Rod and cone activity in patients with dominantly inherited retinitis pigmentosa: comparisons between psychophysical and electroretinographic measurements

Improved Rod Sensitivity as Assessed by Two-Color Dark-Adapted Perimetry in Patients With RPE65-Related Retinopathy Treated With Voretigene Neparvovec-rzyl

Purpose

The purpose of this study was to evaluate rod-mediated function with two-color dark-adapted perimetry (2cDAP) in patients with RPE65-related retinopathy treated with voretigene neparvovec-rzyl.

Methods

Following dilation and dark adaptation, 2cDAP and FST were performed. The 2cDAP was measured on an Octopus 900 perimeter (Haag-Streit) with cyan (500 nm wavelength) and red (650 nm wavelength) stimuli. Hill of vision (HOV) analysis was performed on 2cDAP perimetry with Visual Field Modeling and Analysis (VFMA). Full field threshold stimulus testing (FST) was also measured as a secondary measure of rod-mediated function, and assessed on a Diagnosys Espion with the ColorDome stimulator (Diagnosys LLC).

Results

Eight eyes from 4 patients who were treated with voretigene bilaterally had rod function assessed by 2cDAP testing at least 1 year after treatment. There was statistically significant improvement in 2cDAP following gene augmentation therapy. HOV VFMA analysis showed widespread improvements that extended beyond the treatment bleb and statistically significant improvement in HOV analysis volumetric measurements post-treatment to cyan and red stimuli. FST testing performed in six eyes from three patients demonstrated statistically significant improvement to all chromatic stimuli following treatment.

Conclusions

These findings demonstrated statistically significant improvement in 2cDAP and FST following treatment with voretigene.

Translational Relevance

These findings provide a sensitive method of assessing rod-mediated function in a topographic manner that may be useful in future clinical trials for inherited retinal dystrophies.

Evaluation of photoreceptor function in inherited retinal diseases using rod- and cone-enhanced flicker stimuli

PURPOSE

Clinical assessment of rod and cone photoreceptor sensitivity often involves the use of extended dark adaptation times to minimise cone involvement or the use of bright adapting backgrounds to saturate rods. In this study we examine a new rod/cone sensitivity test, which requires minimal dark adaptation. The aim was to establish whether rod/cone sensitivity losses could be measured reliably in patients with retinal diseases that selectively affect rods or cones when compared to age-matched subjects with normal vision.

METHODS

Flicker modulation thresholds (FMTs) were measured psychophysically, using cone- and rod-enhanced stimuli located centrally, and in four quadrants, at 5° retinal eccentricity in 20 patients (age range: 10-41 years) with cone-dominated (Stargardt's disease or macular dystrophy; n = 13) and rod-dominated (retinitis pigmentosa; n = 7) disease. These data were compared against age-matched normals tested with identical stimuli.

RESULTS

Across all retinal locations, cone FMTs in cone-dominated diseases (Median ± IQR: 32.32 ± 28.15% for central location) were greater than a majority (83%; 49/59) of corresponding rod FMTs (18.7 ± 3.29%; p = 0.05) and cone FMTs of controls (4.24 ± 2.00%). Similarly, rod FMTs in rod-dominant disease (14.99 ± 22.58%) were greater than a majority (88%; 29/39) of the corresponding cone FMTs (9.09 ± 10.33%) (p = 0.13) and rod FMT of controls (6.80 ± 2.60 %).

CONCLUSIONS

Cone-specific deficits were larger than rod-specific deficits in cone-dominated diseases, and vice versa in rod-dominated disease. These results suggest that the new method of assessing photoreceptor sensitivity has potential application in detecting specific rod/cone losses without the need for dark adaptation.

Dark-Adapted Chromatic Perimetry for Measuring Rod Visual Fields in Patients with Retinitis Pigmentosa

Purpose

Although rod photoreceptors are initially affected in retinitis pigmentosa (RP), the full-field of rod vision is not routinely characterized due to the unavailability of commercial devices detecting rod sensitivity. The purpose of this study was to quantify rod-mediated vision in the peripheral field from patients with RP using a new commercially available perimeter.

Methods

Participants had one eye dilated and dark-adapted for 45 minutes. A dark-adapted chromatic (DAC) perimeter tested 80 loci 144° horizontally and 72° vertically with cyan stimuli. The number of rod-mediated loci (RML) were analyzed based on normal cone sensitivity (method 1) and associated with full-field electroretinography (ERG) responses by Pearson's r correlation and linear regression. In a second cohort of patients with RP, RML were identified by two-color perimetry (cyan and red; method 2). The two methods for ascribing rod function were compared by Bland-Altman analysis.

