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Chapter 4 - Capture images
How to assess OCT image artifacts
Poor quality scans may be caused by a number of factors including poor operator performance, poor
patient compliance, a poor interface between the device and the patient, and physical characteristics of the
patient’s eye among other things. A good understanding of common scan artifacts will reduce the potential
negative influence of poor quality scans on clinical judgements.
You can minimize scan artifacts by following the OCT scan quality advice (see How to optimize OCT scan
quality on page 44).
The most common scan artifacts include:
Reference
Artifacts - Low signal strength 47
Artifacts - Eye movements 49
Artifacts - Blinks 49
Artifacts - Clipping 50
Artifacts - Alignment of essential structures 50
4.9.1 Artifacts - Low signal strength
Low signal strength can result in poor quality scans.
CAUTION
Signal to Noise Ratio
SNR has a major impact on OCT image quality and therefore could determine the ability
to distinguish the retinal layers.
Note
As with all retinal imaging devices, ocular opacity may block the transmission of light and view of the
retina which can then impact the SNR.
Overall signal strength
The overall signal strength is measured by the signal-to-noise ratio (SNR). The SNR is calculated by
dividing the overall signal strength by the background noise.
The SNR indicator is displayed during and after the OCT image is captured. The SNR has a range of 10/10
(maximum) to 1/10 (minimum). Higher SNR results in higher quality images) (see
Scan results on the
previous page).
It can be affected by the following:
l
Patient-dependent corneal birefringence.
l
Patient eye polarization.
l
Pupil size.
l
Dry eyes.
l
Voluntary and involuntary eye movements.
l
Poor focusing of the retina.
l
Misalignment of the instrument in relationship to the patient's eye or pupil.
Local signal strength
Some areas of the image may have little or not signal, even when other areas have a strong signal. Areas
with local weak signals appear as black or dark areas from which retinal layers cannot be easily identified.
Local weak signals may be the result of the following:
Part Number: G110230-003-ENG Page 47 of 84
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