Behavioural Test for Early Glaucoma

Overview

Glaucoma-related blindness often results from delayed diagnosis, largely due to the disease's gradual onset, it's early manifestation predominantly in peripheral vision, and the limited sensitivity of current detection methods for its early stages (Stein et al., 2021). This project aims to determine whether early functional loss can be identified using a novel psychophysical task based on perception of contrast-modulated visual stimuli, which reflects the functionality of the retinal neurons thought to be earliest affected in glaucoma (Ramirez et al., 2022). As a proof of concept, this preliminary study will explore both the feasibility and the diagnostic sensitivity and specificity of this approach. Task performance will be compared between areas of the visual field classified by standard clinical testing as affected or unaffected by glaucoma. Psychophysical testing will take place at the Centre for Innovative Medicine (CIM) using computer-based tasks administered to patients with early-stage glaucoma, as well as healthy controls.

The experiments will evaluate motion perception using our previously developed contrast-modulated (CM) stimulus which seems to reveal functionality of the Y-like retinal ganglion cells (RGCs) most affected in early glaucoma (Ramirez et al., 2022). We will compare performance across glaucomatous vs. preserved regions (as indicated by conventional clinical tests) within the visual field of the affected eye(s) of the glaucoma patient group, and corresponding regions of eyes of the healthy control group. A limited number of patients (10-30) will be referred by Dr. Hady Saheb, a glaucoma specialist at the MUHC, who will provide relevant clinical background, i.e., age, relevant medical history, and recent Standard Automated Perimetry (SAP) and OCT (optical coherence tomography) results. Dr. Saheb will selectively refer individuals with early-stage primary open-angle glaucoma (POAG) ("preperimetric" glaucoma). Participants with normal vision will be recruited from McGill Vision Research group members, former consenting participants, or the local community, primarily through direct contact by the experimenters. Participants will undergo a preliminary interview during their first study visit. This interview will be to obtain information about date of birth, past and present health status, and medical history (relevant to vision and ophthalmic conditions). They will also participate in a preliminary evaluation of their visual function, with standard visual acuity (reading letters on a Snellen acuity chart). Information such as date of birth, past and present general health status will be self-reported by participants while other information related to specific ophthalmic conditions and/or treatments may be completed with the assistance of the glaucoma specialist. For participants who meet the eligibility criteria, human psychophysical methods will be used to measure their performance on behavioural tasks. Psychophysical testing will be conducted in the CIM in L3 of the Montreal General Hospital. Participants will be comfortably seated and view visual stimuli presented on a computer-controlled display screen, while they maintain their gaze on a provided fixation target. During testing, one eye will be covered with a patch, so that stimuli are viewed monocularly. Each trial will consist of a brief stimulus presentation during which the participant provides a response. Trials will be organized into blocks lasting 5-10 minutes. Several such blocks will make up a session (of no more than one hour), with rest periods in between the trial blocks. In these trials, contrast modulation (CM) stimuli will be briefly displayed, and participants will indicate their perception by pressing keyboard keys, moving a mouse, or moving their eyes. For example, participants will indicate the perceived direction of motion, or the presence of a visual stimulus versus a blank screen. In some experiments the participant's eye movements will be monitored by a camera and recorded while they view the visual images (only the pattern of the eye movements is recorded, images of the participant's face are not recorded). The eye movement monitoring will provide on-line assessment of whether the participant's gaze is directed to the fixation target - or in some cases, as a behavioural response to the visual stimuli. Correct responses on the behavioural task may be indicated to the participant on each trial. Participants are encouraged to request a break or a rest at any time they desire during a session. Depending on the participant's willingness and comfortability, they may be invited to participate in an additional session as part of the same visit. The computer will collect and store the relevant data (stimulus conditions, button presses, eye movements, mouse movements) for all the trial blocks, for subsequent data analysis. A series of familiarization trials will be provided, for each participant to verify their understanding and become comfortable with the behavioural task, using stimulus parameters designed to make the task relatively easy, at least for their unaffected eye, or for unaffected parts of the visual field of the glaucomtous eye. Participants who are able to perform the behavioural task in their unaffected visual fields will then be invited to participate in at least one additional visit, for systematic comparison of their glaucomatous vs unaffected visual field regions. In these initial study visits, we will employ the CM stimulus and task of reporting its motion direction (Ramirez et al., 2022). For participants willing to continue with further study visits, we may undertake more thorough, systematic perimetry with our CM stimulus/task, or exploratory studies with alternative versions of the stimulus and/or task which might be easier for the patients. Study visits will each be no more than 2 hours. Participants will be financially compensated at the rate of $20/hour.