Results

Method 1 RML were correlated with responses to the 0.01 cd.s/m² flash (P < 0.001), while total sensitivity to the cyan stimulus showed correlation with responses to the 3.0 cd.s/m² flash (P < 0.0001). Method 2 detected a mean of 10 additional RML compared to method 1.

Conclusions

Scotopic fields measured with the DAC detected rod sensitivity across the full visual field, even in some patients who had nondetectable rod ERGs. Two-color perimetry is warranted when sensitivity to the cyan stimulus is reduced to ≤20 dB to get a true estimation of rod function.

Translational Relevance

Many genetic forms of retinitis pigmentosa (RP) are caused by mutations in rod-specific genes. However, treatment trials for patients with RP have relied primarily on photopic (cone-mediated) tests as outcome measures because there are a limited number of available testing methods designed to evaluate rod function. Thus, efficient methods for quantifying rod-mediated vision are needed for the rapidly increasing numbers of clinical trials.

Cellular responses following retinal injuries and therapeutic approaches for neurodegenerative diseases

Retinal neurodegenerative diseases like age-related macular degeneration, glaucoma, diabetic retinopathy and retinitis pigmentosa each have a different etiology and pathogenesis. However, at the cellular and molecular level, the response to retinal injury is similar in all of them, and results in morphological and functional impairment of retinal cells. This retinal degeneration may be triggered by gene defects, increased intraocular pressure, high levels of blood glucose, other types of stress or aging, but they all frequently induce a set of cell signals that lead to well-established and similar morphological and functional changes, including controlled cell death and retinal remodeling. Interestingly, an inflammatory response, oxidative stress and activation of apoptotic pathways are common features in all these diseases. Furthermore, it is important to note the relevant role of glial cells, including astrocytes, Müller cells and microglia, because their response to injury is decisive for maintaining the health of the retina or its degeneration. Several therapeutic approaches have been developed to preserve retinal function or restore eyesight in pathological conditions. In this context, neuroprotective compounds, gene therapy, cell transplantation or artificial devices should be applied at the appropriate stage of retinal degeneration to obtain successful results. This review provides an overview of the common and distinctive features of retinal neurodegenerative diseases, including the molecular, anatomical and functional changes caused by the cellular response to damage, in order to establish appropriate treatments for these pathologies.

Retinal specific measurement of dark-adapted visual function: validation of a modified microperimeter

Background

Scotopic function is an important marker of many retinal diseases and is increasingly used as an outcome measure in clinical trials, such as those investigating gene therapy for Lebers congenital amaurosis. Scotopic visual function has traditionally been measured using an adapted perimetry system such as the Humphrey field analyser (HFA). However this system does not control for fixation errors or poor fixation stability. Here we evaluate the use of an adapted microperimeter to measure visual function at defined retinal regions under scotopic conditions.

Methods

A MP-1 microperimeter (Nidek Technologies, Italy) was modified by adding a 1 log unit Neutral Density filter and a 530nm shortpass filter within the optical path of the instrument. Stray light was shielded. Fine matrix mapping perimetry was performed on five younger (<35 years) and five older (>65 years) subjects with no eye disease and good vision. All subjects were fully dark adapted before testing and pupils were dilated with 1% tropicamide. Tests was performed once on the modified MP-1 microperimeter and once using a modified HFA, in a counterbalanced order.

Results

A foveal scotopic scotoma with a sensitivity reduction of >1 log unit was found using each instrument. In addition, the MP-1 system showed the retinal location of the foveal scotoma. Mean test time was 25 minutes for the MP-1 and 32 minutes for the HFA.

Discussion

A modified MP-1 microperimeter can be used to measure scotopic retinal function, creating results which are comparable to the modified Humphrey field analyser. Advantages of the MP-1 system include the ability to track the retina through testing, retinal localisation of the scotoma and a faster test time.

