Detection of gonioscopically occludable angles and primary angle closure glaucoma by estimation of limbal chamber depth in Asians: modified grading scheme

Abstract

Aim: To evaluate the performance of limbal chamber depth estimation as a means of detecting occludable drainage angles and primary angle closure, with or without glaucoma, in an east Asian population, and determine whether an augmented grading scheme would enhance test performance.

Method: A two phase, cross sectional, community based study was conducted on rural and urban areas of Hövsgöl and Omnögobi provinces, Mongolia. 1800 subjects aged 40 to 93 years were selected and 1717 (95%) of these were examined. Depth of the anterior chamber at the temporal limbus was graded as a percentage fraction of peripheral corneal thickness. An "occludable" angle was one in which the trabecular meshwork was seen in less than 90 degrees of the angle circumference by gonioscopy. Primary angle closure (PAC) was diagnosed in subjects with an occludable angle and either raised pressure or peripheral anterior synechiae. PAC with glaucoma (PACG) was diagnosed in cases with an occludable angle combined with glaucomatous optic neuropathy and consistent visual morbidity.

Results: Occludable angles were identified in 140 subjects, 28 of these had PACG. The 15% grade (equivalent to the traditional "grade 1") yielded sensitivity and specificity of 84% and 86% respectively for the detection of occludable angles. The 5% grade gave sensitivity of 91% and specificity of 93% for the detection of PACG. The interobserver agreement for this augmented grading scheme was good (weighted kappa 0.76).

Conclusions: The traditional limbal chamber depth grading scheme offers good performance for detecting occludable drainage angles in this population. The augmented scheme gives enhanced performance in detection of established PACG. The augmented scheme has potential for good interobserver agreement.

Figure 1

Limbal chamber depth = 5% of peripheral corneal thickness.

Figure 2

Limbal chamber depth = 15% of peripheral corneal thickness.

Figure 3

Limbal chamber depth = 25% of peripheral corneal thickness.

Figure 4

Limbal chamber depth = 40% of peripheral corneal thickness.

Figure 5

Limbal chamber depth = 75% of peripheral corneal thickness.

Figure 6

Limbal chamber depth >100% of peripheral corneal thickness.

Figure 7

Receiver operating curve comparing traditional⁵ and augmented limbal chamber depth grading in the detection of individuals with a drainage angle judged to be occludable on gonioscopic examination. Solid line indicates performance of augmented grading scheme.Broken line indicates the performance of the traditional grading scheme. Dotted line indicates the plot for a test with a predictive value equal to that of chance.

Figure 8

Receiver operating curve comparing traditional⁵ and augmented limbal chamber depth grading schemes in the detection of primary angle closure. Primary angle closure was diagnosed in those subjects with angles judged to be occludable on gonioscopic examination and either elevated intraocular pressure, peripheral anterior synechiae, or a positive dark room, prone provocation test. This group includes those people with glaucomatous optic neuropathy. Solid line indicates performance of augmented grading scheme. Broken line indicates the performance of the traditional grading scheme. Dotted line indicates the plot for a test with a predictive value equal to that of chance.

Figure 9

Receiver operating curve comparing traditional⁵ and augmented limbal chamber depth grading schemes in the detection of primary angle closure glaucoma. Primary angle closure glaucoma was diagnosed in those subjects with an occludable drainage angle and glaucomatous optic neuropathy, corroborated by visual field evidence in mild or moderate cases. Solid line indicates performance of augmented grading scheme. Broken line indicates the performance of the traditional grading scheme. Dotted line indicates the plot for a test with a predictive value equal to that of chance.