Preface VII

PREFACE

The objective of this book is to offer the general ophthalmologists a clinical comprehensive and practical guidance manual for primary angle-closure and primary angle-closure glaucoma to be used in the daily clinical work.

Already in the nineteen seventies our Danish colleague, Poul Helge Alsbirk documented the exceptional high prevalence of angle-closure glaucoma among the Eskimo or Inuit population in Greenland, a North-Atlantic part of Denmark. As Danish ophthalmologists ever since have been responsible for the diagnostics and therapy of primary angle-closure (PAC) and primary angle closure glaucoma (PACG) among these patients, this has led to a profound clinical experience and a growing knowledge of the complicated nature of this entity. We have experienced that the sub-clinical asymptomatic, “creeping” angle closure is a common type and early detection and prevention therefore necessary, just as in open-angle glaucoma. Further that different mechanisms and stages of PAC need different treatments and that a new, more differentiated and objectively based classification and terminology consequently has to be developed. To practice these recommendations we have learnt to use a number of standardised, clinical diagnostic methods.

To support the Danish ophthalmologists a guidance manual for primary angle-closure in Danish was published 2003 based on our long clinical experience, the present evidence based literature and conferences on glaucoma.

As the guidelines in Danish were very well received we were encouraged to produce an updated English edition. The new evidence about the high prevalence of angle-closure in Asians further supports an English edition. The point that early angle-closure may be cured and the fact that the world-wide visual disability from this disease is almost equivalent to open-angle glaucoma emphasizes the “urgent need” of improving the angle-closure management.

The word “glaucoma” is now only used in the presence of structural defects of the optic nerve head or when visual field defects are found.

VIII Preface

Acknowledgment should be given to our Danish colleagues Poul Helge Alsbirk, Erik Krogh and Lisbeth Serup for their advice and guidance of crucial importance.

A special thank goes to Pfizer Denmark, who published the first edition in Danish and sponsored the translation from Danish into English with an unrestricted educational grant.

Copenhagen May 2007

Svend Vedel Kessing and John Thygesen

Introduction 1

INTRODUCTION

AIMS AND METHODS

In February 1997, the Danish Glaucoma Society published a book of guidance describing the classification, diagnostics and treatment of primary open-angle glaucoma (POAG)21. The present book has been published as an attempt to provide a similar guidance manual for primary angle-closure glaucoma and its preliminary stages. The first edition in Danish was already published in 2003 and the contents of the present book in English are the same, with few updates.

In 1998, the European Glaucoma Society published their first edition of Guidelines for Glaucoma and in 2003 the second edition, in which the subject of primary angle-closure glaucoma was also treated. However, the present book suggests a more radical, well-defined and systematic treatment procedure, which in certain substantial areas proposes innovative thinking, to a great extent based on the personal clinical experience and attitude of the authors.

Throughout the book, the term ‘glaucoma’ will only be used when the observed development stage of angle-closure is incurable, i.e in connection with permanently increased intraocular pressure (IOP) due to peripheral anterior synechiae (PAS), latent glaucoma; and increased IOP together with the classical structural/functional glaucoma defects, manifest glaucoma. In principle, this is similar to POAG21. Furthermore, the Anglo-Saxon term ‘primary angle-closure’ (PAC) will be used.

Due to these terminological changes, a successfully treated case of acute PAC without subsequent complications in the form of permanently increased eye pressure or structural/functional glaucoma defects will not, as was previously the case, be classified as being ‘acute glaucoma’. Obviously, this is an undisputed advantage to the patient in question since it provides the opportunity of declaring that the patient has been cured and does not indeed have glaucoma. By not labelling the patient as having a glaucoma diagnosis, the quality of life of the patient will remain

2 Introduction

unaffected, as will any personal insurance policies. For the same reason, it is an advantage that the previously used term ‘latent angle-closure glaucoma’ (oc-cludable angle) has now been replaced by the term ‘imminent (threatening) PAC because of the high risk of developing acute or chronic PAC. Such a patient, following subacute laser treatment, is ensured against the development of not only an angle-closure attack, but also against the development of glaucoma as defined above.

It should be noted that there seems to be a tendency for researchers around the world to change the terminology used to describe the subject of PAC along the same lines as noted above28, 29 although this is not yet generally accepted. It is with this in mind that the above-mentioned terminology has been deliberately chosen for the purpose of outlining the systematic treatment procedures described in this book.

The two main purposes of the PAC-treatment procedures are:

–To contribute towards well-motivated preventive treatment of the various forms of imminent PAC in order to avoid both the acute catastrophe and the more common, asymptomatic, “creeping” angle-closure17, 34, 35.

–To contribute towards an optimal course of treatment for the individual patient by applying specific treatment.

With regard to the first purpose in question, it can be stated that the treatment strategies around the world – even those found in the most recent guidelines concerning PAC28, 29 – first and foremost deal with the prevention of manifest PAC glaucoma in order to prevent loss of vision. The point in question is that the acute PAC attack will diagnose itself and only seldom lead to loss of vision; thus any detection and preventive treatment is deemed unnecessary. But this negative attitude to PAC detection implies that prevention of the most common type of PAC glaucoma, the asymptomatic, “creeping” form34, 35, is missed.

