Acquired unilateral night blindness associated with a negative electroretinogram waveform

Two-Color Dark-Adapted Perimetry Implemented With a Commercially Available Perimeter to Characterize Rod-Pathway Sensitivity

BACKGROUND AND OBJECTIVE

To characterize rod-pathway function across the visual field using 2-color dark-adapted perimetry (2cDAP) implemented with conventional Octopus 900 Pro perimeters.

PATIENTS AND METHODS

Eighteen visually normal individuals and two retinitis pigmentosa (RP) patients participated. Thresholds were measured under dark-adapted conditions at 15 locations along the horizontal meridian using short (450 nm) and long (610 nm) wavelength stimuli. Threshold differences between the two wavelengths were used to determine rod- vs cone-mediated function.

RESULTS

Among controls, peripheral and perifoveal thresholds for the short-wavelength stimulus were approximately 2 log units lower than for the long-wavelength stimulus. Foveal thresholds for the two wavelengths were similar. RP threshold profiles differed considerably from the controls, with normal foveal thresholds and high peripheral thresholds for both wavelengths.

CONCLUSIONS

2cDAP can be performed with an unmodified Octopus perimeter to evaluate rod function across the visual field and obtain information that is not available with standard automated perimetry. [Ophthalmic Surg Lasers Imaging Retina 2022;53:692-696.].

Contribution of post-receporal cells to the cone a-wave of the human electroretinogram in congenital stationary night blindness and autoimmune-like retinopathy

In normal subjects the later part of the cone a-wave to a brief flash increases in amplitude after 50-100 ms darkness due to a contribution from secondary hyperpolarising cells. We recorded these responses along with clinical ON and OFF ERGs in patients with inner retinal dysfunction to see if this part of the a-wave is affected. Patients with autoimmune-like retinopathy and CSNB2 had abnormal ON and OFF responses but the a-wave increased in amplitude in the dark as in normals. Conversely, the OFF-response was normal in CSNB1 but the a-wave did not increase in the dark. Contrary to expectation these results show some hyperpolarising cell function in autoimmune-like disease and CSNB2 and some OFF-pathway abnormality in CSNB1. The a- and d-wave are needed to assess OFF-pathway function.

The negative ERG: clinical phenotypes and disease mechanisms of inner retinal dysfunction

Inner retinal dysfunction is encountered in a number of retinal disorders, either inherited or acquired, as a primary or predominant defect. Fundus examination is rarely diagnostic in these disorders, although some show characteristic features, and careful electrophysiological assessment of retinal function is needed for accurate diagnosis. The ERG in inner retinal dysfunction typically shows a negative waveform with a preserved a-wave and a selectively reduced b-wave. Advances in retinal physiology and molecular genetics have led to a greater understanding of the pathogenesis of these disorders. This review summarizes current knowledge on normal retinal physiology, the investigative techniques used and the range of clinical disorders in which there is predominantly inner retinal dysfunction.

Negative scotopic ERG and photopic ERG ON response impairment in a patient with normal dark adaptation

PURPOSE

To present ocular findings in a patient who showed negative scotopic electroretinogram (ERG) and reduced ON response, but normal dark adaptation.

CASE

An 18-year-old Japanese male patient who complained of severe asthenopia. His corrected visual acuities were 1.2 in both eyes. His fundi were normal. He had normal contrast sensitivity and normal dark adaptation.

METHODS

The patients underwent ERG (including the standard protocol and photopic long flash recordings).

RESULTS

The amplitudes of the rod ERG b-wave were reduced. The scotopic standard combined ERG response showed negative configuration. The photopic response to long flash revealed the reduced b-wave (ON response), while the amplitude of the first peak of the d-wave (OFF response) was within the normal range.

