Showing papers on "Photopic vision published in 2002"

Prospective randomized trial of an anterior surface modified prolate intraocular lens.

Abstract: PURPOSE: We compare the contrast sensitivity obtained with an anterior surface modified prolate intraocular lens with the contrast sensitivity obtained with a standard spherical intraocular lens. METHODS: Patients presenting for cataract surgery in one eye were randomized to receive either the Tecnis Z9000 intraocular lens (Pharmacia) or the AMO AR40e Opti-Edge intraocular lens (AMO). Sine wave grating contrast sensitivity testing under mesopic and photopic conditions served as the principal outcome measure. RESULTS: The Tecnis Z9000 intraocular lens provided statistically significantly better contrast sensitivity at 1.5 and 3 cycles per degreee under mesopic conditions and at 6, 12 and 18 cycles per degree under photopic conditions. CONCLUSION: The use of a modified prolate intraocular lens during cataract surgery has the potential to improve contrast sensitivity under both mesopic and photopic conditions.

Mutations in the RPGR gene cause X-linked cone dystrophy

Abstract: X-linked cone dystrophy is a type of hereditary retinal degeneration characterized by a progressive dysfunction of the day vision or photopic (cone) system with preservation of night vision or scotopic (rod) function. The disease presents with a triad of photophobia, loss of color vision and reduced central vision. This phenotype is distinct from retinitis pigmentosa (RP) in which there are prominent night and peripheral vision disturbances. X-linked cone dystrophy is a genetically heterogeneous disorder, with linkage to loci on Xp11.4--Xp21.1 (COD1, OMIM 304020) and Xq27 (COD2, OMIM 303800). COD1 maps to a region that harbors the RPGR gene, mutations in which account for >70% of patients with X-linked RP. The majority of these mutations reside in one purine-rich exon, ORF15, encoding 567 amino acids with a repetitive domain rich in glutamic acid residues. We mapped two families with X-linked cone dystrophy to the COD1 locus and identified two distinct mutations in ORF15 in the RPGR gene (ORF15+1343_1344delGG and ORF15+694_708del15) leading to a frame-shift and premature termination of translation in one case and a deletion of five amino acids in another. Consistent with expression of RPGR in rods and cones, our results show that mutations in RPGR, in addition to X-linked RP, can also cause cone-specific degeneration.

Correlating retinal function with melatonin secretion in subjects with an early or late circadian phase.

Abstract: PURPOSE. Evaluate the diurnal variation of retinal function, as measured with the electroretinogram (ERG), in subjects with an early (morning type: M-type) or a late (evening type: E-type) circadian phase. METHODS. Subjects (n = 24) were recruited according to their scores on a Morningness-Eveningness Questionnaire assessing preferences in, e.g., bedtime, waketime, and timing of performance. ERG testing was performed twice on each subject, at 22:30 and at 08:00. Luminance-response functions were obtained in scotopic (blue flashes) and in photopic conditions (white, blue, green, and red flashes). Salivary melatonin samples were taken every half-hour from 20:30 to 00:00 and from 06:30 to 09:30. RESULTS. In scotopic conditions, both groups had lower ERG amplitudes and retinal sensitivity at 08:00. In photopic conditions, the two groups showed an opposite pattern of diurnal variations. The E-types demonstrated a significant reduction in ERG amplitudes at 08:00, whereas the M-types showed an increase in amplitude at the same time. In addition, negative correlations were found between both the cone ERG and mixed rod-cone ERG and the concentration of salivary melatonin, indicating that the ERG amplitude is lowest when melatonin concentration is highest. CONCLUSIONS. The reduction in scotopic ERG responses at 08:00 seen in both groups might be due to the peak of rod disc shedding that takes place, in some mammals, at around light onset. The strong correlation between the cone ERG and salivary melatonin could be attributable to a direct effect of retinal melatonin on the physiology of cones or of the circadian phase of the subjects.

Mesopic contrast sensitivity function after excimer laser photorefractive keratectomy.

