THE EOG IN CHLOROQUINE AND OTHER RETINOPATHIES

Functional roles of bestrophins in ocular epithelia

There are four members of the bestrophin family of proteins in the human genome, of which two are known to be expressed in the eye. The gene BEST1 (formerly VMD2) which encodes the protein bestrophin-1 (Best1) was first identified in 1998. Mutations in this gene have now been associated with four clinically distinguishable human eye diseases, collectively referred to as "bestrophinopathies". Over the last decade, laboratories have sought to understand how Best1 mutations could result in eye diseases that range in presentation from macular degeneration to nanophthalmos. The majority of our knowledge comes from studies that have sought to understand how Best1 mutations or dysfunction could induce the classical symptoms of the most common of these diseases: Best vitelliform macular dystrophy (BVMD). BVMD is a dominant trait that is characterized electrophysiologically by a diminished electrooculogram light peak with a normal clinical electroretinogram. This together with the localization of Best1 to the retinal pigment epithelium (RPE) basolateral plasma membrane and data from heterologous expression studies, have led to the proposal that Best1 generates the light peak, and that bestrophins are a family of Ca(2+) activated Cl(-) channels (CaCCs). However, data from Best1 knock-out and knock-in mice, coupled with the recent discovery of a recessive bestrophinopathy suggest that Best1 does not generate the light peak. Recently Best2 was found to be expressed in non-pigmented epithelia in the ciliary body. However, aqueous dynamics in Best2 knock-out mice do not support a role for Best2 as a Cl(-) channel. Thus, the purported CaCC function of the bestrophins and how loss of this function relates to clinical disease needs to be reassessed. In this article, we examine data obtained from tissue-type and animal models and discuss the current state of bestrophin research, what roles Best1 and Best2 may play in ocular epithelia and ocular electrophysiology, and how perturbation of these functions may result in disease.

Retinal function in X-linked ocular albinism (OA1)

PURPOSE

To characterize retinal function in human recessive X-linked ocular albinism (OA1) across the normal lifespan.

METHODS

Retinal function was evaluated in 14 OA1 patients (ages 11 to 71 years) and five obligate carriers (ages 41 to 50 years) and compared to normal controls using full-field and multi-focal electroretinograms (ERG and mERG, respectively) and electro-oculography (EOG).

RESULTS

No consistent differences in ERG response parameters were observed when OA1 patients were compared as a group to normal controls. A trend in the direction of better correlations of response parameters with age was, however, observed in OA1. EOG Arden ratios were normal or hypernormal for all patients, but were uncorrelated with age. Central retinal function measured with the mERG suggested a flat response topography with depressed macular function compared to normal controls.

CONCLUSIONS

Panretinal function in OA1 is within normal limits at all ages, consistent with previous reports in generalized albinism. The stronger correlations with age in OA1 may suggest a different rate of age-related change in OA1 compared to normal populations, but the precise nature of this change must await an appropriate prospective study. The topography of mERG amplitudes in OA1 is relatively flat across the central retina with a reduction in amplitude in the macular region consistent with anatomical studies demonstrating an underdeveloped macular region in albinism.

Electrophysiologic findings in chloroquine maculopathy

PURPOSE

To describe an interesting case with a typical chloroquine bull's eye maculopathy with important results of the electrophysiological tests and verify if any reduction of focal responses, detected in multifocal electroretinogram (mfERG), are congruent with any possible defects detected in the visual field.

CASE REPORT

A 59-year-old man took a daily dosage of 250 mg chloroquine for his rheumatoid arthritis (up to a total dose of 540 g). He had the typical chloroquine-induced bull's-eye maculopathy. The electro-oculogram was normal. The mfERG, demonstrated reduced focal responses in the areas corresponding to the scotoma detected in the visual field.

CONCLUSIONS

Considering the normality of the electro-oculogram, we can easily conclude that the electro-oculogram is not sensible to detect chloroquine maculopathy and that reported reductions may occur due to the course of the rheumatoid arthritis itself. The mfERG may be an important ophthalmological screening and follow-up management to investigate patients using chloroquine.

The electro-oculogram

The retinal pigment epithelium (RPE) lying distal to the retina regulates the extracellular environment and provides metabolic support to the outer retina. RPE abnormalities are closely associated with retinal death and it has been claimed several of the most important diseases causing blindness are degenerations of the RPE. Therefore, the study of the RPE is important in Ophthalmology. Although visualisation of the RPE is part of clinical investigations, there are a limited number of methods which have been used to investigate RPE function. One of the most important is a study of the current generated by the RPE. In this it is similar to other secretory epithelia. The RPE current is large and varies as retinal activity alters. It is also affected by drugs and disease. The RPE currents can be studied in cell culture, in animal experimentation but also in clinical situations. The object of this review is to summarise this work, to relate it to the molecular membrane mechanisms of the RPE and to possible mechanisms of disease states.

Influence de la variation de la posologie d’hydroxychloroquine (Plaquénil®) sur l’électrorétinogramme

INTRODUCTION

The electroretinogram (ERG) is currently, together with the central visual field test, color vision test and electroculogram (EOG), an examination dedicated to prevent retinopathy due to hydroxychloroquine (HCQ) or chloroquine (CQ) intoxication.

MATERIAL AND METHODS

Thirty-two patients on treatment with HCQ were studied. Each patient had underwent a complete clinical ophthalmological examination and a set of paraclinical examinations including at least an ERG. All the patients were requested to decrease or stop their HCQ treatment. Following this change, a second ERG was recorded for each patient. The ERGs before and after stopping HCQ treatment were compared. We noted a statistically significant increase in the amplitude of "b" wave of the ERG, following after decrease or discontinuation of HCQ treatment.

