[Senile macular degeneration]

The most frequent cause of severe visual deficiency in old age is degeneration-related neovascularization beneath the site of maximum visual discrimination. To date, the therapeutic possibilities are limited, but new methods of examination and treatment give reason for cautious optimism. In recent years, the condition has increased dramatically and, mild cases included, now affects some 20% of over-70-year-olds. A basic knowledge of this degeneration should therefore be required of every family doctor.

A computer-controlled system for measuring dark adaptation and other psychophysical functions

BACKGROUND

Psychophysical thresholds, including dark-adaptation functions and increment threshold sensitivities, are useful for the early detection and diagnosis of visual pathologies. However, few instruments have been designed or adapted for their routine clinical measurement.

METHODS

Here we describe an instrument prototype designed to meet this need, which we refer to as the PULS (Programmier-barer Universeller Licht-Stimulator). The instrument is computer-controlled and fully automated. It allows direct control over target location, luminance, size, duration and temporal profile and over background luminance and spectral composition. It also incorporates an efficient and statistically rigorous strategy for determining threshold.

RESULTS

We present examples of psychophysical functions-dark-adaptation curves, increment threshold sensitivities, estimates of temporal summation in the dark and during the time course of dark adaptation-which have been measured by the PULS prototype in normal observers and clinical patients.

CONCLUSIONS

The PULS instrument provides an automatic and efficient means of measuring dark adaptation and other psychophysical functions. It determines threshold by a more rigorous and faster method than is conventionally employed in clinical adaptometry.

Correlates of photoreceptor rescue by transplantation of human fetal RPE in the RCS rat

This study uses a water maze paradigm as a tool to assess posttransplantation changes in behavior associated with a visual stimulus. A set of dystrophic RCS rats received bilateral injections of freshly isolated human fetal RPE cells into the subretinal space of the superior equatorial hemisphere. Five age-matched control dystrophic RCS rats received subretinal injections of vehicle. All animals were immunosuppressed. At 2 months posttransplantation, each rat was tested in the water escape apparatus. The rat used a single light source, randomly located on the edge of the tank, to locate a submerged platform, placed directly in front of the light. Each rat was timed and videotaped during 10 consecutive trials. The swimming paths and times for all rats were recorded and statistically analyzed. Subsequent to the water escape trials, the eyes were embedded for histologic analysis which included quantitative assessment of photoreceptor cells in predefined retinal regions. The water escape data indicated the differences between the sham and experimental groups changed significantly over time (P = 0.0017). Over time, the transplanted animals learned to use light as a clue (P < 0.0001), whereas the sham animals did not (P = 0.73). Transplanted eyes had a significantly greater mean number of photoreceptors in the superior, grafted region than seen in the inferior region of the same eyes and compared with either region of sham-injected eyes (P = 0.0023). Statistical analyses demonstrated a functional advantage for visually guided behavior in RCS rats transplanted with human fetal RPE cells and a statistically significant PRC rescue effect at 2 months after transplantation.

Photoreceptor orientation and alignment in nasal fundus ectasia

BACKGROUND

We investigated whether Stiles-Crawford (SCE) functions, a measure of photoreceptor orientation and alignment, are disturbed in patients with nasal fundus ectasia (tilted disc; Fuch's coloboma without apparent pupillary involvement).

METHODS

SCE functions were obtained in three observers with nasal fundus ectasia, using psychophysical methods.

RESULTS

In all cases, disruption of photoreceptor alignment can be inferred. Results include location of the SCE peaks outside the pupil in the direction of the lesion, differential alignment, and reduction of the magnitude of SCE at various retinal loci (reduced curvature or p factor). Additional results obtained with the selective adaptation technique imply that receptor disarray (splaying) may be responsible for loss of retinal directional sensitivity.

CONCLUSIONS

From these results, it may be surmised that mechanical tractional forces can play a major role in defining photoreceptor orientation in the retina. Inferred anomalous photoreceptor alignment has heretofore not been specifically linked with Fuch's coloboma/tilted disc syndrome.

