To our knowledge, this is the first study to directly observe if ophthalmology residents were able to check GAT calibration and most (55%) were unable to correctly do so. However, a greater proportion of participants (45%) in our study were able to check GAT calibration compared with 15% reported in other studies [3–4]. It is important to note that previous published studies relied on self-reporting of this skill and not on direct observation of the skill. The authors of this study propose our participants performed comparatively well due to the good coverage of teaching of this practical skill in this region. Allowing for failure to balance the instrument by mounting the prism in the prism mount we found that 13 (65%) ophthalmology residents were able to use the calibration rod correctly.
There was good participation of ophthalmology residents from the region and each of the training grades had good representation, reflecting the numbers of residents at each stage of training within the deanery. There was a trend for junior ophthalmology residents (years 2–4) to be able to check GAT calibration more successfully than senior residents (years 5–8), however this did not reach statistical significance. Most ophthalmology residents recalled being taught this practical skill in years 1 or 2 of training. It is possible that junior ophthalmology residents appeared to be more successful in checking GAT calibration since they had received teaching and undergone assessment of this competency relatively recently. Additionally, it is possible that the time lapse since senior ophthalmology residents were taught and assessed this competency may have contributed to this skill being lost.
The most common error identified with checking the calibration of the GAT was failure to balance the instrument by mounting the prism in the prism holder. It may be that this part of checking GAT calibration is not emphasised as important or is easily forgotten. Observation of this practical skill in the present study was not performed in a clinical setting where it may have been more intuitive for the ophthalmology resident to mount the prism in the prism holder.
Having been taught the skill of GAT calibration appeared to increase the likelihood of ophthalmology residents being able to correctly check the calibration of a GAT (50%) compared with those that had not been previously taught (33%), but this did not reach statistical significance. Similarly, having been taught GAT calibration seemed to increase the likelihood of being able to use the calibration rod correctly (71%) compared with those that had not been taught (67%). Having been assessed on GAT calibration during their training appeared to increase both the ability to check GAT calibration correctly (60% previously assessed group vs 30% not previously assessed group) and ability to use the calibration rod correctly (80% previously assessed group vs 60% not previously assessed group) but this did not reach statistical significance.
Ophthalmology residents participating in this study identified being able to check GAT calibration as an important practical skill to learn. Previous small studies by other groups have shown that 18–100% of GATs within units are uncalibrated [3–4, 7–10]. Furthermore, a survey of all hospital eye services in the UK revealed 39% of GATs were never checked or were not regularly checked in an identifiable pattern [3, 11]. To ensure accurate IOP readings the manufacturer Haag Streit recommend that the calibration of the tonometer is checked monthly and returned for recalibration if found to be faulty . A multicentre study has suggested newer GATs (< 1 year old) could be checked twice yearly while older GATs should be checked monthly .
There are limitations to this study; most notably there was a small sample size, and it was performed within one deanery in the UK. Whilst a good proportion of ophthalmology residents participated, some of the smaller eye-units were not represented. Additionally, the study was performed in a non-clinical setting and performance may vary within a clinical setting. Participants were asked to not communicate with each other regarding the topic of the study, but they were not completely isolated from each other. Hence, prior knowledge of the study may have increased the success rate due to the participants revising the technique before participating in the study.
Checking the calibration of a GAT is of training significance and of clinical significance since using an uncalibrated GAT could lead to under- or over- estimation of IOP. Under-estimation of IOP has the possible consequences of delay in instigating appropriate interventions and could lead to progression of glaucoma. Over-estimation of IOP has the possible consequence of unnecessary intervention. The recommendations of this study are that ophthalmology residents should be trained in checking GAT calibration and supervisors should observe and assess this skill.