### Abstract

Original language | English |
---|---|

Pages (from-to) | 72-77 |

Number of pages | 6 |

Journal | Clinical and Experimental Optometry |

Volume | 95 |

Issue number | 1 |

DOIs | |

Publication status | Published - Jan 2012 |

Externally published | Yes |

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### Cite this

*Clinical and Experimental Optometry*,

*95*(1), 72-77. https://doi.org/10.1111/j.1444-0938.2011.00646.x

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*Clinical and Experimental Optometry*, vol. 95, no. 1, pp. 72-77. https://doi.org/10.1111/j.1444-0938.2011.00646.x

**Effects of illumination and observation angle on the van Herick procedure.** / Leung, Myra; Kang, Sammie Soo Ok; Turuwhenua, Jason; Jacobs, Robert J.

Research output: Contribution to journal › Article

TY - JOUR

T1 - Effects of illumination and observation angle on the van Herick procedure

AU - Leung, Myra

AU - Kang, Sammie Soo Ok

AU - Turuwhenua, Jason

AU - Jacobs, Robert J.

PY - 2012/1

Y1 - 2012/1

N2 - Background: This study reports how illumination and observation angles affect assessments of the openness of the anterior chamber angle using the van Herick technique. Methods: The angle of the tangent to the corneal surface at the temporal limbus was measured for 50 participants. The effect on anterior chamber depth to corneal thickness (AC:C) ratio of varying the illumination angle away from the perpendicular to this tangent was measured. The effect of varying observation angle was also evaluated. An optical model was constructed to simulate the parameters likely to affect measurement of the AC:C ratio. Results: The average angle of the tangent to the corneal surface at the temporal limbus was 43.1 ± 5.4° (SD). With illumination perpendicular to the limbal-corneal surface, varying the observation angle caused clinically unimportant (less than 0.1 ratio difference) but statistically significant changes in AC:C ratios (F = 7.235, p < 0.0001; repeated measures ANOVA). With observation 60° away from illumination, varying the illumination angle away from the perpendicular to the limbal-corneal surface caused clinically important and statistically significant changes in AC:C ratios (F = 75.981, p < 0.0001; repeated measures ANOVA). The optical model confirmed the experimental results and predicts that the conclusions are applicable outside our study population. Conclusions: Illumination should be within 10° either side of the perpendicular to the corneal surface at the limbus for measurements of the AC:C ratio. The observation angle away from the illumination direction is not critical and 60° is appropriate, but smaller angles can be used.

AB - Background: This study reports how illumination and observation angles affect assessments of the openness of the anterior chamber angle using the van Herick technique. Methods: The angle of the tangent to the corneal surface at the temporal limbus was measured for 50 participants. The effect on anterior chamber depth to corneal thickness (AC:C) ratio of varying the illumination angle away from the perpendicular to this tangent was measured. The effect of varying observation angle was also evaluated. An optical model was constructed to simulate the parameters likely to affect measurement of the AC:C ratio. Results: The average angle of the tangent to the corneal surface at the temporal limbus was 43.1 ± 5.4° (SD). With illumination perpendicular to the limbal-corneal surface, varying the observation angle caused clinically unimportant (less than 0.1 ratio difference) but statistically significant changes in AC:C ratios (F = 7.235, p < 0.0001; repeated measures ANOVA). With observation 60° away from illumination, varying the illumination angle away from the perpendicular to the limbal-corneal surface caused clinically important and statistically significant changes in AC:C ratios (F = 75.981, p < 0.0001; repeated measures ANOVA). The optical model confirmed the experimental results and predicts that the conclusions are applicable outside our study population. Conclusions: Illumination should be within 10° either side of the perpendicular to the corneal surface at the limbus for measurements of the AC:C ratio. The observation angle away from the illumination direction is not critical and 60° is appropriate, but smaller angles can be used.

U2 - 10.1111/j.1444-0938.2011.00646.x

DO - 10.1111/j.1444-0938.2011.00646.x

M3 - Article

VL - 95

SP - 72

EP - 77

JO - The Australasian journal of optometry

JF - The Australasian journal of optometry

SN - 0816-4622

IS - 1

ER -