Chinese Medical Journal 2002;115(11):1706-1715
Primary angle closure glaucoma in Chinese and Western populations

WANG Ningli 王宁利,  WU Heping 吴河坪,  FAN Zhigang 范志刚

WANG Ningli 王宁利 (Department of Glaucoma, Zhongshan Ophthalmic Center, Zhongshan University, Guangzhou 510060, China)

WU Heping 吴河坪 (Department of Glaucoma, Zhongshan Ophthalmic Center, Zhongshan University, Guangzhou 510060, China)

FAN Zhigang 范志刚 (Department of Glaucoma, Zhongshan Ophthalmic Center, Zhongshan University, Guangzhou 510060, China)

Correspondence to:Wang Ningli,Department of Glaucoma, Zhongshan Ophthalmic Center, Zhongshan University, Guangzhou 510060, China (Tel: 86-20-87331369. Fax:86-20-87333271. E-mail:wningli@21cn.com; wningli@hotmail.com)
Keywords
primary angle closure glaucoma;ultrasound biomicroscopy;chronic angle closure glaucoma;creeping angle closure;dark room provocative test
Abstract
Objective To review the major progress in primary angle closure glaucoma (PACG).
Methods Contents of this article were selected from the original papers or reviews related to primary angle closure glaucoma published in Chinese and foreign journals. A total of 76 articles were selected from several hundred original articles or reviews. The content of selected articles is in accordance with our purpose and the authors are authorized scientists in the study of glaucoma.
Results Primary angle closure glaucoma is the most common type of glaucoma in the Sino Mongoloid population. PACG in Chinese can be classified into three types depending on the mechanism of angle closure: 1. Multimechanism: 54.8% of Chinese PACG is caused by co existing factors. The pattern of angle closure appears to mainly be creeping closure. After iridectomy, almost 40% of the cases still manifest a positive response to the darkroom provocative test and progressive synechial closure or recurrent angle closure may occur. Several mechanisms are involved in this form of PACG such as pupillary blocking component, iris crowding component and anterior positioned ciliary body. These factors can coexist in the follow patterns: pupillary blocking and iris crowding coexist; pupillary blocking and anterior positioned ciliary body coexist or three of them co exist. 2. Pupillary block: (38.1% of Chinese PACG) is caused by iris bombe due to pupillary block with acute or subacute attack. It responds well to iridectomy or laser iridotomy. 3. Non pupillary blocking: (7.8% of Chinese PACG). They usually have a deeper anterior chamber, and tend to be younger (below 40 years of age). Angle closure in this form of PACG is caused by: iris crowding mechanism or/and anteriorly positioned ciliary body against iris root to angle. It is critical to distinguish multi mechanism PACG from other types. The initial treatment for this type of PACG is also iridectomy, but after the pupillary block component is eliminated by iridectomy, the residual non pupillary blocking components should be highlighted by a diagnostic treatment procedure or by a ultrasound biomicroscopy (UBM) provocative test. Finally, the role of UBM in the observation and evaluation of the mechanism of angle closure is discussed and future research directions on PACG in Asians are proposed.
Conclusion Chinese eyes have been recognized to be prone to the development of creeping angle closure. There is some direct evidence that creeping angle closure is caused by multiple mechanisms. Further study on this topic is needed.

In recent years, partially as a result of the introduction of ultrasound biomicroscopy (UBM) in Asia, the understanding of primary angle closure glaucoma (PACG) in these regions has increased. A better understanding of the anatomic and pathophysiologic mechanisms involved in PACG, particularly the chronic type, has been reached. In this article, Chinese and the English literature are reviewed. A new classification of PACG and the principles for diagnosis and management of the multi mechanism variant of PACG are proposed.

