|Year : 1998 | Volume
| Issue : 4 | Page : 255-261
Ravi Thomas1, Saju Thomas1, G Chandrashekar2
1 Schell Eye Hospital, Christian Medical College, Vellore, India
2 L.V. Prasad Eye Institute, Hyderabad, India
Schell Eye Hospital, Christian Medical College, Ami Road, Vellore - 632 001
Source of Support: None, Conflict of Interest: None
Gonioscopy forms part of a complete ophthalmic examination and is mandatory for the diagnosis and management of glaucoma. Gonioscopy permits identification of eyes at risk for closure and detects angle abnormalities that could have diagnostic and therapeutic implications. The technique of gonioscopy, its value in management, and guidelines for routine use are discussed in this paper.
Keywords: Gonioscopy, glaucomas, angle closure, angle grading, routine use
|How to cite this article:
Thomas R, Thomas S, Chandrashekar G. Gonioscopy. Indian J Ophthalmol 1998;46:255-61
It is our impression that the majority of ophthalmologists in the country do not perform gonioscopy routinely. We hope we are wrong and apologize to the minority who do. Be that as it may, this article aims to encourage ophthalmologists to practice routine gonioscopy.
As this article is intended to be a practical guide, we must address the first question that any general ophthalmologist is bound to ask: "Why should we learn to do gonioscopy?" After all, if you have managed a successful practice with a torch (and slitlamp) what is the benefit in adding on one more examination; especially if it may be uncomfortable to the patient?
The answer is simple. Just like slitlamp examination, tonometry and ophthalmoscopy, gonioscopy forms part of a complete ophthalmic examination which, as ophthalmologists, we must all be able to perform. Gonioscopy allows us to examine the angle of the anterior chamber and is mandatory for the management of glaucoma. This is especially true for the diagnosis and management of angle closures which seem to form the majority of the glaucomas in our country. In fact it is not unreasonable to state that without reasonable proficiency in the technique of gonioscopy, nobody should be managing glaucomas. If the reader is convinced, let us discuss this further.
| Learning Gonioscopy
Having decided to learn gonioscopy, what is the best method? The best method is to learn with an experienced examiner on a slitlamp that has an observer' s scope. In addition to the simple mechanics of insertion and removal of the contact lens, the observer can be shown normal anatomy, variations of the normal, as well as pathology. The next best method is to learn as a group. An experienced observer demonstrates the findings on a TV screen through a slitlamp with a video attachment [Figure - 1]. A high-resolution monitor is desirable. If the facilities required for the above are not available, the interpupillary distance of the binoculars can be widened and the findings demonstrated uniocularly; the examiner looks through one eyepiece and the student observers through the other. The proximity involved makes for a good teacher-student relationship, which is an advantage. If nothing else, get hold of an atlas (suggested in the references), insert the gonioscope (this should be easy enough for anyone capable of performing microsurgery), and begin observing, correlating, and learning.
If you want to learn gonioscopy, make a decision now. Make a decision to do a gonioscopy on the next 1000 adults and 500 children old enough to tolerate it. What! Gonioscope all these predominantly normal people? Sure! That' s how we learn what normal is; and unless we know what normal is, how can we detect the abnormal? Start by doing a gonioscopy on the next patient you see after reading this article.
| Principles of Gonioscopy and Gonioscopic Lenses
Since our emphasis here is on the practical, this section will be mercifully brief (as some ophthalmologists-in-training may be reading this, we cannot omit it completely). Normally the light coming from the anterior chamber angle is totally internally reflected making the viewing of the angle impossible without the aid of a gonioscopic lens. The gonioscopic lens changes the interface from cornea-air to lens-air, changing the critical angle and thus permitting viewing of the anterior chamber angle.
There are basically two techniques of gonioscopy: (1) Direct Gonioscopy, and (2) Indirect Gonioscopy
| Direct gonioscopy
It is performed with a steep convex lens which permits light from the angle to exit the eye closer to the perpendicular at the lens-air interface.
