Frequency of seeing characteristics of the short wavelength sensitive visual pathway in clinically normal subjects and diabetic patients with focal sensitivity loss.

AIMS: To define the frequency of seeing (FOS) characteristics of the short wavelength (SW) sensitive visual pathway in clinically normal subjects and in diabetic patients with focal SW sensitivity loss. METHODS: For clinically normal subjects, FOS was assessed at two retinal locations (4.24 degrees and 9.90 degrees eccentricity) for both white on white (WW) and SW stimulus parameters. Inter-examination variability was quantified for the clinically normal subjects only. For patients with diabetes, FOS was assessed inside an area of focal SW sensitivity loss, and at the same eccentricity in the quadrant diametrically opposite, using SW stimulus parameters only. RESULTS: For clinically normal subjects, the group mean SW FOS slope was significantly flatter (p<0.0001) than that of WW at both locations. The coefficient of repeatability for SW FOS slope was+/-41.55 dB(-1) (relative to a group mean sensitivity of 23.98 dB(-1)) and+/-19.98 dB(-1) (group mean sensitivity 16.15 dB(-1)) for 4.24 degrees and 9.90 degrees , respectively. For the patients with diabetes, the group mean SW FOS slope was significantly flatter (p=0.020), and group mean SW threshold significantly higher (p=0.007) in the area of focal SW sensitivity loss than in that of the non-focal sensitivity loss. CONCLUSIONS: The results of this study suggest that the clinical utility of SW automated perimetry will be limited by a greater magnitude of measurement variability, as indicated by a flatter FOS slope, compared to conventional automated perimetry.

Reproducibility of topographic measurements of the macula with a scanning laser ophthalmoscope.

BACKGROUND: The Heidelberg retina tomograph, a scanning laser ophthalmoscope that uses confocal optics to provide high resolution of images, is able to scan the retina in three dimensions to obtain quantitative topographic measurements. The authors evaluated its usefulness for measuring macular lesions by determining the reproducibility of its topographic measurements at the macula. METHODS: For each of ten healthy patients, the authors took five images with the patient's right eye undilated and five with the eye cyclopleged and dilated. As a measure of reproducibility, the standard deviation of height measurements for the same location at the macula was calculated for each patient and then the pooled standard deviation for all patients was calculated. The authors performed similar calculations for the mean depth within a contour line. RESULTS: The pooled standard deviation for height measurements was 47.4 microns in undilated eyes and 36.0 microns in cyclopleged, dilated eyes. The authors obtained an extremely low standard deviation of 2.2 microns when the software calculated relative differences between measurements, such as the mean depth within a contour line. When the average of three height measurement values on 1 day was compared with the average of the three values on another day, the 95% confidence interval was +/- 58.7 microns for mean height values and +/- 3.7 microns for mean depth values within a contour line. CONCLUSIONS: The authors obtained good reproducibility for height measurements with the Heidelberg retina tomograph and excellent reproducibility when the instrument calculated relative differences in height measurements. The authors recommend that patients, especially young patients, be dilated and cyclopleged to obtain lower variability of measurements. The scanning laser ophthalmoscope could potentially be used to quantify small changes in retinal lesions.

The ornithine aminotransferase (OAT) locus: analysis of RFLPs in gyrate atrophy.

A cDNA probe (HOAT1) for ornithine aminotransferase (OAT) has recently been used to map (1) the structural gene for this enzyme to chromosome 10 and (2) several related DNA sequences to the X chromosome. We have defined six RFLPs for OAT, to explore its possible role in gyrate atrophy (GA) of the choroid and retina, an autosomal recessive genetic disorder associated with a deficiency of OAT activity. The RFLPs, which are detected by noncoding single-copy probes from the OAT gene and by subclones of the HOAT1 cDNA, all map on human chromosome 10, producing an overall level of heterozygosity for the OAT locus of 83%. Using the RFLPs, we have determined that the OAT locus segregates concordantly with GA in one available pedigree. Furthermore, the RFLPs display significant disequilibrium with GA, providing genetic evidence implicating a defect in the OAT structural gene as the cause of this disorder. The RFLPs for OAT are potentially applicable to prenatal diagnosis and carrier detection in families with a previous history of GA. They will also allow identification of specific haplotypes associated with GA chromosomes, as a guide for more detailed molecular-genetic investigations of the mutations underlying the disorder.

Indomethacin v. dexamethasone in the suppression of corneal neovascularization.

A 7-0 silk suture was placed in one of the corneas of each of 18 albino rabbits as a vasogenic stimulus. Two drops of normal saline, a 10.3 mg/ml suspension of indomethacin or a 0.1% suspension of dexamethasone, allocated in double-masked fashion, were then instilled in the 18 eyes three times per day. There was a statistically significant difference (p less than 0.01) in the rate of neovascularization between the 6 control corneas and the 12 treated corneas but no significant difference in the rate or the quality of neovascularization between the 6 indomethacin-treated corneas and the 6 dexamethasone-treated corneas.