The development of subretinal microphotodiodes for replacement of degenerated photoreceptors

There are presently several concepts to restore vision in blind or highly visually handicapped persons by implanting electronic devices into the eye in order to partially restore vision. Here, the approach to replace retinal photoreceptors by a subretinally implanted microphotodiode array (MPDA) is summarized. A survey is given on the present state of the development of MPDAs, the possibility of in vitro and in vivo tests as well as first results on biocompatibility and histology. Additionally, electrophysiological recordings in rabbits and rats are presented which have received such subretinal implants.

Intraretinal transplantation to prevent photoreceptor degeneration

There is great interest in the potential of transplantation to treat retinal degenerative diseases in humans; however, there are still fundamental questions to be addressed in experimental animal studies. We have concentrated on two of these using the Royal College of Surgeons (RCS) rat as a suitable animal model. Firstly, does the loss of photoreceptors lead to secondary changes in the inner retina, which might compromise any photoreceptor preservation strategy? Analysis has shown that there are not only histochemical changes in the inner plexiform layer but also degeneration of retinal ganglion cells. The latter, occurring as a result of a vascular event, appears to have a parallel in some human retinal degenerative diseases. Secondly, what are the functional implications of the progressive photoreceptor loss in the RCS rat and how may transplantation prevent or slow that process? A progressively enlarging visual field defect can be demonstrated in these rats which can be stabilized by transplantation of retinal pigment epithelial cells. There is also a loss or diminished performance in a variety of visual tasks, although the rate of deterioration depends on the task; this too can be limited by cell transplantation. Current results indicate an optimistic future for transplantation in human retinal degenerative disease, but also emphasize the many preparatory steps that still have to be made for a successful clinical outcome.

A correlation between computer-predicted changes in secondary structure and the phenotype of retinal degeneration associated with mutations in peripherin/RDS

PURPOSE

To investigate a molecular understanding of how mutations can lead to different phenotypes, we analyzed the relationship between altered secondary structures predicted by missense mutations in the peripherin/RDS and clinical severity of autosomal-dominant retinal degeneration.

METHODS

We analyzed thirteen different kinds of missense mutations in the second intradiscal loop of peripherin/RDS, previously reported in peer review journals. Alteration of the secondary structure of peripherin/RDS was predicted by computer-assisted protein structure analysis. The number of amino acid residues that would be involved in the secondary structural change produced by a given missense mutation was scored as a grade of molecular change. Clinical severity was estimated by the impairment based on electroretinographic recordings of rods and cones, and was scored according to the severity of their recordings. Regression analysis was carried out between both scores of molecular change and clinical severity. Effects of patients' ages on clinical severity was also analyzed.

RESULTS

Significant correlation was found between scores of molecular change and those of clinical severity (rods, r = 0.89, p < 0.001; cones, r = 0.76, p < 0.005) by regression analysis. There was no correlation between clinical severity and patients' ages.

CONCLUSION

. These findings indicate that the degree of change in the secondary structure of peripherin/RDS can explain in part the correlation between genotype and phenotype in autosomal-dominant retinal degeneration associated with missense mutations in the peripherin/RDS gene.

Diets enriched in docosahexaenoic acid fail to correct progressive rod-cone degeneration (prcd) phenotype

PURPOSE

Results of a previous study show abnormal plasma lipids in progressive rod-cone degeneration (prcd)-affected dogs, with lower docosahexaenoic acid (DHA; 22:6n-3) and cholesterol levels but no differences in other plasma fatty acids, lipids, triglycerides, and fat-soluble vitamins. There is also an increase of the DHA precursor 22:5n-3, so that the ratio of 22:5n-3 to 22:6n-3 is higher in affected than in normal dogs. Because DHA is the predominant esterified fatty acid in rod outer segment (ROS) phospholipids, these findings suggest a possible causal association between abnormal plasma lipid levels and retinal degeneration. In the current study, dietary supplements rich in 22:6n-3 were used to determine whether plasma, liver, and rod outer segment phospholipid composition can be altered to modify the prcd disease phenotype.

METHODS

prcd-affected and normal control dogs were given DHA-enriched supplements for short (7- and 25-day) and long (21-week) periods, and the fatty acid composition of plasma, liver, and rod outer segment phospholipids were examined. In the long-term study, electroretinography and morphology were used to assess modification of the retinal degeneration phenotype.

