What is the role of anterior Optical Coherence Tomography (OCT) using CASIA 2 in the diagnosis and management of a patient with glaucoma or suspected glaucoma?

Anterior OCT in Glaucoma Using CASIA 2

Anterior segment OCT, including CASIA 2, serves as a valuable adjunct tool for evaluating angle anatomy and anterior chamber structures in glaucoma patients, but must always be interpreted alongside clinical examination, gonioscopy, IOP measurements, and posterior segment imaging—it cannot replace comprehensive structural and functional assessment.

Role in Glaucoma Diagnosis and Management

Primary Clinical Applications

Anterior segment OCT provides non-contact, high-resolution imaging of anterior chamber structures that are relevant to specific glaucoma subtypes 1, 2:

• Angle assessment: Quantitative and qualitative evaluation of the iridocorneal angle to identify angle-closure risk factors and anatomical variations 1, 2
• Anterior chamber biometry: Measurement of anterior chamber depth, angle opening distance, and trabecular-iris space angle 1, 2
• Dynamic angle evaluation: Assessment of angle changes with lighting conditions or provocative testing to identify patients at risk for primary angle closure disease 1
• Post-intervention monitoring: Evaluation of surgical outcomes following laser peripheral iridotomy, trabeculectomy, deep sclerectomy, and glaucoma drainage devices 2, 3

Integration with Standard Glaucoma Assessment

The American Academy of Ophthalmology emphasizes that digital imaging technology, including OCT, is approved only as an adjunct to aid in glaucoma diagnosis—clinicians must include all perimetric and other structural information when formulating patient management decisions 4. This principle applies equally to anterior segment OCT.

For comprehensive glaucoma evaluation, you must combine 4:

• Structural assessment: Optic nerve head examination, retinal nerve fiber layer imaging (posterior segment OCT), and macular analysis
• Functional assessment: Visual field testing with standard automated perimetry
• IOP measurement: The only modifiable parameter in glaucoma management 4
• Anterior segment evaluation: Gonioscopy remains the gold standard, with anterior OCT as a complementary tool 1, 2

Specific Indications for CASIA 2 Use

When to Order Anterior Segment OCT

Use anterior segment OCT imaging when 1, 2:

• Angle-closure concerns: Suspicion of narrow angles, plateau iris configuration, or primary angle closure disease requiring quantitative angle assessment
• Difficult gonioscopy: Poor view due to corneal opacity, patient intolerance, or need for objective documentation
• Pre-laser planning: Baseline assessment before laser peripheral iridotomy to document angle anatomy
• Post-surgical evaluation: Monitoring bleb morphology after trabeculoplasty or assessing tube position after glaucoma drainage device placement 2, 3
• Research documentation: Objective, reproducible measurements for longitudinal studies 1

When NOT to Rely on Anterior OCT Alone

Do not use anterior segment OCT as a substitute for 4:

• Posterior segment OCT evaluation of the optic nerve head and RNFL—these remain essential for detecting glaucomatous structural damage that precedes visual field loss 4
• Visual field testing—functional assessment is integral to patient care since some patients show visual field loss without corresponding structural progression 4
• Clinical gonioscopy—direct visualization remains superior for detecting peripheral anterior synechiae, angle recession, and other subtle findings 1

Technical Considerations and Limitations

Advantages of OCT Technology

Anterior segment OCT provides 1, 2, 3:

• Non-contact imaging: Higher patient comfort compared to ultrasound biomicroscopy
• High resolution: Axial resolution of 3-20 μm depending on the platform 2
• Reproducibility: High inter- and intraobserver reliability for measurements 3
• Quantitative data: Objective measurements for longitudinal comparison 1, 2

Critical Limitations

Ultrasound biomicroscopy remains superior for visualizing retroiridal structures including the ciliary body, posterior chamber, and zonules, which can provide crucial diagnostic information for glaucoma assessment 5. Anterior segment OCT cannot adequately image these structures 5.

Interpretation Framework

Avoiding Common Pitfalls

The American Academy of Ophthalmology strongly emphasizes that abnormal results from imaging devices do not always represent disease 4. When interpreting CASIA 2 results:

• Evaluate scan quality first: Poor quality scans lead to measurement artifacts 4
• Review all report components: Do not rely solely on summary statistics or color-coded classifications 4
• Consider normative database limitations: Criteria for establishing normative databases vary between devices, and individual anatomical variations may fall outside normal ranges for reasons unrelated to glaucoma 4
• Integrate with clinical context: Results must be interpreted alongside clinical examination, IOP measurements, posterior segment imaging, and visual field testing to avoid falsely concluding that statistically abnormal results represent true pathology 4

Decision Algorithm for Management

For glaucoma suspects with anterior segment OCT findings 4:

1. Confirm with gonioscopy: Direct angle visualization remains the reference standard
2. Assess posterior segment: Obtain optic nerve head and RNFL imaging with posterior segment OCT
3. Perform visual field testing: Establish baseline functional status
4. Risk stratification: Consider IOP level, central corneal thickness, family history, disc hemorrhages, and cup-to-disc ratio 4
5. Determine monitoring frequency: High-risk patients (thin cornea, elevated IOP, disc hemorrhage, large cup-to-disc ratio) warrant closer follow-up every 6-12 months; lower-risk patients can be monitored every 12-24 months 4

Monitoring and Follow-Up

Both structural and functional assessments remain integral to patient care 4. For patients being monitored:

• Repeat anterior segment OCT when there is unexplained IOP change, suspicion of angle-closure development, or anterior chamber shallowing 4
• Continue periodic optic nerve head and RNFL evaluation with posterior segment OCT 4
• Maintain regular visual field testing based on individual risk factors 4
• Perform gonioscopy periodically, especially when anterior chamber angle abnormalities are suspected 4