Ethnicity and primary angle closure glaucoma
PACG is the most common type of glaucoma in the Asian population. A population based survey of PACG conducted in 1989 in Northern China revealed a prevalence of PACG of 1.37% in those over 40 years of age, and suggested that the rate of PACG among Chinese is 10-15 times higher than that found in Caucasians.[1] In recent years, this has received increasing attention in Asia. With the aid of gonioscopy, clear evidence has been presented which confirms that PACG is more prevalent than open angle glaucoma in Mongolia,[2] Taiwan,[3] Japan[4] and the Vietnam groups.[5,6] In Mongolia, the prevalence was found to be 1.4%, which is approximately 3 times the rate for open angle glaucoma.[ 2,7] An island wide survey of PACG in the heterogeneous population of Singapore showed that Chinese Singaporeans were at higher risk than the Malay and Indian ethnic groups.[8,9] Similarly, a survey aimed at finding the prevalence of occludable angle glaucoma concluded that the Vietnamese had a much higher prevalence of narrow angle disease and a greater risk of angle closure than Caucasians.[5,6]

Recently, similar surveys were conducted in different regions of China and stratified into different nationalities. Zhao Jia liang found the prevalence of PACG in Tibet to be 0.08% in people over 20 years of age and 0.15% in those over 40, using criteria identical to those used in Beijing, Shunyi county.[10] The prevalence of PACG in Tibet is significantly lower than that in Beijing, Shunyi county (Han nationality). In an investigation conducted in Anhui province, in the central eastern part of China, a PACG prevalence of 0.71% in people over 40 was revealed.[11] An epidemiologic survey of PACG in the Southern most region of China, Guangdong, Doumen county, compared the prevalence of PACG in Southern and Northern China and found that the prevalence of PACG in people over 50 is 0.85% in Southern China while it was twice as much (1.99%)[12] in Northern Chinese of the same age group.

Pooling data from epidemiological surveys of PACG conducted in China, we conclude that: 1) the prevalence of PACG in the Sino Mongoloid race is between that found in Caucasians and Eskimos; 2) the prevalence of PACG in Northern China is higher than that found in Southern China; and 3) the prevalence of PACG is different in different Chinese nationalities.

Not only is the prevalence of PACG different among different races, but the clinical manifestations of PACG in Chinese also differs from other races. Approximately 60% of PACG in the Sino Mongoloid population is of the chronic type, asymptomatic until late in the course of the disease, when visual loss occurs.[13] Even after a patient has iridectomy or laser iridotomy, approximately 13%-40% of cases have a positive response to dark room provocative tests and some develop progressive angle closure or delayed recurrent angle closure.[14-22]

Based on those studies and other available data, we conclude that the Sino Mongoloid population and genetically related races are at a higher risk for PACG, especially chronic angle closure glaucoma. However, the underlying etiology and pathogenesis of PACG in the Sino Mongoloid population remains unclear. Why are Sino Mongoloid individuals predisposed to PACG, which mainly presents as the chronic type with creeping angle closure? What are the causes of recurrent angle closure or delayed progressive synechial angle closure after a patent iridectomy or iridotomy in a subset of those individuals? This article will attempt to address these questions.

Anatomic basis for PACG in Chinese
Predisposing factors for PACG are mainly related to the geometry of the anterior chamber.[23-26] In the 1980’s,ocular biometric studies conducted in Chinese established that eyes with PACG show different anterior segment anatomical relationships as compared with normal eyes, irrespective of race. These included shallow anterior chamber, lens position, lens thickness, and short axial length.[27-35] However, of these studies, only one found any significant differences in anterior chamber depth between Chinese and Caucasians after stratifying for age differences.[28,36,37]

Recently, Congdon et al[4] conducted an epidemiological study to test the hypothesis that the anterior chamber analog differs between Chinese and Caucasian populations. Ocular biometric parameters and refractive error were measured among groups of Chinese, Caucasians, and Blacks. This well designed study showed that mean anterior chamber depth and axial length do not differ significantly among the three groups, and that Caucasians have a significantly higher prevalence of hyperopia than Chinese. In contrast, the radius of corneal curvature is significantly smaller among Chinese than in Caucasians or Blacks. These findings and the difference between the prevalence of hyperopia among Chinese and Caucasians is unlikely to explain the increased amount of PACG among Chinese. The only parameter that differs between Chinese and other groups that might underlie the excess risk of PACG among Chinese was their smaller radius of corneal curvature, since it implies a more crowded anterior chamber and chamber angle.

