The Cardiff Screening Test

INTRODUCTION

This Cardiff Acuity Test is designed specifically for acuity measurement in toddlers aged 1 to 3
years.This Cardiff Acuity Test can also be used for older children or adults with intellectual
impairment.
The Cardiff Screening Test has been produced in response to requests for a low cost tool that can be
used for screening purposes. It is NOT recommended for standard eye examinations when precision in
acuity measurements is required.
THE TARGETS
The principle of the target design is that of the vanishing optotype. The targets are drawn with a white
band bordered by two black bands, each of half the width of the white band, all on a neutral grey
background; thus the average luminance of the target is equal to that of the grey background. If the
target lies beyond the subject’s acuity limit, it merges with the grey background, and simply becomes
invisible. Thus resolution, detection and recognition acuity thresholds are all brought together.
The targets used are pictures, all of the same overall size, but decreasing in width of white and black
bands. The acuity is given by the narrowest white band for which the target is visible.
The principle of the test is that of Preferential Looking – a young child will choose to look towards a
target rather than towards a plain stimulus. In the Cardiff Test, each target is positioned either in the
top half or in the bottom half of the card. If the target is visible, the child will look towards it, and the
examiner, watching the child’s eye movements, can judge the position of the target from those eye
movements. An important feature of the preferential looking technique is that the examiner should not
know in advance the position of the target. For any given target width, if the examiner can reliably
estimate the position correctly, the target is assumed to be visible to the child. If the examiner
incorrectly estimates the target position, or is unable to make a judgement from the child’s responses,
then the target is assumed to be beyond the child’s acuity limit.
The Cardiff Screening Test includes three cards at each acuity level, although only two are usually
presented. This is so that once one card at a particular acuity level has been presented, the position of
the next card to be presented cannot be predicted by either child or examiner.
A working distance of 1 metre is recommended. At this distance eye movement position judgements
are reliable. A closer working distance of 50cms may be used to allow closer interaction with a
younger child; acuities are calibrated for both distances.
ACUITY STEPS
The range of acuity values for the cards in the Screening Test is given in Table 1, which shows acuities
for two testing distances, in both equivalent Snellen acuity and LogMAR.The acuity step size is 0.2
This Cardiff Acuity Test is designed specifically for acuity measurement in toddlers aged 1 to 3
years.This Cardiff Acuity Test can also be used for older children or adults with intellectual
impairment.
The Cardiff Screening Test has been produced in response to requests for a low cost tool that can be
used for screening purposes. It is NOT recommended for standard eye examinations when precision in
acuity measurements is required

LogMAR. This a larger step size than is recommended for acuity testing. If precise measurements are
required, or monitoring over time is called for, then one of sets in the Cardiff Acuity Test range should
be employed.
PROCEDURE
The published norms for the Cardiff Acuity Test are appropriate for the standard test with acuity steps
of 0.1 LogMAR. They are not applicable to the Screening Test.
The organisers of a screening programme are advised to develop a pass/fail criterion appropriate to the
population and purpose of their programme.
For practitioners (such as orthoptists and optometrists) familiar with observing eye movements in
children, only a short practice session with the cards will be required. However, if non-qualified
personnel are used for screening, the organisers of the programme should ensure adequate training is
provided.
Beginning with the widest target (lowest acuity), shuffle the three cards, and present the first card at the
child’s eye level, with the centre of the card at your own eye level (Figure 1). In order to maintain the
child’s attention, talk about the picture, or encourage the child to name or point to the picture.
However, in order to ensure a constant procedure amongst children of different ages and levels of
understanding, we believe it is important to use ONLY the child’s eye movements/position to establish
the acuity limit, and not to use the child’s verbal or pointing responses. (It is also important to present
the card quickly and note the child’s immediate response – often a child will glance at the target and
then look away, and if you are slow in bringing the card up to your eye level the child will have seen
the picture and looked away before you note the eye movement!) From the child’s eye
movement/position, estimate the position (top/bottom) of the target. Once you have made your
decision present the second card; you may then check to corroborate your decisions. If two correct
estimates are made, proceed to the next level and repeat along the sequence.
For screening, a criteria for ‘pass’ will be established before testing. Once a child has reached the
‘pass’ level successfully, there is probably no need to proceed further.
If, at a lower level than the ‘pass’ criterion, an incorrect estimate is made (or no estimate is possible),
return to the next LARGER target, and repeat the tests at this and the ‘failed’ level. At this stage in
order to avoid any expectations on the part of the examiner or the child, shuffle the cards between each
presentation. The end-point should be taken as the highest acuity level at which at two out of two
presentations are scored correctly.

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