellular damage. Therefore, early extraction of an iron foreign body is recommended. When the risks of surgical intervention outweigh the danger of siderosis, the patient is periodically examined in order to detect the initial signs of siderosis. The most commonly used test for quantitative and objective assessment of retinal function is the electroretinogram (ERG). We report here a long term ERG follow-up (about 8 years) of a patient suffering from a unilateral iron intraocular foreign body. The development of siderosis was detected by any of the ERG responses; cone-dominated, rod-dominated or mixed cone-rod responses. However, the degree of the assessed damage varied and strongly depended upon the flash intensity used to elicit the ERG response and upon the ERG wave chosen to assess retinal function. The relationship between the ERG b- and a-waves showed a profound deterioration reflecting a reduction in signal transmission from the photoreceptors to the inner nuclear layer. These findings suggested that iron toxicity produced more damage to the inner retina than to the outer retina.

Rhodopsin levels and retinal function in cats during recovery from vitamin A deficiency

Extended vitamin A deficiency in the cat led to an abnormal appearance in the tapetal fundus with the formation of a dark brown streak centered on the area centralis. At this time rod sensitivity, as measured by the b-wave of the electroretinogram, was reduced by more than two log units; the level of rod visual pigment was reduced by about 90% throughout the paracentral retinal region and was essentially absent from the area centralis. Following oral supplementation with vitamin A there was a rapid partial recovery of both rhodopsin levels and rod sensitivity. Further recovery continued over more than 18 days to levels that were not substantially below normal. This recovery was absent from the area centralis, in which measured visual pigment levels remained very low. In supplemented cats, the brown color in the fundus faded but there remained a small hyper-reflective zone at the area centralis. Morphological examination of the central retina in a supplemented cat showed an outer nuclear layer reduced to one or two rows in the small zone with low rhodopsin levels. Cone but not rod photoreceptors were present in this zone and they appeared to lack outer segments. During recovery, the increase in rod sensitivity was approximately linearly related to the recovery of rhodopsin levels. Thus, in these conditions reduction in sensitivity resulting from previous vitamin A deficiency was limited by the ability of the photoreceptors to absorb incident quanta. The time course of the recovery of rhodopsin and sensitivity suggests that at least two processes were involved. The faster of these may be the regeneration of rhodopsin from existing opsin molecules in the outer segments, while the slower may depend on the renewal of the outer segments themselves.

The electroretinogram in preterm infants

With the hope that the electroretinogram (ERG) in preterm infants could help clarify their vitamin A requirements, a technique for recording the full-field ERG in the neonate is described. One hundred seventy-seven ERGs were performed in 59 preterm and 52 term infants. An ERG was recorded as soon as 7 hours after birth and as early as 30 weeks after conception. In preterm infants the a-wave latency was longer and the amplitude less than in term infants of the same age. The amplitude of the ERG in preterm infants increased with the duration of light exposure. Longitudinal data on 15 preterm infants showed a reduction in a-wave latency. None of the ERG findings correlated with postconceptional age, which suggests that the duration of light exposure is a major determinant of the ERG pattern in preterm infants. Despite low circulating levels of retinol, no correlations with any of the ERG values were found.

Attempts to define the minimal serum level of vitamin A required for normal visual function in a patient with severe fat malabsorption

A case with severe malabsorption of fat soluble vitamins is described. The malabsorption developed after an intestinal bypass operation due to morbid obesity. Night blindness occurred as the first symptom of vitamin A deficiency. The cone visual sensory threshold was elevated about one log unit and the rod threshold abot two and a half log units. No changes of the a- and b-waves of the electroretinogram (ERG) was observed. However, during the initial phase of very low serum reninol level (0.21 mumol/l) the summed amplitudes of the oscillatory potentials (OPs) were lower. After parenteral therapy with vitamin A the night blindness disappeared and the dark-adapted rod and cone threshold sensitivity recovered to normal. However, the time-course of rod adaptation first reached normal levels after 5 months. The amplitudes of the OPs of the ERG response returned to normal when the serum retinol level had increased close to normal. Serum retinol levels of 0.7 mumol/l or higher were always associated with normal or close to normal dark-adapted rod sensitivity. However, a normal serum retinol level (> 0.95 mumol/l) and a normal dark-adapted rod threshold sensitivity were not always associated with a normal time-course of the rod adaptation. It is concluded, that the maintenance dosage of vitamin A must be individualized and that patients who have undergone jejuno-ilea bypass surgery must be carefully monitored for vitamin A deficiency by both serum levels and dark adaptation measurements.

Visual function and rhodopsin levels in humans with vitamin A deficiency

Details of rod and cone dysfunction in vitamin A deficiency have been studied in two subjects with primary biliary cirrhosis and one with Crohn's disease, all of whom presented with symptoms of night blindness. Visual function in the mid-peripheral retina was monitored with two-color adaptometry and rhodopsin levels were measured by fundus reflectometry. Initially all three subjects had no measurable rod function and delayed cone adaptation. In one case the dark-adapted cone threshold was also elevated. Oral supplementation with vitamin A restored visual function to normal within 8 days in all subjects. During supplementation, cone function was restored more rapidly than that of rods, though the pattern of recovery was similar for each receptor type. Final thresholds improved first, though the rates at which they were reached were abnormally slow. As recovery continued, adaptation kinetics returned to normal. When rod adaptation was delayed, the regeneration of rhodopsin was also abnormally slow. When rod final threshold was 2 log units higher than normal, rhodopsin regeneration was incomplete, reaching about 70% of the normal level. The initial stages of visual dysfunction during onset of vitamin A deficiency were studied in one subject, and were found to mirror the pattern seen during recovery: rod adaptation was initially slower than normal, but reached completion. Cone adaptation remained normal until rod function was almost absent.

