Occasional Paper Number 15
September 2008
Improving the detection of correctable low vision in older people
This publication summarises findings from research funded by Thomas Pocklington Trust and carried out at the Institute of Optometry by Zahra Jessa and Prof Bruce Evans in collaboration with Prof David Thomson, Prof Gillian Rowlands, Mitesh Amin, Hannah Sawyerr and John Cooper.
Summary
The research sought to investigate new vision screening instruments as methods of improving the take-up of primary eyecare services by older people in South London.
In Screening Study 1, a computerised vision screener (CVS1) was used to test 180 older people (aged 65+) in South London. All participants also received a ‘gold standard’ eye examination, which found that 32% of participants had significant cataract and 39% needed new spectacles.
Overall, 58% of participants had at least one of these problems and the computerised vision screener detected about 80% of these cases. This first study determined the usefulness of each subtest in the screener and two tests were subsequently dropped from the screener.
In Screening Study 2 the revised computerised vision screener (CVS2) and a rapid flipchart vision screener (FVS) were used to test a new sample of 200 older people. The gold standard eye examination found that 31% had cataracts and 30% correctable refractive errors; 51% had at least one of these conditions.
Both screening tools detected about 80% of cases of visual loss due to these problems or to age-related macular degeneration (AMD). The tools also correctly classified about 70% of those with normal visual function. Further analyses revealed the best combination of tests in the screeners and showed, as expected, that simple vision screening is not good at detecting glaucoma, which is known to be difficult to diagnose. Participants reported a significant improvement in quality of life, most marked in those who were prescribed new spectacles.
Vision screening does not replace the need for professional eyecare, but can help to identify older people with correctable visual problems. All people who are screened should be reminded of the need for regular eyecare.
Introduction
A recent systematic review reveals that 20-50% of older people have undetected reduced vision.1 The majority of these people have correctable visual problems (refractive errors or cataract). It is particularly startling that, in a ‘developed’ country, between 7% and 34% of older people have visual impairments that could be cured simply by appropriate spectacles. This has been attributed, at least in part, to inadequate levels of attendance at the community optometrist.
This undetected, yet correctable, reduced vision is associated with impaired quality of life and ability to carry out activities of daily living, depression, and falls and other accidents. Those with low vision are about twice as likely to have falls than fully sighted people. This correctable reduced vision is likely to be particularly prevalent amongst people who suffer from the effects of poverty and/or are from ethnic minorities.
Two different (but not mutually exclusive) approaches to improving the detection of visual problems in older people are better to publicise the need for regular optometric eye examinations and to screen for visual problems. If an older person attended a vision screening programme and was told personally that their visual problem had a high likelihood of being treatable, or at the least might benefit from low vision services, then the research team believes that they would be very likely to follow up on the referral that would result from the screening. It is believed that the likelihood of their seeking care is much greater than a person who has only seen publicity advertising NHS sight tests.
In view of this, it is surprising that there has been relatively little research on vision screening in older people. As part of this project, the research team carried out a detailed and systematic literature review of research on vision screening in older people. This literature review was published in the peer-reviewed journal of the College of Optometrists, Ophthalmic & Physiological Optics.2 Only the main findings will be summarised here.
There is a lack of rigorous research investigating whether vision screening is effective at detecting correctable low vision in older people. Visual function in older people is not fully described by high contrast visual acuity (e.g., the conventional letter chart test), or by self-reports of visual difficulties. Other tests that may be relevant include visual field testing, low contrast visual acuity, contrast sensitivity, and stereoacuity.
1 Evans BJW, Rowlands G (2004) Review article. Correctable visual impairment in older people: a major unmet need. Ophthal.Physiol.Opt. 2004;24:161-80.
2 Jessa Z, Evans B, Thomson D, Rowlands G (2007) Vision screening of older people. Ophthal. Physiol. Opt. 2007;27:527-46.
The review paper noted that there is still uncertainty over the battery of vision tests that are most appropriate. This, and optimum venues for screening, requires further research before it can be determined conclusively whether vision screening of older people is worthwhile. The review noted that if a vision screening programme using a battery of vision tests, perhaps computerised, can be established then this should be tested to determine how well the screening can detect the target conditions.
The literature suggests that quite basic tests (described below) will be able to detect uncorrected refractive errors and cataract. These are the main target conditions in this research because: (a) they have a very high prevalence, (b) they can readily be cured, and (c) their treatment is of direct and immediate benefit to the public through correcting visual loss and improving quality of life.
The computerised vision screener and flipchart screener that were developed for this research also include a test of visual acuity, which will detect visual impairment from another common cause in older people: age-related macular degeneration (AMD). Although this condition is not readily correctable in most cases, it is helpful to detect cases so that they can be referred when appropriate for ophthalmological investigation and for further support and low vision aids (e.g., magnifiers). There have also been recent advances in the treatment of some cases of AMD and it is likely that further technological developments will lead to a higher proportion of cases being treated. In view of these developments, it was decided to evaluate the performance of the screening tools at detecting significant AMD and the cases which were most at risk of deteriorating to the sight-threatening wet AMD.
The only common visual anomaly that it was anticipated would be difficult to detect with vision screening is glaucoma. Although visual loss from glaucoma cannot be treated, it can be prevented through early detection. It is difficult to screen for glaucoma, since all three commonly used glaucoma tests have a poor ability to diagnose glaucoma when taken in isolation and using all three tests in screening by non-healthcare professionals is impractical.
A visual field test, which is likely to be of some use for detecting glaucoma, was included in the computerised vision screener. Nonetheless, it was accepted from the outset that such a test is unlikely to match the accuracy of a full eye examination for detecting glaucoma.