Abstract: PURPOSE To evaluate contrast sensitivity under mesopic conditions in patients who had undergone uncomplicated excimer laser photorefractive keratectomy (PRK) for myopia. METHODS Monocular contrast sensitivity function was measured with the Stereo Optical F.A.C.T. chart in 26 patients who had received PRK using the Nidek EC-5000 excimer laser system. Mean preoperative refractive error was -6.23 +/- 1.69 D (range, -4.00 to -8.25 D); postoperatively, mean refractive error was -0.36 +/- 0.58 D (range, -0.75 to +0.50 D). Contrast sensitivity function was measured 6 months after surgery using four different chart luminances: 85, 5.0, 2.5, and 0.1 cd/m2, the first being a photopic level and the rest mesopic. A control group of eight emmetropic subjects was also studied to allow comparison of results for statistical purposes. RESULTS Logarithmic values of contrast sensitivity at each spatial frequency were used for statistical analysis and normalized values were used for graphical representation. The results showed a statistically significant reduction (P .01 for all frequencies). CONCLUSION Photorefractive keratectomy can induce significant reductions in contrast sensitivity under mesopic conditions, even though the photopic contrast sensitivity function is normal.

Mapping absorbance spectra, cone fractions, and neuronal mechanisms to photopic spectral sensitivity in the zebrafish.

Abstract: The four spectral cone types in the zebrafish retina each contribute to photopic visual sensitivity as measured by the b-wave of the electroretinogram (ERG) The goal of the current study was to evaluate a model of photopic b-wave spectral sensitivity in the zebrafish that mapped first-order cellular and biophysical aspects of cone photoreceptors (visual pigment absorbance spectra and cone fractions) onto a second-order physiological aspect of cone-derived neural activity in the retina Good correspondence between the model and photopic ERG data was attained using new visual pigment absorbance data for zebrafish cones (lambda(max) of the L, M, and S cones were 564, 473, and 407 nm, respectively), visual pigment templates, and linearly gained cone fractions The model inferred four distinct cone processing channels that contribute to the photopic b-wave, two of which are antagonistic combinations of cone-derived signals (L-M and M-S), and two of which are noncombinatorial signals from S and U cones The nature of the gains and the processing channels suggested general rules of cone-specific inputs to second-order neurons The model further suggested that the zebrafish retina utilizes neuronal mechanisms for enhancing sensitivity to luminance contrast at short wavelengths and chromatic contrast at middle and long wavelengths The results indicated that first-order cellular and biophysical aspects of cone photoreceptors can successfully explain physiological aspects of cone-derived neuronal activity in the zebrafish retina

Phenotypic spectrum of autosomal recessive cone-rod dystrophies caused by mutations in the ABCA4 (ABCR) gene.

Abstract: PURPOSE: To describe the phenotype of 12 patients with autosomal recessive or isolated cone-rod types of progressive retinal degeneration (CRD) caused by mutations in the ABCA4 gene. METHODS: The charts of patients who had originally received a diagnosis of isolated or autosomal recessive CRD were reviewed after molecular analysis revealed mutations in the ABCA4 gene. RESULTS: In two of the patients both the photopic and scotopic electroretinogram were nonrecordable. In the remainder, the photopic cone b-wave amplitudes appeared to be more seriously affected than the scotopic rod b-wave amplitudes. Although the clinical presentation was heterogeneous, all patients experienced visual loss early in life, impaired color vision, and a central scotoma. Fundoscopy revealed evidence of early-onset maculopathy, sometimes accompanied by involvement of the retinal periphery in the later stages of the disease. CONCLUSIONS: Mutations in the ABCA4 gene are the pathologic cause of the CRD-like dystrophy in these patients, and the resultant clinical pictures are complex and heterogeneous. Given this wide clinical spectrum of CRD-like phenotypes associated with ABCA4 mutations, detailed clinical subclassifications are difficult and may not be very useful.

