Ophthalmic Imaging by Christye P. Sisson

Author:Christye P. Sisson
Language: eng
Format: epub
Publisher: Routledge

Subtler changes in shape include the variation in thickness of normal retinal layers. For example, the nerve fiber layer becomes thicker as it makes its way toward the disc; this is a trick that can be used to determine which eye you are looking at when viewing an OCT. If the nerve fiber layer (NFL) is thicker on the right of a scan, it is the right eye (OD); if its thickest on the left of the scan, it is a left eye (OS).

The rest of the retinal layers lie flat and compact against each other in normal OCT in a fairly linear pattern, similar to sediment layers in rock. There are not many variations in this pattern across a normal retina, except for the occasional “shadow” that occurs as a result of a retinal vessel blocking the signal of the OCT beam in that area.

Other jagged patterns, particularly those that seem consistent in spacing, can occur as a result of patient movement and are usually associated with older devices without eye tracking technology. These should not be considered abnormal morphology or pathology and are considered an artifact. (These also mean you should try and get a better scan without any movement artifacts). If you recall from earlier in this chapter, artifacts can be products of the instrument or software (rather than something in the eye), and they can be a result of poor capture technique, but they can also be due to dirty optics and internal misalignment.

The overall shape of the OCT scan is not always easily appreciated; it used to be that some software packages “straightened” the scan. An emmetropic eye will result in a fairly straight OCT scan on most individuals. A curved or concave OCT is indicative of someone who is highly myopic, especially in such a small lateral sample.

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