Ian Murdoch

University College London

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Simon Cousens

London School of Hygiene & Tropical Medicine

John G Lawrenson

City, University of London

O E Babalola

Cedars-Sinai Smidt Heart Institute

Julia Theodossiades

University College London

A Abiose

National Eye Centre

Craig Kennedy

Ninewells Hospital

Helen Baker

Moorfields Eye Hospital NHS Foundation Trust

B R Jones

University of Chester

James Kirwan

Queen Alexandra Hospital

Kazim Dhalla

Aga Khan Hospital Dar es Salaam

Cooperative Institutions

University College London

177

Moorfields Eye Hospital NHS Foundation Trust

133

Moorfields Eye Hospital

130

West African College of Physicians

Institute of Ophthalmology

London School of Hygiene & Tropical Medicine

National Institute for Health Research

University of London

National Health Service

City, University of London

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A Simple Model to Predict the Sensitivity to Change of Visual Acuity Measurements

Optometry and Vision Science (2004)

Simon Cousens D A Rosser Ian Murdoch D A H Laidlaw

Background: Estimates of test-retest variability (TRV) in the form of a 95% range have been suggested as providing a cutoff value (or “change-criterion”) against which measured acuity changes can be judged to decide whether they are indicative of a clinically important change. This approach is based on ensuring that the specificity of the procedure is 95% in individuals with no real change. In an earlier article we investigated empirically the ability of the procedure to detect varying degrees of change (its sensitivity). In this article, we develop a simple statistical model to examine further the sensitivity of the approach. Methods. A statistical model was developed, and predictions from the model were compared with empirical visual acuity data. Results. The model predicts that for changes equal in size to the magnitude of the change-criterion, sensitivity will be 50%. For changes 1.65 times the change-criterion, sensitivity is 90% and increasing to 95% for changes 1.84 times the size of the change-criterion. Predicted sensitivities agreed well with those measured empirically. Conclusions. The 95% range for TRV is often used to decide whether measured changes are indicative of clinically important changes. Evaluating the performance of visual acuity charts using a method analogous to that of estimating the sensitivity and specificity of a screening test highlights some limitations of this method. Use of the 95% range as a change-criterion ensures a high specificity, but a simple statistical model indicates that changes must approach twice the size of the change-criterion before they will be detected with sensitivity in excess of 95%. This has implications for the clinician attempting to assess the reliability of visual acuity charts, and in other similar tests, to detect change.

10.1097/01.opx.0000144745.42600.76

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Citations (7)

Correction: How do paper and electronic records compare for completeness? A three centre study

Eye (2019)

Clara Hoi Ka Wu Sheila Luk Richard L. Holder Zena Rodrigues Faisal Ahmed

Completeness (order theory)

10.1038/s41433-019-0335-0

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Citations (0)

Contributors

Elsevier eBooks (2008)

James Acheson G.G.W. Adams Larry Amure Richard N. L. Andrews Keith Barton

10.1016/b978-1-4160-2572-6.50002-2

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Results and safety profile of trainee cataract surgeons in a community setting in East Africa

Indian Journal of Ophthalmology (2016)

Nikolaos Mavrakanas Kazim Dhalla Jerry Jecha Imani Kapesa Capucine Odouard

Purpose: To evaluate the results and safety profile of assistant medical officer ophthalmologists (AMO-O) performing cataract surgery in the last stage of their surgical training, before their appointment to local communities. Methods: We retrospectively analyzed the records of patients who underwent cataract surgery by AMO-Os at Dar es Salaam, Comprehensive Community Based Rehabilitation for Tanzania Disability Hospital between September 2008 and June 2011. Surgical options were either extracapsular cataract extraction (ECCE) or manual small incision cataract surgery (MSICS), both with polymethylmethacrylate intraocular lens implantation. Results: Four hundred and fourteen patients were included in the study. Two hundred and twenty-five (54%) underwent ECCE and 189 had MSICS. Mean logarithm of the minimum angle of resolution (logMAR) uncorrected visual acuity (UCVA) improved from 2.4 ± 0.6 preoperatively to 1.3 ± 0.8 1 week postoperatively (t-test, P < 0.001) and to 1.1 ± 0.7 3 months postoperatively (t-test, P < 0.001). Mean logMAR best-corrected visual acuity (BCVA) was 0.7 ± 0.5 1 week postoperatively and 0.6 ± 0.5 3 months postoperatively. There was no significant difference in mean logMAR UCVA (P = 0.7) and BCVA (P = 0.7) postoperatively between ECCE and MSICS. 89.5% achieved BCVA better than 6/60 and 57.3% better than 6/18 with a follow-up of 3 months. Posterior capsule rupture and/or vitreous loss occurred in 34/414 patients (8.2%) and was more frequent (P = 0.047) in patients undergoing ECCE (10.2%) compared with MSICS (5.3%). Conclusion: AMO-O cataract surgeons at the end of their training offer significant improvement in the visual acuity of their patients. Continuous monitoring of outcomes will guide further improvements in surgical skills and minimize complications.