Direct gonioscopic lenses include the Koeppe, Hoskins-Barkans and Swan-Jacobs lenses. These lenses are used with a portable slitlamp or an operating microscope. Direct gonioscopy is very useful when we want to compare the angles of the two eyes by looking at them simultaneously (well, almost simultaneously) as when looking back and forth between the eyes for subtle signs of angle recession. Direct gonioscopy is useful but fairly impractical for routine use. We use this essentially for examination of children under anesthesia (under the microscope) and for surgical procedures like goniotomy.
| Indirect gonioscopy
Indirect gonioscopy uses mirrors or prisms to overcome the problem of total internal reflection. Moreover, it uses the slitlamp's illumination and magnification system to its advantage. And if we are examining all our patients on the slitlamp, as indeed we should be, it makes sense to use an indirect gonioscope at the same time.
Types of indirect gonioscopic lenses include those that need coupling agents such as: Goldmann 3-mirror, 2-mirror and 1-mirror lenses and similar lenses made by other companies.
The lenses that do not need coupling agents or lenses for indentation gonioscopy include the Zeiss 4-mirror lens, the Posner lens and the Sussmann lens. Some of the lenses used for gonioscopy and the solutions needed are shown in [Figure - 2].
| Aims and Indications of Performing Gonioscopy
Gonioscopy is performed on a patient in order answer at least two questions: (1) Is the angle occludable? (2) Are there any abnormalities in the angle? There are other questions such as grading, but they can wait till later.
To answer the first question, the testing conditions must be appropriate; what we want is an in situ view of the angle. The act of placing any lens on the eye disturbs the angle, but we routinely use a 2-mirror lens in an attempt to obtain as much of an in situ view as possible. With the lens on the eye the patient is asked to look straight ahead. We ensure this by peeking at the other eye of the patient, determining that the eye is indeed looking in the required direction. The room lights are then dimmed; the illumination and the height of the slit beam are decreased so that it does not impinge on the pupil and cause pupillary constriction (with attendant artifactual opening of the angle). The angle is then observed in situ (so to speak) to assess its occludability. We do not use the 3-mirror lens because we feel (in our hands) it artifactually opens up the angle.
The testing conditions for occludability are critical. [Figure - 3] shows the open angle of an primary open-angle glaucoma (POAG) suspect with an intraocular pressure (IOP) of 31 mmHg. Gonioscopy was performed without attention to the lighting conditions. When the ideal testing conditions described above were created, the angle closed and could explain the raised IOP [Figure - 4]. The patient underwent a laser iridotomy to resolve the situation.
Having assessed occludability, we need to answer the second question: what else is there in the angle? To do this, we increase the room and slitlamp illumination, and allow the light to impinge on the pupil, thereby opening up the angle. If this does not open up the angle, we manipulate it open: the patient is asked to look in the direction of the mirror and the lens is pushed on the sclera in a slightly tangential manner to open up the angle. We call this procedure "manipulation" (as opposed to indentation which we'll come to in a moment); in our own hands we can manipulate open the angles with the 2-mirror lens 90 to 95% of the time. This allows us to look for peripheral anterior synechiae, for instance. [Figure - 5] shows an irregularly open angle. Manipulation with the 2-mirror gonioscopy lens demonstrates the peripheral anterior synechiae that allow a diagnosis of chronic angle closure glaucoma (CACG) as shown in [Figure - 6].
If we fail to manipulate open the angle (5-10% of cases), we achieve this by "indentation" using an indentation lens. We prefer to use the Sussman 4-mirror lens for indentation since it is held in the hand in the same manner as the 2-mirror lens we are accustomed to. The Zeiss 4-mirror and Posner lenses are held by a handle, which is a new and difficult trick for some old dogs.
