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In April 2009, National Institute for Clinical Excellence (NICE) issued guidelines on the diagnosis and management of Chronic Open Angle Glaucoma and Ocular Hypertension. Shortly after publication of these guidelines, guidance issued jointly by the Association of British Dispensing Opticians, the Association of Optometrists and the Federation of Ophthalmic and Dispensing Opticians advised optometrists to refer patients with IOP > 21 mmHg even in the presence of normal optic disc and visual fields, citing that practitioners could leave themselves ‘legally exposed’ if they failed to do so. A survey of optometrists conducted shortly after the publication of both the NICE and ophthalmic bodies guidance estimated that the number of new glaucoma referrals to the hospital eye service (HES) based on this guidance had increased by approximately 38%.
There has been much controversy over the interpretation of the NICE guidelines. A joint publication by the College of Optometrists (CoO) and the Royal College of Ophthalmologists (RCOphth) in December 2009 gave further guidance to optometrists when considering the referral of patients with suspect glaucoma to the HES.
Previous work by Vernon et al. has shown that the introduction of local guidelines and protocols helps reduce the number of false positive glaucoma referrals, but only if they are followed accurately. The aim of this study was to evaluate how well new glaucoma referrals to the Glaucoma Service of Moorfields Eye Hospital, London followed these published guidelines.
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A retrospective review of the hospital records of patients who attended the glaucoma new patient service at Moorfields Eye Hospital (City Road site), London over a 6-week period from January 2011 was undertaken. Tertiary referrals and primary referrals that did not contain the optometrists report were excluded. A target of 100 optometrist referral letters was required.
The joint CoO/RCOphth guidelines the published in December 2009 states the following key points that optometrists should consider when referring a patient with suspect ocular hypertension/chronic open angle glaucoma:
Before considering referral, practitioners should take four readings per eye and use the mean as the result. Only when the mean result is >21 mmHg should the practitioner consider referring the patient for further assessment if this is the only abnormality found. Reducing the number of readings per eye increases the chance of recording a mean result of >21 mmHg in eyes of normal persons with Goldmann IOPs of <21 mmHg.
If a patient has not been subject to non-contact tonometry before and the mean result is >21 mmHg for either eye, a new set of readings should be taken for the eye, or eyes, for which this is the case. This is because research in normal eyes shows that the mean of subsequent sets of four readings will often be within the normal range.
When practitioners consider it necessary to refer the patient, they should provide as much factual information derived from the eye examination as possible to the ophthalmologist to whom they are referring the patient. For optic disc assessment, practitioners should state whether the disc appears normal or abnormal, and if it appears abnormal, why this is so. Where practitioners have determined that it is clinically necessary to perform a visual field assessment as part of particular eye examination, a copy of the visual field assessment should also be provided.
The updated CoO/RCOphth guidance issued in December 2010 made further clarifications for referral, but the essence on the method of measuring intraocular pressure (IOP) with non-contact tonometry (NCT) remains the same.
Data collected from the optometrist referral letter included practice and practitioner details, patient details, the clinical data recorded and the cited reasons for referral. Data collected from the hospital record included provisional diagnosis and outcome.
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A total of 289 hospital records were reviewed over a 6-week period between January 4th and February 19th 2011. The majority of new glaucoma referrals were initiated by community optometrists (n = 114, 39%); with the remainder of patients being referred by their general practitioner (GP n = 28, 10%; consisting of patients previously diagnosed with glaucoma who had been lost to follow up) tertiary sources (n = 65, 23%; that is, complex cases referred from outside of Moorfields for further management) or Moorfields other services (n = 82, 28%; those who had an incidental finding or who were thought to be at risk of developing glaucoma following review in a non-glaucoma subspecialty service within the hospital). Of the 114 optometrist initiated referrals, 7 referral letters were with-held by the patients' GPs whilst 2 patients had no letter with the optometrist sending the patient straight to the hospital. Therefore in total 105 letters were included in the data analysis. The mean [standard deviation; SD] age of patients at the time of referral was 57 [15.4] years. The average number of days between the optometry sight test and being seen at the hospital was 122 [90.5] days.
General details available on referral letter
The patient's name was recorded legibly in all letters. Ninety-five letters (90%) contained the patient date of birth and 101 (96%) had recorded the patient's address, complete with post-code. A legible practice address was recorded in 95 (90%) letters. However, the optometrist's name was legible in only 56 (53%) of referral letters.
Clinical details recorded on referral letter
IOP measurements were recorded in 102 (97%) referral letters. NCT was reported as the instrument used in 69 (66%) letters, contact applanation (Goldmann or Perkins) tonometry in 3 (3%) letters, with the remainder of letters not specifying the device used.
