Giving in to the blues.

The molecular players that direct the development of mammalian photoreceptors are slowly coming into focus. A study that elucidates the cause of enhanced S-cone syndrome, a disorder that may be caused by a distortion of retinal cell fate, reveals one such factor-although questions about its effects remain.

Mutation of a nuclear receptor gene, NR2E3, causes enhanced S cone syndrome, a disorder of retinal cell fate.

Hereditary human retinal degenerative diseases usually affect the mature photoreceptor topography by reducing the number of cells through apoptosis, resulting in loss of visual function. Only one inherited retinal disease, the enhanced S-cone syndrome (ESCS), manifests a gain in function of photoreceptors. ESCS is an autosomal recessive retinopathy in which patients have an increased sensitivity to blue light; perception of blue light is mediated by what is normally the least populous cone photoreceptor subtype, the S (short wavelength, blue) cones. People with ESCS also suffer visual loss, with night blindness occurring from early in life, varying degrees of L (long, red)- and M (middle, green)-cone vision, and retinal degeneration. The altered ratio of S- to L/M-cone photoreceptor sensitivity in ESCS may be due to abnormal cone cell fate determination during retinal development. In 94% of a cohort of ESCS probands we found mutations in NR2E3 (also known as PNR), which encodes a retinal nuclear receptor recently discovered to be a ligand-dependent transcription factor. Expression of NR2E3 was limited to the outer nuclear layer of the human retina. Our results suggest that NR2E3 has a role in determining photoreceptor phenotype during human retinogenesis.

Restoration of photoreceptor ultrastructure and function in retinal degeneration slow mice by gene therapy.

The gene Prph2 encodes a photoreceptor-specific membrane glycoprotein, peripherin-2 (also known as peripherin/rds), which is inserted into the rims of photoreceptor outer segment discs in a complex with rom-1 (ref. 2). The complex is necessary for the stabilization of the discs, which are renewed constantly throughout life, and which contain the visual pigments necessary for photon capture. Mutations in Prph2 have been shown to result in a variety of photoreceptor dystrophies, including autosomal dominant retinitis pigmentosa and macular dystrophy. A common feature of these diseases is the loss of photoreceptor function, also seen in the retinal degeneration slow (rds or Prph2 Rd2/Rd2) mouse, which is homozygous for a null mutation in Prph2. It is characterized by a complete failure to develop photoreceptor discs and outer segments, downregulation of rhodopsin and apoptotic loss of photoreceptor cells. The electroretinograms (ERGs) of Prph2Rd2/Rd2 mice have greatly diminished a-wave and b-wave amplitudes, which decline to virtually undetectable concentrations by two months. Subretinal injection of recombinant adeno-associated virus (AAV) encoding a Prph2 transgene results in stable generation of outer segment structures and formation of new stacks of discs containing both perpherin-2 and rhodopsin, which in many cases are morphologically similar to normal outer segments. Moreover, the re-establishment of the structural integrity of the photoreceptor layer also results in electrophysiological correction. These studies demonstrate for the first time that a complex ultrastructural cell defect can be corrected both morphologically and functionally by in vivo gene transfer.

Human gene therapy for RPE65 isomerase deficiency activates the retinoid cycle of vision but with slow rod kinetics.

The RPE65 gene encodes the isomerase of the retinoid cycle, the enzymatic pathway that underlies mammalian vision. Mutations in RPE65 disrupt the retinoid cycle and cause a congenital human blindness known as Leber congenital amaurosis (LCA). We used adeno-associated virus-2-based RPE65 gene replacement therapy to treat three young adults with RPE65-LCA and measured their vision before and up to 90 days after the intervention. All three patients showed a statistically significant increase in visual sensitivity at 30 days after treatment localized to retinal areas that had received the vector. There were no changes in the effect between 30 and 90 days. Both cone- and rod-photoreceptor-based vision could be demonstrated in treated areas. For cones, there were increases of up to 1.7 log units (i.e., 50 fold); and for rods, there were gains of up to 4.8 log units (i.e., 63,000 fold). To assess what fraction of full vision potential was restored by gene therapy, we related the degree of light sensitivity to the level of remaining photoreceptors within the treatment area. We found that the intervention could overcome nearly all of the loss of light sensitivity resulting from the biochemical blockade. However, this reconstituted retinoid cycle was not completely normal. Resensitization kinetics of the newly treated rods were remarkably slow and required 8 h or more for the attainment of full sensitivity, compared with <1 h in normal eyes. Cone-sensitivity recovery time was rapid. These results demonstrate dramatic, albeit imperfect, recovery of rod- and cone-photoreceptor-based vision after RPE65 gene therapy.