DISCUSSION AND CONCLUSION

This study has demonstrated the ERG "b" wave sensitivity due to the variation of HCQ consumption. The amplitude and the culmination time of the ERG "b" wave are important parameters to monitor during long term treatment with HCQ. A decrease of the "b" wave amplitude, coupled with an increase of its culmination time in a patient on long term HCQ treatment showing for the same daily dose, shall be a sign of alert, imposing the performance of additional visual functional tests and leading a decrease or a discontinuation of the treatment with HCQ. The ERG is an objective examination, which needs almost no participation from the patient. Its usefulness has been demonstrated, for the prevention of retinopathy due to hydroxychloroquine or chloroquine intoxication in condition that successive ERGs of the same patient are precisely compared.

Hydroxychloroquine and chloroquine retinopathy: screening for drug toxicity

PURPOSE

To report hydroxychloroquine and chloroquine retinopathy and consider screening for drug toxicity.

DESIGN

Retrospective observational case series.

METHODS

Review of clinical records, visual fields, fundus photographs, and fluorescein angiography of six patients from a retina referral practice.

RESULTS

All cases arose because of failure by physicians to avoid dosing above published safe levels. Five cases developed despite accepted ophthalmologic patterns of screening for toxicity. All cases developed parafoveal retinal pigment epithelial atrophic changes and paracentral scotomas to threshold visual field testing.

CONCLUSIONS

New cases of hydroxychloroquine and chloroquine toxicity continue to develop in a screening environment. Increased ophthalmologic attention to dosing, awareness of location and nature of early visual field defects, and traditional attention to presence or absence of maculopathy can reduce the incidence of this avoidable condition.

Retinal toxicity in human immunodeficiency virus-infected children treated with 2',3'-dideoxyinosine

To assess the safety and antiretroviral activity of 2',3'-dideoxyinosine, we enrolled 43 children with symptomatic (Centers for Disease Control class P-2) human immunodeficiency virus infection in a Phase I-II study and monitored them prospectively for the development of ocular complications secondary to HIV infection or drug toxicity. Follow-up ranged from 12 to 103 weeks with a median follow-up of 71 weeks. Three of 43 children (7.0%) developed peripheral atrophy of the retinal pigment epithelium during treatment with 2',3'-dideoxyinosine. The two children with the most severe retinal atrophy were enrolled in the study at the highest dosage studied (540 mg/m2/day). In contrast to findings in children, no retinal atrophy in HIV-infected adults treated with 2',3'-dideoxyinosine has been evident to date.

Evaluation of several tests in screening for chloroquine maculopathy

Patients receiving antimalarial therapy, specifically hydroxychloroquine, for different periods were evaluated using contrast sensitivity test (CST) and results were compared with those of electro-retinography (EOG), and pattern visual evoked potential (PVEP), and a matching age control group. The results indicated CST to be most sensitive of the evaluated techniques particularly in patients under 40 years old. In 44.4% of the cases CST revealed macular dysfunction of which the other two methods of examination were not capable. Our findings suggest the CST is a reliable and practical method which could be used as an additional screening test for chloroquine maculopathy.

Ocular toxicity of desferrioxamine: light microscopic histochemical and ultrastructural findings

This study documents for the first time light and electron microscopical changes in the retinal pigment epithelium (RPE) following treatment with high dose desferrioxamine for systemic iron overload. The changes include loss of microvilli from the apical surface, patchy depigmentation, vacuolation of the cytoplasm, swelling and calcification of mitochondria, and disorganisation of the plasma membrane. In addition, Bruch's membrane overlying degenerate RPE cells appeared abnormally thickened owing to the accumulation of large amounts of mature elastic fibres, pre-elastic oxytalan, and long spacing collagen. The specificity of these changes and the mechanism of toxicity are discussed.

Ophthalmologic considerations and testing in patients receiving long-term antimalarial therapy

We do not as yet understand all the mechanisms involved in retinal toxicity. Such risk is lower with hydroxychloroquine than with chloroquine. The risk of true retinopathy rises with duration of therapy. The benefit/risk ratio for hydroxychloroquine is at least equal to or better than that of chloroquine, and when the currently recommended dosages of 400 mg per day of hydroxychloroquine and 250 mg per day of chloroquine are not exceeded, this ratio is medically and ophthalmologically acceptable. The most useful tests to detect retinopathy are ophthalmoscopic and/or photographic observation of the macular area for changes in pigmentation, sensitive central visual field testing, and automated computerized perimeter. These tests can be conducted by the attending physician provided that (1) baseline ophthalmologic studies are done (to exclude pre-existing ocular abnormalities); (2) such studies are conducted every six months thereafter; and (3) the patient with ocular abnormalities is immediately referred to an ophthalmologist for further evaluation, even in the absence of symptoms.

Chloroquine retinopathy: is there a safe daily dose?

Published case reports of chloroquine retinopathy rarely include details of daily dosage, but 30 reports where this information was available included 78 patients who developed impaired visual acuity an 13 had received daily doses of 250 mg or less. Eleven cases of ocular toxicity attributed to chloroquine were reported to the Committee on Safety of Medicines but only 2 developed impaired vision on 250 mg daily. A postal questionnaire among 41 rheumatology and 33 ophthalmology centres showed 2 patients who developed impaired vision as a result of treatment with chloroquine in a daily dose not exceeding 250 mg. Serious visual impairment related to chloroquine rarely occurs if the daily dose does not exceed 250 mg.