• CSLO
  • What information
    does CSLO provide?
• SLP
  • What information
    does SLP provide?
• OCT
  • What Information
    does OCT provide?
    • Limitations
    • Imaging Artifact

Imaging Artifact

All technologies, including optic disc photography, will be affected by eye movement, ocular surface disruption such as moderate corneal epitheliopathy, cataract and poor focus. In contrast to GDx and HRT, a small pupillary diameter may produce OCT images with inadequate signal strength or RNFL segmentation errors.

Various factors contribute to imaging artifact and understanding the limitations of these technologies will permit their appropriate use in the clinical setting.

CSLO

With HRT, factors contributing to imaging artifact include:

• Higher refractive errors cause magnification artifact with poor image acquisition technique (incorrect HRT/eye distance).
• Astigmatism uncorrected by appropriate lenses degrades image quality.
• Vitreous floaters overlying the optic nerve during scan acquisition may interfere with topography assessment.
• Incorrect identification of the optic disc border will result in erroneous placement of the contour line. This will translate to incorrect assessment of the optic disc area, and produce erroneous assessments of the neural rim and cup, and impact the Moorfield Regression Analysis.

Figure: Impact of Contour Line on HRT              View large

SLP

With GDx, factors contributing to imaging artifact include:

• Anterior and posterior segment pathology may produce spurious RNFL measurements
• Eyes with corneal pathology, or prior corneal surgery such as penetrating keratoplasty, may have uncompensated corneal birefringence that confounds RNFL assessment.
• A subset of myopic eyes, particularly those with RPE atrophy, generate considerable scleral reflectance and atypical patterns of birefringence characterized by a typical scan score (TSS) below 80 and radial spoke-like patterns of birefringence.
• Eyes with macular pathology have disruption of the Henle fiber layer and failure of conventional methods for corneal compensation.
• Vitreoretinal pathology e.g., myopia (myopic tilting of the optic nerve), reduced RPE pigmentation around the optic nerve especially temporally and infero-temporally. Dense vitreous floaters as with asteroid hyalosis can also interfere with the birefringence pattern.

Figure: GDx Birefringence Patterns

        View large

Figure: Impact of ABP on GDx Assessment

OCT

With OCT, factors contributing to imaging artifact include:

• Extensive parapapillary artifact that involves the scanning zone, media opacities (particularly PSC (posterior subcapsular cataract) cataract and vitreous floaters), and vitreoretinal pathology (such as macular pucker and vitreoretinal traction) may produce reduced signal strength and/or failure of the RNFL segmentation algorithm.
• Clinicians should be aware of such artifacts and their impact on glaucoma diagnosis and monitoring.

        View large

Figure: Impact of Retinal Pathology on OCT: Diabetic Retinopathy

Common Sources of Imaging Artifact

moderate = +
high = ++