Is Microperimetry a Suitable Method for the Investigation of Terminal Glaucomatous Patients?

Abstract

Purpose:: Several anatomical and functional methods have been developed to evaluate the pre-perimetric glaucomatous damage. The assessment of terminal glaucomatous patients, however, represents a challenge because the anatomical methods are not sensitive and the fluctuation of the computerized visual field can be high, partly due to poor fixation. Microperimetry measures differential light threshold allowing precise stimuli presentation on the retina by eye-tracking. We previously observed that short and long term fluctuations with this method are lower than with computerized perimetry. Aim of the study was the assessment of short and long term fluctuations of w/w computerized perimetry and microperimetry in patients with terminal glaucoma.

Methods:: Ten terminal POAG patients underwent two 10-2 Humphrey visual field exams apart and two microperimetric exams (MP1, Nidek) testing the same retinal locations with a full-threshold method within the same day. The order of the exams was pseudo-randomized. All the patients were experienced and underwent at least 10 previous visual field examinations. They had a vertical c/d ratio higher than 0.9 and a VF defect higher than -24 dB. To evaluate the long term fluctuation all the patients underwent visual field and microperimetry examination 20 days later. Short and long term fluctuations were calculated using the formula √ (X_j2-X_j1)²/2n.

Results:: The mean duration was significantly higher for microperimetry (t: 6,5; p <0,001). Mean sensitivity determined by the two methods was highly correlated (r2=0.51). Mean sensitivity proved significantly lower when assessed with MP1 (t=7.1;p<0.001). The mean short term and long term fluctuations proved significantly higher for computerized VF examination (t=2.6; p=0,04 and t=2.7; p=0.03).

Conclusions:: Microperimetry presents lower short and long term fluctuations when compared to Humphrey visual field examinations in terminal glaucomatous patients. The methods are well correlated but microperimetry measures a lower differential light threshold, due to different background and stimuli scaling. This can hinder the visual field examination in terminal glaucomatous patients. Furthermore MP1 is time consuming (mean time 28,5 min). Microperimetry is a promising technique of visual field examination in terminal POAG patients but improvements in the test strategies and stimuli might be needed.

Keywords: visual fields