Electroretinograms as an indicator of disease activity in birdshot retinochoroidopathy

Abstract: Purpose. To determine whether electroretinogram results can help predict the success in tapering of immunosuppressive medication in patients with birdshot retinochoroidopathy. Methods. Fifteen patients with birdshot retinochoroidopathy who had at least three serial electroretinograms (ERG) during the course of their disease were included in the study. Charts of patients seen at the Immunology and Uveitis Service at the Massachusetts Eye and Ear Infirmary, Boston, Massachusetts were retrospectively reviewed. Seven parameters of the ERGs were examined: dim scotopic amplitude, bright scotopic amplitude, bright scotopic implicit time, single-flash photopic amplitude, single-flash photopic implicit time, 30 Hz flicker amplitudes, and 30 Hz flicker implicit times. For each parameter the patients were divided into two groups, those with normal and those with abnormal responses at the time their immunosuppressive medication taper was initiated. The percentage of patients in each group who were able to successfully taper their immunosuppressive medication was calculated. A successful taper of medication was defined as no recurrence of disease signs or symptoms for at least 1 year after the medication was terminated. Results. Abnormalities in the bright scotopic response amplitudes and 30 Hz flicker implicit times were associated with recurrence of inflammation as immunosuppressive therapy was tapered. Conclusion. ERG can serve as a useful adjunct in helping determine when to initiate tapering of immunosuppressive therapy in patients with birdshot retinochoroidopathy.

The Psychophysical Measurement of Visual Function

Abstract: 1. Principles of Psychophysical Measurement 2. Absolute Threshold 3. Intensity Discrimination 4. Adaptation to Light and Dark 5. Spatial Acuity 6. Spatial Vision 7. Temporal Factors in Vision 8. Color Vision 9. Post-natal Human Vision Development 10. The Aging Visual System Appendix: Measuring Light

Inner-retinal contributions to the photopic sinusoidal flicker electroretinogram of macaques. Macaque photopic sinusoidal flicker ERG.

Abstract: The purpose of this study was to examine inner-retinal contributions to the photopic sinusoidal flicker ERG ERGs were recorded from 5 anesthetized monkeys to sinusoidally modulated (100%, 05-120 Hz) red full field flicker at Lmean of 32 log phot td on a rod saturating blue background (37 log scot td; 30 log phot td) before and after intravitreal injections of tetrodotoxin (TTX) to block Na+-dependent spikes of retinal ganglion and amacrine cells, followed by N-methyl-D-aspartate (NMDLA) to suppress all activity of these cells Recordings also were made after blocking bipolar (and horizontal) cell responses with L-2-amino-4-phosphonobutyric acid (APB) and 2-cis-piperidine-2,3-dicarboxylic acid (PDA) or 6-cyano-nitroquinoxaline-2,3-dione (CNQX) Control fundamental (F1) and second harmonic (F2) amplitudes were large and variable at temporal frequencies up to 2 Hz At higher frequencies, Fl amplitude was minimal with a phase step at a frequency between 13 and 19 Hz and maximal at 27-33 Hz F2 was minimal at 2-3 Hz and maximal at 6-8 Hz, again with a phase step near the minimum TTX, or NMDLA, produced small changes in Fl that shifted the amplitude minimum to a lower and the maximum to a higher frequency In contrast, F2 was more strongly affected; both the amplitude minimum (and phase step) and maximum were greatly attenuated, leaving a moderate response from 05 to 8 Hz, which then declined as frequency was increased to 30 HZ After APB and PDA or CNQX, F1 decreased continuously with increasing frequency and F2 was generally much smaller The nearly linear F1 phase plotwas consistent with the presence of a single mechanism (ie photoreceptors) Inner-retinal neurons contribute to the photopic sinusoidal flicker ERG Whereas for F1, inner-retinal contributions are small relative to those from bipolar cells; for F2, they are equal or greater between 2and 16 Hz

Cone-dominated ERG luminance-response function: the Photopic Hill revisited.

