Ординатура / Офтальмология / Английские материалы / Diabetes and Ocular Disease Past, Present, and Future Therapies 2nd edition_Scott, Flynn, Smiddy_2009

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Figure 8.3. The color fundus photograph (top row, left) demonstrates severe nonproliferative diabetic retinopathy with multiple large blot retinal hemorrhages and numerous scattered microaneurysms and hard exudates throughout the posterior pole causing gross macular edema. The early- (top row, center) and late-phase (top row, right) fluorescein angiogram show a diffuse pattern of fluorescein leakage in a circinate arrangement about the foveal center. Enlargement of the foveal avascular zone is also appreciated. The optical coherence tomography (OCT) macular contour map (bottom row, left) depicts a broad zone of extensive macular thickening with a central foveal thickness measuring 627 microns and similar thickness levels noted in the adjacent subfields. The vertically oriented radial OCT scan (bottom row, right) shows an incomplete posterior vitreous detachment, massive outer retinal cystic elements and a peaked fovea. Small hyperreflective intraretinal foci with posterior optical shadowing are consistent with hard exudates. No foveal detachment is noted.

cases where the vision is more significantly compromised than can be explained by the clinical examination [37]. One shortcoming of OCT is the inability, at present, to evaluate the retinal periphery anterior to the equator. B-scan ultrasound remains the most useful adjunct to clinical examination for this region.

FAST MACULAR THICKNESS MAP

The fast scan is similar to the radial lines scan on the Stratus OCT, except that the scan speed is approximately twice that of the radial lines scan. This results in a lower resolution compared to the radial lines scan, but the fast scan is the one most often used in retinal thickness measurements because it is typically less prone to sampling artifacts than the slower scan [34,37]. It is also a good second-choice scan, when poor patient cooperation limits the acquisition of a normal resolution radial lines scan. Even patients with poor cooperation can generally be imaged

Figure 8.4. This is a 74-year-old man with type 2 diabetes mellitus and regressed proliferative diabetic retinopathy following pan retinal photocoagulation. Visual acuity at presentation was 20/200. He developed complex vitreomacular traction, epiretinal membrane, and cystoid macular edema as shown on the vertical (top row, left) and horizontal (bottom row, left) optical coherence tomography (OCT) scans. A shallow foveal detachment is also noted. After pars plana vitrectomy with membrane peeling, resolution of the vitreomacular traction, and residual epiretinal membrane and cystoid macular edema are noted on the vertical (top, right) and horizontal (bottom, right) OCT scans. Visual acuity improved to 20/60 postoperatively.

with the fast scan protocol because all six fast scans are obtained automatically in rapid sequence without interruption between scans, whereas each individual normal resolution radial lines scan is obtained by the OCT operator separately in sequence. Because the fast macular thickness map is easier to obtain, it is used as the primary scan by some practitioners. If the fast macular thickness map appears normal, no further scanning is performed. If the fast macular thickness map scans are abnormal, then additional higher resolution radial line scans are performed to better assess the pathology.

PERIPAPILLARY RETINAL NERVE FIBER LAYER (RNFL) ANALYSIS

Used most often as a glaucoma screening and monitoring tool, the peripapillary RNFL analysis quantifies the thickness of the peripapillary RNFL and compares a patient’s thickness with a normative database [38,39]. A circular scan is obtained in the peripapillary region [37]. RNFL thickness is obtained via boundary analysis and arithmetic difference calculations; however, instead of measuring the inner and outer retinal boundaries, the inner and outer boundaries of the RNFL are identified. Significant deviations in RNFL thickness from the normative database indicate a greater risk for glaucomatous thinning of the peripapillary RNFL in each of the four peripapillary quadrants (inferior, superior, nasal, and temporal) [37–39].

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Figure 8.5. This is a 45 year-old man with type 2 diabetes mellitus and complaints of decreased visual acuity (VA) in the right and left eyes. VA measures 20/20. Compared to the left eye, the color fundus photograph of the right eye (top row, left) shows fewer blot retinal hemorrhages and microaneurysms. Similar to the left eye, the microaneurysms are temporally located. The mid- (top row, center) and late-phase (top row, right) fluorescein angiogram shows an enlarged foveal avascular zone, numerous microaneurysms, and a temporal pattern of diffuse leakage late in the study. Once again, the fluorescein leakage pattern corresponds well with the optical coherence tomography (OCT) macular contour map (bottom row, left) which reveals the greatest retinal thickening temporally. Despite good VA, the central foveal thickness measures 439 microns. The vertically oriented radial OCT scan (bottom row, right) reveals an incomplete posterior vitreous detachment over the macula, foveal cystic elements, and a foveal detachment.