CONCLUSIONS

Postsynaptic abnormalities in both the rod and cone ON-pathways, which are often found in patients with night blindness, were suggested in the ERG findings, but the dark adaptation of our patient was normal. Neuromuscular evaluation of the patient and ophthalmological evaluation, including ERG, of his parents were normal. To our knowledge, the ophthalmological and electrophysiological findings of our patient cannot be attributed to any known clinical entity.

Clinical disorders affecting mesopic vision

Vision in the mesopic range is affected by a number of inherited and acquired clinical disorders. We review these conditions and summarize the historical background, describing the clinical characteristics alongside the genetic basis and molecular biological mechanisms giving rise to rod and cone dysfunction relevant to twilight vision. The current diagnostic gold standards for each disease are discussed and curative and symptomatic treatment strategies are summarized.

Unilateral electronegative ERG of non-vascular aetiology

BACKGROUND

Full field and pattern electroretinograms (ERG, PERG) are performed to assess generalised retinal function and macular function, respectively. An (electro) negative full field ERG usually describes an ISCEV standard maximal response in which the b-wave is smaller than a normal or minimally reduced a-wave and indicates dysfunction that is post-phototransduction. The most common cause of a unilateral negative ERG is central retinal artery occlusion (CRAO) or birdshot chorioretinopathy (BCR). This study examines the clinical and electrophysiological features of patients with unilateral negative ERG who do not have CRAO or BCR.

METHODS

12 patients were ascertained with a unilateral negative ERG in whom a vascular aetiology and BCR were excluded. Most presented with symptoms of central retinal dysfunction. In 11 of the 12 patients additional long duration photopic stimuli were used to test cone system ON and OFF responses.

RESULTS

All 12 patients had unilateral electronegative bright flash full field ERGs indicating total or relative preservation of rod photoreceptor function, but dysfunction post-phototransduction. Seven of these patients had non-specific inflammatory changes in the eye with the negative ERG. Six patients, including five with inflammatory signs, had involvement of the cone ON response with complete preservation of cone OFF responses. A further three patients showed evidence of cone ON response abnormality with less severe OFF response involvement.

CONCLUSION

The ERGs in this heterogeneous group of patients predominantly showed post-phototransduction involvement of the ON pathways. Sparing of the cone OFF response was often observed. The majority of patients had signs of previous inflammation and it is speculated that these highly unusual unilateral changes may be mediated via an autoimmune mechanism.

Acute zonal occult outer retinopathy: a long-term follow-up study

PURPOSE

To report the long-term follow-up of patients with acute zonal occult outer retinopathy (AZOOR).

DESIGN

Observational consecutive case series.

METHODS

Prospective and retrospective review of medical records of patients with AZOOR.

RESULTS

Fifty-one patients (37 women and 14 men) with a median age of 33 years (mean, age 36 years; range, 13-63 years) were followed for a median of 96 months (mean 100 months; range, 36-420 months). At presentation, AZOOR was present in one eye of 31 patients (61%) and both eyes in 20 patients (39%). All patients presented with an acute loss of one or more zones of visual field, and 45 (88%) patients presented with photopsia. Corrected visual acuity was 20/40 or better in 68 (76%) of 90 affected eyes. Funduscopic examination was normal in 82 eyes and revealed signs of AZOOR in 8 eyes. Electroretinographic amplitudes were depressed in all affected eyes. The median delay in diagnosis of AZOOR was 17 months. During follow-up, AZOOR developed in 19 fellow eyes. At final follow-up AZOOR was present in one eye of 12 (24%) patients and both eyes of 39 (76%) patients. Sixteen patients had 23 recurrences of AZOOR. Visual field loss stabilized within 6 months in 37 patients (72%), progressed stepwise in 2 patients (4%), and partly improved in 12 patients (24%). Fourteen patients (28%) had autoimmune diseases, including Hashimoto's thyroiditis in 6 patients and relapsing transverse myelopathy in 4 patients. At last follow-up all patients had residual visual field defects. Final visual acuity was 20/40 or better in 61 (68%) affected eyes. Nine patients (18%) were legally blind. The fundi of 90 affected eyes revealed no changes of AZOOR in 47 eyes (52%) and changes in the pigment epithelium and retina caused by AZOOR in 43 eyes (48%).

