Promising system

A self-testing system developed by researchers in the UK provides an effective means of testing low contrast near visual acuity in ophthalmic patients with a high degree of reliability, according to a study presented at the 15th EURETINA Congress in Nice, France.

“Our study showed an excellent level of repeatability with the system, which is of great clinical value as patient management decisions are frequently based upon change in vision. Moreover, the patients were able to collect data with no operator interference so the potential for self-testing has been clearly demonstrated,” said Humza Tahir PhD, adding that future studies of the device will include contrast sensitivity and colour vision testing using the same principles.

The project was initiated by principal investigator Prof Tariq Aslam, Senior Clinical Lecturer at the University of Manchester, UK, as one part in a series of devices being developed to help assess visual function in both children and adults.

The adult visual testing system team was led by Dr Tahir and co-workers at the University of Manchester and the Manchester Royal Eye Hospital, and is known as MAVERIC (Mobile Assessment of Vision by intERactIve Computer), which consists of an Apple iPad 3 with retina display running purpose-built software housed in a bespoke physical booth. The system has a variable viewing distance of 25cm to 50cm, a natural viewing angle, and it protects from reflections and glare.

“There is a real need for such a system as current devices have limited utility when used by patients on their own. Many eye diseases require ongoing assessments and the burden on patients and hospitals could be reduced through home vision monitoring,” said Dr Tahir.

GAMIFICATION

The rationale for using a booth system to encase the table computer is to avoid problems associated with the significant changes in luminance and contrast that occur when the tablet is used at an angle with a light source above, which is a typical scenario when reading, said Dr Tahir.

The MAVERIC system uses a letter acuity test based on “gamification” principles, which Dr Tahir explained is the concept of applying game mechanics and game design techniques to engage and motivate people to achieve their goals. There were 20 available testing sizes used based on a 40cm testing distance and the current iPad screen resolution. The testing range was -0.08 (6/5 Snellen) to 1.2 logMAR (6/100).

To validate the system, 81 patients were recruited from clinics at the Manchester Royal Eye Hospital. Exclusion criteria were the physical possibility of performing a test that required use of a functioning hand and visual acuity of at least 1.22 logMAR (6/100) in one eye.

The study eye was given the best possible distance correction, with a near add of +2.5D in all presbyopic patients to correct for the near vision test with the fellow eye occluded. Masked to the MAVERIC vision result, the examiner then tested near visual acuity using a near Landolt C chart (Precision Vision) according to standard protocols.

Approximately 15-20 minutes after the original MAVERIC test, a second MAVERIC test was initiated. Out of the 81 patients who agreed to the study, 78 (96 per cent) were able to complete the MAVERIC test without assistance, said Dr Tahir. In terms of pathology distribution, 12 patients had no ocular disease, five had macular degeneration, 12 had other macular diseases, 16 had diabetic eye disease, eight had glaucoma, eight cataract, and 17 with miscellaneous pathologies such as retinal vascular diseases, naevi and vitreous detachment.

The results showed very good repeatability of the MAVERIC test as measured in intraclass correlation coefficient (ICC) units, said Dr Tahir. As a basis for comparison, repeatability with experienced optometrists using the gold standard acuity charts in patients with macular degeneration has been shown to be 0.96 for logMAR visual acuity and 0.75 for reading acuity. With the MAVERIC acuity test, the ICC was 0.96 for single measures.

“The study demonstrated the potential viability of the MAVERIC self-testing system as a means to test low contrast near visual acuity in ophthalmic patients with a high degree of reliability, and thus a potential method of both initial assessment and monitoring of near visual acuity in such patients,” concluded Dr Tahir.

Humza Tahir: humza.tahir@manchester.ac.uk