10.4103/0301-4738.195594

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Citations (6)

Post-operative management of trabeculectomy in the first three months.

PubMed (2012)

Ian Murdoch

Source

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Citations (11)

Visual field constriction as a cause of blindness or visual impairment.

PubMed (1997)

Ian Murdoch B R Jones Simon Cousens I Liman O E Babalola

Reported are the results of a study of onchocerciasis in communities mesoendemic for savanna onchocerciasis in Kaduna State, northern Nigeria. The study involved 6831 individuals aged > or = 5 years who underwent an extensive screening examination for visual function including Friedmann field analysis. A total of 185 (2.7%) were bilaterally blind by acuity and an additional 28 (0.4%) were blind by visual field constriction. Also 118 (1.7%) individuals were visually impaired by acuity criteria. No criteria for visual impairment by field constriction have been established, and we therefore investigated three potential criteria. As a result, a further 60 (0.9%) individuals were identified with significant visual impairment due to field loss by the various definitions. Small islands of remaining peripheral field occurred in 50 individuals, while 40 individuals had marked reduction of binocular visual field below the horizontal meridian. Concentric visual field constriction to < 20 degrees was found in seven individuals. The WHO definition of blindness currently includes visual field damage criteria for blindness but not for visual impairment. Visual field loss is recognized as a major disability. We hope that these findings stimulate international discussion leading to the development of satisfactory definitions for visual impairment by visual field constriction.

Visual Impairment

Meridian (astronomy)

Constriction

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Citations (14)

The Effect of Optical Defocus on the Test–Retest Variability of Visual Acuity Measurements

Investigative Ophthalmology & Visual Science (2004)

D A Rosser Ian Murdoch Simon Cousens

To determine the effect of optical defocus on the test-retest variability (TRV) of visual acuity measurements in normal subjects.Normal subjects underwent repeated visual acuity measurement with optical defocus of 0, 0.50, and 1.00 D. All measurements were taken using the Early Treatment Diabetic Retinopathy Study (ETDRS) version of the Bailey-Lovie logMAR chart. TRV was quantified in terms of its 95% range, both empirically and using the approach of Bland and Altman.According to the Bland and Altman approach, the estimated 95% TRV ranges were +/-0.11 logarithm of the minimum angle of resolution (logMAR) for 0-D defocus, +/-0.18 logMAR for 0.50-D defocus, and +/-0.25 logMAR for 1.00-D defocus.Optical defocus has a considerable effect on the TRV of visual acuity measurements. These findings have important implications for both clinical practice and clinical research. Uncorrected refractive errors as small as 0.50 D may compromise the detection of visual change in individuals, and contribute to unnecessarily large sample sizes in clinical trials in which visual acuity is used as a primary outcome measure.

10.1167/iovs.03-1320

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Citations (53)

Reduction in incidence of optic nerve disease with annual ivermectin to control onchocerciasis

The Lancet (1993)

A Abiose B R Jones Simon Cousens Ian Murdoch A Cassels-Brown

Pallor

10.1016/0140-6736(93)90002-x

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Citations (86)

Is review of enriched populations the way forward for glaucoma case detection?

Eye (2003)

Ian Murdoch Julia Theodossiades

10.1038/sj.eye.6700262

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Citations (8)

Selective Laser Trabeculoplasty in Northern Ghana

Medical Research Archives (2024)

Jean–Claude Simon Thomas Kenny Ian Murdoch

We present an audit in Northern Ghana. A total of 283 selective laser trabeculoplasties (SLTs) were done between September 2021 and September 2024. Because of collinearity between right and left eye response to therapy, 145 eyes in 145 individuals with primary open angle glaucoma were included in the analysis. Outcomes were assessed at 1,3,6 and 12 months post index procedure. A success proportion of 75% (33/44) for any reduction in IOP from baseline and 57% (25/44) for a reduction of ≥20% was seen at one year post index SLT. No complications were seen. These findings are directly comparable to those from a major African centre but lower than Caucasian studies. This proof of effect in a rural setting adds to the evidence supporting use of this therapy as an important element in primary open angle glaucoma management in this region.

10.18103/mra.v13i1.6141

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