Trafficking of membrane-associated proteins to cone photoreceptor outer segments requires the chromophore 11-cis-retinal.

Lecithin retinol acyl transferase (LRAT) and retinal pigment epithelium protein 65 (RPE65) are key enzymes of the retinoid cycle. In Lrat(-/-) and Rpe65(-/-) mice, models of human Leber congenital amaurosis, the retinoid cycle is disrupted and 11-cis-retinal, the chromophore of visual pigments, is not produced. The Lrat(-/-) and Rpe65(-/-) retina phenotype presents with rapid sectorial cone degeneration, and the visual pigments, S-opsin and M/L-opsin, fail to traffic to cone outer segments appropriately. In contrast, rod opsin traffics normally in mutant rods. Concomitantly, guanylate cyclase 1, cone T alpha-subunit, cone phosphodiesterase 6alpha' (PDE6alpha'), and GRK1 (G-protein-coupled receptor kinase 1; opsin kinase) are not transported to Lrat(-/-) and Rpe65(-/-) cone outer segments. Aberrant localization of these membrane-associated proteins was evident at postnatal day 15, before the onset of ventral and central cone degeneration. Protein levels of cone T alpha and cone PDE6alpha' were reduced, whereas their transcript levels were unchanged, suggesting posttranslational degradation. In an Rpe65(-/-)Rho(-/-) double knock-out model, trafficking of cone pigments and membrane-associated cone phototransduction polypeptides to the outer segments proceeded normally after 11-cis-retinal administration. These results suggest that ventral and central cone opsins must be regenerated with 11-cis-retinal to permit transport to the outer segments. Furthermore, the presence of 11-cis-retinal is essential for proper transport of several membrane-associated cone phototransduction polypeptides in these cones.

SCA7 knockin mice model human SCA7 and reveal gradual accumulation of mutant ataxin-7 in neurons and abnormalities in short-term plasticity.

We targeted 266 CAG repeats (a number that causes infantile-onset disease) into the mouse Sca7 locus to generate an authentic model of spinocerebellar ataxia type 7 (SCA7). These mice reproduced features of infantile SCA7 (ataxia, visual impairments, and premature death) and showed impaired short-term synaptic potentiation; downregulation of photoreceptor-specific genes, despite apparently normal CRX activity, led to shortening of photoreceptor outer segments. Wild-type ataxin-7 was barely detectable, as was mutant ataxin-7 in young animals; with increasing age, however, ataxin-7 staining became more pronounced. Neurons that appeared most vulnerable had relatively high levels of mutant ataxin-7; it is interesting, however, that marked dysfunction occurred in these neurons weeks prior to the appearance of nuclear inclusions. These data demonstrate that glutamine expansion stabilizes mutant ataxin-7, provide an explanation for selective neuronal vulnerability, and show that mutant ataxin-7 impairs posttetanic potentiation (PTP).

Correlation between photopic negative response and retinal nerve fiber layer thickness and optic disc topography in glaucomatous eyes.

PURPOSE: To investigate whether there is a significant correlation between the photopic negative response (PhNR) of the electroretinogram (ERG) and retinal nerve fiber layer thickness and optic disc topography in glaucomatous eyes. METHODS: Ninety-nine eyes of 53 patients with open-angle glaucoma (OAG) and 30 eyes of 28 normal volunteers were studied. Photopic ERGs were elicited by red stimuli (644 nm, 1600 cd/m(2)) on a blue background (470 nm, 40 cd/m(2)). The mean deviation (MD) of the visual field was obtained by static visual field analyses. The topography of the optic nerve head was determined by confocal scanning laser ophthalmoscopy. The retinal nerve fiber layer thickness (RNFLT) around the optic nerve head was measured with a scanning laser polarimeter. RESULTS: The amplitude of the PhNR and the PhNR/b-wave ratio decreased with an increase in visual field defects. The logarithmic values of the PhNR amplitude and PhNR/b-wave amplitude ratio were significantly correlated with the MD better than the linear values. The PhNR amplitude and PhNR/b-wave amplitude ratio were significantly correlated with the RNFLT and the rim area of the optic disc and with the cup/disc area ratio. These correlations were higher when expressed linearly than when stated logarithmically. The sensitivity and specificity were 77% and 90% for the PhNR amplitude and 70% and 87% for the PhNR/b-wave amplitude ratio when the optimal cutoff values were used. Although the a-wave amplitude correlated with the MD, the a-wave amplitudes of most of the patients fell within the normal range. The correlation between the b-wave amplitude and MD was not significant. CONCLUSIONS: The PhNR amplitudes correlate with the decrease in function and morphology of retinal neurons in eyes with OAG. The linear relationship between the PhNR and the structural parameters indicates that inner retinal function declines proportionately with neural loss in eyes with glaucoma.

