Fixation loss not reliable gauge of visual-field tests

By Lorraine L. Janeczko

NEW YORK (Reuters Health) - Fixation loss may not be a good way to gauge the reliability of visual-field tests in patients with glaucoma, according to a new study.

"We expect that practitioners caring for glaucoma patients will use these findings to judge when a visual-field test is more likely to show an unexpectedly high sensitivity, which might cover possible disease worsening, or to show an unexpectedly low sensitivity, which might falsely indicate disease worsening," said Dr. Pradeep Y. Ramulu of the Johns Hopkins Wilmer Eye Institute in Baltimore, Maryland.

"These results could help avoid missing disease worsening or minimize any unnecessary treatment," he told Reuters Health by email.

The research was presented May 2 at ARVO 2018, the annual meeting of the Association for Research in Vision and Ophthalmology, in Honolulu, Hawaii.

Dr. Ramulu and his colleagues reviewed more than 10,000 visual fields from 1,538 eyes of 909 patients who had manifest or suspected glaucoma and had taken five or more visual field tests. They used the test data to predict mean deviation (MD), using linear mixed-effects regression models.

The researchers calculated the differences between observed and predicted MD (delta MD) as a reliability measure; and they used logistic regression to identify factors that predicted unexpectedly high (delta MD>1dB, better field) or low (delta MD

About 20% of the visual fields had abnormally high or low sensitivity in the absence of any false positives, false negatives, or fixation losses.

Visual fields with moderate (-6>=MD>-12) or severe (MD-6) (odds ratio>9.0; P

Longer test duration predicted greater likelihood of unexpectedly low sensitivity at all levels of visual field damage (OR, 1.37, 1.75, and 2.56 per 1-minute increase in test duration for mild, moderate, and severe damage, respectively; P

Unexpectedly low sensitivity was also significantly more common in tests conducted between 2 PM and 5 PM than in tests between 7 AM and 10 AM.

False negatives predicted that unexpectedly low sensitivity in eyes with mild or moderate visual field damage would be more likely (OR, 1.72 and 1.35 dB, respectively, per 10% increase in false negatives; P

False positives predicted increased chances of unexpectedly high sensitivity (OR, 1.85, 2.69, and 2.44 per 10% rise in false positive responses for mild, moderate, and severe damage; P

Fixation losses, however, were not significantly linked with increased chances of unexpectedly high or low sensitivity at any level of visual field damage.

"While our results help clinicians decide whether or not a field is trustworthy or not, it is always important to consider the whole picture when making decisions, including important factors such as whether the intraocular pressure is under control and whether there is any symptomatic worsening," Dr. Ramulu said.

SOURCE: https://bit.ly/2JaKXTs

ARVO 2018.