RESULTS

Administration of DHA-enriched supplements resulted in increases in plasma DHA and n-3 polyunsaturated fatty acids and in decreases in some n-6 fatty acids in normal and prcd-affected dogs. Similar increases in DHA and n-3 fatty acids were observed in the liver, but affected dogs had significantly higher levels at all supplementation time points examined. In contrast, the ROS of affected dogs had statistically lower (approximately 20%) DHA levels, and these levels could not be increased with dietary supplementation. The disease phenotype could not be modified by DHA-enriched supplements.

CONCLUSIONS

Regardless of the sustained three- to fourfold elevation in plasma and liver DHA that occurs as the result of supplementation, the ROS DHA levels remain unchanged, and the prcd disease phenotype is not modified by the dietary manipulation. These findings could be the result of a reduction in the synthesis of DHA-containing phospholipids in the retinas of affected dogs; or, alternatively, there could be a reduction in DHA uptake, transport, or storage within the retinal pigment epithelium-photoreceptor complex.

Evaluation of recombinant adeno-associated virus as a gene transfer vector for the retina

PURPOSE

To evaluate recombinant adeno-associated virus (AAV) as an in vivo gene transfer vector for the retina.

METHODS

A recombinant AAV, vCMVp-lacZ, in which the bacterial beta-galactosidase reporter gene (lacZ) was placed under the control of a cytomegalovirus (CMV) early promoter, was injected into the vitreous body or the subretinal space of mouse eyes. The reporter gene expression was followed by histochemical analyses from 10 to 100 days post-injection. The effect of several variables on the extent of AAV-mediated gene transfer was examined, including routes of delivery, presence of an underlying mutation that caused retinal degeneration, and prior treatment with hydroxyurea.

RESULTS

As measured by reporter gene expression, the AAV vector mediated gene transfer to three major cell types in the retina: the retinal pigment epithelium (RPE), ganglion cells and photoreceptor cells. Following a single injection, more than half of the total retinal areas were typically positive for gene transfer. Reporter gene expression was stable for at least 3 months, the farthest time point examined. Gene transfer to photoreceptor cells was observed only following subretinal delivery, and was greatly enhanced in mice undergoing early retinal degeneration. Cells in the inner nuclear layer were rarely transduced. Systemic administration of a genotoxic drug, hydroxyurea, 2 days prior to AAV delivery did not affect the patterns and extent of reporter gene expression. There was minimal histopathology associated with AAV transduction in the retinas of recipient mice, as determined by light microscopy.

CONCLUSION

Recombinant AAV mediates efficient gene transfer to RPE and ganglion cells, and to photoreceptor cells under certain conditions. Persistence of transgene expression is of long duration and without apparent histopathology. The greater stability, lower cytopathicity, and the ability to transduce retinal ganglion cells are three distinct features of the AAV vector compared to current adenovirus-based vectors.

Ocular findings in patients with autosomal dominant retinitis pigmentosa and Cys110Phe, Arg135Gly, and Gln344stop mutations of rhodopsin

This report describes ocular findings obtained in four patients from three families with autosomal dominant retinitis pigmentosa (adRP) due to missense mutations in the rhodopsin gene. Phenotypes were characterized by standard ophthalmologic examinations, visual fields, electroretinography (ERG), dark adaptation, and two-color dark-adapted threshold perimetry. Two patients aged 38 and 45 years, respectively, from a family with the Cys110Phe mutation showed mild fundus changes without bone spicules as well as small arcuate scotomas in the inferior quadrants of their visual fields but displayed severe functional loss of rods and cones in the ERG. Two-color dark-adapted threshold perimetry revealed a regional type of degeneration. A 48-year-old patient with an Arg135Gly mutation had typical RP with concentrically narrowed visual fields and nondetectable ERG responses. Central visual functions were well preserved for a long time. Two-color dark-adapted threshold perimetry indicated a diffuse type of retinal degeneration. An 18-year-old patient with a Gln344stop mutation has been followed for 13 years. His ERG was clearly reduced at the age of 5 years; since that time, disease progression has been very slow. Currently, there are relatively mild alterations in visual acuity, rod sensitivity, and visual fields. Our findings confirm that there is a large phenotypic variety among patients with adRP and different rhodopsin mutations.