Raised IOP was cited as a reason for referral in 77 (73%) of cases. The remainder of patients were referred due to a combination of other factors, detailed in Table 1. Of the patients referred with raised IOP, 33 (43%) patients were referred with raised IOP in isolation (i.e. no other abnormality was recorded). NCT was the tonometer used in the majority of these raised IOP cases (n = 56, 73%); applanation tonometry was reported in 2 letters (3%) whilst the remainder did not record the device used (n = 19; 24%).
Table 1. Reasons for referral cited in optometrist letter
|Reason for Referral|| N ||Percent|
|Raised IOP in isolation||33||30.5|
|Raised IOP and suspicious VF||16||15.2|
|Raised IOP and suspicious discs||17||15.2|
|Raised IOP and suspicious angles (Van Herrick)||4||3.8|
|Raised IOP and positive family history||4||3.8|
|Raised IOP and other (other: known glaucoma and lost to follow up n = 2; floaters n = 1)||3||2.9|
|Suspicious VF in isolation||3||2.9|
|Suspicious VF and discs||4||3.8|
|Suspicious VF and positive family history||2||1.9|
|Suspicious discs in isolation||4||3.8|
|Suspicious discs and positive family history||6||5.7|
|Suspicious discs and asymmetry in IOP (not raised)||1||1.0|
|Suspicious angles in isolation||4||3.8|
|Other: (known history of glaucoma, n = 1; persistent tiredness, n = 1; history of trauma, n = 1; no reason specified, n = 1)||4||3.8|
Guidelines (i): number of NCT readings
In letters where the NCT was specified as the device used to measure IOP, the number of readings recorded in the referral letter is shown in Table 2. The data suggest that the majority of optometrists measured IOP 3 times when using the NCT. The joint CoO/RCOphth guidelines recommend that 4 readings be undertaken.
Table 2. Number of readings of IOP measurements taken in those using NCT
|Number of Readings recorded in referral letter||Number of cases (total n = 69)||Percentage|
Guidelines (ii): repeatable raised IOP
Of the 77 patients referred due to an elevated IOP, 14 (18%) practitioners indicated that repeated measures had been performed and included both sets of data. One of these referrals had repeat measures performed with the Perkins, the others (n = 13, 17%) with NCT. The remainder of letters only recorded the IOP measured at a single time point.
Guidelines (iii): raised IOP in isolation
Of the 33 patients referred with raised IOP in isolation, 24 had IOP measured with the NCT, 1 patient was measured with Perkins tonometry, and the remainder did not specify the tonometer used. Of those referrals where NCT was used, 1 (4%) recorded 4 NCT measures on the referral letter, 16 (67%) recorded 3 NCT measurements, 3 (13%) recorded 2 readings and 4 (17%) recorded a single NCT measure in the referral letter. Ten patients had repeat IOP measures performed, 9 with NCT and 1 did not specify the device used.
Guidelines (iv): Visual field reports and disc assessment
Seventy-five (71%) patients were reported in the referral letter to have had visual fields performed, with all but 4 indicating ‘reports enclosed’ on the referral letter. Sixteen (21%) of these letters had the visual field report enclosed in the referral to HES, whilst 55 (73%) visual field reports appeared to have been with-held by the GP.
One hundred and four (99%) letters gave some description of the optic disc appearance and cup-disc ratio. Two (2%) letters indicated that a dilated disc examination had been performed, but did not specify the method of disc viewing whilst 2 (2%) indicated that indirect ophthalmoscopy had been used for disc assessment. The remainder of letters gave no indication of either dilation or method of disc examination employed.
Outcome of new patient appointment
Table 3 details the outcomes of the patients referred to the service. Three (2.9%) patients did not attend the service for their appointment, leaving 102 patients with outcome data. Thirty-one (30%) patients referred to the Service were discharged; 30 of these patients had no signs of glaucoma, with one diagnosed as ‘low risk’ ocular hypertension. Of the remainder, 24 (23.5%) were diagnosed as having ocular hypertension requiring HES follow up, 18 (17.6%) were classed as glaucoma suspects, 17 (17.6%) had a definitive diagnosis of glaucoma, and 12 (11.8%) were deemed to have narrow angles that required a peripheral iridotomy. Of the latter, 4 practitioners had noted ‘suspicious angles’ in the referral letter, 2 of whom were referred solely on the basis of this finding.