Abstract: Purpose: In response to progressively brighter stimuli, the b-wave of the photopic ERG gradually augments in amplitude, reaches a plateau for a narrow range of intensities and then rapidly decreases with further increments in the luminance of the flash. This unique luminance–response function was originally introduced as the Photopic Hill. The purpose of this study was to further characterize this unique feature of the cone ERG, investigate if it was only limited to b-wave measurements and if it could be obtained under different photopic background luminances. Methods: Photopic ERGs and oscillatory potentials were generated in response to flashes of light ranging from 0.5 to 16 cd m−2 s in intensity and presented against photopic backgrounds varying from 18 to 525 cd m−2 in luminance. Results: All but the brightest background yielded a clear Photopic Hill like luminance-response function which could only be evidenced with the b-wave, the i-wave and OP4 amplitude measurements. Interestingly, the maximal amplitude reached remained almost identical irrespective of the background luminance. Conclusions: Our results suggest that the retinal mechanisms at the origin of the Photopic Hill effect could represent a voltage limitation mechanism, intimately tied to the OFF pathway. The latter would however be intrinsic to the cone system only and not to the entire retinal network since significantly higher peak amplitudes are reached with dark adaptation.

Decline of photopic multifocal electroretinogram responses with age is due primarily to preretinal optical factors

Abstract: Age-related changes in photopic retinal function were evaluated topographically with the multifocal electroretinogram (mfERG). Thirty-two subjects between the ages of 16 and 69 participated. There was a strong dependence on age for all mfERG response measures that was strongest for the group of central retinal responses (i.e., within 5 deg eccentricity) and approximately equal for responses between 5 and 20 deg. After adjustment for crystalline lens optical density and pupil diameter, significant effects of age were limited to central first-order (i.e., within 5 deg) and second-order response kernels. Simulation studies support an optical basis for the observed age-related changes. It is concluded that mfERG changes between the ages of 20 and 70 are due predominantly to preretinal optical factors.

Evidence for a brief period of enhanced oxygen susceptibility in the rat model of oxygen-induced retinopathy.

Abstract: PURPOSE. Findings in a previous study have shown that the retina of newborn rats exposed to hyperoxia during the first days of life sustain permanent functional (as determined with the rod ERG) and structural (as determined with histology) damage that appears to be determined by the level of retinal maturity reached at the time of oxygen exposure-the retinas of rat pups being more susceptible to hyperoxic shock during the second week of life than during the first week. Given that the cone ERG has been shown to mature later than the rod ERG, the purpose of the present study was to examine whether cone responses also demonstrates a similar maturational susceptibility to postnatal hyperoxia. Also examined was whether the oscillatory potentials (OPs) were affected by postnatal hyperoxia. METHODS. Newborn rats were exposed to hyperoxia during selected postnatal day intervals either initiated at birth (early-onset exposure) or at a later postnatal age (late-onset exposure). Photopic and scotopic (mixed cone-rod) electroretinograms were recorded at 30 days. RESULTS. Data analysis reveals that photopic and scotopic responses (b-wave and OPs) demonstrated a similar maturational susceptibility to postnatal hyperoxia, in which exposure regimens initiated during the second week of life were most detrimental to retinal function. The results also revealed a temporal window of enhanced oxygen susceptibility at approximately postnatal day 10. The duration of this window was longer when estimated with the scotopic responses, but the extent of the functional damage was more pronounced when estimated with the photopic signals. Finally, compared with the b-wave, the OPs, especially the short-latency OPs, were proportionally more affected. CONCLUSIONS. The results suggest that cone function is significantly more susceptible to postnatal hyperoxia than rod function, and the OPs appear to be the most susceptible ERG components, thus suggesting a differential susceptibility to oxygen toxicity of the different retinal components. However, despite a clear demonstration of its existence, the exact nature of the temporal window of enhanced oxygen susceptibility as well as a possible equivalence in other animal models of oxygen induced retinopathy, including the human form (retinopathy of prematurity), remains to he determined.

Spatial contrast sensitivity of migraine patients without aura.

Abstract: Visual disturbances are frequent symptoms in migraine. Since there is a possibility of separate damage in the magno- or parvo-cellular visual pathway in migraine patients, we performed a study including the measurement of static and dynamic spatial contrast sensitivity on 15 patients suffering from migraine without aura under photopic and scotopic conditions. Fifteen healthy volunteers without primary headache served as controls. The results revealed a marked decrease in contrast sensitivity at low spatial frequencies in the migraine patients. Spatial contrast sensitivity demonstrated some lateralization, as the sensitivity to low spatial frequencies obtained through separate eyes showed significantly larger side-differences in migraine patients than in control subjects. These findings suggest that the mechanisms responsible for vision at low spatial frequencies are impaired in migraine patients. This might indicate impaired function of the magnocellular pathways in this condition.