Disease expression in X-linked retinitis pigmentosa caused by a putative null mutation in the RPGR gene

PURPOSE

To determine the disease expression in X-linked retinitis pigmentosa (XLRP) caused by a putative null mutation in the RPGR (retinitis pigmentosa GTPase regulator) gene.

METHODS

In a family with XLRP, haplotype analysis was performed with polymorphic microsatellite markers from the Xp chromosomal region, and genomic polymerase chain reaction sequencing was used to identify sequence variations in the RPGR gene. Hemizygotes and heterozygotes were evaluated clinically and with visual function tests. Optical coherence tomography (OCT) was performed on heterozygotes. Postmortem donor retinas from a heterozygote were examined by microscopy and immunocytochemistry.

RESULTS

X-linked inheritance was confirmed by haplotype analysis using Xp markers. Sequence analysis of the RPGR gene identified a single base pair change, a G-->T transversion, that converts codon 52 GGA (Gly) to TGA (stop codon); the mutation segregates with the disease. A hemizygote in the third decade of life had barely measurable rod function and severely impaired cone function that diminished further over a 7-year interval. Heterozygotes varied in degree of disease expression from mild to severe. Perimetry showed loci with normal rod and cone sensitivity interspersed with loci having either equal rod and cone dysfunction or rod > cone dysfunction. Electroretinographic photoreceptor responses had equal reductions in rod and cone maximal amplitude. OCT cross sectional reflectance images of retinal regions with severe dysfunction showed reduced thickness of the retina and retinal pigment epithelium-choriocapillaris (RPE-CC) complex and increased reflections posteriorly. Regions with mild dysfunction showed similar OCT findings but with preserved retinal thickness. Retinal histopathology in a heterozygote revealed loss of photoreceptors throughout, with retention of only a few islands of cones with tiny or absent outer segments and rods lacking outer segments.

CONCLUSIONS

This RPGR gene mutation, in its mildest expression in heterozygotes, causes a relatively equal disturbance of rod and cone photoreceptor function. Detectable structural change by OCT at the level of the RPE-CC can be present in patches of retina with minimal functional disturbance. More advanced disease stages in heterozygotes show greater rod than cone dysfunction, and the end stage in hemizygotes and heterozygotes is that of typical RP, with only barely detectable cone function from residual cones in a thinned retina with abnormal RPE and choriocapillaris.

Cone and rod function in cone degenerations

Progressive cone dystrophy (CD) is usually marked in the initial stages by reduced visual acuity, color vision deficiency and alterations in the photopic electroretinogram, while morphological alterations can be very mild; in some forms rods are affected in a later stage as well. We examined 40 patients with progressive cone dystrophy to determine the extent of functional losses in the cone system with psychophysical tests. A great variety of visual acuity and fundus alterations was found. Myopia was present in 74% of the patients. An autosomal dominant pattern of inheritance predominated (32%). No prevalence of gender was found. The age of onset ranged between 10 and 30 yr. All patients had progression of their symptoms. The total error score in color arrangement tests, the saturated Farnsworth Panel D-15 and the Farnsworth-Munsell 100-hue test, was pathologic with a predominance of confusions along the tritan and scotopic axis. Especially if visual acuity was below 0.5, color vision defects increased, but color vision defects were also found in patients with normal visual acuity. A general decrease of sensitivity in all three cone mechanisms was observed in measurements of spectral sensitivity. Moreover, cone-cone interaction as tested by transient tritanopia measurements was usually disturbed. In the dark adaptation function the threshold of the cone branch was usually elevated. These tests provide a good means to ascertain the correct diagnosis in early stages of the disease and to monitor progression in patients suffering from cone dystrophy.

