Ishihara plates on your handheld computer

Awad, Z.,* Natt, R.S.* & Pothier, D.D.�

*Department of Otolaryngology, St Mary’s Hospital NHS Trust, London, UK, and �Department of Otolaryngol-

ogy, Royal United Hospital, Bath, UK

Accepted for publication 4 September 2006

Keypoints

• Testing for colour vision is important in assessing peri-

orbital cellulitis and its complications.

• Electronic Ishihara colour plates are used effectively for

this purpose.

• Portable LCD devices are widely available and most of

us already have one.

• We use hand-held computers to store and present the

plates to the patient as a quick and readily available

method of testing colour vision.

Periorbital cellulitis and intra-orbital abscesses are

ophthalmological emergencies, with the potential for sig-

nificant morbidity when vision is affected. Testing for

early signs of orbital involvement should be done on

regular basis to administer early effective treatment.1 One

of the first defects of vision to become apparent is the

loss of colour vision, particularly red–green discrimin-

ation. The most commonly used method of testing of

colour vision is the use of pseudoisochromatic Ishihara

plates. It is often very difficult to find an intact set of

plates in an emergency situation, particularly on a ward

where vision is not commonly assessed.

A total of 100 on-call Junior ENT doctors were tele-

phoned and questioned about the availability of Ishihara

plates in the work environment, in what format and how

much time and effort is spent finding them. All of them

had participated in the management of periorbital cellu-

litis and 93% had used Ishihara charts in the assessment

of colour vision for this purpose. Ninety-four per cent

had some problem locating and getting access to these

charts. Participants who had no access to an electronic

version estimated that they initially spent an average of

40 min looking for one.

Unfortunately, only eight of the participants used the

charts from a portable device, despite the fact that 96%

had access to a portable LCD device, at work, whether a

laptop (76%) or a PDA (78%) or both (51%).

We describe a more practical alternative to printed

Ishihara plates to be used for this purpose; the use of

Ishihara plates on a handheld computer. Computer pro-

jected Ishihara charts have already been validated2 and

are widely used in screening children for colour blindness

as well as for testing colour vision for occupational health

purposes.3 To use Ishihara plates on a handheld device,

they must first be standardised and validated.

Methods

We downloaded pseudoisochromatic Ishihara plates from

the Internet. They are freely available from many univer-

sity based as well as commercial sites. The images were

standardised in terms of size, to 5.3 cm diameter, as well

as having their hue and saturation standardised using

Adobe Photoshop Elements� software, Adobe systems

UK, Uxbridge, UK. These plates can be downloaded from

http://www.entresearch.org.uk/ishihara.

We then validated the electronic plates by testing them

using a web-based testing programme (Vischeck�) that is

available freely to convert any image into what would be

perceived by the colour-blind individual. Vischeck� is

based on SCIELAB from the Wandell Lab at Stanford

University, Stanford, CA, USA.4

The images were then transferred to a handheld per-

sonal computer and the images were again standardised

for resolution and colour intensity. We tested five par-

ticipants with a known defect of the red–green colour

perception. All results were consistent with their condi-

tion.

There are different versions of the Ishihara test, used to

differentiate between minor subtypes of colour blindness.

There is also a version available with symbols for testing

children. For this process, we used a simplified seven

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Correspondence: Z. Awad, MRCS, DOHNS, SHO in Otolaryngology,

St Mary’s Hospital NHS Trust, Praed Street, London W2 1NY, UK.

Tel.: 07984833582; Fax: 02078861847; e-mail: mail@zaidawad.com

58 Correspondence

� 2007 The Authors

Journal compilation � 2007 Blackwell Publishing Limited, Clinical Otolaryngology, 32, 42–59

plate test as, when used for testing, these plates are con-

sidered sufficient to detect deterioration in colour vision

in a previously healthy individual, i.e. acquired visual

defects.5

Conclusion

We have demonstrated that using simple, free technology

that is available to most clinicians can save time, and

effort, particularly seeing patients at locations with which

the clinician is not familiar. Hand held computers, are

becoming more popular amongst surgeons, the majority

of which have large, well illuminated screens that can dis-

play high quality images. We recommend handheld elec-

tronic Ishihara colour plates as a reliable and quick

method to test patients colour vision; we have found

them to be an effective tool that is instantly available and

easy to operate.

Conflict of Interest

None declared.

References

1 Howe L. & Jones N.S. (2004) Guidelines for the management of

periorbital cellulitis/abscess. Clin. Otolaryngol. Allied Sci. 29, 725–

728

2 Ing E.B., Parker J.A. & Emerton L.A. (1994) Computerized colour

vision testing. Can. J. Ophthalmol. 29, 125–128

3 Thomson W.D. & Evans B. (1999) A new approach to vision

screening in schools. Ophthalmic Physiol. Opt. 19, 196–209

4 Vischeck (2002) Ophthalmic Physiol Opt. URL http://www.vis-

check.com/vischeck/ [accessed on 21 September 2006]

5 de Alwis D.V. & Kon C.H. (1992) A new way to use the Ishihara

test. J. Neurol. 239, 451–454

Correspondence 59

� 2007 The Authors

Journal compilation � 2007 Blackwell Publishing Limited, Clinical Otolaryngology, 32, 42–59