Risk factors predisposing to PACG, such as a shallow anterior chamber and narrow angle (occludable angle) were further investigated in different races and the results show that 6.4% of Mongolian individuals have occludable angle on gonioscopic evaluation.[2,7] In our studies, we found that 7.4% of Chinese have narrow angle.[38] In Americans, different investigations have found that the prevalence of narrow angle ranges from 0.8%-5%, depending on the ethnic group.[27,36,39] The highest prevalence of narrow angle is found among Eskimos[40] and we conclude that narrow angles are found at a higher prevalence in those races prone to PACG. Furthermore, it has been demonstrated that approximately 10% of people found to have anatomically narrow angles develop angle closure. In one of our studies, 485 patients who were judged to be at risk for developing angle closure glaucoma based on anterior chamber depth examination were followed prospectively. Analysis showed that this group had a 1.0%, 1.4%, 2.4%, 3.3%, 3.5% and 7.6% risk of developing angle closure within one year, two years, three years, four years, five years and six years, respectively.[16] Data from other sources shows that there is no single or combination of parameters that is sensitive enough to predict whether eyes with shallow anterior chamber and "occludable angle" will develop PACG. From this, we moved our focus to iris insertion, position of the ciliary body, configuration and thickness of the peripheral iris. A newly developed instrument, ultrasound biomicroscopy (UBM), permits a quantitative assessment of population differences in these parameters. Specificity and sensitivity of the anatomic factors needs to be validated in population based surveys so that a more sensitive and specific parameter can be detected before the onset of PACG and subsequent visual loss.

Inheritance of PACG
A crowded anterior segment is often observed in relatives of patients with PACG. The risk of developing PACG is 3.5 times higher in first degree relatives of affected Inuit patients,[9] and 6 times higher in family members of affected Chinese patients.[41] In China, one inheritance study of PACG found that in first and second degree relatives of PACG patients, the prevalence of PACG is 7.10% and 2.33%, respectively. On a theoretical basis, the prevalence of PACG in first and second degree relatives of PACG patients should be 14.08% and 4.53% respectively. Therefore, the heritability of PACG in the studied population is about 65%.[42]

If the risk of angle closure were purely genetic, the percentage of inheritance results would be higher than that found here. So, depending on the data, we conclude that genes alone may not explain the future development of PACG.A nation wide glaucoma survey in Japan found that the prevalence of PACG was 0.34%, while the prevalence of POCG was 0.58%, and normal tension glaucoma 2.04%.[43] In another clinic based study,[44] PACG in China and Japan were compared. The study found that in China, 76.4% of glaucoma patients seen in clinics had PACG, while in Japan, it was 34.5%, suggesting that the incidence of PACG is higher in China than Japan, and that the incidence of PACG is higher than that of primary open angle glaucoma in China.

Why does the prevalence of PACG differ, although these two races share many similarities? Environment may be one difference between these populations. As far as we know, the prevalence of myopia has increased over the past several decades with economic development in Japan.[45,46] Whether the changes of ocular anatomic parameters due to myopia, such as longer axial length and deeper anterior chamber influence the prevalence of PACG should be evaluated. If this is indeed true, the prevalence of PACG in more developed regions may decrease in the next generation, hand in hand with the increased rate of myopia.

Application of UBM in the study and diagnosis of PACG
Knowledge of the etiologic mechanisms of PACG was mainly inferred from slitlamp bio microscopy, gonioscopy, and histopathology.[47] Although slit lamp bio microscopy and gonioscopy allow the anterior chamber and angle to be viewed in situ, the posterior chamber, iris lens relationship and posterior surface of the iris, ciliary body, the insertion of the iris and iris thickness remain hidden, for the most part. Histopathologic data from enucleated eyes is often unreliable because of deformation and deterioration secondary to fixation and sectioning of specimens, making the interpretation of any relationship of anatomic structure and histopathology very difficult.

UBM, developed by Pavlin et al[48,49] is high frequency B scan ultrasound which provides high resolution images of the anterior segment and angle region. It has two advantages: 1) the examination can be conducted in various illuminations; and 2) the original and primary configuration of anatomic structure and the relationship of the anatomic structure of the anterior segment of the eye can be revealed in real time, since a water bath immersion technique (non contact technique) is used in scanning, without the interference found from manipulation in a contact technique, such as gonioscopy. In particular, UBM enables us to quantitatively assess the configuration of the angle and analyze the mechanism of angle closure dynamically.[50]However, UBM is not superior to gonioscopy in every aspect and it cannot replace gonioscopy. Gonioscopy remains the best technique for determining the extent of angle closure, the presence of synechial closure, pigmentation of the trabecular meshwork, and to discriminate color alterations of the trabecular meshwork and neovascular tissue.