Functional consequences of oncogene-induced horizontal cell degeneration in the retinas of transgenic mice

Visual function was evaluated in transgenic mice expressing the simian virus 40 early region under the control of the promoter for phenylethanolamine-N-methyltransferase. These transgenic mice undergo a degeneration of the retinal horizontal cells and the outer plexiform layer. Electroretinograms (ERGs) were recorded under stimulus conditions chosen to elicit both receptoral and postreceptoral responses. The dark-adapted a-waves obtained from transgenic mice were not different from control recordings, indicating that the degenerative process does not interfere with function of the rod photoreceptors. In comparison, the ERG b-wave was markedly reduced in transgenic mice under both dark- and light-adapted conditions. Reproducible visual evoked potentials (VEPs) were recorded from transgenic mice in response to both low luminance stimuli that isolate rod function, and to higher luminance stimuli, indicating that retinal activity is transmitted centrally to the visual cortex. However, VEPs were delayed at all stimulus luminances compared to controls. Analysis of luminance-response functions suggests that the VEP delays could reflect the combination of a decrease in synaptic efficacy and an overall loss in visual sensitivity. These functional abnormalities correlate well with the anatomical abnormalities that have been previously observed in the transgenic retina (Hammang et al., 1993), namely a reduced number of synapses between photoreceptors and second-order neurons.

Retarding photoreceptor degeneration in Pdegtm1/Pdegtml mice by an apoptosis suppressor gene

PURPOSE

Mice (Pdegtm1/Pdegtm1) homozygous for a mutant allele of the gamma subunit of retinal cyclic guanosine monophosphate phosphodiesterase (PDE gamma) suffer a severe photoreceptor degeneration. To determine whether the antiapoptotic BCL2 gene is effective in delaying the cell death pathway in this new strain of mutant mice, a transgene encoding the BCL2 gene product was introduced by mating into the mutant background, and the resulting mice were examined for possible rescue of the retinal degeneration.

METHODS

Electroretinograms (ERGs) of the Pdegtm1/Pdegtm1 mice carrying BCL2 were taken to monitor the responses to light. Light and electron microscopy of sections were used to examine degeneration at different times after birth.

RESULTS

The ERGs of the mutants with the transgene were larger than those without the transgene at 2 and 3 weeks after birth. The maximum differences occurred at 2 weeks postpartum. At 4 weeks after birth, no ERG could be detected in either strain. Histologic analysis showed a greater preservation of photoreceptor nuclei in the Pdegtm1/Pdegtm1 mice containing the BCL2 transgene, which paralleled the electroretinography.

CONCLUSIONS

The introduction of an antiapoptotic transgene BCL2 can delay temporarily and partially the degeneration of photoreceptors in a new autosomal-recessive murine model of retinal degeneration.

Relative effects of aging and age-related macular degeneration on peripheral visual function

The purpose of this study was to determine the extent of peripheral visual deficits in patients with early age-related macular degeneration (ARMD) using electrophysiological and psychophysical techniques. Dark-adaptation curves, electro-oculograms (EOGs), and electroretinograms (ERGs) were obtained from patients with early ARMD and from normally sighted control subjects. The control subjects' data were used to calculate age-dependent 95% confidence intervals for each measure of visual function. For the control subjects, performance on all our measures of visual function decreased with age. For the patients with early ARMD, the cone system absolute thresholds, EOG ratios, and cone-dominated ERG amplitudes and implicit times were within the range of normal age-related changes. Rod system absolute thresholds, cone-rod break times, and rod-dominated electroretinographic measures were abnormal in some patients. These results suggest that when the effects of aging are taken into account, some patients classified as early ARMD may not show significant changes in peripheral retinal function with standard clinical tests.

Electroretinographic and psychophysical findings during early and late stages of human immunodeficiency virus infection and cytomegalovirus retinitis

PURPOSE

The authors examined electrophysiologic and psychophysical measures of retinal function in patients infected with human immunodeficiency virus (HIV) at different stages of infection, including patients with cytomegalovirus retinitis (CMVR).

METHODS

All patients had complete ophthalmologic examinations. Rod-mediated psychophysical thresholds were measured using a modified two-color dark-adapted perimetry technique. Rod-dominated full field flash electroretinograms (ERGs) were obtained as a function of flash intensity, followed by cone-dominated ERGs. The 26 patients infected with HIV (26 eyes) were categorized into three groups. Six patients were infected with HIV but had not progressed to acquired immunodeficiency syndrome (AIDS), and 14 had AIDS. Six patients had CMVR with less than 10% of the retina involved. The data were compared with results from age-similar control subjects.