The relationship between full field electroretinogram and perimetry-like visual thresholds in RCS rats during photoreceptor degeneration and rescue by cell transplants

Dark-adapted full field electroretinogram (ERG) and visual receptive field thresholds (recorded from the superior colliculus) were correlated in a model of retinal degeneration, the Royal College of Surgeons rat. In both untreated and retinal pigment epithelium cell transplanted rats, optimal correlation was between b-wave amplitude and preserved visual field area with thresholds under a defined level. The work shows that the magnitude of the b-wave can be used to predict the computed area and degree of visual field preservation recorded in the central nervous system. These observations validate using ERG to assess residual visual function and the effect of transplantation.

A method for comparing psychophysical and multifocal electroretinographic increment thresholds

The multifocal electroretinogram (mfERG) has been commonly used as a method for obtaining objective visual fields. Although qualitative comparisons have been good, quantitative comparisons between the results from mfERG and the results from Humphrey Visual Field Analyser (HVFA) have found variable degrees of agreement depending upon the mfERG response parameter examined and/or the disease studied. Lack of agreement may be due to differences in methodology, differences in the sites of response generation, and/or differences derived from comparing suprathreshold versus threshold responses. In addition, the two procedures are performed at different levels of adaptation. We developed an approach for matching stimulus parameters and compared mfERG and psychophysical thresholds to assess the effects of technique and level of adaptation on the two responses. Psychophysical and mfERG thresholds were obtained as a function of the adaptation level (1.5-4.0 log td) and retinal location. The derived increment threshold-versus-intensity functions for both measures were fitted using the equation logT=logT(0)+log((A+A(0))/A(0))(n). We found that the values of A(0) for the mfERG data were one log unit higher than those for the psychophysical data. In addition, the value of the slope (n) for the mfERG data was shallower (0.8) than that of the psychophysical data (1.0). Predictions were made about comparisons of HVFA threshold and mfERG amplitude data in patients with retinal disease based upon a two-site model of adaptation. The data for some groups of patients could be best-fitted with a model of a disease acting at a site distal to all gain changes, whereas data from other patients were best fitted with a model of a disease acting at a site proximal to all retinal gain. The relationship between the Humphrey visual field threshold losses and mfERG amplitude reductions depends upon the site and mechanism of a particular disease process and the model of retinal gain assumed. In no case is a one-to-one relationship between the losses in the two measures predicted.

Assessment of local retinal function in patients with retinitis pigmentosa using the multi-focal ERG technique

To assess local retinal function in patients with retinitis pigmentosa (RP), multi-focal ERGs and local thresholds (static visual fields) were obtained on eight RP patients with visual acuities of 20/25 or better. All eight patients showed multi-focal responses with normal timing within the central 5 deg. However, there were few responses with normal timing in the areas outside the central 7.5 deg, except in the case of the only patient with a 30 Hz full-field response with normal timing. Since full-field ERGs are dominated by responses from the periphery, this finding supplies a foundation for the commonly observed delays in the full-field cone ERGs of patients with RP. With respect to amplitude, only two patients showed multi-focal responses with near normal amplitudes anywhere in the field. The loss of amplitude at any point was not a good predictor of visual sensitivity in the Humphrey visual field. On the other hand, all areas with normal timing had near normal sensitivity. Timing changes appear to be an early indication of local retinal damage to the cone system. Nearly all areas with sensitivity losses greater than 0.5 log unit, and some areas with near normal sensitivity, showed significantly delayed multi-focal ERGs. Finally areas with extreme sensitivity loss show multi-focal responses with a wide range of amplitudes and implicit times across patients, suggesting different mechanisms of disease action in different patients.

Retinal photoreceptor dystrophies LI. Edward Jackson Memorial Lecture

PURPOSE

To assess the state of knowledge of photoreceptor dystrophies.

METHODS

The current literature concerning photoreceptor dystrophies is reviewed, and their potential impact on concepts of pathogenesis of disease and clinical practice is assessed.

RESULTS

As a result of cooperative investigative work between researchers in various disciplines, major advances in the classification of retinal photoreceptor dystrophies have been made. Until recently, classification of retinal dystrophies was based on clinical observation alone, and it was evident that this method was imprecise and of limited value. Largely through the work of molecular biologists, it has been shown that diseases clinically indistinguishable from one another may be a result of mutations on a variety of genes; conversely, different mutations on a single gene may give rise to a variety of phenotypes. It is reassuring that it is possible to generate concepts as to potential pathogenetic mechanisms that exist in retinal dystrophies in light of this new knowledge. More important for the clinician is the potential impact on clinical practice. There is as yet no therapy by which the course of most of these disorders can be modified. However, there is a considerable body of work in which therapeutic intervention is being explored, and many researchers now see treatment as a justifiable objective of their work.

