14.9  What Racial Differences Exist

in Angle Anatomy?

Definite differences in angle anatomy have been demonstrated among racial groups. The iris insertion is most posterior in Caucasians, more anterior in Afro– Americans, and most anterior in Far East Asians. The incidence of angle-closure is correlated in the three groups, with Asians having the highest incidence of angle-closure by far [6]. Eskimos present an extreme situation. The highest incidence of angle-closure glaucoma in the world occurs among Alaskan Eskimos and the Greenland Inuit. Eskimos tend to have shallower anterior chamber depths than other racial groups, associated with hyperopia and shorter axial lengths [13].

East Asian eyes tend to have what is called “creeping angle-closure” without the symptoms of an acute angleclosure attack. This scenario may be due to anatomical differences. The ciliary body may be more anterior in Asians [5]. Pupillary block may not be as important a factor in angle-closure among Asian eyes, as evidenced by the fact that persistent angle-closure following iridotomy has been found in as much as one-fifth of treated eyes in the Liwan eye study [4]. Gonioscopy in Asian eyes can be very difficult due to the relative crowding of the anterior chamber angle with a thickly textured brown iris. A study from South Africa showed similar rates of angle-closure glaucoma among whites and blacks, but three times the rate among patients with mixed Asian origin [8]. An interesting gonioscopy finding in black Africans is that trabecular meshwork pigmentation is generally lighter than one would expect with dark skin pigmentation.

Summary for the Clinician

››Angle anatomy is different amongst different groups of people and the prevalence of angleclosure is the highest in Asians.

››Gonioscopy may be more difficult in Asian eyes due to the relative crowding of the angle.

››In Asian eyes, pupillary block may not be the most important factor in angle-closure.

14.10  Can Anterior Segment Imaging

by Ultrasound Biomicroscopy

(UBM) or Anterior Segment OCT

Replace Gonioscopy?

A dynamic picture of the iridocorneal angle is extremely important in deciding whether or not an iridotomy is indicated. Only indentation gonioscopy provides real time dynamics. Sophisticated modern imaging such as UBM and anterior segment OCT, do not provide this information. These instruments can show differences in angle morphology when illumination is turned on or off which changes the pupil size, but they cannot differentiate nearly closed from appositional closure or distinguish apposition from PAS. The UBM and the anterior segment OCT are very useful to identify iris and ciliary body cysts or tumors as well as to show patients what angle-closure and plateau iris are; but these examinations are totally inadequate to make the indication for an iridotomy.

Central anterior chamber depth can be measured by ultrasound,­ optical pachymetry, and anterior segment OCT. Shallower anterior chambers tend to have more angle-closure. Optical pachymetry measurement of anterior chamber depth as a screening tool has been found to have good sensitivity and specificity in diagnosing angleclosure in Mongolia, and no PAS were found with anterior chamber depth greater than 2.4 mm [3]. However in an ophthalmic office practice, with careful slit lamp examination and gonioscopy, it is rare that precise measurement of central anterior chamber depth is clinically useful.

An excellent way to study the iridocorneal angle is videogonioscopy. The reader is referred to Dr. Lee Alward’s internet site [2].

Summary for the Clinician

››UBM and AS-OCT are useful complements to gonioscopy.

››The change in angle configuration that is seen in a light versus dark room can be easily appreciated on UBM and AS-OCT.

››UBM and AS-OCT are not replacements for gonioscopy which can more easily distinguish PAS from appositional angle-closure.