Results

SUBJECTS

A total of 201 consecutive patients were enrolled into the study and 39 (with a score of less than 25 on the MMSE) were subsequently excluded. The remaining 162 had a mean age of 78 years (SD 6.16) with 69% female (113 patients). The majority of patients (101 patients, 63%) were awaiting first eye surgery.

The median visual acuity for the patients’ better eye was 6/9, for the worse eye was 6/18, and for the eye to be operated on was 6/18: 133 patients (82%) had the eye with the worse visual acuity operated on.

There was no statistically significant difference (in terms of age, sex, visual acuity, and number of patients having first eye surgery) between the scale development group and the scale evaluation group.

Table 1 provides information regarding the range of visual acuity of all patients in the study.

CSS SCORES

The CSS was interviewer administered and all patients were able to respond and complete the scale within 5 minutes. The mean instrument score was 29% (SD 20.7), with scores ranging from 0 to 84. The median score was 26% with multiple modes at 5%, 20%, and 25%. The Kolmogorov–Smirnov test of normality was 0.96, p=0.004 indicating a non-normal distribution. One patient scored zero (male, aged 77 years, second eye surgery, visual acuity: 6/6 in aphakic eye and 6/9 in eye to be operated on).

RELIABILITY

As previously described, the test-retest correlation coefficient for the total instrument score was r = 0.91 (p<0.0001); while the coefficient for individual items ranged fromr = 0.48 to r = 0.91, mean correlation was 0.65 (n = 50). For the 118 patients, internal consistency of the CSS was measured by the Cronbach’s alpha coefficient (alpha = 0.88).

In all, 65% of patients could complete all of the items of the CSS compared with 1.2 % for the VF-14.

FACTOR ANALYSIS

Principal component factor analysis was undertaken to determine the interrelations of the different items. The appropriateness of the factor model was assessed by the Kaiser–Meyer–Olkin measure of sampling adequacy, which was 0.70 and by Bartlett’s test of sphericity, which was 457.9. Both of these are results are satisfactory and demonstrate the legitimacy of the factor analytic procedure. Factors identified may be seen as distinct elements consisting of related symptoms that tend to occur together. For instance, patients who perceived problems negotiating pavements also tended to experience problems with going downstairs. Three factors were identified (Table2). Three items failed to load against any of the factors—namely, “recognising coins”, “trouble with bright sunlight”, and “blurred vision”.

Correlations—visual acuity, visual function, health, and psychological status

The results (total score) for the CSS (n = 118) were compared with results obtained from Snellen visual acuity in the better eyer = 0.52, worse eyer = 0.33, operated eye r= 0.25. For the remaining test battery, correlations were obtained with the VF-14 (visual function) r= −0.83, the NEADL (activities of daily living)r = 0.52, the GHQ (perceived health status)r = 0.43, and HAD (anxiety and depression)r = 0.46. For the patient’s global assessment of visual symptoms, a correlation of r= 0.64 was obtained.

Discussion

There is increasing awareness of the difficulties and limitations in assessing patients for cataract surgery based on visual acuity data alone. While it is recognised that greatest importance should be placed on the amount the cataract interferes with a patient’s functional ability and quality of life, objective measures need to be developed as an adjunct to visual acuity in preoperative assessment. Although measures of glare and contrast sensitivity have been developed, at present there are no standardised measures available and they are not routinely used in clinical practice.18Scales of visual function have already been produced in the USA, but these are not utilised in clinical practice in the UK. A major limitation of existing scales is that they are not wholly appropriate to a UK population, where both sociodemographic factors and other pre-existing medical problems may influence the applicability of some of the items. In a recent study in which the VF-14 was adapted for use in cataract patients in Canada, Denmark, and Spain, only 19% of the total non-US sample of patients responded to all 14 items in the questionnaire.13 In the present study, only 1.2% of our patients could answer all 14 questions of the VF-14. Much of this difference can be attributed to the fact that many had not previously driven a car and did not participate in hobbies such as tennis, bowls, and golf. Although the VF-14 could have been adapted for use in our population we specifically sought to develop a scale from patients’ perceptions of their own problems. Six of the CSS items are similar to items in the VF-14; however, the remaining nine items (60%) differ in content from the VF-14, but examine similar aspects of visual disability. Using our method of identifying problems with everyday function in cataract patients awaiting surgery we have achieved a scale appropriate to an older UK population. Inevitably some patients will not be able to answer all of the questions in the CSS—for example, those who are housebound for reasons other than visual problems cannot answer questions related to outdoor activities.

We have demonstrated a correlation between the CSS and other measures of functional ability (NEADL), perceived health status (GHQ), and also with patients’ own perceptions of how much their visual problems affect their everyday life. This suggests that the CSS is able to identify those patients with significant disability and handicap secondary to their cataracts. Determinants of the need for cataract surgery should include overall functional ability, general health, and patient perceptions, and it is therefore relevant that we have demonstrated a correlation between measures of these variables and the CSS.

We also found a correlation between the CSS and visual acuity in the better eye (as visual acuity decreases the CSS score increases), but not with visual acuity in the eye to be operated on or in the worse eye. Similar findings were observed in studies of the VF-14 suggesting that the ability of a patient to perform sight dependent activities is determined more by vision in the better eye than the worse affected eye.4

On the basis of the semistructured interviews we found that the items which patients complained of could be grouped into three main categories, confirmed by subsequent factor analysis. These are (1) sight related mobility, (2) recognition and perception, and (3) hand eye coordination. This implies that the CSS measures areas of functional importance to patients.

As the CSS is a scale for patients with visual impairment it is by necessity interviewer administered. The CSS consists of 15 questions, is easy to administer, and takes only a few minutes to complete. The CSS provides information regarding the symptomatic and functional status of the cataract patient, which will not be recognised by the measurement of visual acuity alone. This information could be used to assist healthcare professionals in identifying clinical need for cataract surgery in older people and hence in prioritisation of access to ophthalmology services. The fact that one of our patients had no perceived visual problems and hence scored zero on the CSS suggests a wide variation in current practice. We propose in a longitudinal study of patients undergoing cataract surgery to identify factors that may be of value in predicting outcome from surgery and thereby developing an algorithm for the preoperative assessment of older patients.

Given the demographic changes in the elderly population and the increase in demand for surgery at the extreme of old age we sought to develop a scale specifically for older people. Consequently the CSS may not be applicable to patients under 65 years of age, although in this group the need for surgery may be much more evident. Irrespective of age, where cataract symptoms threaten driving or employment the CSS may not be wholly appropriate. In our study only 4% of patients had difficulty driving due to cataracts. The suitability of the scale to those patients under 65 years would need to be assessed in a further study.

The CSS was developed in a cohort of older people living in the north east of England and therefore further work is needed to confirm its general applicability to the UK population. In addition, it will be necessary to determine whether the CSS is responsive to changes in visual symptoms and functional status following cataract surgery.