Measuring rod and cone dynamics in age-related maculopathy.

PURPOSE: A cathode-ray-tube (CRT) monitor-based technique was used to isolate clinically significant components of dark adaptation. The utility of the technique in identifying adaptation abnormalities in eyes with age-related maculopathy (ARM) is described. METHODS: A CRT dark adaptometer was developed to assess cone and rod recovery after photopigment bleach. The following measures were obtained: cone recovery rate (R(c); in decades per minute) and absolute threshold (Tf(c); log candelas per square meter), rod recovery rate (R(r); decades per minute), and rod-cone transition (rod-cone break [RCB], in minutes). These components were isolated by appropriately selecting stimulus size, stimulus location, pigment bleach, and test duration and by coupling the CRT with judiciously selected neutral-density (ND) filters. The protocol was developed by using 5 young observers and was tested on 27 subjects with ARM in the study eye and 22 age-matched control subjects. RESULTS: The parameters necessary for effective isolation of cone and early phase rod dark adaptation were a 2.6 ND filter (for a standard CRT monitor, 0.08-80 cd . m(-2) luminance output); a 4 degrees foveated, 200-ms, achromatic spot; approximately 30% pigment bleaching; and a 30-minute test duration. These settings returned obvious rod and cone recovery curves in control and ARM eyes that were compatible with conventional test methods and identified 93% of participants with ARM as having delayed dynamics in at least one of the parameters. Cone recovery dynamics were significantly slower in the ARM group when compared with age-matched control subjects (R(c), 0.99 +/- 0.35 vs. 2.63 +/- 0.61 decades . min(-1), P < 0.0001). Three of the 27 eyes with ARM did not achieve RCB during the allowed duration (30 minutes). The remaining eyes with ARM (n = 24) exhibited a significant delay in rod recovery (R(r)(,) ARM, 0.16 +/- 0.03 vs. controls, 0.22 +/- 0.02 decades . min(-1), P < 0.0001) and the average time to RCB (+/-SD) in the ARM group was significantly longer than in the control subjects (19.12 +/- 5.17 minutes vs. 10.40 +/- 2.49 minutes, P < 0.0001). CONCLUSIONS: The CRT dark-adaptation technique described in this article is an effective test for identifying abnormalities in cone and rod recovery. Slowed cone and rod recovery and a delayed RCB were evident in the eyes with ARM. The test method is potentially useful for clinical intervention trials in which ARM progression is monitored.

The status of cones in the rhodopsin mutant P23H-3 retina: light-regulated damage and repair in parallel with rods.

PURPOSE: This study tests whether cones in the rhodopsin-mutant transgenic P23H-3 retina are damaged by ambient light and whether subsequent light restriction allows repair of damaged cones. METHODS: P23H-3 rats were raised in scotopic cyclic (12 hours of 5 lux, 12 hours of dark) ambient light. At postnatal day 90 to 130, some were transferred to photopic conditions (12 hours of 300 lux, 12 hours of dark) for 1 week and then returned to scotopic conditions for up to 5 weeks. Photoreceptor function was assessed by the dark-adapted flash-evoked electroretinogram, using a two-flash paradigm to isolate the cone response. Outer-segment structure was demonstrated by immunohistochemistry for cone and rod opsins and by electron microscopy. RESULTS: Exposure for 1 week to photopic ambient light reduced the cone b-wave, the rod b-wave, and the rod a-wave by 40% to 60% and caused shortening and disorganization of cone and rod outer segments. Restoration of scotopic conditions for 2 to 5 weeks allowed partial recovery of the cone b-wave and the rod a- and b-waves, and regrowth of outer segments. CONCLUSIONS: Modest increases in ambient light cause rapid and significantly reversible loss of cone and rod function in the P23H-3 retina. The reduction and recovery of cone function are associated with shortening and regrowth of outer segments. Because the P23H mutation affects a protein expressed specifically in rods, this study emphasizes the close dependence of cones on rod function. It also demonstrates the capacity of cones and rods to repair their structure and regain function.

