Partly in response to the increasing burden on the hospital eye service resulting from demographic changes, major modifications to the way glaucoma detection and care are carried out in the United Kingdom are likely in the near future. Government plans envisage a significant proportion of clinical glaucoma management being transferred from hospital to primary care.
Central to the new system will be the development of a cadre of specialist optometrists, who, it is proposed, will assume much of the work of screening and initial management of referrals for suspected glaucoma currently carried out by ophthalmologists.
In light of these impending developments in service provision, we examined the outcomes of glaucoma referrals to our unit under the current system. Our principal aim was the provision of feedback to local referral sources, comparing our own data with previously published results. Given the large number of referrals surveyed, the information furnished should also be of interest to a geographically and professionally wider audience, aiding planning and resource allocation and providing a baseline against which the effectiveness of any novel system can be compared.
DISCUSSION
Differences between surveys are evident across a range of parameters including diagnostic definitions and classification systems, methods of data collection, referral sources and population demographics. Some studies included only a small number of patients, and have been criticised for the resultant limited statistical legitimacy. It is important to emphasise in this context that our own reported diagnostic outcomes are based exclusively on the information available at the initial consultation. This should also be borne in mind when considering our figures for the initiation of treatment.
Our confirmed glaucoma rate of just over 20% is similar to the 17% rate found in the Edinburgh study of 271 patients seen over 6 months from 1993 to 7 and the 22% found by Harrison et al and Theodossiades and Murdoch. The diagnosis of NTG is complicated by considerations such as diurnal IOP variation. Theodossiades and colleagues specifically excluded NTG as a category distinct from open angle glaucoma in their study of referrals as it was thought that the diagnosis could not be made authoritatively following a single clinic appointment. Based on the IOP at the initial hospital examination, approximately one third (31%) of our confirmed glaucomas fell within the NTG group, a similar rate to the 33% reported by the Edinburgh study.
Our OHT rate was just under 30%. There has been substantial variation in reported rates, which in recent studies range from 14% to 42%. Not all published studies have included OHT as a distinct diagnostic category, including the largest before our own, which grouped patients with OHT and glaucoma suspects together in the category “uncertain, follow up required.” We found a glaucoma suspect rate of 5.0%. Half of the studies reviewed did not have an explicit “glaucoma suspect” grouping, and valid comparison with other published data is particularly difficult with respect to this category, which, almost by definition, may be prone to a higher degree of subjectivity.
Treatment to reduce IOP was instituted for 458 patients (18.3% of referrals), mainly for glaucoma. A minority of those treated had OHT or were glaucoma suspects. While some previous surveys detail the proportion of patients with OHT commenced on treatment, none has reported the number of treated confirmed glaucoma patients. Some of our patients are likely to have been treated subsequent to the first consultation upon which the presented findings are based. This may apply particularly to patients with NTG, for whom treatment is often withheld pending evidence of progression; in our survey, 79% (276/350) of those with glaucoma featuring elevated IOP were treated at the first visit, but only 54% (87/160) of those with NTG.
A total of 1148 (45.8%) patients were discharged from ophthalmological review, the majority of whom had no evidence of glaucoma; some had OHT but were considered to be at extremely low risk of developing glaucoma, and others had pathology which did not require further ophthalmological intervention at the time of assessment. Four patients with glaucoma (including three with NTG) and one glaucoma suspect were discharged, as their life expectancy was considered low in comparison with the risk of visually significant glaucomatous progression.
In the only other study reporting a specific figure for patients who were discharged, 30% required no follow up. By no means will every referral have been made in the belief that the patient definitely had glaucoma. This has been studied by Tuck, who found that 74% of the patients referred by an optometrist with “almost definite” glaucoma were confirmed as having the condition, compared with only 21% of “possible” glaucomas. Community optometrists are under considerable pressure to detect every case of sight threatening disease, with a missed diagnosis having potentially serious ramifications for the responsible practitioner.
In contrast, little disadvantage results from a false positive referral. Many patients will have been referred in the belief that they had OHT rather than glaucoma and that only monitoring was required. Under the present system there may be no alternative in these circumstances to a request for appraisal by the hospital eye service, but these patients may in the future be managed in the community by a specialist optometrist. Henson et al have reported a cost effective 40% reduction in new glaucoma referrals to Manchester Royal Eye Hospital from a scheme involving initial assessment by specially trained community optometrists, although figures for diagnostic accuracy have not yet been published.
In conclusion, this study is the largest survey to determine the outcomes resulting from optometric referrals for suspected glaucoma to a specialist hospital eye clinic. It is hoped that planned changes to the system of referral for suspected glaucoma in the United Kingdom will lead to a substantial decrease in the number of false positives reaching the hospital eye service, without a commensurate increase in false negatives.
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