In one of our studies,[51] angle configuration was assessed based on data acquired by UBM and gonioscopy and showed that the parameters acquired by the two techniques were consistent when the angle was wide and open. However, consistency was not very good when the angle was narrow. In this situation, the width of angle evaluated by gonioscopy was always wider than that by UBM because of the unavoidable influence of illumination and manipulation. When used to determine the position of iris insertion in an extremely narrow angle eye, UBM was found to be superior to gonioscopy because a tangential section of the anterior segment surrounding the angle can be observed in detail by UBM in real time without indentation. Since it is difficult to use gonioscopy to expose the recess of an angle even with indentation, insertion of the iris cannot be evaluated. When attempting to evaluate the convexity of the iris, we conclude that data from UBM is more reliable than that from gonioscopy, because the convexity of the iris described by UBM is based on the regular and even posterior surface of the iris while gonioscopy is based on the irregular and uneven anterior surface of the iris.[52]

Because of these advantages, UBM is also employed in dark room provocative testing.[53-55] Provocative tests were designed to predict the chances of future angle closure in anatomic narrow angle eyes and the dark room provocative test is considered the most physiologic of these tests. In the conventional dark room test, a patient is placed in a dark room for 1-2 hours and then undergoes tonometry and gonioscopy. An increase of intraocular pressure of 8 to 10 mm Hg is considered positive if confirmed by a narrow angle on gonioscopy. One limitation of this test is that it uses light for gonioscopy, at least partially reversing the conditions that caused the occlusion in the first place. So, when used to determine whether there is appositional angle closure, conclusions from UBM seem to be more reliable than gonioscopy.

As mentioned earlier, because ultrasound is used in the UBM examination, the configuration of the angle can be examined dynamically under different illumination. We used the UBM darkroom test and compared its sensitivity and specificity to the conventional test. In our comparison, UBM was performed under darkroom and illuminated conditions. Four images at pre determined meridians (3, 6, 9 and 12 o’clock) were obtained and we showed that if appositional angle closure is found in dark room conditions, the test was positive. The sensitivity of conventional darkroom and UBM darkroom tests was 31.8% and 68.2%, respectively. The specificity of the UBM darkroom test increased to almost 100%. Furthermore, when appositional angle closure was revealed, the underlying mechanisms can be analyzed in real time[54] (see next section).

On the whole, because UBM allows imaging of dynamic changes in anterior ocular structures as they occur, the UBM darkroom test improved the sensitivity of the darkroom test to provide detailed information regarding angle occludability in dark illumination conditions.

Mechanisms of angle closure in Chinese PACG
A clinical study by Hung in Taiwan, as well as our own data,[8-22,55,56] show that after a patent iridectomy, there is still about a 40% chance of positive response to a darkroom provocative test and slow progressive synechial closure or recurrent angle closure may also occur.[14-16] We hypothesize that the majority of PACG, especially chronic PACG, may be caused by multiple mechanisms, such as the coexistence of both pupillary and non pupillary blocking factors.

This hypothesis was confirmed in a recent study[18] using ultrasound biomicroscopy (UBM) where 126 patients who met the study criteria from 292 cases with PACG were examined. Forty seven eyes which had undergone iridectomy experienced a positive UBM darkroom provocative test when the mechanism of angle closure of PACG patients was analyzed. Three distinct patterns of angle closure were identified: pupillary block, non pupillary block, and multi mechanism.

Angle closure due to pupillary block [18-22,57]
These patients usually have shallower anterior chambers, a more anterior lens position, and a stronger pupillary block tendency. According to Mapstone’s pupil block force (PBF) formulae, [PBF=(D+E) cosα+Scosβ where PBF stands for pupil block force, S refers to sphincter contracting force, D is pupil dilating force, E is iris stretching force, α is the angle between the vector (D+E) and the line from iridolenticular apposition to the central of the radius of lens surface curvature and β is the angle between the vector S and the line from the iridolenticular apposition to the central of radius of lens surface curvature] can be calculated. These parameters can be obtained from the image of the anterior ocular segment acquired by UBM with newly developed software. In this situation, we can infer that the patients with this feature of anatomic relation have stronger PBF. The more anterior the lens is, the stronger the PBF. When pupillary block force increased beyond the posterior pressure blocking the aqueous flow from posterior chamber to anterior chamber, the iris assumes an iris bombe configuration (anterior iris bowing), consequently creating a narrow angle or angle closure (Fig. 1a). After iridectomy, the pressure between the anterior and posterior chambers was equalized allowing the iris to assume a planar configuration and the angle to become wider than that of pre operation (Fig. 1b). Our clinic based study shows that 38.1% of PACG in Chinese is caused by iris bombe due to pupillary blocking. Clinically, they manifest as an acute or sub acute attack and have an ideal response to laser iridotomy or iridectomy.

