Photometric compliance of tablet screens and retro-illuminated acuity charts as visual acuity measurement devices

Mobile technology is increasingly used to measure visual acuity. Standards for chart-based acuity tests specify photometric requirements for luminance, optotype contrast and luminance uniformity. Manufacturers provide some photometric data but little is known about tablet performance for visual acuity testing. This study photometrically characterised seven tablet computers (iPad, Apple inc.) and three ETDRS (Early Treatment Diabetic Retinopathy Study) visual acuity charts with room lights on and off, and compared findings with visual acuity measurement standards. Tablet screen luminance and contrast were measured using nine points across a black and white checkerboard test screen at five arbitrary brightness levels. ETDRS optotypes and adjacent white background luminance and contrast were measured. All seven tablets (room lights off) exceeded the most stringent requirement for mean luminance (≥ 120 cd/m2) providing the nominal brightness setting was above 50%. All exceeded contrast requirement (Weber ≥ 90%) regardless of brightness setting, and five were marginally below the required luminance uniformity threshold (Lmin/Lmax ≥ 80%). Re-assessing three tablets with room lights on made little difference to mean luminance or contrast, and improved luminance uniformity to exceed the threshold. The three EDTRS charts (room lights off) had adequate mean luminance (≥ 120 cd/m2) and Weber contrast (≥ 90%), but all three charts failed to meet the luminance uniformity standard (Lmin/Lmax ≥ 80%). Two charts were operating beyond manufacturer’s recommended lamp replacement schedule. With room lights on, chart mean luminance and Weber contrast increased, but two charts still had inadequate luminance uniformity. Tablet computers showed less inter-device variability, higher contrast, and better luminance uniformity than charts in both lights-on and lights-off environments, providing brightness setting was >50%. Overall, iPad tablets matched or marginally out-performed ETDRS charts in terms of photometric compliance with high contrast acuity standards

Photometric compliance of standard and digital infant acuity tests

Amblyopia or “lazy eye” affects approximately 2–5% of the general population in the UK[1]. Treatment must be started as early as possible as it is less effective after age 8[2]. The current gold standards for infant acuity testing are based on printed cardboard targets (‘standard tests’) and have been in place for almost 35 years[3]. In spite of this, no national nor international standard criteria are in place to quality assure them. Electronic platforms show promise to replace card-based tests[4]. However, the fast-changing nature and photometric differences across manufacturers of electronic devices makes them potentially inaccurate when used for visual testing[5]. This work studied the photometric compliance of three standard tests (Teller cards, Keeler cards, Lea Paddles) and four electronic displays (phone, tablet, laptop and 4k monitor)

3D reconstruction of the fundus of a phantom eye through stereo imaging of slit lamp images

In the detection of glaucoma, the second leading cause of blindness worldwide, the alteration of the optic disc's morphology is a key clinical indicator. The current gold standard test, stereo funduscopy using stereo fundus cameras, is subjective. Quantitative devices exist but are prohibitively expensive. Work carried out elsewhere has demonstrated quantitative results from stereo matching fundus camera images. Building on this idea, the slit lamp microscope (a mainstay of eye diagnostics, present in practically all ophthalmology and optometry practices) has the potential to be used as a quantitative device. This study explored the feasibility of uncalibrated 3D reconstructions of retinal structures of a phantom eye's fundus using a slit lamp

New technologies in paediatric acuity assessment

The present research has evaluated the utility of the computer tablet as a means to test vision in an infant population. The following points summarise the main findings: Regards the physical properties of mobile tablet computer with reference to National and International Standards for Chart Design: Photometric standards of luminance, contrast, and luminance uniformity are met more effectively by the range of iPads under test than by dedicated ETDRS (Early Treatment Diabetic Retinopathy Study) charts in active clinical use in a tertiary referral unit. The study met its aim of documenting the suitability of this mobile technology regards high contrast acuity standards, providing a practical guide to health care professionals working within eye care. These standards were then, where possible, extended to card-based infant vision tests. There are intrinsic advantages to digital platforms regards achieving a mean average luminance “grey” background relative to the black and white values of composite foreground gratings. There is marked heterogeneity across traditional card-based platforms regards luminance and contrast measurements relating to black, white and grey components. These observations informed the design of a prototype build of a computer-tablet based infant acuity test, peekaboo vision (PVb1). This build was evaluated in a blurred adult cohort. PVb1 performed well across a range of artificially degraded acuities, with observed potential benefits regards test-retest repeatability. PVb1 was then evaluated in an infant population in rural Africa in a pilot study (Study 1). A subsequent formal build (PVi) was evaluated in a UK setting with a similar methodology (Study 2), comparing with Keeler Acuity Cards for Infants (KACI) as the reference standard. Across Studies 1 and 2, the mean difference between reference standard and digital version was modest (-0.03 to 0.01), with notable differences in upper and lower limits of agreement in favour of the digital platform (exhibiting narrower LoA). Peekaboo Vision evidenced improved repeatability than KACI: coefficients of repeatability were 0.27 for Peekaboo Vision versus 0.37 for Keeler cards in study 1, and 0.32 for Peekaboo Vision versus 0.42 for Keeler cards in study 2. The mean time-to-test was over 1 minute shorter (by 26%) for Peekaboo Vision than for Keeler cards (p= 0.0021)