RESULTS

Psychophysical thresholds as a function of retinal eccentricity were elevated for each of the three stages of HIV infection. The group of patients with CMVR had the greatest amount of threshold elevation and threshold elevation increased with retinal eccentricity. In addition, all three patient groups had abnormal electroretinographic findings. Patients with CMVR were affected more severely on all measures than were the other HIV-infected groups.

CONCLUSIONS

Results reveal that a diffuse functional retinal pathology exists in eyes with the funduscopic appearance of localized peripheral CMVR. Additionally, patients infected with HIV, including those without cotton wool spots, may have abnormal retinal function.

[Macular light sensitivity and afferent pupillary function in children's amblyopia]

OBJECTIVE

To study the characteristics of macular light sensitivity (MLS) and relative afferent pupillary defect (RAPD) in anisometropic and ametropic amblyopia in school-aged children.

METHODS

By using the static perimetry technique and swinging light test, we assessed MLS and RAPD in normal subjects, anisometropic and ametropic amblyopia in school-aged children.

RESULTS

In comparison with the normal group, the MLS in both anisometropic and ametropic amblyopic eyes was significantly depressed. The MLS of the fellow eyes of the amblyopic eyes in anisometropic subjects was also depressed as compared with that of the normal group. The rate of RAPD was positive in 34.29% in the anisometropic amblyopic group.

CONCLUSIONS

The static perimetry technique demonstrates a marked depression of MLS in all amblyopic eyes tested, suggesting a defect of visual X-channel. The pathogenesis of monocular amblyopia and binocular amblyopia is probably different, thus MLS examination can help assess prognosis. RAPD in anisometropic amblyopia may reflect a deficiency of peripheral visual system. The fellow eye of the anisometropic amblyopia eye may also be abnormal in terms of psychophysical standard.

Impaired retinal function in young labrador retriever dogs heterozygous for late onset rod-cone degeneration

Xenon-flash d.c.-electroretinograms were recorded from dark adapted, rod-cone degenerate homozygote affected (n = 6), heterozygote carrier (n = 3) and control retinas (n = 4) at 3 and 4 months of age, starting at 0.6 log units below control PII threshold. One log unit higher stimuli were necessary to evoke PII in heterozygote and affected retinas compared to controls. Unique to the heterozygotes, double peaked PII responses that were evoked by -2 log relative units intensity stimulation were significantly (P = 0.028) lower in amplitude than those of controls. PII amplitudes of homozygotes were significantly (P = 0.005) lower in amplitude than those of controls at both ages examined in response to -2 and 0 log relative intensity stimulation. No differences were found in scotopic threshold response amplitudes or times to peak between the three groups. Homozygote affected PII times to peak were significantly (P = 0.005) shorter in relation to controls at -2 log units. Findings suggest that heterozygotes exhibit an impaired retinal function which can be demonstrated at 3 and 4 months in this mutant.

[Retinitis pigmentosa--clinical, genetic and pathophysiologic aspects]

Retinitis pigmentosa defines a genetically heterogenous group of disorders characterized by degenerations of photoreceptors and pigment epithelium. This article reviews our current knowledge of the genetical, clinical and pathophysiological aspects of this disease complex. Therapeutic concepts under current investigation are discussed as well. In recent years tremendous new insights have been made using molecular techniques for the investigation of retinal dystrophies. Ophthalmoscopically very similar patterns of photoreceptor dystrophies have been related to different gene mutations. In contrast, mutations in a single gene may cause different clinical patterns of photoreceptor dystrophies. Therefore, these recent results suggest that a reclassification of retinal dystrophies on the basis of their genetic origin may be favourable. In the future molecular genetics and the recent developments may play an increasing role for clinical classification and evaluation of photoreceptor dystrophies. The continued clinical and experimental research on hereditary disorders may help to elucidate further the wide disease spectrum and thereby developing new classifications and efficient therapeutic concepts.

