Pupil and Eyelid Biometry using the BPEI Photosensitivity Tester

Abstract

 

Purpose

 

To quantify pupil diameter, eyelid closure, and blink rate as a function of light intensity to quantify photosensitivity.

 

Methods

 

BPEI Photosensitivity Tester was designed to deliver precise quantities of LED illumination to subjects without temperature variation. A camera with a 6.5 pixels/mm resolution operating at 60fps recorded subject response to the light stimuli. Subjects were instructed to indicate discomfort using a button. The video was processed with software developed using LabVIEW to measure pupil diameter, eyelid closure, and blink rate as a function of varying light intensity. The software identifies the location of the pupil using pattern recognition to locate the reflection of an infrared LED on the cornea. The region of interest (ROI) is created around the reflection to enclose the pupil. After thresholds and morphological operations are applied to the ROI, the pupil contour is fit to an ellipse using LabVIEW’s IMAQ Detect Ellipse. If no reflection is detected, the software asks the user if a blink is occurring. Once a blink is correctly identified, the software stores a template and uses pattern matching on each subsequent frame to detect blinks. Additionally, lid closure is determined by applying thresholds and morphological operations to isolate upper and lower eyelids and measuring their separation. The pupil diameter, eyelid closure, and blink rate are plotted with respect to the light stimuli during each frame. Thus far, three healthy subjects were tested under an approved IRB protocol.

 

Results

 

Subjects 1, 2, and 3, with ages 21, 22, and 63, indicated discomfort at a mean of 1520±122 lux. The mean percent pupil constriction of each subject with no discomfort was 22%, 24%, and 26% and with discomfort was 25%, 26%, and 27%. All subjects exhibited a gradual decrease in baseline and illuminated pupil diameter. The eyelid closure of all subjects began decreasing around the first reported discomfort, and their blink rate increased.

 

Conclusions

 

Pupil diameter, eyelid blink and separation can be measured continuously as a function of light intensity.

 

 

Figure 1. A: Top Left: Raw video. Top Right: ROI with pupil contour (purple) and eyelid closure (blue). Middle: Pupil diameter (pixels) and scaled light intensity per frame. Bottom : Lid closure (pixels) and scaled light intensity per frame. B: Descending trend of baseline and illuminated pupil diameter for Subject 3.

 

 

Figure 2.

 

Keywords: 612 neuro-ophthalmology: diagnosis • 522 eye movements • 550 imaging/image analysis: clinical