Factors Affecting Cirrus-HD OCT Optic Disc Scan Quality: A Review with Case Examples

Table 1

Factors affecting Cirrus HD-OCT scan quality.

	Patient-dependent					Operator-dependent		Device-dependent
	Dry eye and cataract	Floaters/vitreous opacities	Blinks	Motion artifacts	Signal strength	OCT lens opacities	Incorrect axial alignment	Inaccurate optic disc margin delineation	Inaccurate RNFL segmentation
Visible as
	Tomograms: signal attenuation	(i) RNFLT map: cold-colored/black area of missing data; (ii) RNFL deviation map: clusters of “superpixels”; (iii) Tomograms: vertical shadow of signal interruption	(i) RNFLT and deviation maps: well-defined rectangular black area of missing data, red “superpixels”; (ii) Tomograms: absence of signal; or vertical shadow of signal interruption	En-face image: horizontal shift of the retinal blood vessels’ path; optic disc shape distortion	Numerical scan quality index, displayed on the printout (range: 0–10)	(i) RNFLT map: cold-colored/black area of missing data; (ii) RNFL deviation map: clusters of “superpixels”; (iii) Tomograms: signal attenuation	(i) RNFLT map: crescent-shaped black area of missing data; (ii) RNFL deviation map: clusters of “superpixels”; (iii) Tomograms: image truncation	En-face image: malposition of the optic disc and/or cup contour lines	Circular tomogram: malposition or interruption of RNFL segmentation lines
Effects	(i) ↓ Signal strength; (ii) ↓ RNFLT	(i) Floater on scan circle: ↓ RNFLT; (ii) Floater on optic disc area: unreliable optic disc parameters, possible scan circle displacement with RNFLT measurement variability	(i) Blink affecting optic disc: unreliable optic disc parameters, possible scan circle displacement with RNFLT measurement variability; (ii) Blink affecting scan circle: ↓ RNFLT	(i) Inaccurate optic disc margin delineation, unreliable optic disc parameters; (ii) Scan circle displacement with RNFLT measurement variability	Low signal strength associated with ↓ RNFLT	↓ RNFLT	(i) Inner retina truncation: inaccurate RNFL segmentation; (ii) Optic disc truncation: unreliable optic disc parameters, possible scan circle displacement with RNFLT measurement variability	(i) Unreliable optic disc parameters (e.g., ↑ or ↓ disc area, depending on the cause); (ii) Possible scan circle displacement with RNFLT measurement variability	↑ or ↓ RNFLT, depending on the cause
Suggestions	(i) Blinks prior to scan acquisition; (ii) Lubricants for dry eyes; (iii) Redirect light beam through areas of least cataract opacity	Ask patient to perform brief to-and-fro eye movements immediately before scan acquisition to displace floater	(i) Blinks prior to scan acquisition; (ii) Lubricants for dry eyes; (iii) Prompt notification of imminent scan acquisition	(i) Blinks prior to scan acquisition; (ii) Lubricants for dry eyes; (iii) Prompt notification of imminent scan acquisition; (iv) Verify: continuity of blood vessels’ path, optic disc shape, accuracy of optic disc margin delineation	Identify and address cause (e.g., OCT lens cleaning, adjust camera alignment, lubricants, pupil dilation)	(i) Careful instrument handling; (ii) Periodic OCT lens cleaning	(i) Proper patient positioning; (ii) “Optimize” feature for automated axial alignment	Identify and address cause (e.g., floaters, motion artifacts)	Identify and address cause (see patient- and operator-dependent factors)

RNFLT: retinal nerve fiber layer thickness.
Note: case examples obtained using Cirrus HD-OCT (Carl Zeiss Meditec, Dublin, CA; software version 5.0.0.326). The content of this table may not be applicable to different Cirrus HD-OCT models or to other Spectral-domain OCT devices.