Post-retinal Pathway Research Articles

Detection of early diabetic retinopathy using visual electrophysiological tests

Detection of functional impairment of vision in pre-clinical stages helps early identification of diabetic retinopathy. We aimed to determine the functional integrity of retina and post retinal pathways using electro-oculography (EOG), pattern electroretinography (PERG) and pattern-reversal visual evoked potentials (PR-VEP) in newly diagnosed diabetic patients who have not developed fundoscopic features of diabetic retinopathy. Twenty-five adults with newly diagnosed diabetes mellitus without fundoscopic evidence of retinopathy and a control group of healthy adults were subjected to visual electrophysiological assessment. Retinal pigment epithelium (RPE)-photoreceptor interaction, photoreceptors and ganglion cells of the macula and post retinal pathways were assessed by EOG, PERG and PR-VEP, respectively. Fourteen of the 25 diabetic patients, i.e. 56% (95% confidence intervals 34.9%, 75.6%), had LP:DT (light peak to dark trough) ratio less than 1.7, to the cut-off defined by the International Society for Clinical Electrophysiology of Vision (ISCEV). All control group subjects had LP:DT ratios above 1.7. The median LP:DT ratio in diabetic group (1.62 ± IQR 0.27) was significantly lower than that of the controls (1.8 ± IQR 0.21). Four patients had prolonged PR-VEP P100 latencies, and seven had prolonged PERG P50 latencies as per the ISCEV cut-offs, whereas none of the control group had abnormal PERG or PR-VEP measures. With a limited sample, we found that 56% of newly diagnosed diabetic patients with normal fundoscopy had defective RPE-photoreceptor interaction. Further studies are needed to obtain more precise point estimates of these EOG abnormalities, and to determine the conversion rates into more advanced stages of diabetic retinopathy.

Normal values of pattern reversal visual evoked potentials (PRVEP) and pattern electroretinography (PERG) in healthy adults in Sri Lanka

Background: Visual electrophysiological tests can be used effectively to evaluate the functional integrity of retina and post retinal pathways. The main aim of this study was to determine the normal values for pattern reversal visual evoked potentials (PRVEP) and pattern electroretinography (PERG) in a group of healthy adults in Sri Lanka. Methods: Fifty healthy adults were recruited for the study. PRVEP and PERG tests were performed using surface skin electrodes. Amplitude (μV) and peak latency (msec) values of N75, P100 and N145 components in PRVEP and N35, P50 and N95 components in PERG were measured. Mean values of each PRVEP and PERG measures in both sides were compared between males and females using independent sample t-test to determine the effect of gender on those measures. Results: There were 11 males and 39 females (age range: 20-62, mean (SD): 37.2 (10.94) years). There was no significant difference in PRVEP or PERG measures with regard to gender. Conclusions: Only few studies are reported on normative data of PRVEP and PERG in the world. Ideally, each laboratory has to establish normal values for its own equipment and patient population. However, the normal values of PRVEP and PERG in normal healthy adults obtained in this study would be of immense value to evaluate the patients with several post retinal and retinal disorders in the future visual electrophysiological studies done in Sri Lanka using the similar technical parameters

Evaluation of the diagnostic value of visual electrophysiological examination in childhood nystagmus

Objectives To evaluate the use of electroretinography (ERG) and recording of visual-evoked potentials (VEP) as diagnostic tools in children with early-onset nystagmus to clarify the need to include them as a basic step in the evaluation of cases of early-onset nystagmus, especially with normal ocular examination. Background Nystagmus in children can be caused by many causes, starting from idiopathic motor nystagmus compatible with relatively good vision, ending with ocular abnormalities that impair vision or other neurologic abnormalities that may be life threatening. Knowledge of the exact diagnosis is essential in the rehabilitation of a visually impaired child. Patients and methods In 32 children with early-onset nystagmus, ERG was recorded under light sedation, and VEP were simultaneously recorded to flash stimulus in all patients. Results The study comprised 64 eyes of 32 patients, with their age ranging from 3 months to 7 years. Indications for referral included children with early-onset nystagmus. Children with obvious cause for nystagmus were excluded from the study. Overall, 37.5% of children had been diagnosed as having retinal dysfunction, including cone dystrophy (6.3%) and cone/rod dystrophy (31.2%). Neurological nystagmus was recognized in 34.3% of children. Ocular albinism was diagnosed in 6.3% of cases. One (3.1%) case was diagnosed as optic nerve hypoplasia. Six (18.8%) cases were diagnosed as idiopathic nystagmus. Conclusion This study clarified the need to investigate children with nystagmus by ERG and suggested that the ERG was useful where the diagnosis was uncertain, particularly at an early age with no obvious cause on ocular examination. VEP are complementary to ERG and can be tested simultaneously. Visual electrophysiological examination of children with early-onset nystagmus can establish or exclude retinal and postretinal pathway dysfunction, thus assisting in its classification and subsequent rehabilitation.

