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Glaucoma is an insidious condition which remains asymptomatic until very advanced with nerve damage occurring before detectable visual field loss.1 Early detection and treatment result in a better prognosis with retardation of progression.2
The Heidelberg retinal tomograph (HRT) II (Heidelberg Engineering, Germany) and the GDx Nerve fibre analyser (Laser Diagnostic Technologies Inc, San Diego, CA, USA) are instruments which use scanning laser technology to diagnose and monitor the progression of glaucoma.
We conducted a questionnaire survey of subjects undergoing imaging by these methods in a primary care setting to compare patient acceptability of the two tests.
Seventy new patients referred with a possible diagnosis of glaucoma were asked to complete a questionnaire about their experience of optic disc imaging. Informed consent was obtained and the study had approval from the Moorfields Eye Hospital research and ethics committee. None of the subjects had undergone disc imaging previously. Subjects underwent sequential disc imaging by experienced technicians using HRT II then GDx or vice versa in approximately equal numbers. Only subjects who had vision of at least 6/12 and who had successful imaging by both methods were included.
The questionnaires consisted of two identical sets of six direct questions using a size 14 font (Appendix 1). Questionnaires were completed immediately after imaging to reduce the potential for recall bias. Statistical significance was determined using Binomial and McNemar’s tests.
Sixty seven questionnaires were completed. Demographic and diagnostic data are shown in table 1 and patient responses in table 2. The majority of patients found both tests agreeable with regards to each characteristic under study other than chin rest comfort. Sixteen patients found the HRT II comfortable but not the GDx, compared with just one patient finding the GDx comfortable but not the HRT II (p = 0.0003). Despite this, there were slightly more patients reporting that the HRT II chin rest only was uncomfortable (p = 0.052). Nine patients found that imaging with GDx but not HRT II took too long compared with no patients finding the HRT II but not GDx too long (p = 0.0039). Similar numbers of patients reported that only one of the imaging techniques was too bright. Nineteen patients had trouble fixating with the GDx but not the HRT II compared with just three patients having trouble fixating with HRT II but not GDx (p = 0.009).
Despite these differences, 28 subjects (42%) stated no preference for either imaging technique. Of the 39 subjects who did state a preference, 31 (79%) preferred HRT II compared with eight (21%) who preferred GDx (p = 0.0003, Binomial test). Twenty of the 31 subjects (65%) who chose HRT II did so because it was of a shorter duration, five of the 31 (16%) said that it was more comfortable, and six of the 31 (19%) said that it was easier to perform the test. Four of the eight subjects (50%) who chose GDx did so because it was easier, two (25%) said that it was more comfortable and two (25%) did not give a reason.
Diagnostic and screening tests should be safe, specific, sensitive, and acceptable to patients. The HRT and GDx have cited sensitivities of 0.42–0.88 and 0.64–0.96 and specificities of 0.84–0.90 and 0.74–0.96 respectively.3–9
Most patients found both tests to be fairly acceptable. Twenty eight (42%) subjects stated no preference but of those who did, a significant proportion of patients preferred HRT II over GDx. The most common reason given was a shorter test duration implying that acquisition time may have an impact on acceptability. Examination with the GDx may be longer because of the external fixation target, which a greater proportion of subjects found difficult to focus on. In contrast, the HRT II has an internal fixation target. Although the HRT II was found to be a more comfortable test, a higher proportion found the HRT II chinrest to be uncomfortable possibly because of the forward sloping angulation.
We did not correlate patient preference with image acquisition time. More open questions may have helped to find the reasons for certain preferences. We were unable to determine the strength of preference from the collected data. Our study was also not randomised but roughly equal numbers had either HRT II or GDx first. We do not feel that there was a significant order effect. As our patients were new referrals, their responses were not biased by familiarity with previous tests. Patients underwent both tests sequentially on the same day by trained technicians reducing the likelihood of prolonged acquisition time due to inexperienced operators. All patients had good vision so locating the target was not an issue. Additional work examining the factors which affect acquisition time (for example, refractive error, presence of media opacity, pupil size) is needed to further understand patient preference.
It is uncertain if the differences in preference between the two tests will have a significant impact on patient satisfaction and compliance with clinic visits as a whole. Other factors, such as waiting time and comfort of waiting room, will have to be examined as well.
In conclusion, our study highlights the importance of both test characteristics and comfort in instrument design. It is hoped that manufacturers take into account these factors in the design of the next generation of glaucoma imaging devices.
The questions were:
Was the test comfortable? Yes or No?
Was the light too bright? Yes or No?
Was the chin rest uncomfortable? Yes or No?
Was the test too long? Yes or No?
Did you have trouble keeping your eye still? Yes or No?
(a) Which test did you prefer? HRT or GDx? (b) Why?
No financial interest or support.