If we need to use an indentation lens 5% to 10% of the time, why not use it routinely? Unfortunately, in inexperienced hands it is sometimes very difficult to get an "in situ view" of the angle with indentation. Indentation gonioscopy requires more patient cooperation than a 2-mirror lens. The indentation lens has to be continuously held just in apposition to the cornea without any pressure. Initially we may exert some pressure and artifactually open up the angle. As we get more experienced, this happens less often. One of the authors has converted totally to using the identation gonioscope and the others are working on it with considerable success. The other reason for using the 2-mirror lens is that it is about half the price of an indentation lens. It would be nice to have both, but if you can afford only one lens you can certainly manage very well with a 2-mirror lens alone, which is useful 95% of the time.
We are often told that in a busy practice there is no time to gonioscope everybody. Frequently I'm asked for guidelines on who needs gonioscopy. Firstly, when learning, the doctor needs to do gonioscopy routinely. So in that situation our 1500 guideline stands. After that: how do we determine which patients to gonioscope ?
The other tests routinely performed to screen for occludable angles are the Flashlight test and the Van Herricks test. In a study done in our department we found that these tests are poor predictors for our occludable angles. That is, if these tests are positive, quite often the angles are not occludable. However, if both these tests are negative you can be 98% sure that the angle is open. That is, in your busy practice if you omit gonioscopies on patients who are negative for occludable angles on the Flashlight and Van Herrick tests, you will miss only 2% of occludable angles. The tests (when negative) are useful in ruling out narrow angles in the clinic setting. This guideline is only to determine occludability. Patients with positive tests should undergo gonioscopy. It is mandatory to gonioscope patients with raised IOP, and glaucoma suspects (suspects for whatever reason) irrespective of the findings of the Flashlight and Van Herricks test. Gonioscopy may need to be done for other reasons like Uveitis, or suspected IOFB.
It is obvious then that each one of us should know how to do a complete ophthalmic examination. Gonioscopy is an important part of a complete ophthalmic examination and we must learn this too: initially, in all patients we see (to learn what is normal) and then when necessary.
| Gonioscopic Anatomy and Gonioscopic Grading Systems
While performing gonioscopy one can identify the structures from anterior to posterior or vice versa. In order to avoid misinterpretation, we prefer to identify the structures from the anterior to posterior. The angle structures from anterior to posterior include the Cornea, Schwalbe's line (termination of Descemet's membrane), anterior nonpigmented trabecular meshwork, the filtering posterior pigmented trabecular meshwork, the scleral spur, the ciliary body band, and the iris insertion into the ciliary body.
Several grading systems have been described. The system we use [Table - 1] is based on structures actually visualized. The gonioscopic examination is performed with minimum illumination compatible with good visualization as described earlier. The slit beam is shortened so that it does not fall on the pupil. This system was developed and taught at the Rajendra Prasad Center for Ophthalmic Sciences, All India Institute of Medical Sciences, New Delhi and was initially published in the Eastern Archives of Ophthalmology and later described again in the Australian and New Zealand Journal of Ophthalmology. We have demonstrated good inter-observer agreement of this system (a weighted Kappa of 0.81).
Grades 3 or less are considered narrow. Grade 2 and less are considered closed. The above classification can easily be modified to state the structure seen as shown in [Table - 2]. This grading system has the advantage that it does not have to be committed to memory; the angle is graded according to the structure seen without converting it into a numerical representation, thus decreasing the chance of inter-observer variability.
Whatever the classification used (or not used), in addition to the grading, the ophthalmologist should make a forced-choice decision as to whether the angles are occludable or not based on type of entry into the angle (narrow or wide) and the angle structures visible.
The numerical component can be eliminated by simply stating the structure seen and stating occludable, possibly occludable or not occludable. The presence of other abnormalities of the angle such as peripheral anterior synechiae, foreign bodies, angle recession, and cyclodialysis cleft are specifically noted for location, extent, and so on.
| Identification of Angle Structures
The technique of inserting and removing gonioscopes are detailed in most standard textbooks. The procedure is briefly described below.
- 1. The eye is anaesthetized with the topical anesthetic agent of your choice. Coupling fluid is poured into the well of the gonioscope.
- 2. The patient is asked to look down.
- 3. The thumb of one hand is used to retract the upper lid.