Variability, repeatability and test-retest reliability of equine flash visual evoked potentials (FVEPs)

BackgroundVisual evoked potentials (VEPs) are electrical potentials generated by neurons in the central nervous system in response to visual stimuli. A series of positive and negative wavelets in response to flash-stimuli (flash-VEP; FVEP) or reversing, iso-luminant patterns (pattern-VEP; PVEP) are recorded. Pathological conditions affecting the post-retinal pathways can alter overall waveform morphology, and also affect wavelet peak times and amplitudes. FVEPs have recently been described in horses, but more data on the variability within and between subjects is required, to adequately interpret results from clinical equine patients. Therefore, the purpose of this study was to describe the variability, repeatability and test-retest reliability of equine FVEPs in normal, adult horses.ResultsEquine FVEPs were recorded from one randomly selected eye in 17 horses, from both eyes in eight of these horses, and also at two separate recording sessions in six horses. N1, P2, N2 and P4 wavelets were present in 100% of the recordings in all horses, while P1, N2a, P3 and P5 were only present in some recordings. Coefficients of variation (CVs) were low for P2, N2 and P4 peak times, but higher for all amplitudes. There were no statistically significant differences comparing peak times and amplitudes between eyes or between sessions. Coefficients of repeatability (CRs) are reported for P2, N2 and P4 peak times between eyes (P2; 5 ms, N2; 18 ms, P4; 18 ms) and also between sessions (P2; 5 ms, N2; 16 ms, P4; 39 ms). Intraclass correlation coefficients (ICCs), as an estimate of test-retest reliability, was assessed to be fair to excellent for most parameters.ConclusionsThis study provides important data on variability, repeatability and test-retest reliability of FVEPs in normal, adult horses. We conclude that P2, N2 and P4 peak times should be included in the evaluation of equine FVEPs. The large inherent variability of FVEP amplitudes is likely to make them less suitable and useful for establishing a diagnosis on their own in most clinical patients, but they may occasionally provide support to a clinical diagnosis.

Dysfunction in macula, retinal pigment epithelium and post retinal pathway in acute organophosphorus poisoning

Context Organophosphorus (OP) insecticide poisoning is a significant health problem in South Asian countries. Although cholinergic receptors are present at the junction between photoreceptors and the retinal pigment epithelium (RPE), human studies of the effects of OP poisoning on the visual pathways are very few. This study aims to demonstrate the pattern of changes in retina and post retinal pathways in patients with acute OP poisoning using visual electrophysiological tests. Methods This is an observational, cross-sectional study conducted at the Neurophysiology Unit, Teaching Hospital, Peradeniya, Sri Lanka. We tested 16 patients recovered from cholinergic phase, at least 24 h after deatropinization and within 8 weeks of OP ingestion. We assessed the functional integrity of the photoreceptors and ganglion cells of the macula by pattern electroretinography (PERG); RPE by electro-oculography (EOG); and post retinal pathways by pattern reversal visual evoked potentials (PR-VEP). Latencies and amplitudes of PR-VEP and PERG, light peak (LP), dark trough (DT) and Arden ratio of EOG were determined in patients and compared with 16 controls using the Mann–Whitney U test. Results Of the 16 OP-poisoned patients (median age of 37 ± IQR 20 years), six (37.5%) had reduced Arden ratio with reference to the International Society of Clinical Electrophysiology of Vision cut-off value of 1.7. The median Arden ratio in patients (1.69 ± IQR 0.36) was significantly lower compared to controls (1.90 ± IQR 0.4). The median latencies and amplitudes of PR-VEP or PERG were not significantly different between patients and controls. However, three patients had prolonged P100 latencies in PR-VEP and one had prolonged P50 latency in PERG. Conclusions Acute OP poisoning seems to affect the functions of the RPE and the visual electrophysiological changes outlast the cholinergic phase. Limited evidence suggests that photoreceptors of the macula region and post retinal pathway might be affected in some patients.

