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Characteristics of frequency-of-seeing curves in normal subjects, patients with suspected glaucoma, and patients with glaucoma.

PURPOSE
The authors performed this study to determine factors that affect the characteristics of frequency-of-seeing curves in normal subjects, patients with suspected glaucoma, and patients with glaucoma.


METHODS
The sample consisted of 70 subjects (22 normal subjects, 12 patients with suspected glaucoma, and 36 patients with glaucoma). A program was written to interface with the Humphrey Field Analyzer (Humphrey Instruments, San Leandro, CA) to measure frequency-of-seeing curves. The authors presented stimuli 8 dB either side of the estimated threshold in 1-dB intervals with five repetitions at each stimulus intensity. The authors tested four to six locations in each subject, with randomization of the stimulus intensity and location. Fixation was monitored with the Heijl-Krakau method. Using a probit program, the authors calculated the threshold and slope (estimated by the interquartile range) of each curve.


RESULTS
The authors obtained 124 curves from the normal subjects, 71 from the patients with suspected glaucoma, and 183 from the patients with glaucoma. In all three groups, the slope of the frequency-of-seeing curve was correlated highly with the threshold or threshold deviation, although the correlation was significantly higher in the normal subjects compared with the patients with suspected glaucoma and patients with glaucoma, even after controlling for the range of the threshold and threshold deviation. For this reason, the authors found considerably different frequency-of-seeing curves, between subject groups and also within the group of patients with glaucoma, in locations with the same threshold.


CONCLUSIONS
There may be fundamental differences in areas of normal subjects and patients with glaucoma with similar thresholds or threshold deviations. These differences also may exist within patients with glaucoma.