Fast, Accurate And Continuous Recording Of The Red-eye Reflex For Objective Calibration Of Eye Position With Daisy

Abstract

 

Purpose:

 

The red reflex of the pupil darkens when the observed person fixates on a light that is coaxial with the observer (Brückner). To objectively calibrate eye position in the Delft Assessment Instrument for Strabismus in Young children (DAISY) fast, accurate and continuous recording of luminance against horizontal eye position is needed.

 

Methods:

 

15 orthotropic subjects (17-26 yrs) with 1.0 vision followed a 0.2mm red LED at 1.01m in linear smooth pursuit at 3.6°/s oscillating from 6° left to 6° right. In the dark, their eyes were illuminated by a 5mm, 870nm, 240mW LED that was coaxially placed with a Proscilica GC2450 camera at 1.10m, using a small aluminum coated mirror. 250-300 images were made in 120s. Luminance was assessed as the average grayscale of the pupil measured in automatically segmented images. Horizontal eye position was assessed as position of the first Purkinje image within the pupil and converted into degrees (±0.3° accuracy). 1 subject was measured 3 times for validation. Finally, OCT’s were made.

 

Results:

 

The relation between horizontal eye position and luminance showed a V-shaped luminance profile (Fig.). The correlation between the luminance profiles of all subjects was r=0.67 for left eyes and r=0.77 for right eyes. The average correlation between the luminance profiles of left and right eyes was r=0.57. The average range of difference in luminance was 2.24±0.63dB for all left and 2.46±0.79dB for all right eyes. In the validation experiment the correlation of luminance between 3 measurements of the left and 3 of the right eye was r=0.91 and r=0.88. Reflectance was highest at maximum excursion at 6° and not where the retina was thickest as found with OCT.

 

Conclusions:

 

The minimum in luminance could be determined in all volunteers fast and accurately. Our findings distract from the idea that the Brückner is caused by the reflection of the internal limiting membrane.  

 

Keywords: strabismus: diagnosis and detection • eye movements: recording techniques • pupil