The PUPIL Study - Automated, Quantitative Pupil Assessment Using Binocular OCT

Healthy Volunteers, Pupil Anomaly, Relative Afferent Pupil Defect

Optical coherence tomography, Pupillometry, Automated, Binocular

In current, clinical ophthalmology, a range of specialised testing allows comprehensive evaluation of ocular health. These tests have typically evolved over many years to ensure their clinical validity. For example, the assessment of visual acuity has traditionally been measured with Snellen letter charts from a distance of six metres (20 feet), leading to the phrase 20/20 vision. Despite this, the limitations of Snellen testing are well established and more sophisticated testing is now available (e.g., logMAR testing using ETDRS (Early Treatment Diabetic Retinopathy Study) charts). Many other diagnostic tests have undergone similar cycles of refinement, often over extended time periods. Therefore, it should be incumbent on any new device to undergo detailed evaluation of its validity (how its measurements agree with other testing) and its repeatability (the variability when a further measurement is obtained in short time period, by the same operator and under the same conditions). Binocular OCT extends the application of OCT devices beyond that of simple, cross- sectional imaging to a diverse array of diagnostic tests. The binocular design also removes the need for additional personnel to perform testing (i.e., the device can be self-operated in an automated manner), and allows for novel testing to be performed that is not possible with monocular imaging. In particular, binocular OCT devices have the potential to perform automated, quantitative pupillary measurements - an entirely novel application for this imaging modality. This study will assess the validity and repeatability of pupil measurements using binocular OCT.

Binocular OCT has the potential to allow for objective, quantitative measurement of pupillary reflexes, that can be performed in a fast, safe, and automated manner. Importantly, binocular OCT pupillometry can be performed alongside binocular retinal OCT imaging in a single testing session, in an automated manner (imaging of the retina using OCT is the commonest ophthalmic imaging procedure worldwide - in 2011, it is estimated that more than 20 million retinal OCT images were obtained, more than the sum of all other ophthalmic imaging procedures combined). Assessment of pupillary reflexes is an essential component of a comprehensive ocular examination. In patients with visual loss, for example, detection of an RAPD often indicates the presence of serious ophthalmic diseases, such as optic neuropathies or severe retinal disease. As such, RAPD testing is essential as a screening test in the assessment of patients with less serious conditions such as cataract. RAPD testing is commonly performed using the swinging flashlight method (SFM). A positive SFM test suggests the presence of asymmetric damage involving the afferent limb of the pupillary light reflex pathway. The SFM is a qualitative test, and relies upon visualising no pupillary constriction or immediate or delayed pupillary dilation; if either of these responses is observed, an RAPD is believed to be present. The SFM requires a trained examiner and many potential sources of error may confound the results, including anisocoria, off-axis pupil illumination, and unequal retinal bleaching. Pupil abnormalities may be subtle and easily missed using the SFM. Automated pupilometers allow examiners to precisely and objectively quantify the pupillary response to light by measuring parameters such as minimum and maximum pupil diameter, the amplitude of constriction, latency of constriction, velocity of constriction, and duration of maximum constriction. Dedicated pupillometry devices are commercially available and have been shown to be highly sensitive and specific for RAPD detection e.g. RAPDx; Konan Medical USA, Inc., Irvine, CA. These devices are also capable of detecting the presence of more subtle RAPD, typically not found using the SFM, in diseases such as glaucoma. Unfortunately, automated pupilometers such as the Konan RAPDx system are not widely used in clinical practice. This is largely because they are expensive devices, limited to a single purpose. A binocular OCT system that could perform both automated pupillometry and retinal OCT imaging would thus have great clinical utility.

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