Given the seriousness of the retinopathy in this patient, extensive pretreatment counseling is essential. With or without treatment this eye is at risk of visual loss. The patient should understand that extensive laser treatment is anticipated and vitrectomy surgery may be needed in an effort to preserve vision. The alternatives, risks, benefits, and limitations of treatment are routinely reviewed. Finally, clear infor-

mation on the benefits of optimal management of systemic disease is given to the patient.m,115,116

16.14Case 14: How Is Diabetic Macular Ischemia Related to Visual Acuity?

16.14.1 Definition of the Problem

The clinician may be faced with the dilemma of attempting to predict the visual outcome in a case

of diabetic retinopathy complicated by diabetic macular ischemia. For example, a patient may present with a combination of diabetic macular edema and ischemia, or combined preretinal membrane and macular ischemia. In these situations a general determination must be made regarding the visual potential in order to weigh various management options. The following exercise is designed to explore the confidence of the clinician in predicting the best corrected visual acuity based on the magnitude of macular capillary dropout (Fig. 16.53).

A 73-year-old man has had type 2 diabetes mellitus for 11 years and hypertension for 25 years. He has had multiple focal/grid macular laser and panretinal photocoagulation treatments in the past and is bilaterally pseudophakic. Presently, there is no evidence of diabetic macular edema (DME) detected by fundoscopy or optical coherence tomography (Fig. 16.53). What visual acuity would you predict based on the degree of macular capillary

Fig. 16.54 Early-phase frame of the fluorescein angiogram from the right eye of case 14

Fig. 16.55 Late-phase frame from the fluorescein angiogram of the right eye of case 14

nonperfusion shown on the fluorescein angiogram (Figs. 16.54 and 16.55)?

16.14.2 Discussion

This patient has severe diabetic macular ischemia. The optical coherence tomogram (OCT) shows loss of inner retinal structural details as shown on the line scan and generalized thinning of the macula is evident on the false color map. The central subfield macular thickness (CSMT) is remarkably reduced at 152 mm. There is no evidence of preretinal membrane or vitreomacular traction. Although we cannot rule out the possibility of permanent structural damage from

past DME, there is no sign of degenerative cystic change. The early-phase fluorescein angiogram (FA) reveals no significant central macular defects in the retinal pigment epithelium. Central macular capillary nonperfusion is detected on the late phase of the FA as an area of relative hypofluorescence surrounded by low-grade diffuse leakage of fluorescein. Although the area of the foveal avascular zone is not given, it appears to be approximately equal to one disc area (1.77 mm2). Thus, the primary vision-limiting factor for this eye is diabetic macular ischemia (DMI).

The chapter authors who independently reviewed this case were asked to comment on their ability to predict the visual acuity based on the presence of severe DMI. In general, the doctors expressed a fairly low confidence in their ability to reliably predict the visual acuity of this patient. Doctor A commented on the irregularity of the foveal avascular zone (FAZ), but interpreted the OCT as showing a ‘‘relatively physiologic foveal architecture.’’ He predicted a range of visual acuity from 20/40 to 20/300. Doctor B estimated the diameter of the irregular FAZ to be 1,000–1,700 mm, which he interpreted to be consistent with 20/100 to 20/300 vision. Doctor C expressed a very low confidence in predicting vision by offering a range from 20/40 to count fingers. The actual best corrected visual acuity in this case was 20/100.

The literature offers limited information regarding the impact of diabetic macular ischemia on visual acuity. The most specific data correlating visual acuity with FAZ area was published by Arend et al.,117 who studied diabetic eyes with video-fluor- escein angiography using a scanning laser ophthalmoscope for high-resolution images of the foveal avascular zone. Image analysis software was used to calculate the area of the FAZ in a masked fashion without prior knowledge of the visual acuity. In their study, decreased visual acuity correlated significantly with increasing FAZ area (R2 = 0.51). Visual acuity less than 20/50 was found to be consistent with an FAZ 0.55 mm2. Their study was limited to 30 diabetic eyes and showed considerable latitude in visual acuity for any given FAZ area measurement (Fig. 8.16). Thus, it is not surprising that there was such a wide range on opinions among the authors who responded to this exercise.n

n Discussed by Scott E. Pautler, M.D.