Does lighting need more photopic luminous efficiency functions

Abstract: In 1924 the Commission Internationale de l’E clairage (CIE) established the photopic luminous efficiency function, V(γ), that subsequently has been used to measure luminance. Some have assumed luminance to be synonymous with brightness. Luminance is based mainly upon flicker photometry, and this methodology does not provide data predictive of the apparent brightness of steadily viewed lights. This paper discusses alternative photopic luminous efficiency functions that could be used for measuring luminance. A proper treatment of brightness is outside the scope of the present paper, although the CIE is actively studying this topic. Moreover, this paper does not discuss the scotopic luminous efficiency function established by the CIE in 1951. Vision research conducted since 1924 using methodologies other than flicker photometry has shown that the V(λ) function slightly underestimates human foveal spectral sensitivity at short wavelengths in the visible spectrum. This has been partly corrected by recommending...

Vigabatrin; its effect on the electrophysiology of vision

Abstract: Vigabatrin is known to induce visual field defects in approximately one third of patients treated with the drug. It is apparent from electrophysiological studies that the cause of this defect is at retinal level probably as a result of the build up of GABA. Studies of electrophysiological retinal parameters such as the EOG and photopic, scotopic and 30-Hz flicker ERG have revealed changes in Arden Index, photopic a and b wave latency and amplitude, changes in oscillatory potentials, and changes in latency and amplitude of the 30Hz response. However, many of these changes such as the Arden Index, oscillatory potentials, latency and amplitude of photopic b wave appear to be related to current anti-epileptic drug treatment rather than visual field defects. Certain parameters, particularly the amplitude of the 30-Hz flicker response, do appear to correlate with the severity of the field defect. Paediatric patients treated with the drug at age 9 years or below cannot reliably perform visual field perimetry. To identify these patients a special VEP H-Stimulus has been developed to produce separate responses from central and peripheral field stimulation by alternating at slightly separate rates. Forty-five healthy children between ages 3 and 10 years have been used to develop a normal database. This technique has a sensitivity of 75% and a specificity of 87.5% in identifying the field defect and may be used in children with epilepsy from age 3 upwards.

Ganzfeld ERG in zebrafish larvae.

Abstract: In developmental biology, zebrafish are widely used to study the impact of mutations. The fast pace of development allows for a definitive morphological evaluation of the phenotype usually 5 days post fertilization (dpf). At that age, a functional analysis is already feasible using electroretinographic (ERG) methods. Corneal Ganzfeld ERGs were recorded with a glass microelectrode in anaesthetized, dark-adapted larvae aged 5 dpf, using a platinum wire beneath a moist paper towel as reference. ERG protocols included flash, flicker, and ON/OFF stimuli, both under scotopic and photopic conditions. Repetitive, isoluminant stimuli were used to assess the dynamic effect of pharmacological agents on the ERG. Single flash, flicker, and ON/OFF responses had adequately matured at this point to be informative. Typical signs of the cone dominance were the small scotopic a-wave and the large OFF responses. The analysis of consecutive single traces was possible because of the lack of EKG, breathing, and blink artefacts. After application of APB, which selectively blocks the ON channel via the mGluR6 receptor, the successive loss of the b-wave could be observed, which was quite different from the deterioration of the ERG after a circulatory arrest. The above techniques allowed to reliably obtain Ganzfeld ERGs in larvae aged 5 dpf. This underlines the important role of the zebrafish as a model for the functional analysis of mutations disrupting the visual system.

Design and optimization of a retinal flux density meter

Abstract: We present the design and calibration of a retinal flux density (RFD) meter. This device can serve as a standard illuminance meter or can measure flux density on the retina, using both photopic and scotopic spectral responses. In addition, through post processing, the instrument can determine standard illuminances and RFDs at mesopic levels. This device is an extension of an earlier instrument, reported on by us, which replicated the spatial efficiency function of the human eye to determine retinal exposure. In this paper we describe the need for such a measurement device, detail its design, and report on its performance.

