Fundus Autofluorescence. Jonathan A. Micieli, MD Valérie Biousse, MD

Transcription

1 Fundus Autofluorescence Jonathan A. Micieli, MD Valérie Biousse, MD

2 The retinal pigment epithelium (RPE) has many important functions including phagocytosis of the photoreceptor outer segments Cone Rod The metabolism of the photoreceptor outer segments leads to the formation of lipofuscin Disease states and potentially increased oxidative damage can lead to the buildup of lipofuscin in the RPE lipofuscin Retinal pigment epithelium Figure 1. Choroid

3 When stimulated with a broad wavelength of light (500 to 800 nm) Lipofuscin autofluoresces (it contains > 10 fluorophores) Retinal pigment epithelium Figure 2. Choroid

4 Excess accumulation of lipofuscin leads to hyperautofluorescence Death or absence of the RPE leads to the disappearance of lipofuscin and hypoautofluorescence RPE death Figure 3.

5 Fundus autofluorescence (FAF) is a clinically useful tool to rapidly evaluate RPE function Primary methods to obtain FAF images Confocal scanning laser ophthalmoscopy (cslo) - Uses a low-power laser to rapidly scan the retina in one plane - Software algorithm combines signal from one plane into final image Modified fundus camera - Images the entire retina with a single flash - Unable to differentiate the source of autofluorescence (there may be some contribution from anterior segment structures) - Autofluorescence from anterior segment structures minimized

6 Normal fundus autofluorescence Right eye Left eye Figure 4.

7 Normal fundus autofluorescence Fovea is dark (absorption of light by luteal pigments) Optic nerve head is dark (it lacks RPE) Figure 5. Blood vessels are dark (blood absorbs light)

8 Figure 6. Case 1 - Bilateral central scotomas Clinical information: Visual acuity: 20/25 OD, 20/30 OS No relative afferent pupillary defect Color vision: 6/14 OD, 7/14 OS correct Ishihara plates VIsual fields: central scotomas OU OD OS Fundus autofluorescence Optic disc photos Right eye Left eye OD OS

9 Figure 7. Central hypoautofluorescence (red arrows) corresponds to areas of RPE loss in the macula Areas of hyperautofluorescence (yellow arrows) surround the hypoautofluorescence (red arrows) and represent areas of RPE dysfunction OD OS This patient has a macular dystrophy

10 Figure 8. Case 2 - A man with ring scotomas and night blindness Clinical information: Visual acuity: 20/20 OD, 20/25 OS No relative afferent pupillary defect Color vision: 6/14 OD, 7/14 OS correct Ishihara plates VIsual fields: central scotomas OU OD OS Fundus autofluorescence Left eye Right eye OD OS

11 Figure 9. Fundus autofluorescence demonstrates RPE changes as concentric rings of hypo-and hyperautofluorescence in a bull s-eye pattern Macular OCT shows extrafoveal loss of the RPE and ellipsoid zone (yellow arrows) corresponding to the bull s-eye pattern from acute macular neuroretinopathy

12 Figure 10. Case 3 - A man with difficulty driving at night Clinical information: Visual acuity: 20/20 OD, 20/30 OS No relative afferent pupillary defect Color vision: 14/14 OD, 14/14 OS correct Ishihara plates OD OS Humphrey 24-2 visual fields Fundus autofluorescence OS OD OD OS

13 Figure 11. Fundus autofluorescence demonstrates large areas of RPE loss (hypoautofluorescence) and dysfunction (hyperautofluorescence) in a large bull s-eye pattern Macular OCT shows extrafoveal loss of the RPE and ellipsoid zone (yellow arrows) corresponding to the hypoautofluorescent area caused by chloroquine toxicity

14 Figure 12. Other applications of fundus autofluorescence Case 4 - A patient referred for possible optic disc edema Clinical information: Visual acuity: 20/20 OD, 20/20 OS Fundus (optic nerves) autofluorescence No relative afferent pupillary defect Color vision: 14/14 OD, 14/14 OS correct Ishihara plates VIsual fields: normal OU Optic disc photos Right eye Left eye Right eye Left eye Right eye Left eye

15 There are hyperautofluorescent structures (seen in white -red circles) evident in the optic disc representing optic disc drusen Figure 13. The hyperautofluorescence may be due to the large amount of mitochondria in optic disc drusen. Mitochondria have large amounts of porphyrins, which are autofluorescent.

16 Summary points: Fundus autofluorescence is a non-invasive tool to rapidly evaluate retina pigment epithelium (RPE) function It has particular value in neuro-ophthalmology in differentiating central visual field defects from maculopathies and optic neuropathies, and in detecting optic disc drusen