Questionnaires differ in strabismus quality-of-life measures

Two questionnaires used to measure quality of life in people with strabismus overlap but differ in important areas, according to researchers.

Of the two, only the Adult Strabismus Quality of Life Questionnaire (AS-20) includes functional problems such as avoidance of reading, difficulty in concentrating, eye stress, reading problems, inability to enjoy hobbies and the need for frequent breaks when reading, wrote Dr Elizabeth S. van de Graaf of the University Medical Centre Rotterdam in the Netherlands, and colleagues.

They put this down to AS-20 only being designed to evaluate strabismus, whereas the Amblyopia & Strabismus Questionnaire (A&SQ) looks at both strabismus and amblyopia. In addition, there are differences in the populations used in developing these instruments. The researchers outlined their findings in Graefe’s Archive for Clinical and Experimental Ophthalmology.

Amblyopia and strabismus can both affect patients’ quality of life, and clinicians should take this into consideration when prescribing treatments. Therefore, it is important to know how the two most widely used questionnaires for evaluating quality of life in strabismus compare with each other, the researchers wrote.

The AS-20 was originally designed using two samples of adult patients who came for treatment, most of them with diplopia and adult-onset strabismus. The first group of patients responded to 11 open-ended questions to generate 1,301 key phrases. Meeting with the second group, the designers reduced the pool of phrases to 20 items and categorised them into two subscales.

The A&SQ was developed by an expert focus group and validated among adults with childhood strabismus and/or amblyopia, whose complaints were categorised into themes before being defined according to domains of strabismus- and amblyopia-related qualify of life. The designers identified six factors that together explained 70.5% of the total variance among patients.

They excluded functional problems because they did not think asthenopic items were sufficiently specific for strabismus.

Study participants

To compare the two questionnaires, Dr van de Graaf and colleagues invited 173 adults who had been treated by one orthoptist for amblyopia and strabismus as children between 1969 and 1974 at the orthoptic outpatient clinic of the Waterland Hospital in Purmerend, the Netherlands, to complete the AS-20 between 2009 and 2010. The A&SQ had been presented to the patients in 2002.

The researchers received 110 questionnaires. The mean age of the respondents was 44 years. For 93 of them, data about eye examinations and vision testing was available. Fifty-three had strabismus and amblyopia; 17 had anisohypermetropia and amblyopia; 20 had strabismus, anisohypermetropia and amblyopia; and three had deprivation amblyopia. This means that of the 93 persons, 20 did not have strabismus and none had diplopia.

Dr van de Graaf and colleagues identified factors that were common in the questions and assigned them a strength based on the percentage of variance in the responses of all items that was explained by the factor.

They found that six factors together explained 79% of the total variance of the combined AS-20 and A&SQ, which was similar to the findings of previous studies.

They also found that visual acuity of the worse eye was correlated most with all factors of both questionnaires. Strabismus angle did not correlate significantly with the factors.

Most of the patients with strabismus in their cohort had been treated adequately by surgery, and binocular vision correlated with psychosocial and social contact items. Impaired stereopsis might make it difficult for these patients to locate faces and gazes of other people, and limit their ability to initiate eye contact in conversation, Dr van de Graff and colleagues speculated.

One reason the AS-20 includes functional problems that are missing in the A&SQ is that it was developed with patients with adult-onset strabismus and diplopia who were more likely to develop these problems than patients who had these conditions in childhood, Dr van de Graaf and colleagues wrote.

“Whether a quality-of-life instrument for strabismus patients should contain such items, which may not be specific for strabismus, is open for debate,” they wrote.

In their analysis, the A&SQ overrepresents depth perception complaints.

Some experts have argued that two separate questionnaires in patients with strabismus and amblyopia should be used. Dr Van de Graaf and colleagues believe that administering one questionnaire is preferable, however, because the two conditions often occur together.

In one birth cohort study of 4,624 people, 3.4% had amblyopia, of which a third was caused by strabismus alone and a third by strabismus in combination with anisohypermetropia, they pointed out.

Dr van de Graaf and colleagues noted that the gap between the administrations of the A&SQ in 2002 and the AS-20 in 2010 is a limitation of their study. During the interval, some patients may have developed presbyopia, which could have caused their complaints of avoidance of reading, difficulty in concentrating, eye stress, reading problems, inability to enjoy hobbies and the need for frequent breaks when reading, they wrote.

Other visual functions, such as contrast sensitivity, could also have deteriorated during this time due to the decline in the refractive function of the lens, they added. Still, these factors are more likely to be of importance in older patients than those in their cohorts, they wrote.

Based on their analysis of the most important factors in these two questionnaires, Dr van de Graaf and colleagues are “considering the possibility of combining the best items of both questionnaires into a new quality-of-life instrument.”