Cyclotorsional eye movements during a simulated PRK procedure.

PURPOSE: Eye alignment is a serious concern when performing corneal surface ablation. Although several excimer lasers monitor horizontal and vertical movements, little is known about the potential impact of cyclotorsional movements. Dynamic cyclotorsions have been measured on 10 emmetropic subjects during a simulated PRK treatment. METHODS: Cyclotorsional eye movements were measured using a 3D videoculographic system (SMI) in 10 emmetropic subjects in upright and supine position. The subjects were wearing an eyelid speculum and were asked to fixate on a 1 degrees red spot. The fixation target was either in focus or optically degraded by electronic filters. Data were collected at the University Eye Clinic, Torino, Italy, and the different setting measurements were compared using Student's t-test for paired data. RESULTS: Cyclotorsions were significantly higher when subjects were fixating an optically degraded stimulus (upright: P=0.04; supine: P=0.0002). The cyclotorsional movements ranged from -13 to 17 degrees. A significant difference in eye orientation was present when changing from the upright to the supine position (P=0.03). Even when correcting for this positional error, significantly higher cyclotorsional movements were detected in the supine position (in focus: P=0.0043; optically degraded: P=0.0008). The torsional range was from -14.85 to 14.55 degrees. CONCLUSIONS: The high range of cyclotorsional eye movements during a simulated PRK procedure suggests that 3D tracking could improve surface ablation results when treating high astigmatism or when wavefront guided.

The gold foil electrode in pattern electroretinography.

A recent study found that the gold foil electrode produces large pattern electroretinogram amplitudes, but the test-retest reliability was low. In a three-center study, we observed that 90% of 29 patients who were tested with gold foil electrodes used three times appeared to have markedly lower amplitudes than when tested with new electrodes during the same session. Across study centers, the mean of the new electrode recordings was 3.78 microV (standard deviation, 1.13 microV), versus 2.93 microV (1.29 microV) for used electrodes. This 0.85-microV reduction (22%) was statistically significant (F = 7.10 p = 0.01). Electrodes used three times demonstrated an average change in the coefficient of variation of 14% (standard deviation/mean = coefficient of variation; new, 1.13/3.78 = 30%; used, 1.29/2.93 = 44%). Two of the study sites (Houston/Indianapolis) conducted test-retest pattern electroretinograms on a total of 18 patients and found the mean evoked potential to be 3.55 microV with new electrodes and 2.82 microV with used electrodes. The coefficient of variation for the test-retest data was 30% and 47% for new and used electrodes, respectively. Light microscopy showed small cracks on the surface of the electrode, with the number and configuration of the cracks varying in each electrode. The presence of cracks is further complicated by their proximity to the tear film. These sources of variation can result in significantly different impedances. We propose that constant flexion, as a result of patient blinking, causes cracks in the thin gold surface of the electrode. Used electrodes will produce lower pattern electroretinogram amplitudes and poor test-retest reliability.(ABSTRACT TRUNCATED AT 250 WORDS)

Visual fields in 4- to 10-year-old children using Goldmann and double-arc perimeters.

We report the comparison of field extent measured using two kinetic perimeters: 1) a double-arc perimeter developed by van Hof-van Duin for use in infants and young children, and 2) the standard Goldmann apparatus. Targets used were the V-4-e target on the Goldmann and both 2- and 6-degree targets on the double-arc perimeter. Visual fields were measured by assessing looking responses toward targets presented in a pseudorandom order at 45 degrees, 135 degrees, 225 degrees, and 315 degrees. Fifty-six children (mean age: 6.8 years, range: 4 to 10 years) were tested, with retests undertaken in 20%. The extent of total field size was highly correlated among the three tests (P less than .001) and test-retest reliability was high for all three targets (P less than .001). Our previous observation of continued growth with age in visual field extent using the 6-degree target in 4- to 10-year-old children was confirmed and also seen with the 2-degree target in arc perimetry and with the V-4-e in the Goldmann apparatus. Kinetic perimetry using a double-arc perimeter with 2- and 6-degree target sizes appears reliable and comparable, in the four meridia tested, to conventional kinetic perimetry techniques in 4- to 10-year-old children.