Van Herick Grading System
The Van Herick grading system is a slit-lamp technique that estimates anterior chamber depth by comparing the peripheral anterior chamber depth to peripheral corneal thickness at the limbus, using grades ranging from 0 to 4 (or a modified 7-point percentage scale), primarily to screen for narrow angles and angle-closure glaucoma risk. 1
Technique and Grading Scale
The Van Herick method uses a narrow slit beam positioned at the temporal or nasal limbus, perpendicular to the corneal surface, to assess the ratio of peripheral anterior chamber depth to peripheral corneal thickness 2, 3:
Traditional 4-Point Grading Scale:
- Grade 4: Peripheral anterior chamber depth (ACD) ≥ 100% of corneal thickness (wide open angle) 3
- Grade 3: ACD = 25-75% of corneal thickness 3
- Grade 2: ACD = 15-25% of corneal thickness 3
- Grade 1: ACD = 5-15% of corneal thickness (narrow angle) 3
- Grade 0: ACD < 5% of corneal thickness (extremely narrow, high risk) 3
Modified 7-Point Percentage Scale:
A more intuitive augmented scale uses percentages: 0%, 5%, 15%, 25%, 40%, 75%, and ≥100% of corneal thickness, which offers potentially greater accuracy for grading narrow angles 3, 4
Clinical Application and Interpretation
Angles graded ≤ 25% corneal thickness (Grade 2 or below) warrant gonioscopy for definitive angle assessment, as these represent potentially occludable angles 3. The American Academy of Ophthalmology guidelines emphasize that gonioscopy remains the gold standard for evaluating angle anatomy in suspected primary angle-closure disease 1.
Key Technical Points:
- The slit beam should be short (approximately 1 mm), bright, and positioned to avoid passing through the pupil to prevent pupillary constriction that artificially widens the angle 1
- Examination should be performed in a dark room 1
- Temporal and nasal measurements show good agreement (κ = 0.61), so if nasal assessment is limited by nasal bridge anatomy, temporal measurements can substitute 2
Reliability and Limitations
Interobserver Agreement:
- Grades 1 and 4 demonstrate high reliability (80-85% consistency, low standard deviation of 0.26-0.45) 2
- Grades 2 and 3 show poor reliability (5-58% consistency, high standard deviation of 0.71-0.89), requiring confirmatory gonioscopy or anterior segment OCT 2
- Community optometrists show moderate agreement (κw = 0.50), while glaucoma specialists demonstrate moderate to substantial agreement (κw = 0.54-0.65) 4
Performance Characteristics:
Using a cutoff of ≤25% corneal thickness for narrow angles, the Van Herick method demonstrates:
- Sensitivity: 84.9%
- Specificity: 89.6%
- Area under the curve: 0.872 3
This performance is superior to automated devices like SPAC, which tend to overestimate narrow angles 3.
Modified "Van Herick Plus" Technique
A newer modification uses a short vertical slit beam at the inferior angle (not reaching the pupil) at the sclerolimbal junction, which correlates well with anterior segment OCT measurements (r = 0.918 for trabecular-iris angle) 5. Using a cutoff of peripheral ACD:corneal thickness ratio <1/4 for narrow angles yields sensitivity of 85.2% and specificity of 88.2% 5.
Clinical Pitfalls
- False negative rate of 13% for narrow angles when using photographic grading by community optometrists, emphasizing the need for direct examination 4
- The method overestimates anterior chamber depth by approximately 0.25 grades compared to objective imaging 6
- Corneal edema in acute angle-closure may impair visualization; topical glycerin can clear the cornea for better assessment 1
- The test is highly subjective, particularly for intermediate grades, necessitating gonioscopy for definitive assessment in borderline cases 2, 4