Angle closure due to non pupillary blocking mechanism[18-22]


These patients often have a relatively deeper central anterior chamber and relatively posterior lens position. The assumed line between iridolenticular apposition (iris lens contact point) and the point of iris insertion is at the same level or even more anterior than iridolenticular apposition. In this situation, according to Mapstone’s Pupillary blocking force formula, pupillary blocking force should be zero or negative. Images acquired from such patients by UBM show the anterior chamber to be relatively deeper, the iris surface appears flat but the angle is narrow, with a sharp drop off of the peripheral iris at the inner aspect of the angle (Figs. 2a and 2b). In most Western literature, this type of PACG is named "plateau iris" and most authors propose that it is the result of a large or anteriorly positioned ciliary body pushing the peripheral iris root against the trabecular meshwork.[49,58]However, in our study, we found only half of our cases have these anatomic features. The other half have a relatively normal size and normal positioned ciliary body and the ciliary processes are far away from the peripheral iris. What is the mechanism of the angle narrowing or closure in this subset of patients? We found that in these patients, the peripheral iris is thick and fleshy, the iris root angulates posteriorly and is short. In these cases, the narrow angle or angle closure is not caused by anteriorly positioned ciliary processes (Figs. 2a and 2b) but by the iris crowding into the angle when the pupil dilates. In illuminated conditions, the thickness of the peripheral iris is dramatically reduced and thus departs from the trabecular meshwork (Figs. 3a and 3b). Non pupillary blocking PACG is rare in Chinese. In our clinic based study, only 7.8% of PACG is due to this mechanism. These patients are often younger than those in the other PACG groups.

A ngle closure due to multiple mechanisms[8-22,58,59]
In China, 54.8% of PACG is caused by multiple mechanisms. Because the pupillary mechanism is involved in all cases, it is hard to distinguish this form of PACG from others before the pupillary blocking component is eliminated by iridotomy. These patients have a shallow anterior chamber, an anterior lens position, and an iris bombe configuration such as those in the pupillary blocking group.Fortunately, UBM provides us with useful information on the anatomic configuration of the angle structure. In one quantitative study comparing multimechanism PACG with pupillary blocking PACG, we found that iris root insertion is located closer to the angle in the former. Patients with multimechanism PACG have thicker and fleshier peripheral irises and anteriorly positioned ciliary bodies as compared with patients with pupillary blocking PACG. The pattern of angle closure in this form of PACG mainly displays creeping synechiae closure. When an eye has this anatomic feature, the pupillary blocking force increases due to the lens moving forward, the iris crowding the angle during pupil dilation, or the ciliary processor lifting the iris against the angle due to ciliary body anterior rotation. Any of these subtle changes may lead to angle closure in the quadrant with the most anterior iris insertion. If these changes progress gradually, angle closure will become chronic. This becomes a progressive process as the peripheral anterior synechiae gradually creep over the face of the ciliary body band to reach the scleral spur and then the trabecular meshwork. Sakuma T et al;[60] using ultrasound biomicroscopy, demonstrated that two distinct patterns of angle closure were seen: type B, in which closure starts from the bottom of the angle, and type S, in which closure starts in the vicinity of Schwalbe’s line. In type B eyes, the iris root was located closer to the chamber angle than in type S. The topology of the iris root is related to the pattern of appositional angle closure.