A difficult beginning

The AMJ is a peer-reviewed, triannual health journal published by Anuradhapura Clinical Society (ACS).The Journal strives to be a forum for all health professionals to publish original research and review articles in their area of expertise. The AMJ publishes articles in clinical medicine, public health and health promotion. Our priority is given to manuscripts on health related issues which affects the communities living in rural tropical communities. Established as a journal in 2006 as a publication parallel to ACS annual scientific sessions, the journal was relaunched as a proper journal in 2013. Anuradhapura Medical Journal is a member of COPE and is included on DOAJ. Cover Image:High-resolution fundus photograph of a normal fundus. The optic disc has sharp margins and is normal in colour. Vessels have normal colour, sheen, and course.Bottom right: Natus EMG/NCV/EP machine used to record visual evoked potentials (VEP)Bottom left: Normal pattern reversal VEP waveforms showing P100 latency and amplitude values within normal range, consistent with normal post retinal pathways Dr. Padmini Dahanayake

Rhinosporidiosis in Sri Lanka: An overview

The AMJ is a peer-reviewed, biannual health journal published by Anuradhapura Clinical Society (ACS). The Journal strives to be a forum for all health professionals to publish original research and review articles in their area of expertise. The AMJ publishes articles in clinical medicine, public health and health promotion. Our priority is given to manuscripts on health related issues which affects the communities living in rural tropical communities. Established as a journal in 2006 as a publication parallel to ACS annual scientific sessions, the journal was relaunched as a proper journal in 2013. Anuradhapura Medical Journal is a member of COPE and is included on DOAJ. Cover Image:High-resolution fundus photograph of a normal fundus. The optic disc has sharp margins and is normal in colour. Vessels have normal colour, sheen, and course.Bottom right: Natus EMG/NCV/EP machine used to record visual evoked potentials (VEP)Bottom left: Normal pattern reversal VEP waveforms showing P100 latency and amplitude values within normal range, consistent with normal post retinal pathways Dr. Padmini Dahanayake

Knowledge, attitudes and practices on hand hygiene among ICU staff in Anuradhapura Teaching hospital

The AMJ is a peer-reviewed, biannual health journal published by Anuradhapura Clinical Society (ACS). The Journal strives to be a forum for all health professionals to publish original research and review articles in their area of expertise. The AMJ publishes articles in clinical medicine, public health and health promotion. Our priority is given to manuscripts on health related issues which affects the communities living in rural tropical communities. Established as a journal in 2006 as a publication parallel to ACS annual scientific sessions, the journal was relaunched as a proper journal in 2013. Anuradhapura Medical Journal is a member of COPE and is included on DOAJ. Cover Image:High-resolution fundus photograph of a normal fundus. The optic disc has sharp margins and is normal in colour. Vessels have normal colour, sheen, and course.Bottom right: Natus EMG/NCV/EP machine used to record visual evoked potentials (VEP)Bottom left: Normal pattern reversal VEP waveforms showing P100 latency and amplitude values within normal range, consistent with normal post retinal pathways Dr. Padmini Dahanayake

Studying electrophysiological characteristics in children with congenital sensory nystagmus‐ case presentations

Abstract Purpose In classification of sensory congenital nystagmus (CN) is important to recognize the underlying retinal or visual pathway dysfunction. The aim was to distinguish ERGs and VEPs charcteristics which may identify among variety of disorders associated with sensory CN. Methods In infants and small children that were ophthalmologically classified as sensory CN were ERGs and VEPs recorded simultaneously in the same session. ERGs were detected without dilated pupils and with skin electrodes. Under darkened laboratory conditions were ERGs recorded to white (cone/rod mediated response) and dim blue (rod mediated response) flash and under lighten room were ERGs recorded to white, red and 30 Hz flicker flash (cone mediated responses). VEPs were recorded from three occipital electrodes to flash and onset stimulation. Results Cases with abnormal ERGs showed: in Leber’s congenital amaurosis were undetectable both rod and cone mediated responses from early infancy; in cone‐rod retinal dystrophy abnormal cone and rod mediated responses progressed in time; in achromatopsia abnormal cone mediated responses did not progress in time; in congenital stationary night blindness a negative ERG did not progress in time. Cases with abnormal VEPs showed: in ocular albinism VEP contralateral asymmetry; in achiasmia VEP ipsilateral asymmetry; in severe optic nerve hypoplasia flash VEP was non‐recordable, while in moderate optic nerve hypoplasia flash and pattern onset VEP findings might not correlate with clinic findings. Conclusion Sensory CN is associated with a variety of disorders affecting the retina, optic nerve, chiasm and electrophysiology may characterize retinal or postretinal pathway dysfunction and therefore help in early diagnosis.