Ocular NAD-dependent alcohol dehydrogenase and aldehyde dehydrogenase in the baboon

Isoelectric focusing (IEF) techniques and spectrophotometric analyses were used to examine the distribution and properties of alcohol dehydrogenase (ADH) and aldehyde dehydrogenase (ALDH) isozymes in ocular tissue of olive and yellow baboons. Cornea extracts exhibited very high specific activities of the 'stomach-specific' ADH and ALDH isozymes (designated ADH-3 and ALDH-III respectively), and were devoid of the major liver and kidney isozymes. Lens extracts exhibited lower activities of ADH-3 and ALDH-III, and also showed significant activity of ALDH-II (the major liver cytosolic isozyme) and a group of 'lens-specific' ALDHs of low isoelectric point. Extracts of baboon retina also exhibited ADH-3 and ALDH-III activities, together with activities of the major liver cytosolic (ALDH-II) and mitochondrial (ALDH-I) isozymes of ALDH; and ADH-5 (or chi-ADH) activity. Evidence was obtained for individual variation of ALDH-III activity in the lens. An electrophoretic variant for ADH-3 indicated genetic identity of the major stomach and ocular ADH isozyme. The catalytic properties of the high specific activity corneal ADH and ALDH isozymes indicated a role in the detoxification of lipid peroxidation by-products.

Macular electroretinograms: their accuracy, specificity and implementation for clinical use

The pattern and the focal electroretinogram (ERG) are both non-invasive, electrophysiological responses recorded from circumscribed retinal areas and are most easily recorded from the macula. This paper describes how our department has incorporated these tests into our clinical protocol, shows how the recording technique and the method of electrode construction may be improved, and describes the normal limits of the macular responses we obtain. The ERG signal-noise ratio we obtained was better than that of the binocular visual evoked potentials (VEPs) recorded simultaneously. Pattern and focal ERGs, using improved methods of recording, show promise of being a valuable addition to the clinical investigation of subtle maculopathies and some forms of optic nerve dysfunction. Three illustrative cases are described. The first demonstrates normal macular ERG responses with abnormal Ganzfeld ERGs due to peripheral retinal damage. The second reveals differential pattern ERG reduction with normal focal ERG in recent optic neuritis. The third case demonstrates reversible simultaneous loss of Ganzfeld ERGs and macular ERGs in vitamin A deficiency.

Night vision in a case of vitamin A deficiency due to malabsorption

Night vision was tested electroretinographically and psychophysically in a vitamin A deficient patient before and after therapy. Vitamin A deficiency resulted from malabsorption due to a jeujunoileal bypass operation. Before therapy the patient had severely reduced cone and rod function. After the reversal operation, accompanied by 5 injections of a total of 500,000 units of vitamin A, complete recovery of cone and rod functions was observed within 7 months. Shortly after therapy rod sensitivity reached the normal level, while the time course of rod adaptation remained slower than normal and the dark-adapted electroretinographic (ERG) responses were subnormal. At later stages the ERG responses reached normal amplitudes but rod adaptation stayed slow. Only after 7 months did night vision reach the normal level with regard to the time course of rod adaptation, rod sensitivity, and ERG responses.

Retinitis pigmentosa and allied diseases: applications of electroretinographic testing

Electroretinograms (ERGs) have provided criteria for establishing the diagnosis of retinitis pigmentosa in early life even at a time when fundus abnormalities visible with the ophthalmoscope are minimal or absent. Patients with widespread progressive forms of retinitis pigmentosa have shown not only reduced amplitudes but also delays in cone or rod b-wave implicit times, or both, while patients with self-limited sector retinitis pigmentosa or stationary forms of night blindness have had reduced amplitudes with normal b-wave implicit times. In families with retinitis pigmentosa ERGs can be used not only to identify which patients are affected but also to establish which patients are normal as those patients, age 6 and over, with normal cone and rod amplitudes and normal cone and rod b-wave implicit times have not been observed to develop primary retinitis pigmentosa at a later time. ERGs from patients with retinitis pigmentosa and allied night blinding disorders are presented to show their usefulness in genetic typing, documenting natural; histories, and defining possible pathogenetic mechanisms. The potential application of the ERG in evaluating the efficacy of therapeutic trials is also considered.

The application of visually evoked cerebral potentials in ophthalmological diagnosis

A short survey is presented of what can be done with electrophysiological techniques in ophthalmological diagnosis. It is stressed that more investigation has to be done to elucidate the discrepancies between electrophysiological and psychophysical disturbances. These discrepancies can be used for the differential diagnosis. More, though still too little, is known about differences between a disturbance of latency time and that of amplitude. It seems that latencies are more disturbed in active pathological processes like demyelination, compression of nerve fibres and oedema, whereas isolated reduction of amplitudes occurs in optic atrophies. Some optic nerve diseases are found to be combined with ERG abnormalities, such as tobacco-alcohol neuropathy and some hereditary diseases.