This is especially serious, as the visual loss due to the asymptomatic form seems to be greater than that of the acute PAC41.

Furthermore, a simple and functional method for detecting PAC (limbal chamber depth (LCD) evaluation) does exist, as well as

Introduction 3

adequate and uncomplicated preventive treatment procedures (YAG iridotomy and laser iridoplasty). The basic requirements for the detection and prevention of imminent PAC are therefore available. A more general recommendation will, however, require a well-defined, standardised PAC examination protocol with regard to both professionally and ethically clear and acceptable indications for treatment. In this book, this requirement is met through the use of combined diagnostic PAC methods (standardised PAC gonioscopy and axial anterior chamber depth (AACD)) besides the generally applied glaucoma examinations (Goldmann’s applanation tonometer, ophthalmoscopy and automatic perimetry).

It should be noted that both of the international PAC guidelines mentioned above are inconsistent in their rejection of preventive treatment of imminent PAC in that they, in spite of this attitude, recommend preventive laser treatment in some not clearly defined conditions. This suggests a tendency towards a change in the international outlook. It is also worth mentioning that apart from these official guidelines, there are a few well-documented studies which do recommend preventive iridotomy. These are described in the chapter: YAG-laser iridotomy: Evaluation (p. 67).

Detective, preventive treatment of imminent PAC should, of course, be carried out in the primary ophthalmological health sector, and the practical possibilities for doing so are to a great extent already present. For instance, approx. 2000 YAG-laser iridotomies per year were registered in Denmark during the period between 1996 and 1998 of which 800 were carried out within the framework of private practice settings.

However, it is uncertain how many of these laser treatments were carried because of imminent PAC.

The second purpose of the PAC-treatment procedure: An optimal course of treatment for the individual patient may to a great extent be gained by applying a specific treatment. This is defined as a treatment which, guided by the findings from the initial objective examina-tion, is adapted to the observed specific type of pathoanatomy and PAC development stage of each individual eye.

The opposite of this, i.e. unspecified treatment, may be described as the “trial and error” method in which the different treatment

4 Introduction

procedures are tested successively, often leading to considerable and understandable frustration for the patient. It should be noted that the “trial and error” method is still recommended in connection with one of the above-mentioned official international guidelines29. Whereas the other guideline28 suggests a procedure which in some respects is similar to the present specific treatment. But in a recent review the same authors emphasize the need for a new PAC treatment procedure based on the same principles as the present specific treatment35. Therefore, also in this matter, there is a tendency towards a changing international outlook.

In order to simplify the prescription of a specific treatment, we use a standardised, objec-tively based identical subclassification (staging) of each of the three main PAC forms so that a specific, recommendable treatment with an expected satisfactory effect is attached to each clinical entity.

In this way, it is possible to work out a concise flow chart for specific treatment of PAC (fig. 19), which can be used in the busy daily clinical world. This flow chart, together with the diagram showing the standardised PAC gonioscopy method (fig. 11), involves the essence of the systematic PAC-treatment procedures and will therefore hopefully be found on the notice board at eye clinics in the future.

It must be stressed that the above-mentioned classification is thus only based on objective findings and not – as is the case of the prevailing method of classification – based on both subjective symptoms and objective signs.

In order to demonstrate the importance of specific treatment, case reports containing examples of unspecific treatment with regard to causes and consequences have been inserted in relation to each individual clinical subgroup. In connection with each case report, the concluding and final examination at the Glaucoma Clinic, Copenhagen University Hospital, has been carried out using the specified systematic PAC procedure in order to demonstrate the applicability of the recommendations.

With regard to the occurrence of PAC, the prevalence of manifest PAC glaucoma among persons over 40 years of age was found to be 0.6% (women: 0.9%, men: 0.2%) in a population glaucoma study carried out in Northern Italy in 200034. This number is higher than

Introduction 5

numbers found in earlier studies in Europe and North America and does not even include the early stages of PAC without structural and/or functional glaucoma defects. Therefore, it may be concluded that the occurrence of PAC in Europe seems to be higher than previously assumed.

Moreover new population studies show that the prevalence of manifest PAC glaucoma in Asians and Indians is about the same as or higher than the prevalence of POAG, and that the world-wide visual disability from PAC glaucoma is proportionately greater than that from POAG30, 40.

All in all, according to the opinion of the authors, there is a need for clarifying PAC recommendations with the purpose of further improving PAC treatment. As has been mentioned several times, similar tendencies can be detected internationally.

The present guidelines should neither be regarded as being fixed rules nor as representing a general consensus, with possibilities for medicolegal sanctions! Rather, the guidelines should be seen as suggestions based on the personal experiences of the authors gained through their everyday clinical lives, conferences on glaucoma and the present literature. Therefore, there is no solid scientific documentation for all the opinions and guidelines put forward in this book. Consequently the next step should be to carry out controlled studies, possibly based on the present clinical treatment procedure.