CONCLUSIONS

Visual loss in AZOOR is characterized by one or more episodes of acute dysfunction, and in some cases, death of retinal receptor cells in one or more zones of one or both eyes. Central vision is often spared, but recovery of visual field occurs infrequently. The etiology of AZOOR is unknown. Electroretinography is essential for early diagnosis. The value of treatment is uncertain.

"On" response dysfunction in multifocal posterior pigment epitheliopathy

PURPOSE

To determine the electroretinographic properties of one patient with multifocal posterior pigment epitheliopathy.

METHODS

Rod and cone electroretinograms (ERGs) and photopic ERGs elicited by long-duration stimuli were studied in a patient with multifocal posterior pigment epitheliopathy.

RESULTS

The amplitudes of both the rod and cone ERGs were significantly reduced. Photopic ERGs elicited by long-duration stimuli demonstrated that the b-wave ("on" response) was abolished but the d-wave ("off" response) was reduced by only amplitude.

CONCLUSION

The ERG findings in multifocal posterior pigment epitheliopathy indicate that there is dysfunction not only of the photoreceptors but also in the signal transmission specific for the "on" pathway.

The incidence of negative ERG in clinical practice

INTRODUCTION

A negative electroretinogram (ERG) is one in which there is a selective reduction in amplitude of the b-wave, such that it does not exceed that of the a-wave. The purpose of this study was to determine the incidence and clinical causes of negative ERGs at a tertiary referral centre. In addition, interesting and previously unreported aetiologies are described.

PATIENTS AND METHODS

Retrospective review of all ERGs done at Moorfields Eye Hospital from November 1995 to December 1998 under ISCEV standard conditions. Many patients had photopic ON- and OFF-response recording in addition to conventional ISCEV Standard ganzfeld ERG.

RESULTS

A total of 2,640 ERGs were performed during the study period. 128 cases (4.8%) showed a negative ERG. The causes, where a firm clinical diagnosis was possible, include X-linked juvenile retinoschisis, congenital stationary night blindness, central retinal artery occlusion, birdshot chorioretinopathy and melanoma-associated retinopathy (MAR). Unilateral negative ERG waveforms with normal fundal appearances were seen in 7 patients. Photopic ON- responses could be selectively affected.

CONCLUSIONS

The incidence of negative ERGs over a 34-month period presenting to a large tertiary centre was almost 5%. The presence of a negative ERG may be instrumental in demonstrating the site of visual dysfunction, with many cases showing minimal or no fundus abnormality. ON- and OFF-response recording yielded additional information regarding photopic post-receptoral/phototransduction function.

An electrophysiological follow-up study on acquired unilateral nyctalopia

PURPOSE

To describe the clinical picture and electrophysiological findings in acquired unilateral nyctalopia.

METHODS

A patient who had acquired unilateral visual loss with normal fundus was followed for a period of 2.5 years with basic ophthalmological examinations including standard electroretinogram and photopic on and off responses.

RESULTS

A 46-year-old woman suffered from acquired unilateral nyctalopia. She complained of photopsia and blurred vision in her left eye. The initial examination of the left eye showed 1+ cells in the anterior chamber and a granular appearance in the fovea. After 1 month of treatment she still complained of photopsia in her left eye. Ophthalmoscopy and fluorescein angiography revealed no abnormality in either eye. A bright flash electroretinogram (ERG) in the left eye was a negative shape. Photopic ERG elicited by a 150 ms stimulus showed a depressed b-wave and enhanced a- and d-waves in the left eye.

CONCLUSIONS

This ERG waveform suggested that the transmission between photoreceptor and on-bipolar cell might be affected by idiopathic retinal disease.