ONLINE CIRCULAR CONTRAST PERIMETRY (OCCP)

 

Online Circular Contrast Perimetry (OCCP) is a web-based computer application. The method allows patients to undergo routine perimetry from the comfort of their homes via a personal computer or tablet.

The method has several advantages, such as, improved access to perimetry, the option of home perimetry, significant cost saving benefits in perimetric hardware for clinicians, cheaper healthcare delivery for healthcare funders, a more enjoyable user experience for patients, ease of sharing data between clinics for collaborative care, and data integration within electronic medical records.

Studies comparing OCCP to SAP have shown favorable results regarding similar perimetric outcomes, similar diagnostic accuracy, and an improved user experience. A pilot study has demonstrated the benefit of the personal computer-based OCCP test to distinguish glaucoma from normal eyes with sensitivity 92% and specificity 87%

The OCCP test is built on a python-based web application and hosted on Azure (Microsoft, Redmond US), with tailored database integrity and high-security architecture.

A study to assess the effectiveness of OCCP used computers with screen size 24-inches diagonally (white temperature at 6500K, gamma set at 2.2 and resolution of 1920 × 1080 pixels).

The test was performed in a dark room with lighting solely from the computer monitor, minimal background noise, and computers turned on 15 minutes prior to OCCP testing to ensure consistency of screen brightness and adaptation.

OCCP utilizes flickering circular targets to assess visual sensitivity. These targets are similar to those in Pulsar perimetry (Haag-Streit International, Bern, Switzerland) with the same level of contrast in all radial directions, to avoid stimulation of those cells that selectively respond to a given orientation, but differ from Pulsar spots by being smaller in size and of consistent contrast throughout the spatial extent of the target despite a thin rim of contrast reduction at the peripheral target edge.

Targets consist of concentric sinusoidal contrast rings. The bright peaks have the same luminance as the background monitor, while the dark troughs determine the difficulty level of the target. On flicker, these targets alternate with their inverse image (with dark troughs replacing bright peaks, and vice versa).

Targets are present for 360 milliseconds with three counterphase flicker cycles each lasting 60 milliseconds and utilize sinusoidal contrast with spatial frequency 0.5 cycles/degree and temporal counter phase flickering at 9 hertz.

The contrast is ramped up and down at the beginning and end of target presentations respectively.

A continuously spinning golden star (3.5 degrees of visual angle) is used as a fixation target, located at the screen center throughout the test.

The study found mean sensitivity per loci of central 10-degree OCCP similar to traditional perimetry when mapped against SAP including adherence to a physiological hill of vision.

OCCP sensitivity reduces with eccentricity more than SAP, which implies that a magnification correction factor will be useful to provide consistent normal sensitivities at each locus.

On average, the OCCP test duration is 1:20 (minutes: seconds) longer than SAP.

REFERENCES:

Skalicky, S.E., Bigirimana, D. & Busija, L. Online circular contrast perimetry via a web-application: optimising parameters and establishing a normative database. Eye 37, 1184–1190 (2023). https://doi.org/10.1038/s41433-022-02085-4.

Meyerov J, Deng Y, Busija L, Bigirimana D, Skalicky SE. Online Circular Contrast Perimetry: A Comparison to Standard Automated Perimetry. Asia Pac J Ophthalmol (Phila). 2023 Jan-Feb 01;12(1):4-15. doi: 10.1097/APO.0000000000000589. Epub 2023 Jan 2. PMID: 36706329.