Response variability in the visual field: comparison of optic neuritis, glaucoma, ocular hypertension, and normal eyes.

PURPOSE: To compare the relationship between sensitivity and response variability in the visual field of normal eyes and eyes with optic neuritis (ON), glaucoma (POAG), and ocular hypertension (OHT). METHODS: Frequency-of-seeing (FOS) data were collected from four visual field locations in one eye of 71 subjects (12 ON, 25 POAG, 11 OHT, and 23 normal), using a constant stimulus method on an Henson 4000 perimeter (Tinsley Instruments, Croydon, UK). At each location, at least 20 stimuli (subtending 0.5 degrees) were presented for 200 ms at six or more intensities above and below the estimated threshold. The mean and SD of the probit fitted cumulative Normal function were used to estimate sensitivity and response variability. Cluster regression analysis was carried out to determine whether there were differences in the sensitivity-log (variability) relationship between the four groups. RESULTS: Variability was found to increase with decreased sensitivity for all four groups. The combined data from the four groups was well represented (R2 = 0.57) by the function log(e)(SD) = A.sensitivity (dB) + B, where the constants A and B were -0.081 (SE, +/-0.005) and 3.27 (SE, +/-0.15), respectively. Including other statistically significant covariates (false-negative errors, P = 0.004) and factors (diagnosis, P = 0.005) into the model increased the proportion of explained variance to 62% (R2 = 0.62). Stimulus eccentricity (P = 0.34), patient age (P = 0.33), fixation loss rate (P = 0.10), and false-positive rate (P = 0.66) did not reach statistical significance as additional predictors of response variability. CONCLUSIONS: The relationship between response variability and sensitivity is similar for ON, POAG, OHT, and normal eyes. These results provide supporting evidence for the hypothesis that response variability is dependent on functional ganglion cell density.

Ophthalmic management of Cockayne's syndrome.

Cockayne's syndrome is a rare, autosomal recessive condition which usually presents in early childhood, and is characterised by dwarfism, premature ageing, mental retardation and a typical facial appearance and body habitus. Retinal dystrophy, enophthalmos, strabismus, cataract, nystagmus and corneal opacities are associated ocular features. At a genetic level, a defect occurs in the pathway for the repair of transcriptionally active DNA, and the most common form of Cockayne's is associated with mutations in the human repair gene ERCC6. These patients pose a difficult management problem. A significant proportion will require cataract extraction at an early age, which may present technical difficulties due to enophthalmos, which is a constant finding, poor pupillary dilation and growth retardation. Also, the fitting and assessment of aphakic contact lenses during the post-operative period requires great skill. General anaesthesia in these patients may be hazardous. In particular, difficulty with endotracheal intubation should be anticipated. Two patients with Cockayne's syndrome requiring bilateral cataract extraction in early infancy are presented. The problems associated with surgery, anaesthesia and subsequent follow-up in these mentally retarded infants are discussed.

Pattern electroretinogram and automated perimetry in patients with glaucoma and ocular hypertension.

To determine whether the pattern electroretinogram can improve the objectivity of visual field assessment, 39 patients with glaucoma and ocular hypertension were studied. This was to establish whether there is a correlation between the pattern electroretinogram and the global indices (mean deviation and corrected pattern standard deviation) provided by automated perimetry using the Humphrey visual field analyser. A significant correlation was found between the amplitude of the P50 + N95 wave of the pattern electroretinogram and the mean deviation and corrected pattern standard deviation components of the visual field. The larger the deviation from normal of these indices, particularly the corrected pattern standard deviation, the smaller the amplitude of the pattern electroretinogram. This correlation between the pattern electroretinogram and visual field indices provides an additional measure of confidence when interpreting equivocal results of automated perimetry.

Nitrous oxide and internal tamponade during vitrectomy.

We analysed the nitrous oxide composition of the intraocular gas bubble following vitrectomy and fluid-air exchange in 12 patients. Samples were taken under standardised conditions at 20 minutes after completion of the fluid-air exchange. Analysis was conducted by a Medishield MS2 mass spectrometer. The percentage composition of nitrous oxide in the samples varied between 4 and 21% (mean 9%). This influx of nitrous oxide was associated with an increase of intraocular pressure. Pressure rises of greater than 20 mm Hg were not seen owing to venting of gas through the sclerostomies. An inverse relationship was noted between the extent of retinal detachment preoperatively and the amount of nitrous oxide entering the eye. A possible explanation for this relationship is proposed. The importance of nitrous oxide movement is stressed.