Nrl-knockout mice deficient in Rpe65 fail to synthesize 11-cis retinal and cone outer segments.

PURPOSE: To define rod and cone function further in terms of visual cycle mechanism, the retinal phenotype resulting from Rpe65 (retinoid isomerase I) deficiency in Nrl(-)(/)(-) mice having a single class of photoreceptors resembling wild-type cones was characterized and outcomes of retinoid supplementation evaluated. METHODS: Rpe65(-)(/)(-)/Nrl(-)(/)(-) mice were generated by breeding Rpe65(-)(/)(-) and Nrl(-)(/)(-) strains. Retinal histology, protein expression, retinoid content, and electroretinographic (ERG) responses were evaluated before and after treatment with 11-cis retinal by intraperitoneal injection. Results Retinas of young Rpe65(-)(/-)/Nrl(-)(/-) mice exhibited normal lamination, but lacked intact photoreceptor outer segments at all ages examined. Rpe65, Nrl, and rhodopsin were not detected, and S-opsin and M/L-opsin levels were reduced. Retinyl esters were the only retinoids present. In contrast, Nrl(-)(/)(-) mice exhibited decreased levels of retinaldehydes and retinyl esters, and elevated levels of retinols. ERG responses were elicited from Rpe65(-)(/-)/Nrl(-)(/-) mice only at the two highest intensities over a 4-log-unit range. Significant retinal thinning and outer nuclear layer loss occurred in Rpe65(-)(/-)/Nrl(-)(/-) mice with aging. Administration of exogenous 11-cis retinal did not rescue retinal morphology or markedly improve ERG responses. CONCLUSIONS: The findings provide clarification of reported cone loss of function in Rpe65(-)(/-)/Nrl(-)(/-) mice, now showing that chromophore absence results in destabilized cone outer segments and rapid retinal degeneration. The data support the view that rod-dominant retinas do not have a cone-specific mechanism for 11-cis retinal synthesis and have potential significance for therapeutic strategies for rescue of cone-rich retinal regions affected by disease in the aging human population.

Detection of mosaic retinal dysfunction in choroideremia carriers electroretinographic and psychophysical testing.

PURPOSE: To test whether choroideremia carriers have a mosaic pattern of retinal dysfunction, as noted in carriers of X-linked recessive retinitis pigmentosa and X-linked retinoschisis. DESIGN: Prospective observational case series. PARTICIPANTS: Seven obligate choroideremia carriers (age range, 18-72) with visual acuity (VA) of 20/25 or better were recruited into the study. METHODS: The carriers underwent VA testing (Snellen chart), ophthalmic examination, Humphrey visual field (VF), and multifocal electroretinographic testing. The amplitude and implicit time scales were measured by the algorithm of Hood and Li. The amplitude measures (a scales) and implicit time measures (t scales) were reported abnormal when they were >2 standard deviations above the mean of age-similar normally sighted control subjects. MAIN OUTCOME MEASURES: Mapping of local 103 electroretinographic response amplitudes and implicit times. RESULTS: Only 1 of the 7 carriers showed abnormal Humphrey VF thresholds, whereas 6 of the 7 carriers showed a mosaic pattern of retinal dysfunction measured by multifocal electroretinographic testing. All 6 carriers showed statistically significant implicit time delays, whereas 4 carriers showed statistically significant amplitude reductions and implicit time delays (P<0.05 to P<0.0006). One carrier with a normal-appearing macula and normal Humphrey VF showed a cluster of statistically significant implicit time delays within the macula (P<0.05 to P<0.0006). The overall extent of local electroretinographic abnormalities corresponded to the severity of ophthalmoscopically apparent pigmentary changes. The one carrier with mild threshold elevation on Humphrey VF testing showed the most ophthalmoscopically apparent extensive fundus pigmentary changes. CONCLUSIONS: We demonstrated a mosaic pattern of retinal cone dysfunction in carriers of choroideremia. Our findings are consistent with the Lyon hypothesis of random X-chromosome inactivation. Multifocal electroretinographic testing is potentially sensitive to detect local retinal dysfunction in choroideremia carriers even in those with a normal-appearing macula and good VA.

