Testing retest interval times

Legal adviser to the AOP, Trevor Warburton, investigates the results of the AOP’s retest intervals survey, gauging the view of practising clinicians

NHS sight test

Optometrist and legal adviser to the AOP, Trevor Warburton, investigates the results of the AOP’s retest intervals survey, gauging the view of practising clinicians.


In January 2002, a joint group of optical bodies (now part of the Optical Confederation) agreed with the Department of Health on a Memorandum of Understanding (MoU) regarding the frequency of GOS sight tests in England. The agreement was reached on behalf of the whole profession and was adopted in Wales and Northern Ireland. The memorandum specifies that payment agencies will “automatically pay all bona fide claims for GOS fees for sight tests carried out at the intervals listed…” Testing at shorter intervals is acceptable where there is clinical justification due to presenting symptoms or concerns (either from the patient or the optometrist), with the MoU specifying codes to be used when justifying a test at a shorter interval than those specified. 

The Memorandum also states that “…GOS regulations require practitioners to satisfy themselves that a sight test is clinically necessary. Therefore, the intervals given below are not to be read as applying automatically to all patients in a category.” Nevertheless, it has always been clinically accepted that an appropriate interval since the previous sight test is itself justification for a further sight test. 

The main drivers for the creation of the memorandum were the actions of a small number of practitioners who were testing at very short and regular intervals, particularly in the case of children. There was no intention to interfere with the established peer practice on recall intervals for the majority of the profession. Indeed, the intervals listed in the memorandum were based on the retest intervals used by the majority of the profession at the time (Warburton et al, 2000). Therefore, far from practitioners following the MoU intervals, it is more the case that the MoU follows established clinical practice among the majority of practitioners. 

Recently, reports emerged from a small number of areas that GOS contractors are being told that “things have changed” and that the intervals no longer apply. However, there has been no renegotiation of the memorandum, which remains in force and constitutes the only agreement on this issue between the profession and the Department of Health. In order to establish whether the peer view of safe practice has changed, the AOP conducted a survey reviewing current clinical practice. The survey was established online using Survey Monkey, and on 13 March a link to complete it was sent to all AOP members in England, Wales and Northern Ireland with valid email addresses (n = 8,551). Reminders to complete the survey subsequently appeared in OT, as well as the AOP’s newsletter Blink.The survey closed on 31 March, at which point there had been 3603 entries – a response rate of 42%.

The headline result shows that peer practice on retest intervals has not changed and thus the MoU still reflects the peer view of safe retest practice, just as it did when first introduced.


Table 1 shows that for straightforward adults in the private test age range, most practitioners advise two years as a safe retest interval.  

In patients aged 40 years or older, and with a family history of glaucoma, 92% of practitioners advise a retest after one year. For those with diabetes, 76% of the profession advise one year as the typical interval, thus representing peer practice. However, a significant minority do advise two years. This is shown in Table 2. 

There have been reports of pressure being applied on practitioners to lengthen retest intervals in a small number of areas, but this does not reflect the peer view of safe practice. 

Table 3 shows that up to the age of 69 years, and in the absence of problems, most practitioners continue to advise a two-year retest interval. However, above the age of 70 years this begins to change. In the absence of any pathology, just over half of practitioners review at one year, 14% review at two years and slightly under a third review between one and two years. The reason for advising one year rather than two is predominantly pathology, with over 80% of practitioners citing slight cataract, slight AMD, other non-referable pathology and, frequently, all three as reasons for recommending a retest after one year. Driving was a much less common reason for reduced interval testing times (28%), and was usually selected in conjunction with one of the other pathologies. 

Table 4 deals with children under seven years of age. In the case of those with no binocular vision anomaly or corrected refractive error, the majority recommend one year, although the MoU provides flexibility for six month intervals where this is appropriate. Where these younger children have a refractive error, almost a third of practitioners still recommend one year. 

These results, and those for the over 70 year old category, suggest that practitioners do not blindly follow the MoU intervals but use their clinical judgement and experience to recommend an appropriate retest interval for each patient. 

The results for older children are listed in Table 5. This shows once again that the MoU reflects the practice of the majority of practitioners, although a significant minority advise two years in the absence of any problems. 

When asking whether practitioners are more likely to turn GOS patients away when they present early, 62% said ‘yes,’ with a handful of PCT areas flagging up as applying particular pressure. It is entirely reasonable to apply pressure to conform to the intervals as long as it does not result in patients with genuine symptoms or concerns being refused sight tests. However, it should be noted that the letter accompanying the publication of the MoU (DoH 2002) says that claims within one month of the intervals should not be challenged, in order to give patients and practitioners some flexibility.

The AOP survey shows that, although practitioners propose sight test recall intervals to reflect the needs of each patient, the MoU nevertheless continues to reflect safe sight test intervals in the view of the majority of practising clinicians, just as it did when it was first introduced. Commissioners and those advising them should be mindful of this and ensure that they are familiar with peer practice when providing advice. Practitioners should note that the choice of recall interval is a clinical decision for the individual patient and should not be a blanket interval imposed by practice systems.

About the author 

Trevor Warburton is an AOP director and clinical adviser to the AOP legal services team.


  1. Warburton et al, 2000. A survey of specified recall intervals for eye examinations. Optometry Today. August 18, 2000 
  2. Department of Health 2002. Memorandum of Understanding on the Frequency of GOS Sight Tests
  3. Department of Health 2002. MoU Letter.