Current Issues in Primary Angle Closure Glaucoma in Asia

Glaucoma is considered to be the second most frequent cause of blindness in Asia and there could be as many as 6 million people with bilateral blindness by the end of the year 2000.¹ Therefore, it is clear that glaucoma requires early detection and adequate treatment for prevention of visual loss. Most people with primary angle closure glaucoma (PACG) live in the western coastal regions of Asia; since more than 50% have the asymptomatic, chronic type, we can expect many to be unaware of the disease.¹ Therefore, early diagnosis of PACG is as important as early diagnosis of primary open angle glaucoma (POAG) for early treatment and safe application of laser iridotomy to prevent blindness. The current gold standard for diagnosis, proposed by Kronfeld in 1948, is "elevation of IOP [intraocular pressure] with simultaneous angle closure."² From a public health point of view, in order to prevent blindness in the early stages of PACG, it is time to reconsider a new criterion based on recent technological progress.³

PACG frequently occurs in smaller-than-average eyes that manifest as hyperopic eyes with a small cornea, shallow anterior chamber, shorter axial length, and thick lens. Biometric and chamber angle image examinations provide important parameters characteristic of PACG.⁴ Our study of A-scan biometry for acute glaucoma demonstrated that an anterior chamber depth of less than 2.7 mm is the most sensitive (94%) and specific (94%) parameter to differentiate acute glaucoma from non-glaucomatous eyes.⁵ Optic nerve studies of parapapillary and intrapapillary changes are other important parameters for chronic PACG, as well as for follow up studies for each patient. Stereophotographic study of nerve fibres is probably the most practical method when compared with sophisticated optic nerve analysers. Combined dark prone position test for PACG offers another method for early detection. These three tests: A-scan biometry, fundus optic disc examination and combined dark prone position test can all be performed in the office or as a screening method.⁶

Optic nerve changes in POAG have been well studied.⁷ The importance of such studies in normal tension glaucoma or PACG is discussed in a separate article in this issue. This paper indicates that optic nerve studies in smaller-than-average eyes with PACG may elucidate some important information for glaucoma as a whole.⁸ Another important issue is to reconsider the classification of PACG based on certain practical view points.² Such a classification should include patients with the potential for future PACG development. It is reasonable to classify who is at high risk for PACG using the above-mentioned test parameters. In the treatment of any disorder with a risk for potential blindness, such as PACG, the 'risk-benefit ratio' is also essential. In a well developed society, laser iridotomy is probably only performed for higher risk groups, while in under developed areas, a 5% low risk may be reason enough to perform a safe and relatively simple laser iridectomy procedure. The classification could reflect such ideas for clinical practice.

In conclusion, the prevalence of PACG and disease-related blindness are increasing due to the increasing ageing of the world's population and continuing socio-economic development. Current diagnostic criteria and laser treatment may be based on the risk-benefit ratio for early treatment to prevent PACG-related visual damage. Furthermore, the study of PACG such as optic nerve changes may contribute to the elucidation of important information for all types of glaucoma.

PT Hung
Taiwan

1. Quigley HA. Number of people with glaucoma worldwide. Br J Ophthalmol 1996;80:389-393.
2. Kronfeld PC. Primary glaucoma II Diagnosis. Trans Am Acad Ophthalmol Otolaryngol 1948, 53:175-178.
3. Kim YY, Jung HR. Clarifying the nomenclature for primary angle closure glaucoma. Surv Ophthalmol 1997;42:125-136.
4. Lowe RF. Causes of shallow anterior chamber in primary angle closure glaucoma, ultrasonic biometry of normal and angle closure eyes. Am J Ophthalmol 1969;67:67-87.
5. Lin YW, Wang TH, Hung PT. Biometric study of acute primary angle closure glaucoma. J Formos Med Assoc 1997;96:908-912.
6. Hung PT, Hou YC, Lan WL, et al. Chamber angle and biometric study in PACG and its lens. In: Krieglstein GK (Ed). Glaucoma Update. Vol V. Heiderberg: Kaden Verlag; 1995:309-315.
7. Weinreb RN. Evaluating the retinal nerve fiber layer in glaucoma with scanning laser polarimetry. Arch Ophthalmol 1999;117:1403-1406.
8. Sugiyama K, Ishida K, Uchida H, et al. Disc haemorrhages in normal tension glaucoma. Asian J Ophthalmol 2000;2(3):3-8.