A study of unusual Rayleigh matches in deutan deficiency.

Rayleigh match data were modeled with the aim of explaining the locations of match midpoints and matching ranges, both in normal trichromats and in subjects with congenital color deficiency. Model parameters included the wavelength of peak sensitivity of cone photopigments, the effective photopigment optical density, and the noise amplitude in the red-green color channel. In order to avoid the suprathreshold, perceptual effects of extreme L:M cone ratios on color vision, selective post-receptoral amplification of cone signals is needed. The associated noise is also amplified and this causes corresponding changes in red-green threshold sensitivity. We propose that the noise amplitude and hence the size of the matching range in normal trichromats relates to the known inter-subject variation in the relative numbers of L and M cones. If this hypothesis can be shown to account for the extremes of the red-green matching range measured in normal trichromats, it is of interest to establish the extent to which it also predicts the unexpected, small matching ranges that are observed in some subjects with red-green color deficiency. A subset of subjects with deutan deficiency that exhibited less common Nagel matches were selected for genetic analysis of their cone pigment genes in order to confirm the type of deficiency, and to predict the corresponding peak wavelength separation (delta lambda(max)) of their two, long-wavelength cone pigments. The Rayleigh match model predicted accurately the midpoint and the range for the spectral differences specified by the genes. The prediction also required plausible selection of effective optical density of the cone pigments and noise. The noise needed varied, but the estimates were confined to lie within the limits established from the matching ranges measured in normal trichromats. The model predicts correctly the small matching ranges measured in some deuteranomalous subjects, principally accounted for by a low estimate of noise level in the red-green channel. The model also predicts the "normal" matches made by some subjects that rely on two hybrid genes and therefore exhibit red-green thresholds outside the normal range, typical of mild deuteranomaly.

Novel KCNV2 mutations in cone dystrophy with supernormal rod electroretinogram.

PURPOSE: To describe patients with cone dystrophy and supernormal rod electroretinogram (ERG) and search for mutations in the recently described KCNV2 gene. DESIGN: Clinical and molecular study. METHODS: Patients from three families originating from France, Morocco, and Algeria had standard ophthalmologic examination and color vision analysis, Goldmann perimetry, International Society for Clinical Electrophysiology of Vision (ISCEV) protocol in accordance with ERG testing, autofluorescence evaluation, and optical coherence tomography 3 scanning. The two coding exons of KCNV2 were polymerase chain reaction amplified and sequenced. RESULTS: All patients had the characteristic features of supernormal, delayed rod ERG responses at the highest levels of stimulation and markedly reduced cone responses. In the French family, two affected sisters were compound heterozygotes for the recurrent c.1381G>A (Gly461Arg) mutation and for a novel c.442G>T (Glu148Stop) mutation. In the Moroccan family, affected members were homozygotes for the novel c.1404delC mutation (His468fsX503) and in the Algerian family, the proband was homozygote for the novel c.1001delC mutation (Ala334fsX453). In the three families, parents were unaffected heterozygote carriers. None of the mutations were present in 50 control chromosomes. CONCLUSIONS: The three novel truncative mutations are likely to be null mutations leading to loss of function, with no difference in the phenotype presentation. Amino acid changes are found exclusively in the N-terminal fragment of the protein and in the P-loop, indicating the importance of those regions for the function of the KCNV2 protein.

Comparison of focal macular cone ERGs in complete-type congenital stationary night blindness and APB-treated monkeys.

Focal macular cone electroretinograms (ERGs) and multifocal ERGs were recorded to study the macular function in patients with the complete-type of congenital stationary night blindness (cCSNB). The waveforms of the focal macular cone ERGs and the on- and off-responses of the multifocal ERGs in the cCSNB patients were similar to those recorded from monkey retinas treated with L-2 amino-4-phosphonobutyric acid (APB), suggesting that patients with cCSNB have a complete defect of the on-pathway even in the central retina. The results also demonstrated that there was a paradoxical positive response in the central retina of cCSNB patients, as compared to the negative full-field ERGs in the same subjects.

