Microperimetry Thresholds for Complete and Forme Fruste Chorioretinal Colobomas and Adjacent Retina

Abstract

Purpose: : To measure differential light thresholds in chorioretinal colobomas and adjacent retina and correlate structure with functional findings.

Methods: : 13 eyes of 8 patients with chorioretinal coloboma were examined using the MP1 microperimeter (NIDEK, Italy) and a program customized to examine the inferonasal retina involved with the coloboma. Examination settings included Goldmann III stimuli and a 4-2 staircase strategy. The stimuli were projected on a white background with background illumination set to 1.27 cd/m2 and a stimulus presentation time of 200 msec. Testing purposely included points within and just adjacent to the coloboma in an attempt to delineate thresholds for each of these retinal areas. Patients with forme fruste, small "nerve doubling", and large colobomas were included in the study.

Results: : Six female and two male patients with choroiretinal coloboma were tested. Average age was 25.75 years (SD= 14.02). Average testing time was 10 minutes 47 seconds per eye (SD= 90.27 seconds). Average number of tested points inside colobomas was 12.08 (SD= 11.74) with an average sensitivity of 7.36 dB (SD= 7.72). Average number of tested points surrounding colobomas was 12.08 (SD= 5.89) with an average sensitivity of 12.73 dB (SD= 5.67). The sensitivities both in and adjacent to the colobomas ranged from 0 to 20 dB. Areas at the edge of even large colobamas often had normal thresholds. When the sensitivity of areas inside the coloboma was compared to that of areas adjacent to it the most significant difference was observed in patients who had large colobomas and the least was in forme fruste patients.

Conclusions: : MP1 microperimetry seems to show that the area surrounding the coloboma has relatively good sensitivity. Application of the same testing process to other retinal lesions may offer us additional glimpses of structure-function relationships.

Keywords: perimetry • imaging methods (CT, FA, ICG, MRI, OCT, RTA, SLO, ultrasound) • development