CONCLUSIONS

Knowledge of the causative mutation is of value to the clinician in that it provides a precise diagnosis and allows the distribution of the abnormal gene to be documented fully within a family. To take full advantage of the opportunities provided by current research, clinical practice will have to be modified, particularly if therapy can be justified.

Distribution of fundus autofluorescence with a scanning laser ophthalmoscope

BACKGROUND

Variation of fluorescence derived from lipofuscin in the retinal pigment epithelium has been recorded with age and in retinal diseases. Studies have been based largely on in vitro observations on eye bank eyes which has placed severe limitations on the data available.

METHODS

A technique is described whereby in vivo imaging of autofluorescence of the fundus was achieved using a scanning laser ophthalmoscope.

RESULTS

The optical characteristics, distribution, and variation with disease imply that the fluorescence is derived from lipofuscin in the pigment epithelium. Autofluorescence is shown to be abnormally high in certain inherited diseases, and low in the presence of retinal atrophy.

CONCLUSION

This technique may be useful both in clinical practice and research. It may allow the detection of the abnormal phenotype in genetically determined disease at a time when other techniques may not. Longitudinal studies of age related macular disease would permit correlation between changes in the pigment epithelium and Bruch's membrane to be established.

Correlation between Goldmann perimetry and maximal electroretinogram response in retinitis pigmentosa

To evaluate the relationship between Goldmann perimetry and maximal electroretinographic responses in patients with retinitis pigmentosa, analyses were performed on 220 affected subjects and separately on two subgroups with autosomal dominant (n = 35) and autosomal recessive (n = 29) inheritance. Electroretinograms were recorded averaging 100 iterations elicited with a 20-lux/s, 0.5-Hz white flash ganzfeld stimulation. The peripheral isopters of the visual fields were delimited with I4e, IIIe and V4e targets, measured on conventional perimetry charts with a light pen and expressed in square centimeters. Unlike most previously published reports, this investigation showed a definite correlation (p = 0.0001) between maximal electroretinographic response amplitude and visual field areas. This correlation was more evident for I4e and IIIe isopters (r = 0.89 and 0.87, respectively) than for V4e isopter (r = 0.69). This phenomenon appears to be related to distortion occurring on standard isometric charts and to spatial summation effects in the peripheral field. Such correlations held for both the autosomal dominant and autosomal recessive subgroups. It appears that, if enough accuracy is provided, maximal electroretinographic responses and Goldmann visual fields are both good measures of the remaining functioning retina in nonsyndromic retinitis pigmentosa, irrespective of inheritance models and dystrophic patterns.

Ocular findings associated with a 3 base pair deletion in the peripherin-RDS gene in autosomal dominant retinitis pigmentosa

Affected members of a family with autosomal dominant retinitis pigmentosa were found to have a 3 base pair deletion at codon 118 or 119 of the retinal degeneration slow gene. This mutation causes the loss of a highly conserved cysteine residue in the predicted third transmembrane domain of peripherin-rds, a photo-receptor specific structural glycoprotein localised to both rod and cone outer segment disc membranes. Four of these individuals underwent detailed clinical, psychophysical, and electroretinographic testing in order to characterise their photoreceptor dysfunction. Nyctalopia was reported early in the second decade by all patients. Global rod and cone dysfunction was recorded by the third decade with severe reduction of both photopic and scotopic function by age 30 years. This retinal degeneration slow gene mutation may lead to the primary loss of both rod and cone photo-receptor function.

Heterogeneity in retinal disease and the computational model of the human-rod response

Abnormal rod-receptor activity can be quantitatively assessed in humans by fitting a computational model of the rod's response to the leading edge of the a wave of the electroretinogram. One purpose of the present study was to compare two procedures for fitting the model to the electroretinogram. A computationally simpler method gives comparable results to the more labor-intensive method used previously. This finding holds for both normal observers and patients with retinodegenerative disease that affects the receptors unevenly. A second purpose of the present study was to consider the effects of a heterogeneous disease process on the parameters of the model. a waves from a heterogeneous retina are computer simulated and are fitted with the receptor model. This analysis suggests that the model will overestimate the change in the healthiest rods and will underestimate the percentage of the rods that are significantly affected.