Fourier-domain optical coherence tomography and adaptive optics reveal nerve fiber layer loss and photoreceptor changes in a patient with optic nerve drusen.

BACKGROUND: New technology allows more precise definition of structural alterations of all retinal layers although it has not been used previously in cases of optic disc drusen. METHODS: Using Stratus and Fourier domain (FD) optical coherence tomography (OCT) and adaptive optics (AO) through a flood-illuminated fundus camera, we studied the retinas of a patient with long-standing optic disc drusen and acute visual loss at high altitude attributed to ischemic optic neuropathy. RESULTS: Stratus OCT and FD-OCT confirmed severe thinning of the retinal nerve fiber layer (RNFL). FD-OCT revealed disturbances in the photoreceptor layer heretofore not described in optic disc drusen patients. AO confirmed the FD-OCT findings in the photoreceptor layer and also showed reduced cone density at retinal locations associated with reduced visual sensitivity. CONCLUSIONS: Based on this study, changes occur not only in the RNFL but also in the photoreceptor layer in optic nerve drusen complicated by ischemic optic neuropathy. This is the first reported application of FD-OCT and the AO to this condition. Such new imaging technology may in the future allow monitoring of disease progression more precisely and accurately.

Bone marrow-derived stem cells preserve cone vision in retinitis pigmentosa.

Retinitis pigmentosa is a heritable group of blinding diseases resulting from loss of photoreceptors, primarily rods and secondarily cones, that mediate central vision. Loss of retinal vasculature is a presumed metabolic consequence of photoreceptor degeneration. A new study shows that autologous bone marrow-derived lineage-negative hematopoietic stem cells, which incorporate into the degenerating blood vessels in two murine models of retinitis pigmentosa, rd1 and rd10, prevent cone loss. The use of autologous bone marrow might avoid problems with rejection while preserving central cone vision in a wide variety of genetically disparate retinal degenerative diseases.

Temporal response properties of the macular cone system: effect of normal aging and age-related maculopathy.

PURPOSE: To evaluate the influence of aging and age-related maculopathy (ARM) on the temporal frequency response function (TFR) of macular focal electroretinography. METHODS: Macular (18 degrees ) focal electroretinograms (FERGs) in response to sinusoidal flicker, modulated at TFs between 3.7 and 52 Hz, were recorded from 13 young (age range, 14-29 years) and 9 old (age range, 55-80 years) healthy subjects and from 18 patients with ARM (stage 2 disease; age range, 55-80 years; visual acuity >/=0.4). Amplitude and phase of the Fourier-analyzed response fundamental (1F) and seconnd harmonic (2F) were measured. RESULTS: In young healthy subjects, mean 1F TFR showed a maximum amplitude at 41 Hz, a secondary peak at 3.7 Hz, a minimum at 8 Hz, and a high TF (32-52 Hz) roll-off. Mean 1F TFR of old, compared with young, healthy subjects showed amplitude enhancement at 10 to 14 Hz and a small loss at high TF. Mean 2F TFR of young and old healthy subjects had a maximum at 5.7 to 8 Hz and an attenuation beyond 10 Hz. Mean 1F and 2F TFRs of ARM patients were similar to those of old healthy subjects but were depressed in mean amplitude. FERG TFR changes of old healthy subjects and ARM patients were not mimicked by reducing stimulus retinal illuminance or modulation depth in young healthy subjects. CONCLUSIONS: FERG temporal properties are affected by normal aging and ARM. Because FERG TFR is shaped mainly by postreceptoral activity, the findings suggest that photoreceptor and postsynaptic dysfunction underlie aging- and ARM-related FERG changes.

Evaluating retinal function in age-related maculopathy with the ERG photostress test.

