Visual electrophysiology in the assessment of toxicity and deficiency states affecting the visual system

Abstract

Visual disturbance or visual failure due to toxicity of an ingested substance or a severe nutritional deficiency can present significant challenges for diagnosis and management, for instance, where an adverse reaction to a prescribed medicine is suspected. Objective assessment of visual function is important, particularly where structural changes in the retina or optic nerve have not yet occurred, as there may be a window of opportunity to mitigate or reverse visual loss. This paper reviews a number of clinical presentations where visual electrophysiological assessment has an important role in early diagnosis or management alongside clinical assessment and ocular imaging modalities. We highlight the importance of vitamin A deficiency as an easily detected marker for severe combined micronutrient deficiency.

Ethambutol Effect on Retinal and Optic Nerve Structural Changes in Toxic Optic Neuropathy Case: A Literature Review

“…Optic neuropathy was reported at a dose of 3.6 mg/kg/day over 6 months of treatment. This incident further reinforces that there is no longer a supposedly safe dose [10][11][12][13].…”

“…The prolonged use of ethambutol is one of the main risks of thinning the RNFL. Spectral-domain OCT is the most common test to assess the RNFL and the macula [9,10,22]. In a study by Varan et al (2020), RNFL values recorded a statistically significant increase in thinning after 2 years of administering the ethambutol treatment compared to the pre-treatment RNFL value.…”

“…Study in showed that RGCs were significantly damaged by EMB-induced optic neuropathy, functionally and morphologically [25]. Additionally, the toxic impact of ethambutol on the retina also has an effect on other cell types, such as amacrine and bipolar cells, which are clarified in some studies [10] In humans, the first symptom and earliest indicator of EMB-induced optic neuropathy is dyschromatopsia or altered color perception. Ethambutol also causes a blue-yellow color defect in the early stages of the disease [11].…”

Posterior placoid-like maculopathy and macular hole associated with vitamin A deficiency

“… 8 Initial signs of VAD include nyctalopia with visual field defects while other associated symptoms include conjunctival xerosis, Bitot's spots, and keratomalacia. 9 , 10 …”

Visual electrophysiology in clinical practice: current status and future prospects in Sri Lanka.

“…Though it is not revealed extensively, exposure to some toxic substances such as organophosphorus compounds (OP) could cause significant retinal damage. In these instances, objective assessment of visual function is significant, predominantly where structural changes in the visual system have not yet occurred, as there may be a window of opportunity to mitigate or reverse visual impairment [17]. Since OP poisoning is a leading cause of mortality and morbidity in Sri Lanka, it is important to investigate the ophthalmic derangements caused by such substances as well [18].…”