Clinical and ERG data in a family with autosomal dominant RP and Pro-347-Arg mutation in the rhodopsin gene

In a family with autosomal dominant retinitis pigmentosa, documented over six generations, a previously undescribed point mutation in the rhodopsin gene could be identified. The mutation found in the six affected members examined but in none of the controls, including healthy members of the family, was a point mutation in codon 347 predicting a substitution of the amino acid arginine for proline, designated Pro-347-Arg. Six affected members from two generations were examined clinically and with ganzfeld rod and cone electroretinography. The cone and, more dramatically, the rod electroretinograms were reduced to residual b-wave amplitudes or were non-detectable as early as ages 18 to 22 years. The Pro-347-Arg mutation resulted in a subjectively and clinically homogeneous phenotype: early onset of night blindness before age 11, relatively preserved usable visual fields until about age 30, blindness at ages 40 to 60, and change from an initial apparently sine pigmento to a hyperpigmented and atrophic fundus picture between 30 and 50 years of age.

Rhodopsin Thr58Arg mutation in a family with autosomal dominant retinitis pigmentosa

The authors report a family in which a Thr58Arg rhodopsin mutation co-segregates with the disease phenotype of autosomal dominant retinitis pigmentosa (RP) in 16 family members. DNA sequence determination confirms the presence of the same mutation reported previously for one family apparently unrelated to the pedigree now reported. Features of RP in this family included a later onset of symptoms, with night blindness first noticed between ages 12 to 24 years. Although symptoms worsened with age, no complete blindness was observed even with advanced age. Results of psychophysical and electrophysiologic testing showed that a 19-year-old affected woman and her 65-year-old affected uncle had relatively similar extent of visual dysfunction, and that the vision of both was better than 2 of their relatives aged 37 and 53 years. This study presents a range of phenotypic similarities and differences observed between individuals whose RP appears to be caused by the same mutation.

Retinal function and rhodopsin levels in autosomal dominant retinitis pigmentosa with rhodopsin mutations

We studied rod and cone function in 20 patients from six families with autosomal dominant retinitis pigmentosa, who represented five different point mutations in the gene encoding rhodopsin. In a family with a stop codon mutation at the carboxyl end of the molecule (glutamine-344), young members with the mutation were asymptomatic and clinically unaffected but showed about 1 log unit of rod sensitivity loss across the visual field and decreased rhodopsin levels; at this stage, cone function was essentially normal. In three families with mutations at the border of a transmembrane segment (arginine-135-leucine and arginine-135-tryptophan), there was neither detectable rod function nor measurable rhodopsin; cone function was variably impaired. Two families carrying different mutations (threonine-17-methionine and threonine-58-arginine) had altitudinal visual field defects with less impaired rod and cone function in the inferior than in the superior field. Rod adaptation was abnormal in both families, but the time course of adaptation differed between patients with the two mutations. Differences in the pattern of retinal dysfunction were therefore discernible in patients with different rhodopsin mutations.

Correlations between electroretinography, morphology and function in retinitis pigmentosa

In a retrospective study, data from 116 patients suffering from different forms of retinitis pigmentosa were analysed, and 15 categories comprising altogether 34 symptoms or clinical signs were tabulated from each patient's record. The 15 categories evaluated were: visual acuity, visual field diameter, ring or central scotoma, nyctalopia, susceptibility to glare, refraction, cataract, electroretinography, colour of the optic disc, bone-spicule pigmentation of the retina, retinal vessel diameters, tapetoretinal reflex, sex, heredity, and age. Correlations between the tabulated 34 subcategories or symptoms were calculated. The results of a factorial analysis of the data showed a high number of highly significant correlations between the different categories. It seemed possible to discriminate between two groups of categories, with the members of each group being closely correlated but correlations with members of the other group being much smaller, if not nonexistent. We tentatively associated the first group with the functional state of the central retina and the second group with the state of the peripheral retina.

