Keith W. Mitchell

Clinical comparison of ocular blood flow tonometer, tonopen, and Goldmann applanation tonometer for measuring intraocular pressure in postkeratoplasty eyes

Purpose. Intraocular pressure (IOP) measurements vary with different tonometers in irregular corneas. The purpose of our study was to determine the comparability of the ocular blood flow tonometer (OBF) and Tonopen with the Goldmann applanation tonometer (GAT) in measuring IOP in post-keratoplasty eyes. Methods. The IOP was measured using the OBF tonometer, GAT, and Tonopen in 69 post-keratoplasty eyes by two observers. The same instruments were used, and the sequence of measurements was randomized. Pachymetry to measure corneal thickness was done in all patients. Results. Interobserver variation for IOP measured with GAT was statistically significant (p = 0.039). Two-way analysis of variance (ANOVA), however, did not demonstrate any statistical difference between measurements with the three tonometers and two observers. Corneal thickness did not appear to have an effect on measurements with any of the tonometers. Conclusion. There was no significant difference in the overall accuracy of the OBF tonometer over the Tonopen versus the GAT. The OBF tonometer can be a useful alternative in measuring IOP in post-keratoplasty eyes.

Triple cycle audit of primary retinal detachment surgery.

Purposeu2003To determine the effect of increasing subspecialisation on the results of retinal detachment surgery in one city.Methodsu2003Three audit cycles over a 10-year period when major subspecialisation and organisational changes were occurring. Retrospective case note reviews of all primary surgery for rhegmatogenous retinal detachments in each of the audit periods. Statistical analyses used contingency table/chi-square methods for comparing all three audits and Fisher’s exact test/mean odds ratio with 95% confidence intervals (CIs) for the Audit 1 vs Audit 3 comparison.Resultsu2003A marked improvement in success rates occurred: primary reattachment rose from 67% in Audit 1 to 87% in Audit 3 (Pu2009=u20090.0004), and final success from 84% to 97% (Pu2009=u20090.0003). There was a dramatic change in operative techniques over the same period: the percentage of vitrectomies increased from 1.5% in Audit 1 to 48% in Audit 3, while that of ‘open’ conventional procedures decreased from 78% to 32%. However, the improvement in anatomical success was not mirrored by an increase in the percentage of patients with 6/12 or better visual acuity postoperatively (55% in Audit 1, 49% in Audit 3; Pu2009=u20090.34, mean odds ratiou2009=u20090.78; 95% CI 0.48–1.2). The percentage of patients with 6/18–6/36 post op visual acuity did increase in Audit 3 (18% in Audit 1; 29% in Audit 3; Pu2009=u20090.03, mean odds ratiou2009=u20091.9; CI 1.1–3.3), and the percentage with 6/60 or worse decreased (27% in Audit 1, 20% in Audit 3; Pu2009=u20090.26, mean odds ratiou2009=u20090.71; CI 0.40–1.2).Conclusionsu2003With increased subspecialisation there has been an increase in anatomical success, but the goal of 100% reattachment is still not being attained. There remains scope for further improvement in anatomical and functional outcomes.

The prognostic value of flash visual evoked potentials in the assessment of non-ocular visual impairment in infancy

The results of flash visual evoked potentials (VEPs) in 44 infants blind or severely visually impaired from non-ocular causes are presented, and related to the subsequent visual outcome. Ocular causes of visual impairment were excluded by clinical examination and electroretinography. Using a 2 × 2 contingency table, a significant association between YEP and outcome was demonstrated (X2 = 3.51, 1 d.f., p = 0.05). Of 13 infants with normal VEPs, 11 demonstrated substantial visual improvement (negative predictive value = 84.6%). However, of the 31 with abnormal VEPs, only 14 remained severely impaired/blind; the other 17 demonstrating visual improvement (positive predictive value = 45.1%). The sensitivity of the method was high in that 14 of 16 (87.5%) infants who remained impairedlblind had abnormal VEPs, but specificity was low as only 11 of 28 (39.3%) who showed visual improvement had normal VEPs. The accuracy of the technique was therefore low, 25 of 44 (56.8%) being true positive/ negative. With regard to visual outcome when faced with an apparently blind infant, it is important not to be too pessimistic for, as is shown in this study, 28 of 44 demonstrated substantial improvement. There are no absolute indicators of prognosis, but the presence of structural cerebral lesions and a history of either neonatal meningitis or encephalopathy are relatively bad prognostic signs. The flash YEP, despite its limitations, is a useful prognostic tool, particularly in those apparently blind infants whose normal ocular examination/electroretinogram is accompanied by normal VEPs. Those with abnormal VEPs, however, do not necessarily have a poor prognosis, but should be followed-up as maturational changes and/or improvements in function of the sensory pathway will be reflected in the evoked potentials.

THE EFFECTIVENESS OF TOPICAL DICLOFENAC IN RELIEVING DISCOMFORT FOLLOWING TRAUMATIC CORNEAL ABRASIONS

Diclofenac is a non-steroidal anti-inflammatory drug available in an ophthalmic preparation. We present a prospective randomised double-masked placebo-controlled trial involving 40 patients that assessed the effectiveness of topical dicIofenac in relieving pain from traumatic corneal abrasions. Statistical analysis of visual analogue and categorical pain scores revealed a significant reduction in pain experienced by subjects in the diclofenac group (p<0.02).