6 Introduction

Detection of primary angle-closure (PAC) 7

DETECTION OF PRIMARY

ANGLE-CLOSURE (PAC)

Since the development of Goldmann’s applanation tonometry method in 1955, traditional glaucoma detection has consisted of intraocular pressure (IOP) measurement. Today, in the case of POAG, it is generally accepted that IOP screening has an unacceptably low sensitivity and specificity. Assessment with regard to structural glaucoma changes in the nerve head and nerve fibre layer21 is more specific and should be used.

With regard to PAC, it is equally important to stress the fact that detection by means of IOP measurement alone is of no value since the early cases (of PAC) will remain undetected, and consequently prevention of the most common PAC glaucoma, the asymptomatic, “creeping” form34, 35, will not be provided.

As the visual loss due to PAC especially seems to be caused by this form, there has been a call for early detection of the asymptomatic PAC41.

It is, however, becoming generally accepted that limbal chamber depth assessment by means of a slit lamp is the preferred method for detection of PAC31, 32, 38. This assessment should therefore be routinely used in the clinic on all first visit patients.

LIMBAL CHAMBER DEPTH MEASUREMENT (LCD)

The limbal chamber depth assessment was introduced by van Herick, Schaffer & Schwartz as early as in 19691, however the routine use of the method as a means of detecting PAC at an early stage has not yet found general acceptance.

Methodology

The temporal corneal area immediately central to the sclerocorneal junction zone is observed with a high slit lamp magnification and a narrow vertical slit. The angle of the light must be approximately perpendicular to the corneal surface, and the slit lamp microscope must be placed at an angle of approx. 45-60 degrees (not

8 Detection of primary angle-closure (PAC)

decisive) from the source of light (fig. 1). In the optical section of the peripheral chamber angle, the examiner can now assess the distance between the anterior surface of the iris and the posterior corneal surface and relate this to the size of the peripheral corneal thickness (CT).

An iris/corneal distance of 1/4 (LCD = 0.25) of the peripheral corneal thickness arouses the suspicion of a narrow angle (fig. 2), whereas LCD < 0.25 usually indicates PAC. However, in both cases there is a clear indication for subsequent gonioscopy. Conversely, LCD > 0.5 normally excludes PAC.

Fig. 1. Limbal chamber depth (LCD) measurement based on van Herick’s test.

These values regarding LCD assessment are generally accepted as being practically applicable for the routine clinical detection of PAC31, 32. For instance, using a limit value of 0.25 in a population study carried out in Mongolia32, the sensitivity and specificity of the LCD method were set at 99% and 66%, respectively, whereas in a population study carried out in Northern Italy, the sensitivity and specificity were set at 88% and 17%, respectively. Practically all narrow angle systems are thus detected, although at the

Detection of primary angle-closure (PAC) 9

expense of a few too many false positives (specificity 66% and 17%). However, LCD assessment is clearly an acceptable method of detection, especially when considering its simplicity and the speed of implementation of the method.

It should be stressed that the surface of the iris root, as is well known, is by no means level, but has an undulating outline concentric with the limbus in which the “crest” of the iris should normally form the basis for the classification (fig. 2). Thus, the LCD measurement is the result of a subjective assessment, which is why standardised PAC gonioscopy and axial chamber depth measurement are the diagnostic examinations of choice in the evaluation of suspected PAC.

Fig. 2. Limbal chamber depth assessment. a: Positive test (LCD = 0.25). b: Negative test (LCD = 1.0)

Finally, it should be noted that the above-mentioned guidelines for interpreting the LCD method first and foremost apply to the most frequent forms of pupil block PAC in that LCD in the much more seldom pure plateau iris condition lies between 0.25 and 0.5 (ref: Group II: PAC with plateau iris). There is a risk of a false negative LCD interpretation with plateau iris. Therefore, for correct detection of pure plateau iris it is essential that routine use

10 Detection of primary angle-closure (PAC)

of the quickly performed gonioscopy procedure using a Posner lens be carried out, even with the slightest suspicion of PAC with a LCD evaluation around 0.25.

Sources of error

As mentioned, the LCD determination is simple and easy to implement. The safe use of the method does, of course, require some clinical experience.

The sclerocorneal peripheral area may sometimes, especially among elderly people, be indistinct due to limbal corneal changes (arcus senilis, marginal scarring).

Furthermore, the location of the sclerocorneal peripheral area compared to the chamber angle may vary because of normal anatomical variations of the insertion of the cornea into the sclera. Normally, the superficial scleral lip is the longest and covers the angle anatomy. However, quite often temporally the superficial scleral lip is shorter than the deeper one (partial limbal scleral staphyloma2), and this may create a false positive LCD assessment. This is due to the fact that in this situation the sclerocorneal peripheral area is closer to the tip of the angle, and thus the LCD measurement is carried out rather more peripherally where there is a reduced space to the iris. This normal anatomical variant is often seen in combination with embryotoxon posterior (ref: Schwalbe’s line, the normal anatomy of the chamber angle).