Linkage to D3S47 (C17) in one large autosomal dominant retinitis pigmentosa family and exclusion in another: confirmation of genetic heterogeneity

Recently Dryja and his co-workers observed a mutation in the 23d codon of the rhodopsin gene in a proportion of autosomal dominant retinitis pigmentosa (ADRP) patients. Linkage analysis with a rhodopsin-linked probe C17 (D3S47) was carried out in two large British ADRP families, one with diffuse-type (D-type) RP and the other with regional-type (R-type) RP. Significantly positive lod scores (lod score maximum [Zmax] = +5.58 at recombination fraction [theta] = .0) were obtained between C17 and our D-type ADRP family showing complete penetrance. Sequence and oligonucleotide analysis has, however, shown that no point mutation at the 23d codon exists in affected individuals in our complete-penetrance pedigree, indicating that another rhodopsin mutation is probably responsible for ADRP in this family. Significantly negative lod scores (Z less than -2 at theta = .045) were, however, obtained between C17 and our R-type family which showed incomplete penetrance. Previous results presented by this laboratory also showed no linkage between C17 and another large British R-type ADRP family with incomplete penetrance. This confirms genetic heterogeneity. Some types of ADRP are being caused by different mutations in the rhodopsin locus (3q21-24) or another tightly linked gene in this region, while other types of ADRP are the result of mutations elsewhere in the genome.

No evidence for linkage between late onset autosomal dominant retinitis pigmentosa and chromosome 3 locus D3S47 (C17): evidence for genetic heterogeneity

Retinitis pigmentosa is an inherited form of blindness caused by progressive retinal degeneration. P. McWilliam et al. (1989, Genomics 5: 619-622) demonstrated close genetic linkage between autosomal dominant retinitis pigmentosa (ADRP) and locus D3S47 (C17) in a single early onset pedigree. The marker C17 maps to the long arm of chromosome 3. Clinically, the disease phenotype has been subdivided into at least two forms on the basis of age of onset, as well as electrodiagnostic criteria. We demonstrate that C17 is unlinked in a late onset pedigree, indicating that the phenotypic variation seen reflects underlying genetic heterogeneity.

Monitoring of patients taking canthaxanthin and carotene: an electroretinographic and ophthalmological survey

1. Patients who have taken canthaxanthin and beta-carotene to avert phototoxicity have been monitored by electroretinographic testing. 2. Patients took the compounds only during the summer months, but were monitored for more than 1 year to determine if seasonal changes in the ERG were visible. 3. The characteristic refractile retinal crystals reduced during the winter. 4. The scotopic b-wave amplitude increased during the winter, whether evoked by red or blue flashes. 5. No other ERG parameter altered. 6. Changes noted in 3 and 4 above are reversible. 7. A dose/ERG-amplitude response relationship was established, but no correlation between blood level or total cumulative dose and b-wave amplitude could be found. 8. It is suggested that the Müller cells concentrate canthaxanthin and this is the mechanism which affects the ERG.

Retinal sensitivity in hereditary retinal degeneration in Abyssinian cats: electrophysiological similarities between man and cat

The functional and electrophysiological similarities in the changes in the electroretinogram (ERG) of man and cat affected by hereditary retinal degenerative disease were studied. The results of a series of log intensity-amplitude studies in a group of young affected Abyssinian cats were fitted to the Naka-Rushton relationship by means of a mathematical package on the University of London mainframe. The analysis showed that the amplitude of the maximum dark-adapted b-wave was significantly reduced by the end of the period studied but that the value of k, a variable inversely equivalent to retinal sensitivity, was only slightly reduced by the retinal degenerative process. The electrophysiological findings thus are similar to those found in cases of human diffuse dominantly inherited retinitis pigmentosa.

Autosomal dominant retinitis pigmentosa: a log quotient analysis of the photopic and scotopic b-wave amplitude

The relationship of the photopic and the scotopic b-wave amplitudes of the electroretinogram was studied in 85 normal subjects and 25 patients with autosomal dominant retinitis pigmentosa, in which one amplitude was at least 20 microvolts. The log quotient of their b-wave amplitudes--that is log of the photopic b-wave amplitude divided by the scotopic b-wave amplitude--was considered to represent the activity of cones relative to rods. The log quotient values had a normal gaussian distribution in the normal control eyes, while they formed two groups in the patients with autosomal dominant retinitis pigmentosa. In the first group (type 1), the scotopic b-wave was non-recordable while the photopic b-wave amplitude was larger than 20 microvolts in all cases, indicating that the log quotient is larger than 0.5 and that the rod system is much more severely affected than the cone system. The second group (type 2) had a log quotient smaller than 0.5 and its distribution almost overlapped the normal one, indicating more symmetrical damage in the cone and rod systems. The mean final rod threshold at 45 minutes for type 1 was significantly higher than that for type 2. The log quotient proved to be a useful index for analysing the cone and rod involvement and consequently provides a better understanding of autosomal dominant retinitis pigmentosa.