Table 3. Outcome following referral to HES
|Reason for Referral|| N ||Kept within service (%)||Discharged from service (%)|
|Raised IOP in isolation||33||21 (64)||12 (36)|
|Raised IOP and suspicious VF||16||9 (56)||7 (44)|
|Raised IOP and suspicious discs||17||15 (88)||2 (12)|
|Raised IOP and suspicious angles (Van Herrick)||4||2 (50)||2 (50)|
|Raised IOP and positive family history||4||3 (75)||1 (25)|
|Raised IOP and other||3||3 (100)||0 (0)|
|Suspicious VF (without raised IOP)||9||8 (89)||1 (11)|
|Suspicious discs (without raised IOP)||11||7 (64)||4 (36)|
|Suspicious angles in isolation||4||3 (75)||1 (25)|
|Other reason for referral||4||3 (75)||1 (25; patient with ‘persistent tiredness’)|
Of the 33 patients referred on the basis of raised IOP in isolation, 3 did not attend the hospital appointment leaving outcome data for 30 patients. Ten (33%) of these patients were discharged following their hospital review. Of the remainder, 6 (20%) had an IOP < 21 mmHg at their hospital appointment, measured with slit-lamp mounted Goldman applanation tonometry (GAT). The diagnoses for these 6 patients were as follows: glaucoma suspect (based on optic disc appearance), n = 2; glaucoma suspect (based on visual field appearance), n = 1; glaucoma, n = 2; chronic narrow angle glaucoma requiring bilateral peripheral iridotomies, n = 1. These patients may not have been referred on to the HES if they had attended a ‘repeat IOP measures only’ refinement scheme.
In total, 25 patients were referred with suspicious visual fields with or without raised IOP; 8 (32%) were discharged following their HES appointment. Of the 28 patients referred with suspicious optic discs (with or without raised IOP) 6 (21%) were discharged following their HES appointment.
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The results of this study suggest that many optometrists do not appear to follow the recommendations issued jointly by the CoO and RCOphth with respect to referring a patient with suspect glaucoma to the HES. Whilst NICE recommend using GAT to measure IOP when referring, and studies suggest that more appropriate referrals would be made if GAT were used, it is recognised that the majority of optometrists will routinely use NCT devices. In a recent survey of optometrists conducted by Myint et al. 78% of UK community optometrists reported that they used NCT to measure IOP in the detection of glaucoma. Our study showed that NCT was used in almost three-quarters of referrals. The joint CoO/RCOphth guidelines suggest best practice for performing NCT IOP measures, which includes undertaking 4 measures and repeating if necessary, particularly if the patient has not undergone NCT measurements previously. We found that only a minority (4%) took four readings when basing a referral on elevated IOP alone, and that less than a fifth of optometrists repeated IOP measures when elevated IOP was found. The recommendation of 4 repeat NCT measures is based on evidence that shows an increased chance of obtaining an elevated IOP measurement when using the mean of <4 readings.
The data from our study shows that the vast majority of optometrists take 3 repeated NCT measures per eye; this behaviour may be as a result of ‘entrenched’ learning that starts at undergraduate level. The NCT was first developed by Bruce Grolman in the early 1970s, and at that time it was recommended that 3 readings be taken per eye in order to minimise the effects of the cardiac cycle on IOP measurements. Many of the newer NCT manufacturers advise this original recommendation, which has also been recommended by authors who have evaluated the effects of repeat NCT testing on non-glaucoma populations;; thus the practice of taking 3 repeat measures is likely to be performed ‘by rote’ and thus remains unchanged. It is also quite possible that IOP measurements are performed by non-optometric staff at the ‘pre-screening’ part of the sight test. Perhaps the recommended change in practice of taking an average of 4 readings rather than 3 should be advertised further by optometrist governing bodies, and this should also be disseminated to the staff undertaking the IOP measurement, if the optometrist is not undertaking the measurement themselves.
It is also quite plausible that in letters where only 1 measurement was recorded, this represents an average of multiple readings, particularly as some NCT devices only report an average of multiple readings. It may be useful to recommend that this be clarified in the referral letter if this is the case.
As a response to the potential influx of false positive referrals to the HES based on raised IOP alone, some areas are adopting ‘refinement’ services, whereby patients presenting to the optometrist with IOP over 21 mmHg measured with NCT are sent for repeat applanation tonometry measures. Peer-reviewed literature regarding the efficacy of these repeat-measures schemes is currently sparse, although it is likely that more information will become available with increased longevity of such schemes. In this study, 33% of patients referred on the basis of raised IOP in isolation were discharged from the service, which is comparable to the false positive rate of optometrist glaucoma referrals pre-NICE.[13-15] It is worth highlighting that a fifth of patients referred to the hospital with raised IOP in isolation had IOP within normal limits when measured with GAT, but were deemed to have an abnormality that required HES monitoring. These patients may not have been referred for HES review had they been seen in a ‘repeat IOP measures’ scheme.