Therefore we believe there are several mechanisms involved in PACG. Such mechanisms include the pupillary blocking component, an iris crowding component, and an anterior positioned ciliary body. These factors can coexist in the following combinations: pupillary blocking and iris crowding, pupillary blocking and anterior positioned ciliary body, or all three. (Figs .1-6)

After the pupillary blocking component is eliminated by iridectomy, the iris bombe configuration becomes planar. However, under gonioscopy or UBM, a narrow or appositional angle closure can be revealed.[61,62] Under UBM examination and UBM dark room test, the underlying non pupillary components can be highlighted and analyzed (Figs. 4a and 4b, 5a and 5b, 6a and 6b). Non pupillary blocking PACG tends to be found in younger patients with less hyperopic and a deeper central anterior chamber as mentioned earlier. Because the anterior chamber depth typically decreases with age, pupillary blocking components may become apparent later in life in those patients with anatomic anterior positioned ciliary body, anterior iris insertion, and fleshy crowding peripheral iris. If pupillary blocking is a dominant coexisting factor, the post iridectomy angle may become wider, but not as dramatically changed as it would be in pupillary blocking PACG. If the non pupillary blocking factors are the dominant components, the post iridectomy angle will remain narrow or closed.[63] Hung[15,1 6] call this form of PACG "post iridectomy glaucoma" because there is residual glaucoma after iridectomy. He also postulates different mechanisms, in addition to the pupillary blocking mechanism, co existing in the same eye.

Several authors reported that coexisting factors may include ciliary blocking and lens blocking mechanisms. From our point of view, if ciliary blocking and lens blocking mechanisms were involved in PACG, these patients should be considered as having malignant glaucoma, another distinct form.[64,65] So these factors should not be included in the PACG group. Including these factors will cause unnecessary confusion in the classification of PACG.

A new classification system based on the mechanism of angle closure[18-20,56]
Establishing a classification system for PACG is important since the lack of established nomenclature for subtypes of PACG creates confusion in the interpretation of literature on the subject, as highlighted in a review by Congdon and Kim YY et al.[36,66] Little attention has been paid to separate what may be etiologically distinct subtypes, manifesting as acute, sub acute, chronic and plateau iris.

Based on a deeper understanding of the mechanisms of angle closure in PACG from recent research, and after reviewing the various nomenclature systems, we propose a new classification system, which is intended to highlight the different anatomical mechanisms of angle closure underlying PACG. We believe that this system will optimize the management of this disease.

PACG, and especially PACG in Chinese, may be classified into three types: angle closure glaucoma due to pupillary blocking; angle closure glaucoma due to non pupillary blocking; angle closure glaucoma due to multiple mechanisms. Sub classification of angle closure glaucoma due to a non pupillary blocking mechanism and angle closure glaucoma due to a multi mechanism can be done, such as: angle closure glaucoma due to non pupillary blocking, subtype: anterior positioned ciliary body, iris crowding; angle closure glaucoma due to multimechanism, subtypes: pupillary blocking and iris crowding coexist; pupillary blocking and anterior positioned ciliary body coexist or three of them co exist.

Guidelines for diagnosis and management PACG in Chinese
As mentioned earlier, multi mechanism PACG accounts for the majority of PACG in Chinese. This form tends to be misdiagnosed, leaving the underlying non pupillary blocking components untreated. Distinguishing both multi mechanism PACG components is critical in the diagnosis and management of these individuals.

First, depending on the configuration of the iris and the depth of the central anterior chamber, we can divide PACG into two categories: plateau iris and iris bombe. For early stage PACG with iris bombe, iridectomy or laser iridotomy are performed. After surgery, the configuration of the angle and iris should be re evaluated. If the angle widened dramatically, a diagnosis of the pupillary blocking form can be established. If the angle is still narrow, or appositional closure still exists under gonioscopy, or if the patient is found to have a positive response to dark room provocative test after iridectomy, and in dark room conditions an appositional angle closure is revealed by UBM, a multi mechanism diagnosis can be established.[13,18,56,67]

Further diagnosis of this form of PACG should then be undertaken. Prophylactic treatment can be given to such patients, which consists of usually topical Pilocarpine to strengthen the iris and reduce the thickness of the peripheral iris by contracting the pupil. In this circumstance, if the appositional closure is opened or a narrow angle is widened, the underlying non pupillary blocking mechanism could be iris crowding due to a fleshy and thick iris. If the angle remains narrow or even appositionally closed after iridectomy and miotic treatment, the underlying non pupillary blocking mechanism could be a plateau iris mechanism due to the anterior placement of the ciliary body. If UBM is available, it is useful to confirm an underlying non pupillary blocking mechanism, as it can directly confirm the presence of large or anteriorly positioned ciliary body or fleshy, comparative thick crowding peripheral iris under illuminated or dark conditions.[18,56]