Clinical and serum lipid findings in a large family with autosomal dominant retinitis pigmentosa

Retinitis pigmentosa, of unknown cause, has recently been associated with decreased amounts of the polyunsaturated fatty acid, docosahexaenoic acid, in the plasma of affected as compared with unaffected relatives. It has been suggested that this finding may serve as a marker for the disease and might indicate alterations in photoreceptor cell metabolism. The authors studied 54 members of a family with dominantly inherited retinitis pigmentosa in five generations. In addition to the typical clinical findings of retinitis pigmentosa, eight persons also had a bull's eye maculopathy, and four persons had uni- or bilateral optic nerve drusen. When the authors determined the plasma fatty acid and lipid contents, they saw the expected age-related effect on cholesterol and triglycerides, but an unexpected, significant reduction in fatty acids in the unaffected controls as compared with persons with retinitis pigmentosa. The authors' results emphasize the heterogeneity of phenotypic expression of retinitis pigmentosa within a single family.

Retinitis pigmentosa

Retinitis pigmentosa is a clinically and genetically heterogeneous group of hereditary disorders in which there is progressive loss of photoreceptor and pigment epithelial function. The prevalence of retinitis pigmentosa is between 1/3000 and 1/5000 making it one of the most common causes of visual impairment in all age groups. The natural history, differential diagnosis, diagnostic clinical and electrophysiologic findings are reviewed. Generalization about the different genetic subtypes of retinitis pigmentosa are reviewed along with the uses of DNA probes for linkage studies. Syndromes in which retinitis pigmentosa is a manifestation are summarized.

Clinical investigation of retinitis pigmentosa

The diagnostic features and future research directions of retinitis pigmentosa were documented in this update and review of the subject. An extensive and current bibliography is provided.

Rod and cone psychophysics and electroretinography: methods for comparison in retinal degenerations

Methods have been developed to compare full field rod and cone electroretinograms with results of rod and cone static perimetric measurements across the visual field. In a limited number of patients with retinal degeneration, including two subtypes of retinitis pigmentosa, there were close relationships between electroretinographic and psychophysical parameters. Maximum b-wave amplitude and visual field area were highly correlated, as were electroretinographic and perimetric measures of sensitivity loss. Future application of the methods to large numbers of patients with typical retinitis pigmentosa may help elucidate different mechanisms of retinal degeneration.

Clinical findings and common symptoms in retinitis pigmentosa

Data analysis was performed in a prospective study of clinical symptoms and findings in 500 patients with retinitis pigmentosa. The symptoms and findings in these patients met the usual definitions of the disease. At initial examination the patients were questioned in a standardized manner; symptoms and associated health problems were reviewed. Some patients were unable to answer all of the questions. Of the patients 274 (55%) were men and 226 (45%) were women, with a race distribution of 21 (4%) black, 47 (9%) Hispanic, 26 (5%) Oriental, three (1%) American Indian, and 403 (81%) white. Sixty-nine patients reported no symptoms of night blindness and 116 patients claimed no visual field changes; 90 stated that they saw better at dusk. The most common problem noted by 263 (53.3%) was headaches, 31 on a daily basis, 42 at least weekly, 124 infrequently, and the remainder nonspecifically. Numbness or tingling, mainly in extremities, was reported by 99 patients. The second most common problem affecting 170 patients (34.6%) was light flashes; since eight patients had retinal detachments, light flashes cannot be totally discounted. Of 143 patients who had been pregnant, 14 had visual changes.

Statistical evaluation of visual functions in dominant and recessive autosomal pigmentary retinopathy

A statistical study of the progress of fundus lesions and functional loss in relation with age and with inheritance modus was performed in patients with pigmentary retinopathy. A three-way interaction was found between following parameters: inheritance modus, age and pigment anomalies of the fundus; inheritance modus, age and visual field; inheritance modus, age and ERG; inheritance modus, vision and ERG; inheritance modus, dark adaptation and visual field.

Stimulation of rods can increase cone flicker ERGs in man

Recent psychophysical studies in man and electrophysiological studies in lower vertebrates show that dark adapted, unstimulated rods inhibit cone mediated flicker. This investigation uses comparable psychophysical and ERG procedures in man to demonstrate rod-cone interaction of this type. With either procedure the rod cone interaction cannot be demonstrated with Ganzfeld stimulation. A single small, red, flickering test field, which is a common psychophysical stimulus for testing rod-cone interaction, elicits an immeasurably small cone ERG. But an array of many such targets, flickering synchronously, is an effective psychophysical stimulus and produces an ERG with larger cone than rod components. With such an array, it can be shown that a steady, rod-stimulating background selectively enhances cone ERG components.