With respect to visual field testing, the guidance is for optometrists to perform this test if deemed clinically necessary. In this study, the majority of optometrists (71%) appeared to have undertaken a visual field test; however, only a fifth of letters had visual field reports forwarded to the HES. This suggests that the majority of visual field reports had either been with-held by the GP or had not been enclosed in the initial GP referral. This is similar to findings of Scully who found that in referral letters to HES for glaucoma suspect patients only 27% had visual fields plots enclosed. Work has shown that undertaking visual field testing in addition to optic disc and IOP evaluation increases the positive predictive value of new glaucoma referrals.[17, 18] Having the optometrist's visual field report to compare against that performed at the HES may assist the ophthalmologist's decision making process regarding the index of suspicion for the presence of disease. HES departments should perhaps inform GPs that forwarding a letter with all the relevant information enclosed will ensure that patients are seen, and therefore treated, in an appropriate time frame.
Few optometrists indicated whether a dilated optic disc examination was performed or whether indirect ophthalmoscopy was used to evaluate the disc. Best practice for disc evaluation is a stereoscopic view through a dilated pupil, but it is impractical to expect community optometrists to perform a dilated disc exam on all glaucoma suspect referrals. A recent survey of UK optometrists indicates that the majority of community optometrists are constrained by time, being required to see a patient every 20–30 min, making it virtually impossible to undertake all the ideal clinical tests when evaluating a patient with suspect glaucoma. However, of the patients referred with suspicious discs (with or without raised IOP), only a fifth were discharged from the service. This may suggest that optometrists' interpretation of optic disc appearance is somewhat better than their interpretation of visual fields, agreeing with previous findings. It may also reflect how the time constraints within general community optometry practice affect the reliability of visual field testing; indeed some practices employ non-optometry staff to undertake these ‘ancillary’ tests who may not necessarily have the same training in visual field test procedure as the optometrist.
Of note is the finding that of the 12 patients who were found at their HES visit to have narrow anterior chamber angles requiring peripheral iridotomies, only 4 of these patients had been referred on the basis of suspicious angles detected by the optometrist. Undetected narrow angle glaucoma is becoming an increasing concern. Worldwide, approximately one-third of all primary glaucomas are caused by angle closure mechanisms, but approximately 75% of patients never experience an acute attack. Whilst gonioscopy is the gold standard for viewing the anterior chamber angle, the slit-lamp Van Herick technique, if done correctly, may be just as sensitive at picking up those at risk of angle-closure. The Van Herick technique does not take much time to administer, and perhaps should be more readily employed routinely by community optometrists.
In the 6-week period covered by our study we found that there were a total of 114 optometrist generated glaucoma suspect referrals to the HES. This represents an ~ 50% increase in optometrist-initiated referrals compared with that found by Scully, who reported 140 optometrist-initiated referrals over a 4 month period from December 2006, prior to the introduction of the NICE guidelines However, as the number of new referrals varies from month to month and the two studies were carried out over different time frames it is not possible to draw any firm conclusions from this observation. Shah and Murdoch reported a similar increase in referrals to a Moorfields Glaucoma Community service over a 2-month period post-NICE guidelines. Despite this increase in the number of new referrals, the proportion of patients being diagnosed with glaucoma or glaucoma suspect appears to remain unchanged. Our study found that 30% of patients referred were diagnosed as glaucoma or glaucoma suspects, similar to that found in a large-scale study by Bowling in 2005. Thus it appears that whilst referral numbers may have increased, the proportion of those being diagnosed with glaucoma has remained the same. This is in contrast to the findings of Shah and Murdoch who found a reduction in the positive predictive value of new referrals compared to studies they had performed in their Community Glaucoma Service pre-NICE. The presented study reports the referrals to the main hospital site in central London, whereas the Shah and Murdoch study reports that from a suburban area in West London; thus the finding may reflect a difference in the referral practice of optometrists serving the different catchment areas.
The study was performed at a single site in inner city London and there may be regional differences in optometrist practice. Despite this it is clear that there is room for improvement by optometrists in following published guidelines for the referral of suspect glaucoma patients. With an increase in the total number of referrals to HES, the added burden to the NHS is considerable. Community optometrists should be encouraged to use GAT to measure IOP but those using NCT for measurement should be reminded of the guidelines on number of readings to take and also the value of repeating NCT measures when appropriate. This may help to increase the accuracy of glaucoma suspect referrals to hospital eye service.