PURPOSE: To evaluate the diagnostic potential of the electroretinogram (ERG) photostress test and the focal cone ERG in age-related maculopathy (ARM). METHODS: The cohort comprised 31 patients with ARM and 27 age-matched control subjects. The ERG photostress test was used to monitor cone adaptation after intense light adaptation. Focal 41- and 5-Hz cone ERGs were recorded monocularly (central 20 degrees) to assess steady state retinal function. Univariate analysis identified electrophysiological parameters that differed between groups, and receiver operating characteristic (ROC) curves were constructed to assess their diagnostic potential. Logistic regression analysis determined the diagnostic potential of a model incorporating several independent predictors of ARM. RESULTS: The rate of recovery of the ERG photostress test was reduced (recovery was slower) in subjects with ARM. The parameter exhibited good diagnostic potential (P = 0.002, area under ROC curve = 0.74). The implicit times of the 5-Hz (a-wave, P = 0.002; b-wave, P < 0.001) and the 41-Hz (P < 0.001) focal cone ERGs were increased, and the 41-Hz focal cone ERG amplitude (P = 0.003) and focal to full-field amplitude ratio (P = 0.001) were reduced in the ARM group. Logistic regression analysis identified three independent predictors of ARM, including the rate of recovery of the ERG photostress test. CONCLUSIONS: Early ARM has a marked effect on the kinetics of cone adaptation. The clinical application of the ERG photostress test increases the sensitivity and specificity of a model for the diagnosis of ARM. Improved assessment of the functional integrity of the central retina will facilitate early diagnosis and evaluation of therapeutic interventions.

Longitudinal evaluation of retinal ganglion cell function and IOP in the DBA/2J mouse model of glaucoma.

PURPOSE: To characterize progressive changes of retinal ganglion cell (RGC) function and intraocular pressure (IOP) in the DBA/2J mouse model of spontaneous glaucoma. METHODS: Serial pattern electroretinograms (PERGs) and IOPs measures were obtained from both eyes of 32 anesthetized DBA/2J mice over an age range of 2 to 12 months at 1-month intervals. Cone-driven flash-ERGs (FERGs) were also recorded. The endpoint was defined as the age at which the PERG amplitude reached the noise level in at least one eye. At that point, both eyes were histologically processed to evaluate the thickness of the retinal fiber layer (RNFL). RESULTS: IOP increased moderately between 2 and 6 months ( approximately 14-17 mm Hg) and then more steeply, until it leveled off at approximately 28 mm Hg by 9 to 11 months. The mean PERG amplitude decreased progressively after 3 months of age to reach the noise level (85% reduction of normal amplitude) at approximately 9 to 12 months in different animals. When the PERG was at noise level, the RNFL showed a relatively smaller reduction (40%) in normal thickness. The FERG displayed minor changes throughout the observation period. IOP and PERG changes were highly correlated (r(2) = 0.51, P < 0.001). CONCLUSIONS: Results indicate that inner retina function in DBA/2J mice progressively decreases after 3 months of age, and it is nearly abolished by 10 to 11 months, whereas outer retina function shows little change and the RNFL thickness is relatively spared. This result suggests that surviving RGCs may not be functional. Progression of inner retinal dysfunction is strongly associated with increased IOP.

Electroretinographic features of the retinopathy, globe enlarged (rge) chick phenotype.

PURPOSE: The purpose of the study was to characterize the electroretinographic features of the autosomal recessive retinopathy, globe enlarged (rge) phenotype, in chickens (Gallus gallus). METHODS: Dark-adapted, light-adapted intensity series and light-adapted 30 Hz flicker responses were recorded from rge and age matched normal control chicks from one to 270 days of age. Retinal sections from rge and control retinas were examined in 7 and 270-day-old chicks. RESULTS: Electroretinogram (ERG) thresholds of rge birds were raised, the intensity response plots were shifted toward brighter intensities, and retinal sensitivity was reduced. The leading slope of the dark- and light-adapted a-waves was more shallow than normal, suggesting altered photoreceptor responses. The inner retinal components to the ERG were also abnormal; there was a marked lack of oscillatory potentials and an abnormally smooth and broad shape to the b-wave. Additionally, the b-wave was supernormal in response to brighter stimuli in the earlier stages of the disease. There was a progressive deterioration in ERG amplitudes with age that mirrored a slowly progressive thinning of the photoreceptor layer. CONCLUSIONS: The rge chicken has unusual ERG changes from an early age with altered waveforms and initially they develop a supernormal b-wave. This is followed by a progressive reduction of ERG amplitudes with age. The changes suggest that both photoreceptor and inner retinal responses are abnormal. Additional studies are needed to further elucidate the origin of the abnormal ERG components in the rge chick.