Preferential Looking in the Mentally Handicapped

Eye (1989) 833-839 3, Preferential Looking in the Mentally Handicapped *A. CHANDNA, tc. KARKI, tJ. DAVIS, *R. M. L. DORAN Bristol Summary We have assessed the feasibility of Preferential Looking (PL), using Teller Acuity Cards, for the estimation of binocular and monocular visual acuities in a group of mentally handicapped adults. Our results show the comparison between grating and recognition acuities, inter-observer variation, success rate, time taken and the sensi tivity of this method in identifying monocular visual deficit in this group of subjects. The reasons for success or failure with PL methods in relation to criteria for mental handicap are discussed. We are all familiar with the problems associ the target and acuity is determined as the ated with the assessment of visual acuity and finest spatial frequency which repeatedly ocular status in the mentally handicapped. elicits a positive response. Similar difficulties of variable behaviour and This study was designed to assess the appli inability to give verbal responses are encoun cability of Preferential Looking in a group of tered when dealing with preverbal children adults with varying degrees of mental hand (children below the age of three years). Over icap and behavioural disorders. We investi the past decade Preferential Looking (PL) has gated the comparison between grating (PL) been investigated in vision research labora and recognition acuity (Snellen), the success tories as a means to determine the visual rate in obtaining reliable estimates of bin acuity of preverbal children,I.4 and is at pres ocular and monocular acuity in one visit and ent undergoing clinical evaluation.5.7 the time taken for each test. Interobserver Preferential Looking, a behavioural tech variation and the ability to identify monocular nique, is based on the principle that a subject visual deficit was also assessed. (usually a young child) when presented with a patterned target, such as a high contrast grati ng in a uniform featureless environment, will Materials and Methods Teller Acuity Cardst developed by Dr. D. prefer to look at the target as long as it is Y. within its visual resolution capabilities. The Teller at the University of Washington, method involves the sequential presentation U.S.A. were used. These cards have high con of gratings in an increasing order of spatial trast black and white gratings printed in a frequency until the subject appears not to see square patch on a plain grey background of • University Department of Ophthalmology, Bristol Eye Hospital, Lower Maudlin Street, Bristol; and tPurdown Hospit.al, Purdown, Bristol. This work was supported by a grant from the South Western Regional Health Authority and by the National Eye Research Centre, Bristol. Teller acuity Cards obtainable from Vistech Consultants Inc; 1372 North Fairfield Road, Dayton, OHIO. :I: 45432, USA. Correspondence to: A. Chandna, D.O. F.R.C.S. Ed. Research Associate, Department of Ophthalmology, Bristol Eye Hospital, Lower Maudlin Street, Bristol BS1 2LX. A. CHANDNA ET AL 834 equal average luminance. A standard set of 16 presented again in order to observe a shift of cards spans a frequency range from 0.32 to attention by the subject to the other side. If 38.0 cycles/cm in half octave steps. * The cards obtained, the grating one octave higher on the were displayed through an opening in a staircase was selected. If incorrect on either of specially designed portable screen (the Bristol these presentations the staircase descended. University Screen) (Fig. 1). Luminance was Long Staircase (4 up; 2 down): The obser maintained above 1 log cd/m2• 8 As far as poss ver remained masked to the grating location ible the test distance was maintained between throughout the test and a scorer conducted 57 cm and 75 cm. The distance of the subject the test and recorded the results. Each trial from the screen was measured before and consisted of five presentations. Four out- of after the test. This was then averaged for each fivecorrect responses led to a step up the scale subject, 66 cm being the most common by one octave. Two incorrect responses distance. resulted in a step down the scale. A modified staircase method of presen The response was either, observed through tation was used to control the test.9 The cards the central peephole of the card or the subject were presented sequentially in an ascending was encouraged to point at the gratings (Fig. or descending order of spatial frequency in a 2). Some mentally handicapped subjects series of trials, as described in detail showed signs of anxiety when the observer previously. 