FIXATION MONITORING DURING RADIATION-THERAPY FOR SUBFOVEAL NEOVASCULARIZATION

Purpose: The aim of the study was to determine movement of the fovea d uring each irradiation session by monitoring movement of the cornea. K nowing the extent of foveal deviation permits minimization of the fiel d size. Methods: (1) Eye movement was monitored in 10 patients during irradiation. A TV camera with an attached fixation light was installed 3 cm away from the cornea of the treated eye. The fixation light was positioned at a 10 degrees angle to the TV camera on the opposite side of the gantry, resulting in a 90 degrees angle between the optical ax is of the eye and the irradiation beam. (2) The relationship between m ovement of the anterior and posterior eye segments of 10 volunteers wa s examined using a scanning laser ophthalmoscope (SLO). Volunteers wer e asked to fix their gaze on positioning lights installed in the SLO. Gaze movements of the anterior and posterior eye segments were recorde d simultaneously. Results: (1) The patients' ability to retain fixatio n differed interindividually. The median corneal deviation during 10 i rradiation sessions was 1 mm mediolaterally and 0.7 mm craniocaudally. (2) Deviation of the fovea could be determined by monitoring deviatio n of the cornea. Measured by SLO, the correlation between movements of the anterior and posterior eye segments was 1:0.9 horizontally and 1: 1.5 vertically. Conclusion: (1) Irradiation field size can be reduced, depending on the patient's fixation stability. (2) If monitoring reve als a foveal deviation beyond the 95% isodose, irradiation can be inte rrupted.