Infectious mononucleosis presenting as bilateral acute dacryocystitis.

A case of infectious mononucleosis presenting as bilateral acute dacryocystitis in a 7-year-old girl is reported. Acute dacryocystitis is uncommon in this age group, and an underlying systemic illness should be suspected particularly when it is bilateral.

Mechanisms leading to an acute rise in intraocular pressure in retinal vein occlusion.

Forty patients with retinal vein occlusion were studied to investigate possible mechanisms leading to an acute rise in intraocular pressure. A rise in intraocular pressure on recumbency was found in 64% of eyes with a central retinal vein occlusion and 65% of eyes with a branch retinal vein occlusion. This finding correlated with glucose tolerance test score, and may be the result of abnormal glucose tolerance in these patients. Following provocative testing using pilocarpine and phenylephrine, no eye showed irido-corneal contact or angle closure, however over 50% of eyes release pigment into the anterior chamber. Fifty-two per cent of central retinal vein occlusion and 71% of branch retinal vein occlusion eyes that released pigment showed a rise in intraocular pressure.

Subretinal gas.

Two cases of subretinal gas are described. The circumstances in which this complication arose are important in understanding the mechanism by which gas gains access into the subretinal space. Evacuation of subretinal gas by posturing should be avoided as this leads to an increase in the extent of the retinal detachment and its extension anterior to involve the nonpigment epithelium of the pars plana. A technique for removing subretinal bubbles of expanding gases using vitrectomy and fluid/gas exchange is recommended.

Per-nasal swabbing as an aid to the diagnosis of chlamydial and adenovirus conjunctivitis.

Two hundred and thirty four patients (adults and babies) with conjunctivitis were investigated by taking eye swabs and in addition by taking per-nasal swabs. Chlamydia trachomatis was isolated from 20 patients and adenovirus from 14 patients. Per-nasal swabbing led to a 53% increase in chlamydia diagnosis and a 27% increase in the diagnosis of adenovirus infection. It is suggested that per-nasal swabbing has an important role to play in detecting chlamydial conjunctivitis which itself may be an indicator for high morbidity in patients and their contacts.

The prism bar--Prentice and frontal positions.

The prism cover test has been in use for many years for measuring ocular alignment. The measurements obtained are used for both calculating the amount of correction needed in strabismus surgery, and monitoring any change in ocular alignment with recovery from muscle imbalance. Variability may arise from its use in either the frontal position or the Prentice position. Most prism bars used in the United Kingdom are calibrated for use in the Prentice position. Inaccurate results arise when a prism bar is used in a position for which it is not calibrated. The theoretical calculation for adjusting measurements obtained in the frontal position with prisms calibrated for use in the Prentice position was assessed clinically. A new modified equation is proposed incorporating practical aspects of performing the prism cover test. A table of values is included to assist in determining the necessary adjustment, so allowing for a more reliable assessment.

A closed microsurgical technique for anterior vitrectomy using a continuous air infusion.

A new technique of anterior vitrectomy using a continuous air infusion is described. It has a number of advantages over conventional techniques and is recommended for the management of vitreous loss during cataract extraction. The vitreous gel is displaced posteriorly by the surface tension of an air bubble. The identification of vitreous strands is facilitated by the air/vitreous interface. Air in the anterior chamber reduces the refractive power of the cornea, providing direct visualisation of the posterior segment.

Corneal mosaic patterns--morphology and epidemiology.

The corneas of 1485 consecutive patients were examined for the presence of a mosaic pattern. One hundred and ninety-nine peripheral mosaic patterns, ten posterior crocodile shagreens and two cloudy dystrophies were found. Peripheral mosaic pattern is age related and distinct from corneal arcus. Posterior crocodile shagreen is also age related and in one case was found to be unilateral. The morphology of the mosaic patterns is discussed.