For treatment of the form of angle closure due mainly to pupillary blocking combined with iris crowding, peripheral iridoplasty should be considered to reduce the crowding of the peripheral iris.[56,68-74] If a laser unit is not available, miotic treatment should be considered. Because long term topical application of Pilocarpine can cause complications, we suggest pilocarpine as a temporary means of preventing recurrence of angle closure. The best choice is to send the patient to a hospital equipped with a laser for laser iridoplasty therapy.However, for the form of angle closure due to pupillary blocking combined with anteriorly positioned ciliary body or pupillary blocking combined with anteriorly positioned ciliary body as well as iris crowding mechanism, treatment is not as efficient as that in pupillary blocking combined with iris crowding. A periodic gonioscopy or UBM examination remains indicated, as the angle can narrow further with the forward movement of the ciliary body.

If a patient is diagnosed with the non pupillary blocking form, iridectomy is not indicated. Laser iridoplasty is usually the first choice. After iridoplasty, the angle should be re evaluated. If the patient has an iris crowding form, the iridoplasty is usually effective and sufficient. But if the patient has an anteriorly positioned ciliary body after iridoplasty or miosis therapy, the height of the "plateau" is only reduced to some degree. As long as it does not block the "functional zone" of trabecular meshwork in the dark room condition, the treatment should be considered relatively effective. On the other hand, if the iris is still blocking the "functional zone" of the trabecular meshwork in dark room conditions, close follow up is indicated.

Regardless of the form of PACG, once significant peripheral anterior synechiae (PAS) are formed, it may become difficult to control intraocular pressure (IOP) even with the above mentioned techniques. Under these circumstances, a filtering procedure may become necessary. However, there are potential risks for filtration surgery, such as a flat anterior chamber, choroidal detachment, suprachoroidal hemorrhage, malignant glaucoma and hypotony maculopathy. Are there any alternative methods to filtering surgery for lowering IOP? As long as at least one quadrant of angle circumference remains open and IOP is not over 30 mm Hg, optic disc damage is usually mild. First laser iridotomy and/or iridoplasty is performed. After surgery, IOP and diurnal curvature should be re measured. In some cases, after iridectomy and/or iridoplasty, IOP will be reduced as compared with pre operative conditions because some areas of angle apposition are re opened by deepening the anterior chamber. If IOP is reduced to a normal level and at least two quadrants of angle are open after iridectomy or/and iridoplasty, medication should not be considered. Only close follow up is needed.

If IOP is not well controlled after iridectomy or/and iridoplasty or IOP control is lost on long term follow up, then topical IOP lowering agents are given based on the diurnal curvature and severity of optic nerve injury to achieve a "target" IOP. In clinical studies, we found that approximately 65% of these patients can obtain satisfactory IOP control by medication, and therefore avoid filtering surgery. If IOP cannot be brought under control, filtering surgery is indicated. When patients with PACG undergo filtering surgery, we suggest using scleral flab releasable sutures or laser scleral suture lysis technique to prevent over filtration related complications in the early postoperative period.[50,75]

On the whole, with greater understanding of the mechanisms of PACG, the application of new IOP reducing agents, improvement of current surgical techniques, design of new surgical techniques, and the application of new diagnostic instruments in PACG, the concepts and principles of diagnosis and management have changed in many respects.

Summary
PACG is a common cause of blindness in China and in all of Asia. Worldwide, PACG probably affects more than 30 million people, as many as open angle glaucoma does,[53] making it important to ophthalmologists throughout the world. In East Asian, and particularly Chinese people, a high prevalence of a creeping angle closure[76] had been obsearved. There is some direct evidence that creeping angle closure is caused by multiple mechanisms. The iris insertion and position of ciliary body is a decisive anatomic factor involved in creeping angle closure in this form of PACG. To distinguish this form of PACG from others is critical in the diagnosis and management of PACG in this population. Although rapid progress has occurred, there are still many issues to be resolved. We remain unable to fully answer the questions posed in the beginning of this review. Further study on this topic is needed and we hope this review will stimulate research in this field.

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