Clinical features of a novel TIMP-3 mutation causing Sorsby's fundus dystrophy: implications for disease mechanism

AIMS To describe the phenotype in three family members affected by a novel mutation in the gene coding for the enzyme tissue inhibitor of metalloproteinase-3 (TIMP-3). METHODS Three members of the same family were seen with a history of nyctalopia and visual loss due to maculopathy. Clinical features were consistent with Sorsbys fundus dystrophy. Exon 5 of the gene coding for TIMP-3 was amplified by the polymerase chain reaction, single strand conformation polymorphism analysis undertaken and exon 5 amplicons were directly sequenced. RESULTS Onset of symptoms was in the third to fourth decade. Five of six eyes had geographic macular atrophy rather than neovascularisation as a cause for central visual loss. Peripheral retinal pigmentary disturbances were present. Scotopic ERGs were abnormal in all three. Mutation analysis showed a G→T transversion in all three resulting in a premature termination codon, E139X, deleting most of the carboxy terminal domain of TIMP-3. CONCLUSIONS The patients described had a form of Sorsbys fundus dystrophy which fell at the severe end of the spectrum of this disease. Postulated disease mechanisms include deposition of dimerised TIMP-3 protein.

Visual evoked cortical potential to paracentral retinal stimulation in chronic glaucoma, ocular hypertension, and an age-matched group of normals

Visual evoked cortical potentials (VECPs) to midperipheral stimulation of the visual field were elicited in age-matched groups of patients with unilateral chronic simple glaucoma or ocular hypertension and normal subjects. With a multimodal stimulus approach comprising transient and steady-state pattern reversal and transient onset-offset VECPs, 82.1% of the glaucoma group and 50.9% of the ocular hypertensives revealed significant abnormalities (p < 0.01) in one or more of the electrophysiological features measured, i.e., latency, phase, amplitude, and contrast threshold.

The effect of long-term use of benzodiazepines on the eye and retina

Thirty patients on long-term benzodiazepine medication were subjected to full ophthalmoscopic examination. Of these 19 (63.3%) complained of symptoms of irritation, blurred vision or difficulty in reading. None, however, had reduced visual acuities apart from two where the cause was longstanding amblyopia. Thirteen patients had some form of retinal finding, 9 macular and 4 non-macular. Of the 14 who presented for flash and pattern electroretinography (ERG), none showed any abnormality which could be ascribed to the medication, its total dose, or duration. We conclude, on the basis of the evidence from this small cohort, that long-term benzodiazepine medication has little effect upon retinal function as signalled by the ERG.

Electrophysiologically determined contrast sensitivity in patients with ocular hypertension and chronic glaucoma.

Subjectively assessed contrast sensitivity has been found to be abnormal in many patients with glaucoma. We previously reported the use of onset-offset visual evoked potential measurements to determine contrast threshold objectively. We now studied 216 patients (79 with ocular hypertension and 137 with chronic simple glaucoma) with this technique. In comparison with an age-matched control group (68 subjects), mean contrast threshold was found to be significantly different in both patient groups, the degree of significance being greater in the patients with chronic simple glaucoma. Additionally, the slope of the CI-CII amplitude versus log contrast plot was shown to be depressed in the majority of affected eyes in patients with unilateral chronic simple glaucoma. This measure appears to give an indication of suprathreshold contrast processing and is related to the difference in luminance between pattern elements, rather than the quality of the border or “edge” between them. The data support not only an increase in contrast threshold (reduced sensitivity) in early glaucoma and some patients with ocular hypertension but also a suppression in suprathreshold function that is not readily measurable with standard psychophysical methods. The findings are consistent with recent theories concerning the effect of early chronic simple glaucoma on the function of Y-type units of the M (magnocellular)-type pathways.

The effect of contrast reduction on pattern-reversal VEPs in suspected multiple sclerosis and optic neuritis.

A retrospective study was conducted to investigate whether the use of low-contrast stimuli in addition to the standard high-contrast stimuli would increase the sensitivity of the pattern-reversal P100 when testing for multiple sclerosis (MS) and optic neuritis (ON). We found that there was a statistically significant increase in the number of abnormal results when using 25′ checks, but not for 50′ checks. Examination of patient records showed that VEP abnormalities to low-contrast stimuli only was not prognostic for subsequent development of multiple sclerosis.

Cortically visually impaired children

Editor,—While Hoyt and Fredrick rightly state the heterogeneous aetiology of cortical visual impairment (CVI) in children,1 we were disappointed in their bland and unjustified dismissal of the value of electrophysiological studies in these cases. They fail to quote any electrophysiological studies more recent than 1979 in their review, of which there have been a not inconsiderable number. As for our own work we have found that a normal flash VEP indicates statistically and clinically a better prognosis in blind babies with non-ocular visual impairment even though we would concede that in some cases flash VEPs can be normal in CVI.2 It is therefore clinically useful …