Evolution of benign concentric annular macular dystrophy

In 1974, Deutman described a family with an autosomal dominantly inherited macular dystrophy that he termed "benign concentric annular macular (bull's-eye) dystrophy." Ten years later, we performed a follow-up examination. Some patients complained of deterioration of visual acuity, night vision, and color vision. The macular dystrophy had progressed. The fundus periphery was more involved and in two patients there were bone corpuscle-like pigmentations. Electrophysiologic examination showed increased photoreceptor dysfunction with equal involvement of the rod and cone system. The patients had an acquired type III blue-yellow color vision defect with pseudoprotanomaly.

Rod-cone interactions and analysis of retinal disease

Cone flicker threshold rises as the rods dark adapt, though the cone threshold to continuous light remains constant. The rise is normally about 1 log unit, but in certain patients who complain of night blindness it may be as great as 2.5 log units. In these persons the kinetics of the rod-cone interaction are those of the recovery of rod sensitivity. The rods impose a low-pass filter on the cones. This effect is absent in congenital nyctalopia and X-linked retinoschisis. We suggest that cone flicker is maintained through a feedback system involving horizontal cells, and when the rod dark current returns in dark adaptation this feedback is altered. Rod cone interaction thus tests rod dark current, and cases of abnormal interaction in patients with retinitis pigmentosa occur, which indicate that the transduction mechanism and the membrane dark current may be differentially affected.

A clinical, psychophysical, and electroretinographic survey of patients with autosomal dominant retinitis pigmentosa

We have surveyed 104 patients (44 families) with autosomal dominant retinitis pigmentosa. The range of the survey includes clinical history, ocular examination, documentation of genetic history, Goldmann kinetic perimetry with IV/4 and I/4 white targets, two-colour static perimetry, and scotopic and photopic electroretinography. Comparison of interfamilial and intrafamilial patterns in the static perimetry data strongly suggests there may be at least two genetic subgroups within the disease characterised by the pattern of loss of rod function: in subgroup D (13 patients, 4 families) this is diffuse and severe, while in subgroup R (28 patients, 13 families) it is regional. In both D and R loss of cone function is regional, and in R it coincides with loss of rod function. In D patients the rod electroretinogram is absent; in all but two R cases it is present and usually substantial. All D patients were aware of night blindness before the age of 10, but most R patients not until after the age of 20. Many of the patients could not be classified because their disease was so advanced. The effect of disease duration on visual acuity and visual field area is described for all patients.

Studies on retinitis pigmentosa in man. II. Erythrocyte osmotic fragility

The osmotic fragility of erythrocytes from patients with genetically classified forms of retinitis pigmentosa (RP) has been studied. The mean fragility was increased in autosomal dominantly inherited RP, where the dystrophy was expressed regionally in the retina, with both rods and cones affected. In contrast it was normal in patients with the dominantly inherited disease, which leads to a diffusely distributed dystrophy of, predominantly, rod photoreceptor cells. Raised osmotic fragility of erythrocytes has also been observed in female patients with multiplex (recessive) RP and in female carriers of the X-linked form of the disease.

A study of retinitis pigmentosa in the City of Birmingham. II Clinical and genetic heterogeneity

This is a study of 138 index patients with retinitis pigmentosa (RP) and their families, in which the selection of index patients was solely on the basis of their residence in Birmingham. Clinical analysis showed that severe disease was as likely to indicate dominant or non-genetic RP as to indicate recessive disease, and that each of three genetic types of uncomplicated RP could probably be divided into two entities. Autosomal dominant RP accounted for at least 22% of index patients but this was likely to be an underestimate because of the low penetrance of the disease. Autosomal recessive disease accounted for not more than 10% of index patients and its rarity was indicated by a high consanguinity rate. Recognisable X linked disease occurred in about 14% of index patients, a similar figure to other studies. The 37% of patients with uncomplicated RP and no obviously affected relative have either autosomal dominant RP or non-genetic RP; it is difficult to know the relative proportions of each. The risks for descendants of patients with recessive disease are clear. The risks of symptomatic RP in the offspring of patients who do, or who might have, dominant RP range from 1 in 2 to 1 in 37 according to the family history and the severity of the RP.