Prof John Wild
My research involves three areas: the development of methodologies for the refinement of the visual field examination; the relationship between structure and function in glaucoma; and the investigation of drug-related visual field loss particularly that associated with anti-convulsant therapy.
Isolation of factors influencing the short-term and long-term fluctuation of the threshold response and the separation of the optical component of perimetric sensitivity from that of the neural component. The outcome of the visual field examination can be influenced by a variety of artifacts which can mimic the appearance of both diffuse and focal loss thereby impairing the clinical precision of the examination. We have documented the presence of a learning effect in automated perimetry whereby perimetric sensitivity improved with repeated examination both within-and between-eyes at a given examination and also between-examinations - a finding of considerable ramification for the monitoring of the efficacy of therapeutic intervention. We have also shown that forward light scatter arising from media opacities causes an apparent diffuse depression of the visual field in primary open angle glaucoma and to produce an apparent reduction in the size and/or depth of focal visual loss.
Development of statistical procedures for the identification of progressive visual field loss: The short-term and the long-term variability hinder the identification of progressive visual field loss in serial visual field analysis. Over a number of years collaborative work in Canada with John Flanagan at the Universities of Waterloo and Toronto and Graham Trope at the University of Toronto has resulted in the development of a mathematical model for the pointwise distribution of sensitivity in normals, ocular hypertensives and primary open angle glaucoma based upon polynomial and multiple regression.
Short wavelength automated perimetry: Considerable interest currently centres on the use of short-wavelength automated perimetry (SWAP) for the early detection of visual field loss in primary open angle glaucoma. Five research groups, including my own, have now suggested that SWS visual field loss can occur in primary open angle glaucoma prior to conventional white-on-white (W-W) field loss and can exhibit progression in advance of that when recorded with conventional W-W perimetry. However, we have shown that the between-subject normal variability of the threshold response obtained with SWAP in non-elite observers, and from which the confidence limits for normality are constructed, is greater than that for conventional W-W perimetry. In addition, we have also reported that the within-subject within-test variability and the within-subject between-test variability are also greater for SWAP than for W-W perimetry. The increased confidence limits for SWAP hinder the detection of abnormality whilst the greater within-test and between-test variability impedes the detection of progressing field loss. The technique in its current format is therefore too difficult and consequently has not become established as a routine part of ophthalmological practice.
Structure and functional assessment in primary open angle glaucoma: The relationship between the appearance of the optic nerve head in primary open angle glaucoma and the appearance of the conventional W-W visual field is tenuous. The lack of correlation implies structural change prior to functional loss. Optical Coherence Tomography is a recently introduced imaging technique which can perform cross-sectional or tomographic imaging. The technique is based upon low-coherence interferometry which is used to measure the echo delay time of light reflected from the various microstructural features under investigation. The technology is capable of measuring the retinal nerve fibre layer (RNFL) thickness. We have developed a methodology which yields a reproducible measure of the RNFL in glaucoma. Studies relating structure to function are currently in progress involving RNFL analysis, optic nerve head tomography, conventional white-on-white perimetry SWAP and Frequency Doubling Perimetry.
The prevalence and aetiology of visual field loss associated with anticonvulsant medication: The anti-epileptic drug vigabatrin is an effective and well-tolerated drug used for the treatment of partial seizures in adults and children. A characteristic pattern of visual field loss is associated with vigabatrin; namely, a bilateral constriction. We have shown that within the central field, only, (i.e. out to 30¡ from fixation) the vigabatrin-attributed visual field loss can take on a variety of forms. In mild and moderate cases, the defect manifests as a steeply bordered, crescent-like loss in the nasal field which typically extends superiorly and inferiorly with a preservation of the temporal field. In severe cases, the defect is steeply bordered and concentric to within approximately 15¡ from fixation. In early cases, the defect can occur inferior-nasally. The field loss is asymptomatic in the majority of patients. Seemingly, the preservation of good central visual acuity together with reasonable sparing of the temporal field enables the patient to carry on the usual activities of daily living without apparent difficulty. Collaborative research with Graham Harding at Aston University has shown that certain visual electrophysiological abnormalities of the ERG (the photopic a-b amplitude, scotopic a wave latency and the latency of OP2) are significantly associated with current vigabatrin therapy. We have also shown that the latency of the a wave under 30 Hz conditions, the amplitude of the 30Hz a-b response and the latency of the photopic a wave are significantly associated with the presence of severe visual field loss.
Wild, £60,000, ‘Dynamic Noise Perimetry’ Cardiff partnership Fund, 2010-2012