Reduced perception of Haidinger’s brushes in MacTel type 2 patients

Abstract

Purpose: : Linearly polarised light induces the perception of a blue-yellow propeller-like structure in the centre of vision. This is an entoptic percept called Haidinger’s brushes. The orientation of the blue and yellow arms depends on the direction of the polarised light. It is believed that the perception of this phenomenon is based on the dichroic properties of luteal pigment in Henle’s fibre layer. To test this, we assessed Haidinger’s brushes perception in MacTel type 2 patients, who are known to lack luteal pigment in the macula.

Methods: : Linear polarising filters were placed in front of a back illuminated white diffuser disc. Subjects were asked to look at the disc from 1 m distance and identify the orientation of the yellow arms. To train the subjects and to control for visual acuity we printed a pattern resembling Haidinger’s brushes on non-polarising filters. 5 training filters and 7 polarising filters with different orientations were used to test both eyes independently.

Results: : Of 20 healthy subjects (mean age 59) and 27 MacTel patients (mean aged 68) 7 MacTel patients failed the training session and were excluded because they could not correctly identify the orientation of the yellow arms in the printed control patterns. From the remaining patients the eye with the better visual acuity was chosen. The healthy control group managed to identify 81% of the Haidinger’s brushes orientation correctly. In comparison the MacTel patients only scored 18% correctly. The performance of the two groups was statistically significant different (p < 0.00001). Within the MacTel group there was no correlation between visual acuity and test scores (Spearman’s rank r=-0.17, p=0.52).

Conclusions: : Our results demonstrate that MacTel type 2 patients are not able to perceive Haidinger’s brushes.

Keywords: macular pigment • clinical (human) or epidemiologic studies: systems/equipment/techniques • macula/fovea