NONPROLIFERATIVE DIABETIC RETINOPATHY (NPDR)

AND DIABETIC MACULAR EDEMA (DME)

OCT’s greatest utility in evaluating patients with nonproliferative diabetic retinopathy (NPDR) is the ability to detect and quantify the central retinal thickness in patients with clinically diagnosed DME [1,2,40–47]. In patients with mild NPDR and vision loss, OCT is often a good first diagnostic test if clinical exam and refractive changes do not account for vision loss (Figs. 8.1B–8.7) [40–42].

Structural macular derangements in patients with CSME include OCT patterns that demonstrate: (1) focal foveal and parafoveal intraretinal cystic thickening (Figs. 8.1B and 8.2); (2) diffuse intraretinal cystic thickening throughout the macular region (Fig. 8.3); (3) focal or broad vitreoretinal adhesions with resultant cystic retinal thickening and loss of the foveal contour consistent with a clinical diagnosis of taut posterior hyaloidal traction (Figs. 8.4 and 8.5) [1,2].

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Figure 8.6. This is the left eye of the same patient in Figure 8.5. Visual acuity is 20/40. The color fundus photograph (top row, left) shows several areas of blot hemorrhages and numerous microaneurysms that are grouped temporal to the thickened fovea. The early- (top row, center) and latephase (top row, right) fluorescein angiogram shows diffuse leakage on the temporal aspect of the macula and throughout the posterior pole. The optical coherence tomography (OCT) macular contour map (bottom row, left) matches the areas of leakage, showing the greatest retinal thickness in the temporal and superior macular regions. Central retinal thickness measures 608 microns. The vertically oriented radial OCT scan through the macula demonstrates incomplete posterior hyaloidal separation and a faint surface membrane with a blunted foveal depression, the presence of moderately sized cystic spaces in the outer retina, multiple highly-reflective foci in the fovea consistent with hard exudates, and a foveal detachment.

Historically, DME has been characterized as being focal or diffuse [48], but OCT has broadened our understanding of the relationship between DME and visual acuity. There is some controversy regarding the notion that OCT may serve as a proxy for visual acuity insofar as DME with significant central foveal thickening is associated with poor vision, while a nonedematous macula with a normal central retinal thickness is associated with good vision [49,50]. This somewhat simplified view does not take into consideration causes of vision loss other than macular swelling (e.g., foveal ischemia, epiretinal membrane, vitreomacular traction). It is true that not all visual loss in patients with diabetic retinopathy may be attributable to retinal thickening, cystoid macular edema, or subretinal fluid seen with OCT. Sometimes, occult concomitant retinal vascular disease is present that can confuse the clinical evaluation and OCT can be helpful in addition to clinical examination and fluorescein angiography. Commonly, macular ischemia may be present and appear as a relatively thin-appearing retina on OCT. Fluorescein angiography best characterizes macular ischemia by demonstrating enlargement of the capillary free zone (or foveal avascular zone), but can also demonstrate leakage

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Figure 8.7. These images are from a 65-year-old man with type 2 diabetes mellitus and moderate to severe nonproliferative diabetic retinopathy. Visual acuity in the right eye is 20/25. The color fundus photograph (top row, left) shows several dot-blot hemorrhages and scattered hard exudates throughout the posterior pole. Although foveal exudates are present, questionable thickening is seen centrally. The mid- (top row, center) and late-phase (top row, right) fluorescein angiogram show leakage in an area superior to the fovea, although the foveal region is not affected by leakage. The optical coherence tomography (OCT) macular contour map (bottom row, left) mirrors the pattern of OCT leakage, ascribing the greatest thickening to the perifoveal region in the superior macula. The central 1-mm subfield foveal thickness measures just 274 microns, while more peripheral subfields show greater thickening, ranging from 360 to 380 microns. The vertically oriented radial OCT scan through the fovea demonstrates an incomplete posterior vitreous detachment, a relatively normal foveal contour with small cystic elements, and hyperreflective retinal foci consistent with foveal hard exudates. No subretinal fluid is appreciated in this case.

late in the study in patients with chronic macular ischemia. This synergy of diagnostic modalities is especially helpful when considering laser or pharmacologic treatment options for vision loss in diabetic retinopathy. Pharmacotherapies (e.g., triamcinolone acetonide, antivascular endothelial growth factor agents) typically improve vision, by reducing the vascular permeability that is causing CME. In the instance of thin/atrophic-appearing retina on OCT with nonperfusion (early) and leakage (late) in the angiogram, it would therefore not be anticipated that a pharmacologic agent would be effective at improving vision.