Color identification data obtained from photopic to mesopic illuminance levels

Abstract: To use colors properly as an aid in visual tasks, it is necessary to know how colors are identified under various illuminating environments. In this study color identification was examined under a wide range of illuminances, from photopic to mesopic levels. Fifteen subjects named a color chip using one of the preselected color terms: red, orange, yellow, yellow-green, green, blue-green, blue, purple, pink, brown, white, gray, and black. The 256 color chips were selected from value planes of 4, 6, and 8 of the Munsell color space. The illuminance levels tested were 1000, 10, 1, and 0.1 lx. At 1000 lx the color chips were identified consistently by each of the color terms. At 10 lx the pattern of color identification was very similar to that at 1000 lx, though the consistency of the identification evidently declined. At 1 lx great changes in color identification occurred. By 0.1 lx reliable color identification was completely lost, though blue and red responses remained. At the lower illuminances green was replaced with blue, and red, orange, and pink were frequently confused with each other. However, the border between blue and purple was almost constant. These results provide a scientific basis for the appropriate use of colors in various illuminating environments. Also, they are useful for studies in color appearance modeling. © 2002 Wiley Periodicals, Inc. Col Res Appl, 27, 252–259, 2002; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/col.10065

Effects of rod activity on color perception with light adaptation.

Abstract: To investigate the effect of rod activity on color perception with light adaptation, chromaticity shifts of monochromatic test lights were measured as a function of background field intensity at 17 deg in the nasal field of view. The measurements were performed both after complete dark adaptation and during the cone-plateau period at a mesopic test intensity level of 15 photopic trolands. To clarify the mechanisms underlying the chromaticity shifts obtained, six supplementary experiments were performed. The results of the experiments strongly suggest that at scotopic background intensities, light adaptation of rods, both within and adjacent to the test area, may reduce rod signals triggered by the test light and thereby produce marked chromaticity shifts with light adaptation. At mesopic background intensities, cones in the background field become activated and may influence the chromaticity shift with light adaptation both by suppressing signals from rods elicited by the test light and by producing a selective chromatic adaptation.

Iatrogenic ring scotoma after laser in situ keratomileusis.

Abstract: A 37-year-old ophthalmologist had bilateral simultaneous laser in situ keratomileusis (LASIK) for moderate myopia with astigmatism using the Alcon Summit LADARVision laser; an ablation zone of 5.5 mm was used. Five months after surgery, the uncorrected visual acuity was 20/20 and 20/25 but despite regular corneal topographies, the patient experienced prominent ghost images under photopic and scotopic conditions. To elucidate the nature of the problem, automated static perimetry was performed, which revealed a significant depression between 10 degrees and 30 degrees compared with a baseline study obtained 3 years earlier. The patient started brimonidine 0.2% 1 drop in both eyes every morning, which caused 1.5 to 2.0 mm of pupillary miosis (tonic pupil size 3.0 to 4.0 mm in dim light) and eradicated the ghost images. Repeat perimetry showed significant improvement in all indices. The mechanism of improvement is unclear but may be due to elimination of light scatter from the transition zone between the ablated and unablated cornea. The issue of perimetric changes after refractive surgery deserves more attention; postoperative testing may be indicated for patients in whom the ablation zone diameter is close to the mesopic or scotopic pupil size to provide an accurate lifetime baseline visual field.

ON-pathway disturbance in two siblings.

Abstract: Purpose: To present two clinical cases diagnosed with predominant cone dystrophy and demonstrating early disturbance in the on-centre bipolar cells (ONpathway). Methods: Electrophysiological findings are presented in two siblings with predominant cone dystrophy. The subjects showed no remarkable ophthalmoscopic or fluorescein angiographic retinal changes, but demonstrated progressive visual disturbance during their 20s. Results: The electroretinograms (ERGs) showed reduced dark-adapted responses but the positive component of the photopic ERG was absent. Response to 30 Hz flicker was severely reduced. Electroretinograms elicited by long-duration stimuli showed a loss of the b-wave, and the off-response was slightly reduced. In both patients, multifocal ERGs (m-ERGs) were more reduced within the central 10ae, where the ON-pathway is normally a major contributor. Conclusion: We conclude that these patients may be affected by an abnormality of the synapses of the cone receptors and that their decrease in vision might, at least initially, be due to selective ON-pathway dysfunction.