This research followed the tenets of the Helsinki declaration for research involving human subjects and conformed to the Department of Health’s Research Governance Framework. The research received approval from appropriate ethical and NHS committees. All participants were given full information about the research, both verbally and in writing, and it was explained that participation was optional and that refusal to participate would not in any way influence their continued medical, optometric or social care. Particular care was taken not to alarm or confuse older people.
Preliminary study on the provision of NHS eyecare & eyewear in South London
Introduction
All people over the age of 60 are entitled to eye examinations in the community funded by the NHS, and people on low incomes or with unusually high optical prescriptions are entitled to an NHS Optical Voucher. This is a voucher that can be used to pay for or reduce the cost of spectacles. This preliminary study was carried out to determine which optical practices in the South London area have a reasonable range of spectacles whose cost is fully covered by the NHS Optical Voucher (referred to below as Voucher Value Spectacles: VVS).
Methods
A questionnaire was developed for sending to optical practices. This was designed to determine the availability of NHS-funded eyecare and eyewear.
Results
In South London, 65 questionnaires were sent out and there were 53 responses (response rate 82%). Nearly a third of the practices that responded to the survey do not provide VVS.
It has been suggested that optometric practices are deterred from providing VVS because the values of the vouchers are uneconomic. Compelling practices to provide VVS could be counter-productive if the values of the vouchers remain uneconomic, because it could force practices to withdraw from providing NHS services altogether. It seems likely that the limited availability of spectacles fully funded by the NHS is one of the reasons why so many older people in the UK have poor vision simply through lack of appropriate spectacles.
The list of practices where VVS spectacles are available was printed and issued in Screening Study 1 and Screening Study 2 to participants who were eligible for VVS.
Screening Study 1
Introduction
The main goal of Screening Study 1 was to determine the most appropriate screening tests for inclusion in the final version computerised vision screener and flipchart screener. Some basic epidemiological data were also obtained. Most participants were seen at the Institute of Optometry but some community based venues were also used. The Institute of Optometry is situated in Lambeth, which has the eighth highest ethnic minority representation nationally. Over half of the local population is part of an ethnic minority group.
The required number of participants was calculated using sample size calculations. The target sample size in Screening Study 1 was 180.
Methods
Participants were people aged 65 or older who consented to participate in the study. People of all ethnic backgrounds and with or without physical or mental disabilities were welcomed.
Computerised vision screener (CVS1)
The CVS1 was a software program that ran on a laptop computer, the display of which had been calibrated. The following seven tests were included:
· symptoms & history
· near visual acuity (binocular)
· visual field test
· fixation disparity (a test of eye coordination)
· stereoacuity (depth perception)
· high contrast visual acuity
· low contrast visual acuity.
In addition to the CVS1, all participants underwent a full ‘gold standard’ eye examination by an optometrist. The optometrist and the lay person carrying out the screening were unaware of each other’s results. The gold standard eye examination included the following tests:
· detailed symptoms & history
· checking the prescription in the current glasses
· determination of refractive error by both objective and subjective tests
· six tests of binocular coordination
· high and low contrast distance visual acuity and near visual acuity
· visual fields
· four tests of ocular health (tonometry, pupil reactions, anterior segment biomicroscopy, dilated fundoscopy).
Based on the results of the gold standard eye examination, standardised methods were used to diagnose under-corrected refractive error (an improvement of two lines of a letter chart with new spectacles), cataracts (the Lens Opacities Classification System III), AMD (Clinical Age Related Maculopathy Staging System). Participants with or at risk of glaucoma were identified according to conventional clinical criteria.
The performance of the screening test was assessed by determining the sensitivity (the ability of a test to identify correctly people who have the target conditions) and specificity (the ability of a test to identify correctly people who do not have the target conditions). The optimum test cut-off values (pass/fail criteria) were determined using a standard method, involving plotting graphs that show the trade-off between sensitivity and specificity (receiver-operator characteristic (ROC) curves).
Results
The average age of the 180 participants was 77 years (range 67-99 years), 46% were male and 12% were seen in the community. Overall, 58.3% had correctable visual loss (31.7% cataract, 39.4% correctable refractive error; some both) and 28.9% had significant AMD. All participants were able to carry out the CVS1 and none complained that it was difficult to do.
Extensive analyses were carried out to determine the value of each component subtest of the CVS1 for detecting under-corrected refractive error, cataract, AMD, glaucoma, and a history of falls. Two of the tests were found to be of little value: the fixation disparity and the stereoacuity tests. These were dropped from the screener for the second study.
The most valuable test was high contrast visual acuity, which detected nearly 80% of cases of under-corrected refractive error or cataract and correctly classified nearly 60% of participants who were visually normal.
A supplementary study was included in Screening Study 1 to evaluate whether cataracts could be reliably graded using a portable version of the table top slit lamp biomicroscope that conventionally is used to grade cataracts. This study showed that cataracts can be reliably graded in this way, which allowed Screening Study 2 to be based in the community to a greater extent.
Screening Study 2
Introduction
Screening Study 2 evaluated the revised computerised vision screener (CVS2) and a flipchart vision screener (FVS) on a new group of 200 people aged 65+. Many of the participants were seen in the community, either at a community centre or a GP practice.
Methods
CVS2 was similar to CVS1, except that the fixation disparity and stereoacuity tests were not included. The FVS included three tests, presenting binocular near visual acuity, and presenting monocular distance high contrast and low contrast visual acuities. The gold standard eye examination was the same as in Screening Study 1.
Since Screening Study 2 investigated the ‘final versions’ of the screening tools, greater emphasis was placed on follow-up. The Quality of Life (QoL) questionnaire,3 a brief standardised test4 (one side of A4 paper, taking approximately 5 minutes) was applied at the time of the eye examination and up to three months after any intervention.