Spectral domain OCT (SD-OCT) is also able to quantify and qualitatively evaluate DME [51]. Although quantitative comparisons may be made between central retinal thickness measurements for the same patient imaged on the same SD-OCT unit, it appears that such comparisons cannot be made for a patient imaged on one visit with a time domain OCT unit and on another visit with an SD-OCT unit [51]. SD-OCT does provide spectacular views of macular anatomy in diabetic patients

Figure 8.8. A 45-year-old man with proliferative diabetic retinopathy (PDR) presented with macular tractional retinal detachment (TRD) in his right eye. Preoperative montage color fundus photography revealing PDR with fibrous tuft on the optic disk with macular TRD (top row, left). Postoperative montage color fundus photography (bottom row, left) showing surgical release of fibrous epiretinal membranes and retinal reattachment. Preoperative SD-OCT revealing extensive subretinal fluid and intraretinal fluid below a tractional membrane (top row, right). The central subfield in the macula was 682 microns. Postoperative SD-OCT (bottom row, right) showing significant improvement in subretinal fluid, absence of the membrane, and retinal reattachment. The central subfield in the macula was 312 microns. (Source: Adapted from Kay et al, Ophthalmic Surg Lasers Imaging [61].)

and is particularly helpful in evaluating the vitreoretinal interface when planning the surgical approach to a patient with PDR and tractional retinal detachment of the macula (Figs. 8.8, 8.12, and 8.14).

TREATMENT MONITORING WITH OCT

OCT’s qualitative and quantitative analytical capabilities make it a versatile tool not only for static evaluation of the patient, but also to monitor changes in the patient’s condition from one visit to the next. One thing we have learned is that OCT is more sensitive than the ophthalmologist’s clinical examination (even with stereoscopic contact lens biomicroscopy) at detecting macular edema [40–42,52]. Although some interoperator variability exists, overall, OCT has been found to be quite reproducible in its ability to detect and quantify DME [43–45,53].

For many, if not the majority, of cases of typical DME (patients without foveal ischemia, vitreomacular traction, foveal exudates (Fig. 8.7), or epiretinal membrane), CME with markedly increased central foveal thickness is the

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Figure 8.11. This is a 42-year-old type 1 diabetic man with bilateral “table-top” traction retinal detachments involving the macula due to advanced proliferative diabetic retinopathy as shown in the montage color fundus photographs of the right (top row, left) and left (bottom row, left) eye. The hyperreflective membrane shallowly separated from the inner retinal surface in both optical coherence tomography (OCT) scans represents the posterior hyaloid face. The oblique optical coherence tomography (OCT) scan (starting superonasal to the fovea and ending inferotemporal to the fovea) of the left macula (bottom row, right) shows the proximity of the subretinal fluid to the foveal center. Remarkably, visual acuity was 20/80 (right eye) and 20/60 (left eye).

usual presentation in patients with vision loss (Fig. 8.6). In these cases, changes in the central foveal thickness often do correlate with changes in visual acuity (Fig. 8.7) [54]. Patients generally appreciate improved vision (subjectively and objectively) associated with the rapid reduction in central foveal thickness following intraocular pharmacotherapy and, conversely, notice the rebound increase in their central foveal thickness (and worsening vision) after the anatomic effects of pharmacotherapy have subsided. Likely because of the multifactorial nature of vision fluctuation in diabetic eyes [40–47,55], the correlation between central retinal thickness and visual acuity is not always appreciated [49,50,56,61,62].

Nevertheless, OCT is a valuable tool to monitor treatment response. Following focal laser photocoagulation or intraocular pharmacotherapy, documented reduction in macular thickness confirms a positive anatomic response. In addition, maintenance of reduced macular thickness may help aid the clinician in deciding to withhold follow-up treatments. Recrudescence of macular edema and associated

Figure 8.12. A 71-year-old man with proliferative diabetic retinopathy (PDR) presented with macular traction retinal detachment in his right eye. Preoperative color fundus photography demonstrates macular traction retinal detachment from PDR (top row, left). Postoperative color fundus photography (bottom row, left) demonstrates absence of epiretinal membranes and retinal reattachment. Preoperative spectral domain OCT (SD-OCT) (top row, right) reveals extensive subretinal fluid and epiretinal membranes. The central subfield in the macula was 476 microns. Postoperative SD-OCT (bottom row, right) depicts considerable resolution of this fluid, absence of the membrane, and retinal reattachment. The central subfield in the macula was 333 microns. (Source: Adapted from Kay et al., Ophthalmic Surg Lasers Imaging [61].)

increases in the central retinal thickness after a period of stability may indicate the need for additional therapy. Besides the valuable quantitative and qualitative information that the OCT provides on each patient longitudinally, the physician obviously integrates all available patient data to make informed and appropriate treatment decisions.

VITREORETINAL TRACTIONAL ABNORMALITIES AND DME

In the early 1990s, there was a recognition that diffuse DME was often associated with a taut and thickened posterior hyaloidal face that exerted tractional forces on the macula [57]. Without the benefit of OCT, it was recognized that a shallow foveal detachment was also present in these cases (Figs. 8.4, 8.5, and 8.7) [57]. Later evaluation of such patients with OCT documented the presence of both the posterior hyaloidal traction and the foveal detachment, although the latter was not always appreciated [58]. In these cases of posterior hyaloidal traction, OCT demonstrates resolution of the macular edema and foveal detachment after vitrectomy relieves the tangential traction exerted by the taut and thickened posterior hyaloid