7 disappeared behind the screen. With these Two different staircases were used. In both, individuals the tt\st was conducted with the the test was initiated at the lowest spatial fre observer remaining in full view but masked to quency i.e. 0.32 cy/cm. Acuity threshold was the location of the grating whenever required determined as the highest spatial frequency at by the staircase. which the subject's correct responses were significantly above chance and at or below chance at the next higher spatial frequency. Subjects Between presentations the observer attracted All subjects were residents at Purdown Hospi the subject's attention to the centre of the tal in Bristol. Due to historical reasons there is opening of the screen. a male preponderance in the hospital and this Short Staircase (2 up; 1 down): The obser is reflected in our subject groups. ver was masked to the grating position for the Case selection was random, without prior first presentation of each trial only. Having knowledge of the degree of mental handicap, judged its location, the observer confirmed associated systemic abnormalities, ocular this by looking at the face of the card. If cor history, present ocular status or visual acuity. rect the card was rotated by 180 degrees and Monocular and binocular PL tests were Fig. 2a. Subjects response observed through the Fig. Portable desktop screen for presenting Teller central peephole in the acuity cards by the observer. An 1. Acuity Cards. independent scorer provides a feedback. * An octave is a doubling or halving of spatial frequency. PREFERENTIAL LOOKING IN THE MENTALLY HANDICAPPED 835 discharged. PL acuity tests with the long stair case were repeated either by Observer 2 (CK) or Observer 3 (JD) after being trained in the technique by Observer 1 (AC). The observers were masked from each other's results. Group III: A further 15 subjects (nine males, six females; age range 29-82 years, mean age 54 years) were selected randomly, with mental handicaps similar in range to the 23 successful subjects in the previous group. Monocular PL acuity tests were carried out to assess the feasibility of monocular tests and Fig. 2b. Subject being encouraged to point at the the sensitivity of PL in identifying ocular grating. defect. Each subject had an ocular examination performed by an ophthalmologist (AC) with after the PL test which included ocular history previous experience of PL methods but little as gathered from case notes, cover test, ocular experience of mentally handicapped patients. movements, pupillary reflexes, slit lamp For interobserver variation PL tests were examination of the anterior segment carried out by a psychiatrist (CK) and a staff wherever possible, or failing which a penlight nurse (JD) with considerable experience of examination. The optic disc and macular area mentally handicapped patients but no pre were examined through an undilated pupil. vious experience of PL methods. Visual acuity was estimated by conven Group I: 15 subjects. (14 males, one tional methods (e.g. Catford Drum) by an female, age range 29-83 years, mean age of orthoptist unfamiliar with the PL acuity 53.9 years) were selected from a group of res i results. dents in whom Snellen visual acuities had been recorded previously. Five subjects Results underwent binocular testing, five had bin ocular and monocular tests and five had only Comparison Between Grating (PL) and monocular PL acuity tests using the short Recognition Acuity-(Snellen Acuity; Group staircase. Snellen visual acuities were I Subjects) recoraed after the PL test. Figure 3 shows the correlation between the Group II: 40 subjects (33 males, seven monocular and binocular acuity estimates, females; age range 24-81 years, mean age obtained by PL methods plotted against Snel 49.7 years) were selected to achieve equal len acuities. The line corresponds to the numbers, (ten in each subgroup), with vary points at which recognition and grating acu ing degrees of mental handicap. Binocular ities are in perfect agreement. (Corr. RE: acuity estimates were performed by Observer 0.93. LE: 0.74. Binocular 0.48). Ninety-five 1 (AC) using the long staircase. Twenty-three per cent of the monocular and 100% of bin subjects were successfully tested in one visit. ocular acuity measures of grating acuity were Seventeen subjects failed to give a reliable within 0.5 octaves of recognition acuity val result on the first visit. ues. There was no evidence for over (5 = +0.5) or under (4 = -0.5 1 = -1.0) These 17 subjects were retested on a dif & ferent occasion by Observer 1 using the short estimation of acuity by PL for monocular staircase. A third PL acuity test was per results but some evidence of a trend towards formed by" a different observer-a 'key under-estimation of acuity by PL for bin worker'. A key worker is a person who is ocular results (2 = 0; 8 = -0.5 octaves). actively involved in the daily care of the Another method of examining the extent of subject. agreement between the values obtained by Twenty-two out of the 23 successfully tested the two methods,IO is seen in Figure 4, where subjects were recalled.

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