Optical coherence tomography (OCT) for detection of macular oedema in patients with diabetic retinopathy

Diabetic macular oedema (DMO) is a thickening of the central retina, or the macula, and is associated with long-term visual loss in people with diabetic retinopathy (DR). Clinically significant macular oedema (CSMO) is the most severe form of DMO. Almost 30 years ago, the Early Treatment Diabetic Retinopathy Study (ETDRS) found that CSMO, diagnosed by means of stereoscopic fundus photography, leads to moderate visual loss in one of four people within three years. It also showed that grid or focal laser photocoagulation to the macula halves this risk. Recently, intravitreal injection of antiangiogenic drugs has been investigated to try to improve vision in people with macular oedema due to DR.Optical coherence tomography (OCT) is based on optical reflectivity and is able to image retinal thickness and structure producing cross-sectional and three-dimensional images of the central retina. It is already widely used because it provides objective and quantitative assessment of macular oedema unlike the subjectivity of fundus biomicroscopic assessment, which is routinely used by ophthalmologists instead of photography. Optical coherence tomography is also used for quantitative follow up of the effects of treatment of CSMO. Disadvantages of using OCT are the cost to purchase it and the need for trained personnel to perform the examinations.

To determine the diagnostic accuracy of OCT for detecting macular oedema in people with DR. A secondary objective is to compare the diagnostic accuracy by study-specific characteristics, such as factors related to methodology, patients or OCT.

We searched the Cochrane Database of Systematic Reviews (CDSR), the Database of Abstracts of Reviews of Effects (DARE), the Health Technology Assessment Database (HTA) and the NHS Economic Evaluation Database (NHSEED) (The Cochrane Library 2011, Issue 5), MEDLINE (January 1950 to May 2011), EMBASE (January 1950 to May 2011), ISI Web of Science (January 1970 to May 2011), BIOSIS Previews (January 1969 to May 2011), MEDION and the Aggressive Research Intelligence Facility database (ARIF). There were no date or language restrictions in the electronic search for trials. The electronic databases were last searched on 16 May 2011. We checked bibliographies of relevant studies for additional references.

We selected studies that assessed the diagnostic accuracy of any OCT model for detecting DMO or CSMO in patients with DR who were referred to eye clinics. Diabetic macular oedema and CSMO were diagnosed by means of fundus biomicroscopy by ophthalmologists or stereophotography by ophthalmologists or other trained personnel.

Three authors independently extracted data on study characteristics and measures of accuracy. We assessed data using random-effects hierarchical sROC meta-analysis models.

Nine studies (768 participants, 1325 eyes) were included. Prevalence of CSMO was 19% to 65% (median 50%). Study quality was good for half the QUADAS items, whereas unclear or inadequate quality was found in some studies regarding selection criteria, index and reference test masking (blinding), availability of clinical information, uninterpretable results and withdrawals. There was a specific 'unit of analysis' issue because both eyes of the majority of participants were included in the analyses as if they were independent.Central CSMO was the target condition in all but one study and thus our results cannot be applied to non-central CSMO. In eight studies providing data on CSMO (697 participants, 1241 eyes), pooled sensitivity was 0.78 (95% confidence interval (CI) 0.72 to 0.83) and specificity was 0.86 (95% CI 0.76 to 0.93). The median central retinal thickness cut-off we selected for data extraction was 250 µm (range 230 µm to 300 µm).Data from three studies reporting accuracy for detection of DMO (180 participants, 343 eyes) were not pooled. Sensitivities and specificities were about 0.80 in two studies and were both 1.00 in the third study.

Central retinal thickness measured with OCT cannot be used as a stand-alone test to diagnose the central type of CSMO and decide on the use of laser photocoagulation in patients who are referred to retina clinics. In fact, there is a substantial disagreement of OCT with the ETDRS definition of CSMO based on clinical examination. Some researchers have observed that OCT can detect macular thickening earlier than clinical examination, but also found that such cases did not necessarily progress to CSMO and need photocoagulation.Care should be taken in applying the conclusions of this review to other test-treatment pathways. In fact, OCT will become an essential tool to manage antiangiogenic therapy, an expanding therapeutic option for patients with macular oedema due to DR, because OCT is a component of the diagnostic algorithms of studies on this new treatment.