Long-term effects of fenretinide on retinal function

The long-term effects of the synthetic retinoid fenretinide (4-HPR) on retinal function were studied by electroretinogram (ERG) in 24 women treated for a median of 30.5 months and in 18 untreated controls belonging to a phase III intervention trial. The six outcome measures were: a wave implicit time, peak-to-peak amplitude and implicit time of b wave following both cone stimulation and maximal cone-rod stimulation in the dark-adapted eye. Multivariate analysis of covariance was applied to evaluate the joint effect on the whole set of ERG measures taking into account their inter-relationship. Predictive factors with a significant effect on ERG measures were: (1) a qualitative interaction between age and treatment duration and (2) the squared (parabolic) function of plasma retinol. Individually, the b wave implicit time following cone stimulation was the only ERG measure significantly influenced by the predictors, indicating a primary effect of 4-HPR on retinal photoreceptor sensitivity without significant alterations of the inner nuclear layer. Thus, in contrast to previous reports at higher dose, administration of 4-HPR at 200 mg/day seems to exert subtle alterations of retinal function as measured by ERG.

Occult macular dystrophy

PURPOSE

Occult macular dystrophy is a hereditary macular dystrophy without any visible abnormality of the fundus or abnormality indicated by fluorescein angiography even when visual acuity is decreased. Normal full-field electroretinogram in both cone and rod components with abnormal focal macular cone electroretinogram is the key to diagnosing this disorder. The purpose of this study was to identify the function of the macular rods and to provide detailed clinical findings in occult macular dystrophy.

METHODS

Thirteen patients from eight families were examined. The fundi of 12 patients were essentially normal (occult macular dystrophy), and the oldest patient in one family disclosed bull's eye maculopathy. In the 12 patients, including the patient with bull's eye maculopathy, the profiles of cone and rod absolute thresholds were performed across the 60-degree horizontal meridian of the posterior pole.

RESULTS

All 12 patients showed cone sensitivity loss only in the macular area. Six relatively young patients revealed normal rod sensitivity, whereas six older patients showed borderline rod sensitivity or abnormal rod sensitivity in the macular area.

CONCLUSIONS

The pathology of occult dystrophy involves either only the macular cone system or macular cone and rod systems without any visible abnormality. This difference of the pathology suggests a different clinical entity or a different stage of occult macular dystrophy.

Overexpression of Bcl-2 or Bcl-XL transgenes and photoreceptor degeneration

PURPOSE

To test the hypothesis that overexpression of genes coding for the anti-apoptotic proteins Bcl-2 or Bcl-XL in photoreceptor cells may prevent or delay photoreceptor degenerations.

METHODS

Transgenic mice were generated in which the bcl-2 or bcl-XL transgenes were expressed in photoreceptor cells under the transcriptional control of a rhodopsin gene promoter. Bcl-2 or bcl-XL transgenic mice were crossed separately to a mouse strain carrying the rd/rd mutation and to another mouse line carrying a dominant rhodopsin gene mutation; both genetic defects result in photoreceptor degeneration. Photoreceptor cell death in mice expressing one of the bcl transgenes and carrying either the rd mutation homozygously or the rhodopsin mutation heterozygously was examined by histologic and electroretinographic measurements. Bcl-2 and bcl-XL transgenic mice also were tested for possible resistance to light-induced photoreceptor damage under two different experimental conditions.

RESULTS

Bcl-2 or bcl-XL transgenes were expressed in photoreceptor cells of all lines of transgenic mice. In both the rd and the rhodopsin mutant mice, expression of either bcl-2 or bcl-XL transgenes did not prevent or measurably delay photoreceptor degeneration. Apoptosis-related nuclear DNA fragmentation, as assessed by in situ labeling with terminal deoxynucleotidyl transferase, was present in 13-day-old rd/rd mouse retinas with or without transgene expression. Twelve days after exposure to 2 hours of high-intensity light, bcl-2 transgenic mice retained approximately four rows of photoreceptor cells in the central retina as compared to none in littermate controls, whereas bcl-XL transgenic mice showed no increased resistance to light damage. Expression of the bcl-2 but not the bcl-XL transgene also was associated with a reduction in rhodopsin content.

CONCLUSIONS

Overexpression of bcl-2 or bcl-XL transgenes does not rescue photoreceptor cells from apoptosis caused by the two genetic mutations tested. Resistance to light damage seen in the bcl-2 transgenic mice is likely from a reduction in rhodopsin content rather than an anti-cell death activity of Bcl-2. Cell death pathways not regulated by Bcl-2 may be operative in photoreceptor degeneration.