Normal Retinal Anatomy and Basic Pathologic Appearances

Normal Retinal Anatomy

Commercially available spectral domain (SD-OCT) scanners have an Axial Resolution of between 4 µm and 7 µm and a transverse resolution of approximately 15 µm. Swept source (SS-OCT) devices, on the other hand, have an axial resolution between 6.3 µm and 8 µm and a transverse resolution of 20 µm. This high resolution allows for exquisite viewing of the retinal detail. Due to the limited penetration of light beyond the pigmented retinal pigment epithelium (RPE) and the drop-off of the OCT signal with depth (also called sensitivity roll-off), the image at the level of the choroid has a lower resolution. Swept source technology provides less sensitivity roll off and therefore can image the choroid better than SD-OCT. The layers of the normal retina are labeled in Figure 4.1.1 .

Additional Vitreous Features

Some additional vitreous features are demonstrated in a normal OCT scan in Figure 4.1.2 :

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  Posterior cortical vitreous (posterior hyaloid)

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  Retro-hyaloidal space

Normal Vasculature

OCT angiography (OCTA) helps visualize the distinct layers of capillary beds in the retina. The superficial capillary plexus and deep capillary plexus are derived from the retinal circulation and nourish the inner two-thirds of the retina while the choriocapillaris is part of the choroidal circulation and helps supply the outer retina ( Fig. 4.1.3 ).

General Appearance of Retinal Pathology on SD-OCT

Cystic Changes in Outer Retina

Discrete hyporeflective spaces are noticed primarily in the outer retina, but usually span multiple layers ( Fig. 4.1.4 ).

The differential diagnosis includes:

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  Diabetic macular edema

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  Branch retinal vein obstruction

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  Central retinal vein obstruction

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  Retinal telangiectasias (e.g., Coat’s disease, macular telangiectasia)

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  Retinitis pigmentosa

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  Uveitis/retinal vasculitis

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  Post surgery

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  Nicotinic acid maculopathy

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  Vitreomacular disorders (vitreomacular traction, epiretinal membrane)

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  Chronic subretinal fluid (e.g., retinal detachment, choroidal neovascular membrane, central serous chorioretinopathy)

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  Idiopathic