Prolonged Multifocal Electroretinographic Implicit Times in the Ocular Ischemic Syndrome

Abstract

PURPOSE.To examine retinal function in chronic ocular ischemia using multifocal electroretinography (mfERG). METHODS. Thirteen patients with unilateral ocular ischemic syndrome (OIS) underwent assessment of ophthalmic systolic blood pressure by ocular pneumoplethysmography, carotid artery patency by ultrasonography, intraocular pressure (IOP) by applanation tonometry, retinal perfusion by fluorescein angiography, and retinal function by mfERG. RESULTS. Ophthalmic systolic blood pressure was 67.0 Ϯ 11.6 mm Hg in eyes with OIS and 106.1 Ϯ 18.0 mm Hg in fellow eyes, whereas IOP was 13.8 Ϯ 3.2 and 14.4 Ϯ 1.7 mm Hg, respectively. Summed mfERG implicit times (N1, P1, N2) were prolonged in eyes with OIS, by 7.6%, 6.2%, and 7.5%, respectively, compared with fellow eyes (P Յ 0.0048). The retardation of retinal function was significant outside the macula, whereas the assessment of responses from the central retina was limited by high variance. Second-order kernel (first slice) summed implicit times (N1, P1, N2) were also prolonged in OIS, by 6.6%, 7.3%, and 6.8%, respectively (P Յ 0.0058). Of the amplitudes, only the second-order N2 amplitude was significantly abnormal, being reduced by 23.2% in OIS (P ϭ 0.011). CONCLUSIONS. The function of the outer and middle layers of the retina was found to be suppressed in chronic ocular hypoperfusion. The moderate delay in retinal function does not appear to explain the prominent photopic symptom of diffuse glare in bright light, and the delay could be evidence of a functional adaptation that serves to maintain and optimize signaling under conditions of compromised perfusion. (ClinicalTrials.gov number, NCT00403195.) (Invest Ophthalmol Vis Sci.O cular ischemic syndrome (OIS) was first recognized as a result of severe carotid artery obstruction in 1963. 1 Definite diagnostic criteria have not been established. The principal symptoms are mild to severe visual loss, ocular pain that can be relieved by lying down, and diffuse glare in bright light. Findings include aqueous flare, iris rubeosis, cataract, narrow retinal arteries, dilated nontortuous retinal veins, retinal hemorrhages, microaneurysms, cotton-wool spots, and preretinal neovascularization. Fluorescein angiography reveals delayed and patchy choroidal filling and diffuse leakage from the retinal vessels and the optic nerve head. 2 OIS is relatively rare. The largest study so far included 52 eyes with OIS in 43 patients collected retrospectively from a background of 1.5 million outpatient visits. 3 Patients found to have OIS are often referred with a diagnosis of diabetic retinopathy, central retinal vein occlusion, or neovascular glaucoma, showing that OIS is underdiagnosed in general clinical practice.There is no strict correlation between the degree of carotid artery stenosis and the presence or severity of ipsilateral OIS, probably because there is considerable variation in the capacity of collateral and retrograde filling of the ophthalmic artery from the external carotid artery and the contralateral internal carotid arter...

Cone pathway function in relation to asymmetric carotid artery stenosis: correlation to blood pressure

“…A significant delay of the first‐order summed N1 and P1 implicit times and a significant decrease in N1 and P1 amplitudes was seen with increasing degrees of carotid artery stenosis. This new observation found within patients with asymmetric carotid artery stenosis and clinically healthy eyes follows a pattern previously observed between patients with the ocular ischaemic syndrome eyes (Kofoed et al. 2010b).…”

“…1983; Russell & Ikeda 1986; Brown & Magargal 1988) and subnormal oscillatory potentials (Story et al. 1995) as well as prolonged implicit times of the N1, P1, and N2 potentials of the multifocal electroretinogram (Kofoed et al. 2010b).…”

“…The ocular ischaemic syndrome secondary to carotid artery occlusion offers a unique opportunity to observe retinal hypoperfusion (Brown & Magargal 1988) in the absence of retinal microvascular occlusion and systemic diseases that can induce retinal microangiopathy such as diabetes. The ocular ischaemic syndrome is associated with electrophysiological abnormalities, including subnormal full-field electroretinography (ffERG) amplitudes (a-wave and b-wave) (Kiser et al 1983;Russell & Ikeda 1986;Brown & Magargal 1988) and subnormal oscillatory potentials (Story et al 1995) as well as prolonged implicit times of the N1, P1, and N2 potentials of the multifocal electroretinogram (Kofoed et al 2010b). Even in the absence of clinical signs of the ocular ischaemic syndrome, carotid artery stenosis can be associated with prolonged dark adaptation and subnormal oscillatory potential amplitudes (Coleman et al 1990;Havelius et al 1997).…”

Association between Asymptomatic Unilateral Internal Carotid Artery Stenosis and Electrophysiological Function of the Retina and Optic Nerve

“…More recently, Kofoed et al identified significant delays in all first-order summed implicit times and a clear trend towards reduced amplitudes in mfERG compared with healthy controls [26]. In the present study, we demonstrated that even in the absence of the clinical signs of ocular ischemic syndrome, significant ICAS may be associated with retinal function abnormalities.…”

Ocular ischemic syndrome – a systematic review

“…Ophthalmologic studies such as visual-evoked potentials (VEP), electroretinography (ERG) and ophthalmotonometry are rarely used to establish the diagnosis of OIS [4,21]. …”