Academic journal article Bulletin of the World Health Organization

Impact of Annual Dosing with Ivermectin on Progression of Onchocercal Visual Field Loss

Academic journal article Bulletin of the World Health Organization

Impact of Annual Dosing with Ivermectin on Progression of Onchocercal Visual Field Loss

Article excerpt

Introduction

Onchocerciasis is one of the major causes of blindness. Two commonly reported ocular sequelae of onchocercal infection are optic nerve disease and chorioretinitis[1], both of which can cause dramatic reductions in the peripheral visual field, leaving only a small island of central vision[2]. In such cases visual acuity may be largely unaffected until a late stage of the disease process.

Ivermectin is now the drug of choice for the treatment of onchocerciasis, and annual dosing with it substantially reduces the incidence of optic nerve disease among infected individuals[3] and produces beneficial effects on other onchocercal eye lesions, including punctate keratitis[4] and iridocyclitis[5]. Less is known, however, about the impact of ivermectin on visual function loss and, in particular, visual field loss. In this article we report the effect of annual dosing with the drug on the progressive deterioration of visual field loss in northern Nigeria.

Methods

The population studied and methods used in the trial have been described previously[3, 6], Briefly, a randomized, double-masked, placebo-controlled trial of ivermectin was conducted in 34 rural communities that were mesoendemic for guinea savanna onchocerciasis, in Kaduna State, northern Nigeria. A census was carried out on the communities and demographic data and pertinent information, such as previous use of diethylcarbamazine (DEC), was collected.

Skin-snips were taken from villagers aged [is greater than or equal to] 5 years, who were then registered for inclusion in the trial and randomly assigned at the individual level using a blocked design to receive ivermectin or placebo. Annual dosing with ivermectin/placebo was performed over a 3-year period. At the fourth annual round, all villagers received ivermectin. Standard exclusion criteria were applied at each dosing.

The trial participants underwent ophthalmic examination prior to the first, third, and fourth annual dosings. At each examination all villages were visited, and registered individuals were asked to report to a central location in their village. Each patient was screened for signs of optic nerve disease by a team of ophthalmic nurses who had received intensive training from two ophthalmologists (I.M., O.E.B.) before the start of the fieldwork. The screening examination consisted of a series of visual function tests (including visual acuity, peripheral visual field assessment by counting fingers in all four quadrants, paracentral visual field assessment using a variety of tests, colour vision, and a test for red desaturation), applanation tonometry, examination of pupillary light response, and undilated fundoscopy to assess optic disc colour and cup: disc ratio. Individuals who failed the screening examination were referred to an ophthalmologist; the referral criteria included reduced visual acuity that did not improve to 6/9 with pinhole, failure of any of the other visual function tests, and intraocular pressure [is greater than or equal to] 2.80kPa ([is greater than or equal to] 21 mmHg), an abnormal pupillary light response, suspicion of disc pallor or a cup: disc ratio [is greater than] 0.5. In addition, individuals belonging to a computer-generated random sample of the trial population were also referred to an ophthalmologist, regardless of the outcome of the screening examination.

The ophthalmologist examined the referred patients in a mobile clinic equipped with a slit-lamp biomicroscope, applanation tonometer, and retinal camera. After the patient's pupillary light response had been checked, the individual concerned returned to the ophthalmic nurse for pupillary dilation, dark adaptation, and Friedmann mark I visual field analysis. Topical mydriatics (cyclopentolate hydrochloride (1% (w/v)) and phenylephrine hydrochloride (10% (w/v)) were instilled until the pupils were maximally dilated and nonreactive to light. …

Search by... Author
Show... All Results Primary Sources Peer-reviewed

Oops!

An unknown error has occurred. Please click the button below to reload the page. If the problem persists, please try again in a little while.