with the grid part of focal/grid photocoagulation, but there is a perspective that such ischemic zones need not be treated with grid laser.60 This point of view may derive from a study on edema associated with perfused versus nonperfused branch retinal vein occlusion in which nonperfused zones of edema resolved spontaneously.65 Although DME and macular edema in BRVO may be quite different, the extrapolation in treatment philosophy seems to exist among a subgroup of ophthalmologists.

Even if one strictly adheres to ETDRS style focal/ grid treatment technique, it is apparent that considerable subjectivity creeps into the process. For example, the ETDRS protocol explicitly omits guidelines on treating microaneurysms involving the perifoveal capillary network, and there is wide variation in reading center grading of what constitutes focal ver-

sus diffuse leakage on the fluorescein angiogram (and hence where to apply focal laser).60,66 Variation

among clinician interpreters of fluorescein angiograms – and thus where they do and do not treat focally – is likely even greater than the variation of professional reading center graders.

In an era of multiple treatment approaches for DME, it is becoming less common to see examples like cases 3 and 11. Rather, futility of focal/grid is often declared after 1–2 treatments if DME persists, and a pharmacologic or surgical approach is taken instead. Nevertheless, focal/grid laser is a superior treatment to serial intravitreal triamcinolone injections, and until a randomized trial shows that some other treatment approach is better, the question of what constitutes maximal focal/grid laser treatment remains important, problematic, and topical for further study.48,h

16.9Case 9: What Independent Information Does Macular Perfusion Add to Patient Management in Diabetic Retinopathy?

The AAO preferred practice pattern on Diabetic Retinopathy states that fluorescein angiography is ‘‘usually’’ useful to evaluate unexplained visual loss.67 Clinicians widely embrace this perspective and look at fluorescein angiograms to assess macular ischemia. Yet the variability of these assessments is unknown. The presumption is that there is enough correlation between the clinician’s interpretation of macular ischemia and levels of visual acuity that the test could be informative for patient care.

Consider the following case in this vein. The patient has had type 1 diabetes for 25 years and has previously had focal/grid laser for diabetic macular edema and panretinal photocoagulation for proliferative diabetic retinopathy. The OCT and FA are shown (CSMT = 262 mm) (Figs. 16.39 and 16.40). What are the bounds on your estimate of the visual acuity based on your interpretation of the macular perfusion?

16.9.1 Discussion

The four reviewers of this case were unanimous in stating their uncertainty in utilizing fluorescein angiography to predict current visual acuity. In spite of this uncertainty the predicted visual acuities were consistent with three reviewers predicting

Fig. 16.40 Frame from the early venous phase of the fluorescein angiogram showing the degree of macular perfusion in an eye that has previously had both focal/grid and panretinal photocoagulation for macular edema and proliferative retinopathy, respectively

20/40 visual acuity and one reviewer predicting 20/ 50 visual acuity. This consistency is interesting in light of the patient’s tested visual acuity of 20/200. Why were all of the reviewers so uniformly off base?

One reviewer pointed out that this case exercise reverses our traditional path of obtaining information from the patient in which a medical history (which includes duration of diabetes and history of blood sugar control) precedes an examination (which includes obtaining a visual acuity) which precedes ancillary testing (optional). The discussant believes that the consistency of the reviewers’ predictions is based on the current widespread use of OCT ancillary testing in preference to fluorescein angiography. OCT technology first became available for clinical practice in 2002. Prior to availability of OCT technology the gold standard for managing diabetic macular edema was based on the Early Treatment Diabetic Retinopathy Study. Color photography and fluorescein angiography were protocol ancillary tests in the Early Treatment Diabetic Retinopathy Study and protocol administration of laser therapy was based on fluorescein angiographic guidance. In 1991 the American Academy of Ophthalmology established Diabetes 2000 as a concerted educational effort to ‘‘reduce – and possibly eliminate – preventable blindness from diabetes by the year 2000.’’ 68 As a consequence it is not surprising that in the 1990s

fluorescein angiography was utilized in clinical practice in nearly 100% of cases to manage diabetic macular edema.

In current clinical practice for management of diabetic macular edema, OCT has supplanted fluorescein angiography in its usage rate. In 2007 a DRCR.net clinical trial to investigate the effect of intravitreal bevacizumab on diabetic macular edema protocol OCTs was obtained routinely. In this setting of mandated OCT testing, the optional usage rate for obtaining fluorescein angiography was 51%.64 In the management of diabetic macular edema this shift in usage from fluorescein angiography to OCT may be due to the reliability and reproducibility of OCT in directly measuring macular edema. In comparison, ischemia, leakage, and RPE abnormalities as assessed by fluorescein angiography have at best a variable correlation with macular edema. The reproducibility of fluorescein angiography to measure macular ischemia is variable even when angiography is performed in academic centers.69

Even though OCT-measured macular thickness correlates modestly with visual acuity the discussant believes that the trend for clinicians to utilize OCT preferentially over fluorescein angiography in managing diabetic macular edema leads to a bias to predict visual acuity preferentially based on OCT data.69 The nearly normal foveal anatomy in this case probably explains the nearly normal visual acuity predicted by the four respondents.

When challenged to predict visual acuity based on macular perfusion two respondents used OCT data to help interpret the fluorescein angiogram. They suggested that the lack OCT thinning implies the lack of significant macular ischemia. These views highlight the reliance on OCT and the difficulty with subsequent lack of confidence in quantifying macular ischemia on fluorescein angiography.

The AAO preferred practice pattern in 2008 indicates that ancillary tests such as color fundus photography, optical coherence tomography, and fluorescein angiography may enhance patient care.67 The ‘‘appropriate’’ role of ancillary testing in this case was touched upon by two respondents with distinctly different viewpoints. One respondent used fluorescein angiography only to guide location of laser therapy but not to prognosticate response. The ETDRS supports this approach with published guidelines to support the use of fluorescein