Electroretinographic changes in the inner retinal layers of the retained eyes of patients with sporadic unilateral retinoblastoma.

Abstract: Purpose: Examination of retinal function as measured by flash electroretinogram (ERG) including oscillatory potentials (OPs) and pattern electroretinogram (PERG) in a series of patients with unilateral sporadic retinoblastoma. Patients: Studies were undertaken in the retained eye (without clinical evidence of retinoblastoma) of 13 patients with sporadic unilateral retinoblastoma and in 13 healthy controls. Methods: Standard flash ERG including scotopic OPs and PERG recordings were performed in accordance with the International Society for Clinical Electrophysiology of Vision (ISCEV) standards. Results: Statistically significant differences between the studied and the control groups were observed with flash ERG (OP1 amplitude increase, p < 0.003; photopic flicker amplitude increase, p < 0.05) and PERG (P50 latency increase, p < 0.008). Conclusions: Inner retinal layer dysfunction may be a characteristic feature of individuals with unilateral sporadic retinoblastoma.

Cellular basis for rod-cone interactions in the outer retina

Abstract: Background. At least twice daily our retinas move between a light adapted, cone-dominated (photopic) state and a dark-adapted, color-blind and highly light-sensitive roddominated (scotopic) state. In between is a rather ill-defined transitional state called the mesopic state in which retinal circuits express both rod and cone signals. Consequently, in the mesopic state the retinal output to the brain contained in the firing patterns of the ganglion cells consists of information derived from both rod and cone signals. Morphology, physiology and psychophysics all contributed to an understanding that the two systems are not independent but interact extensively via both pooling and mutual inhibition. This review lays down a rationale for such rod-cone interactions in the vertebrate retinas. It suggests that the important functional roles of rod-cone interactions is in that they shorten the duration of the mesopic state. As a result, the retina is maintained in either in the (rod-dominated) high sensitivity photon counting mode or in the second mode which emphasizes temporal transients and spatial resolution (the cone-dominated photopic state). Conclusions. Experimental evidence for pre- and postsynaptic mixing of rod and cone signals in the retina is shown together with the preeminent neuromodulatory role of both light and dopamine in controling inter-actions between rod and cone signals. Dopamine is shown to be both necessary and sufficient to mediate light adaptation in the retina.

The photopic negative response of the flash ERG: changes in experimental glaucoma in monkeys and clinical applications in humans

Abstract: The flash electroretinogram (ERG), which can be recorded noninvasively at the cornea, has commonly been used to assess photoreceptor and bipolar cell activity, reflected in the initial negative (a-wave) and positive (b-) waves respectively of the response to a brief flash. In this study we measured light-adapted (photopic) flash ERGs using red flashes on a rod saturating blue background, and discovered a negative-going wave after the b-wave which we called the photopic negative response (PhNR). Pharmacological studies in monkeys indicated that the PhNR arises from the spiking activity of inner retinal neurons proximal to bipolar cells, predominantly retinal ganglion cells. We measured the PhNR in monkeys with experimental glaucoma and human patients with primary open angle glaucoma (POAG), pathologies that eventually destroy ganglion cells. PhNR amplitudes were already significantly reduced (P<0.5) relative to controls in monkey eyes with experimental glaucoma and in POAG patients when visual sensitivity losses, assessed using perimetry, were mild (mean deviation of less than -6dB). PhNR amplitudes also were reduced in glaucoma suspects. These findings suggest promise for the PhNR for early detection of glaucomatous damage.

The photopic ERG response in diabetes mellitus

Abstract: The authors made photopic ERG examinations according to the international standard in 82 diabetic patients. They recorded a significant reduction of amplitudes of the b wave in a group of 38 patients who at the time of the examination did not have yet any pathological changes on the fundus. Regressive analysis did not prove after laser photocoagulation in these patients, contrary to a control group and diabetic patients with simple diabetic retinopathy, any correlation between the patients age and the extent of the retinal response. Photopic electroretinograms must be included in the electrophysiological diagnostic arsenal in diabetes.