Sources of variability of the van Herick technique for anterior angle estimation

Abstract

Background:The purpose of the present study was to investigate two potential sources of variability of the traditional van Herick technique for temporal anterior chamber angle estimation, namely the need to compare the depth of the peripheral anterior chamber (PACD) with the thickness of the peripheral cornea (PCT), and the possible loss of information resulting from restricting the assessment of the anterior chamber angle (ACA) to the temporal limbus. Methods: Both image analysis and Scheimpflug photography were employed to measure PCT and PACD in a group of 82 eyes (mean ± SD age of 32.8 ± 4.1 years) with and without narrow anterior chamber angles. Subjective and semi-objective van Herick grades were compared and the relationship between PCT and PACD was investigated. Scheimpflug photography was also used to determine the value of the narrowest anterior chamber angle and to compare it with the temporal angle. Results: No statistically significant differences were encountered between semi-objective and subjective grades. A weak statistically significant correlation was found between image analysis values for PCT and PACD (r = 0.295; p = 0.007). Upon examining Scheimpflug photographic data, no statistically significant association between PCT and PACD was revealed. Temporal and minimum anterior chamber angles presented statistically significant differences (t = 7.213; p < 0.001). In approximately 65 per cent of the patients, the minimum ACA was not located at the temporal limbus, with a difference of up to 9.8 degrees between minimum and temporal angles. Conclusion:The encountered association between the image analyses of PCT and PACD advocates for the direct measurement of PACD as a better estimation of ACA depth than the ratio between PCT and PACD. All anterior chamber quadrants should be examined, as the minimum ACA may not be located temporally.

Primary angle‐closure glaucoma: an update

“…Figure reproduced with permission of John Wiley & Sons, Inc. (Gispets et al. ), © 2013 The Authors and Optometrists Association Australia.…”

Repeatability and comparison of clinical techniques for anterior chamber angle assessment

“…Assessment of the anterior chamber angle (ACA) is essential for the detection of eyes at risk of PACG prior to the onset of the disease . Gonioscopy is currently considered the gold standard method to assess the ACA .…”

A New Slit Lamp–Based Technique for Anterior Chamber Angle Estimation

“…Thomas and co-workers 10 summarize some of the published sensitivity and specificity values of the traditional Van Herick technique and report values of sensitivity lower than the ones obtained for the SLACE technique (61.9% versus 100%, 91%, 87.5% or 81.2%) and higher values of specificity (89.3% versus 75%, 78%, 71.5% and 74.4%). A more recent study 11 In addition, although SLACE was designed to overcome some of the limitations that may affect the Van Herick technique 12,13 , the need to compare the depth of the peripheral anterior chamber with the peripheral corneal thickness, and its corresponding individual variations, may be considered as a potential source of error for both. Further research including measurements of peripheral corneal thickness may be required to explore its possible influence on angle estimation.…”

“…This is supported by evidence that training results in improvements in interobserver reproducibility 9,10 . In addition, although modifications through digital image capture and analysis to the Van Herick procedure have been proposed to increase the objectivity of the technique 11,12 , the technique remains highly sensitive to slit lamp alignment, with results being affected by deviations of as little as 10 degrees from the perpendicular to the ocular surface in the positioning of the direct slit lamp beam 13 . This might be considered one of the main limitations of the technique, as it is not easy to ascertain when the illumination system is perfectly perpendicular to the ocular surface.…”