Abstract

Background: Ishihara Color vision test are becoming increasingly available on online platforms to the ordinary internet user. Limited research has been conducted to establish the validity of these tests for use as screening tools for colour deficiency.

Aim: To compare the validity of an online version of the Ishihara colour vision test (OV-PSI) with the traditional Ishihara handbook (PSI).

Setting: This study was conducted at the University of KwaZulu-Natal’s optometry clinic in Durban, South Africa, in 2014.

Methodology: One hundred and twenty participants (N = 120), between the ages of 18 and 25 years who visited the University of KwaZulu-Natal’s eye clinic between June and August 2014, were recruited to the study. Colour vision testing was administered using the Ishihara 38 plate test and the ColBlindor Ishihara 38 plate colour vision test available online. Both tests were administered on normal sighted university student participants under standardised conditions, and responses were captured on Ishihara recording sheets. Data were analysed using the Statistical Package of Social Science (SPSS) version 21.

Results: Of the 120 participants, 47.5% were men and 52.5% were women with a mean age of 20.64 ± 2.09 years. Results demonstrated that 5.3% of men (N = 3) were colour deficient, resulting in a prevalence of colour deficiency for the sampled population of 2.5%. Results of the two testing methods were compared, revealing sensitivities and specificities for both tests of 100%. However, while the online test correctly discriminated colour deficient participants from colour normal participants, it was unable to correctly identify the severity or type of deficiency.

Conclusion: The online version of the Ishihara test used in this study proved a valid screening tool for colour vision deficiency. It presents the opportunity for self-screening via convenient online platforms. However, if colour deficiency is detected using this online tool, it is recommended that further clinical investigation be undertaken for a more accurate diagnosis of the extent of colour vision deficiency.

Introduction

• Colour vision testing is the assessment of chromatic discrimination ability and the diagnosis of any perceptual deficiency.It forms part of the functional assessment of the visual system conducted by optometrists during routine eye examinations.
• Technological advances have resulted in digital versions of commonly used colour vision tests, such as the Ishihara test for colour vision, now becoming accessible to the general public via online platforms.
• Colour perception is made possible by cone photoreceptor cells found in the retina.
•  There are three types of cone photoreceptors, each with a different spectral sensitivity and containing a different photo pigment.
• These correspond to the three primary colours, namely, red ([long-wavelength] 558 nm maximum absorption), green ([medium-wavelength] 531 nm maximum absorption) and blue ([short-wavelength] 419 nm maximum absorption), resulting in the term trichromacy.
•  Additive mixtures of these colours then result in all spectral hues. Colour vision is, therefore, derived from the interactions of numerous wavelengths of light energy, the absorption of light by photosensitive pigments in the cone cells of the retina and their subsequent neural interpretation within the visual system.
• Not all people possess trichromacy, however, with some being partially colour deficient, confusing colours that trichromats discern easily, or completely ‘colour blind’ (monochromatic), perceiving no colour at all.
• Certain pathological conditions such as cataract and glaucoma may present with acquired colour vision deficiencies,warranting further examination and routine monitoring.
• Red–green colour deficiency is the most common form of colour deficiency and is a generic term for protanopia (red-deficiency), protanomaly (red-weakness), deuteranopia (green-deficiency) and deuteranomaly (green-weakness). 
• More than 99% of all affected people have red–green colour deficiency, with a greater prevalence in men. Colour deficiency may be caused by ocular disease, trauma or medication, as well as normal physiological processes such as ageing.
• People who are colour deficient may experience challenges with activities of daily living which require colour discrimination.
• Furthermore, specific occupational classes such as pilots and electricians require accurate colour perception to be able to safely perform their duties.
• The Ishihara test is commonly used to diagnose colour deficiency.
• The test consists of pseudo-isochromatic plates and has been found to be a reliable screening method for colour deficiency.
• Pseudo-isochromatic plates consist of a figure or pattern composed of coloured dots of varying sizes embedded in a background of differently coloured dots.
• Colour differences among the circles demarcate the foreground design (digits, simple geometric forms or curved lines) so that for a normal trichromat, the design stands out from its background.
•  When administering the test, observers are required to identify the pattern or figure embedded in the plate.
• Several online versions of the Ishihara colour vision test are now available, suggesting widespread implications for self-screening by the general public.
• With technology now integrated into daily life, a reliable online colour vision test may be a convenient and cost-effective alternative to screening for colour vision defects.
• Birch determined the efficiency of the Ishihara test to identify red–green colour deficiencies using 401 participants.
• Combined sensitivity of the transformation and vanishing plates of the 38 plate Edition of the Ishihara confirmed that it is an efficient screening method for protan and deutan colour deficiency.
• Several studies have compared the Ishihara Pseudo-isochromatic plate test to modified electronic versions. Gündogan et al.
• compared the efficiency of projected colour slides in detecting colour deficiency, compared with the classic method of the Ishihara Pseudo-isochromatic plates.
• The authors concluded that using projected slides was an effective and timesaving method for detecting colour deficiency. Ganley et al.
• conducted a study in which a similar method of projected colour slides were used as a method for mass screening of red–green colour deficient individuals.
• The sensitivity of the screening system was 100%, with authors suggesting that projected colour slides are potentially useful as a screening method to detect individuals with red–green colour deficiencies.
• Hoffmann and Menozzi compared the traditional Ishihara test to a computer-based screening system using 10 colour normal and 10 colour deficient subjects.
• Results indicated that despite the differences between the spectral emission of the monitor and the reflected daylight with conventional Ishihara plates, the computer-based method correctly discriminated subjects with colour deficiencies from those without such deficiencies.
• However, Rodriguez-Carmona et al. noted that approximately 20% of normal trichromats fail the test, suggesting limitations in its application.
• The aim of this study was, therefore, to compare the validity of an online version of the Ishihara colour vision test to the traditional Ishihara 38 plate handbook.
• In the context of this study, validity was considered to be the extent to which the online test was able to distinguish colour normal patients from those with colour deficiency.
• To date, no research has been conducted to test the validity of this online Ishihara test as an alternative screening tool to the traditional handbook typically administered in-office by professionals.
• This study was, therefore, conducted to explore the potential for use of online colour vision tests as a self-screening tool for colour vision deficiency by non-optometric persons.

Methods

• Ethical clearance was obtained from the Biomedical Research and Ethics Committee at the University of KwaZulu-Natal (UKZN).
• A comparative study was conducted using convenient, non-probability sampling of student participants from the UKZN Westville campus in Durban, South Africa.
• One hundred and twenty participants (N = 120), between the ages of 18 and 25 years who visited the eye clinic, were recruited to the study following informed consent.
• Visual acuities at distance and near were assessed, and ophthalmoscopy was performed to rule out the presence of ocular pathology.
• Participants who presented with ocular pathology or visual acuities worse than 6/6 (corrected) were excluded from participating in the study.
• Participants who required spectacle or contact lens correction wore these during administration of the tests.
• The testing was administered under standardised conditions. Room illumination was measured to be 410 lux with the computer monitor for the online test set against recommended display settings.
• A standardised test distance of 75 cm was maintained for both the online and handbook testing methods in keeping with test distances for other pseudo-isochromatic plate designs.
• The two tests were conducted monocularly in succession, beginning with the right eye for uniformity and then repeated on the left eye after an interval of 30 min.