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

I. A. T. Livingstone, C. M. Tarbert, M. E. Giardini, A. Bastawrous, D. Middleton, R. Hamilton

Research output: Contribution to journalArticle

4 Citations (Scopus)

Abstract

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.
LanguageEnglish
Article number0150676
Number of pages12
JournalPLoS One
Volume11
Issue number3
DOIs
Publication statusPublished - 22 Mar 2016

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compliance
Tablets
Visual Acuity
Luminance
Light
Equipment and Supplies
diabetic retinopathy
Diabetic Retinopathy
Handheld Computers
testing
Malus
Compliance
Appointments and Schedules
apples
Technology
Electric lamps

Keywords

  • ETDRS chart
  • visual acuity
  • contrast
  • luminance uniformity
  • tablet computer
  • iPad

Cite this

Livingstone, I. A. T. ; Tarbert, C. M. ; Giardini, M. E. ; Bastawrous, A. ; Middleton, D. ; Hamilton, R. / Photometric compliance of tablet screens and retro-illuminated acuity charts as visual acuity measurement devices. In: PLoS One. 2016 ; Vol. 11, No. 3.
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abstract = "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.",
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Photometric compliance of tablet screens and retro-illuminated acuity charts as visual acuity measurement devices. / Livingstone, I. A. T.; Tarbert, C. M.; Giardini, M. E.; Bastawrous, A.; Middleton, D.; Hamilton, R.

In: PLoS One, Vol. 11, No. 3, 0150676, 22.03.2016.

Research output: Contribution to journalArticle

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