Grade
Mean visual acuity
Ophthalmoscopy
Fundus autofluorescence (FAF)
Optical coherence tomography
Fluorescein angiography (FA)
1
20/20 (range, 20/25–20/16)
Mild pigmentary abnormalities in the central fundus (Fig. 8.1a)
Mild hypoautofluorescent mottling (Fig. 8.1b)
No obvious abnormalities (Fig. 8.1d)
Small hyperfluorescent spots (Fig. 8.1c)
2
20/20 (range, 20/63–20/12.5)
Isolated or multifocal faintly white-yellowish and/or hyperpigmented subretinal deposits in posterior pole (Fig. 8.1e)
Yellow-white spots/flecks correspond to mostly increased FAF; decreased FAF in mildly atrophic areas (Fig. 8.1f)
Irregular thickening and/or attenuation of the line corresponding to the photoreceptor inner/outer segment (ellipsoid) area; underlying retinal pigment epithelium (RPE) somewhat attenuated and irregular
Hypofluorescence of spots/flecks on FA due to blockage of background fluorescence; hyperfluorescent window defects in mildly atrophic zones
3
20/25 (range, 20/40–20/16)
Appearance of one or more areas of well-delineated, profound chorioretinal (“geographic”) atrophy outside the fovea, in addition to grade 2 abnormalities (Fig. 8.2a)
Well-defined areas of absent autofluorescence due to atrophy of the lipofuscin-containing RPE in deeply atrophic areas (Figs. 8.2b)
Attenuated RPE cell layer as well as a markedly attenuated photoreceptor layer and external limiting membrane in areas of chorioretinal atrophy (Fig. 8.2d)
RPE window defects with visibility of the underlying larger choroidal vasculature and atrophy of the choriocapillaris
4
20/80 (range, 20/630–20/40)
Central fovea affected by profound chorioretinal atrophy (Fig. 8.2e)
Area of absent autofluorescence involving the fovea (Fig. 8.2f)
Atrophy of the outer retinal layers (Fig. 8.2g)
RPE window defect and atrophy of choriocapillaris in area of geographic atrophy
Patients with grade 1 MRD have discrete pigmentary abnormalities in the central fundus (Fig. 8.1a–d, Table 8.1) [2] that are also barely visible on autofluorescence and fluorescein angiography. Without prior knowledge of the underlying m.3243A>G mutation, these changes can be easily overlooked. The visual acuity in this early grade MRD is excellent.
Fig. 8.1
Grade 1 and 2 mitochondrial retinal dystrophy (MRD). (a) Color fundus photograph of grade 1 MRD in an asymptomatic 42-year-old patient with a visual acuity of 20/20. (b) On detailed ophthalmoscopy, discrete pigmentary changes could be observed in the macula, which corresponded to mild but clearly visible mottled fundus autofluorescence (FAF) changes in the macula and peripapillary region. (c) Fluorescein angiography showed mild mottled hyperfluorescent abnormalities. (d) Optical coherence tomography in grade 1 MRD shows no obvious abnormalities. (e) Color fundus photograph of grade 2 MRD in a 27-year-old patient carrying the m.3243A>G (visual acuity: 20/20) showing an oval area of mottled hypopigmentation and hyperpigmented spots in the macula and around the optic disc. (f) FAF imaging shows mottled autofluorescence changes, with relative preservation of the foveal autofluorescence which is seen in many MRD cases
In grade 2 MRD, isolated or multifocal faint white-yellowish or hyperpigmented subretinal deposits are present in the posterior pole (Fig. 8.1e, f) [2]. These deposits are visible in addition to the extremely fine pigment changes in grade 1 MRD. Few deposits can be present in early grade 2 disease, but the pigment changes involve the entire macula and sometimes encircle the optic disc in advanced grade 2 MRD. Fundus autofluorescence in grade 2 MRD shows granular changes and/or irregular flecks of increased and decreased autofluorescence. Fluorescein angiography shows mainly hyperfluorescence due to moderate RPE atrophy, except in areas of hyperpigmentation blocking background fluorescence. In all of these imaging modalities, the foveal aspect appears relatively spared, with a correspondingly preserved visual acuity.
Grade 3 MRD is characterized by the appearance of one or more areas of well-delineated areas of chorioretinal (“geographic”) atrophy outside of the fovea (Fig. 8.2a–d) [2]. In grade 3 MRD, the area of geographic atrophy does not involve the central fovea in contrast to grade 4 disease, again explaining the relatively preserved visual acuity in this advanced disease stage. On FAF and OCT, the central foveal structure is relatively preserved compared with the surrounding atrophic zone (see Fig. 8.2a, b, d). Patients with MRD do not have typical drusen on ophthalmoscopy, FAF, or OCT, and choroidal neovascularization is extremely uncommon.
Fig. 8.2
Grade 3 and 4 mitochondrial retinal dystrophy (MRD). (a) Color fundus photograph of grade 3 MRD of a 43-year-old patient (visual acuity: 20/20) showing areas of more profound chorioretinal (geographic) atrophy in the macula with relative foveal sparing. (b) Fundus autofluorescence (FAF) in this patient showed a large dark area of absent FAF in the macula and adjacent to the optic disc corresponding to profound atrophy of the retinal pigment epithelium (RPE), which is also visible in (a). In addition, spots of highly increased FAF were visible throughout the posterior pole. (c) The foveal structure is relatively spared, which also correlates to relative functional sparing on central visual field testing. (d) Optical coherence tomography (OCT) scan (left eye of same patient, horizontal scan) shows some structural sparing of the outer retinal (photoreceptor) structures as compared to the surrounding atrophic areas. (e) Color fundus photograph of grade 4 MRD in a 57-year-old patient who also had mitochondrial encephalomyopathy, lactic acidosis, and stroke-like episodes (MELAS) syndrome, insulin-dependent diabetes mellitus, and deafness due to the m.3243A>G mutation. Marked chorioretinal atrophy in the macula was present since at least 5 years, with a corresponding visual acuity of 20/630. (f) FAF imaging in this patient showed a black area of RPE atrophy in the macula and around the optic disc, bordered by irregular autofluorescence changes. (g) OCT of grade 4 MRD shows profound outer retinal atrophy that includes the fovea
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