- 4. The lower edge of the gonioscope is placed on the lower lid and the gonioscope is tipped onto the cornea in one smooth maneuver (Figure:7] and [Figure - 8]. In the event of difficulty in keeping the gonioscope in place, a solution like Goniospl (Hydroxy propyl methyl cellulose 2.5%) may be used. This is thick and a little messy, so once you are more experienced you can use the less viscous Eyesol (Hydroxy propyl methyl cellulose 0.7%).
If corneal edema prevents visualization of the angle, topical glycerin, or hypertonic saline can be used to clear the cornea after anaesthetising it.
Schwalbe's line is the peripheral termination of the cornea where the Descemef's membrane ends. It can be best identified by locating the corneal wedge. A thin slit of light slightly inclined from the oculars is projected onto the cornea. In the angle, two separate corneal reflections are perceived; one illuminates the inner and the other the outer aspect of the cornea. In addition to the inner and outer parts of the cornea the lines also illuminate the opaque scleral face. The portion between the two lines is called the corneal wedge; the corneal wedge intersects at and identifies Schwalbe's line. The corneal wedge is an important landmark but the appearance can vary from eye to eye. With practice (the 1500 normal gonoioscopies, remember) it can almost invariably be identified. It may be desirable to tilt the goniopscope towards the mirror in order to make the wedge more prominent. [Figure - 9] is a diagrammatic representation of the method we use to identify Schwalbe's line; [Figure - 10] is a clinical photograph of the same method.
Schwalbe's line is an important landmark in identifying the gonioscopic anatomy in confusing angles. It is easy to make a mistake while doing gonioscopy in eyes with closed angles, hazy corneas and pigmentation anterior to Schwalbes line. Such a false angle can be mistaken for an open angle. We would therefore stress on identifying the Schwalbe's line first and then identifying the structures from anterior to posterior.
| Clinical Examples Illustrating Uses of Gonioscopy.
Some of the many uses of gonioscopy are listed below
- 1. To make the crucial differentiation between POAG and PACG.
- 2. To diagnose and provide a prognosis for the congenital glaucomas.
- 3. To diagnose secondary glaucomas, especially subtle angle recession, uveitic glaucoma and that due to early neovascularization, and irido-corneal endothelial syndromes. The black pigment balls seen in [Figure - 11] are quite characteristic of resolved hyphema. This sign may be the only indicator of past trauma. Inflamatory peripheral anterior synechiae in cases of uveitis [Figure - 12] are broad and usually found in the inferior angle. These should not be mistaken for the synechiae caused by angle closure.
- Unusual causes of glaucoma: [Figure - 13] shows the haptic of a posterior chamber lens protruding through the peripheral iridectomy and resting in the angle of the anterior chamber. The resultant pseudo-phakic pigmentary glaucoma could only be diagnosed by gonioscopy. In day-to-day practice, a careful gonioscopy frequently provides the diagnosis in an otherwise baffling unilateral glaucoma.
- Other conditions like tumors of the anterior segment, ciliary body cysts, intraocular foreign body, and early detection of a Kayser Fleisher Ring. The foreign body in [Figure - 14] could only be detected by gonioscopy.
- Gonioscopy for treatment. A mastery of gonioscopy is necessary to perform argon laser trabeculoplasty.Gonioscopy is also necessary to follow up on patients who have undergone peripheral iridotomy, trabeculectomy, etc. [Figure - 15] shows the iris partially blocking the trabeculectomy opening. It now becomes obvious that in addition to patient care and academic purposes, learning gonioscopy has the potential to more than pay for the cost of gonioscopes.
- Indentation gonioscopy can be used to break an attack of acute angle closure glaucoma.
We hope this article will encourage more ophthalmologists to learn and perform gonioscopy routinely. The authors would be happy to help by answering queries in the mail (e-mail as well as the usual "bullock-cart" postal variety). We are also happy to welcome you to our institutions to learn with us.
| Suggested Reading
- 1. Alward WLM. Colour Atlas of Gonioscopy. London: Wolfe Publishing, an imprint of Mosby Year Book Europe Limited; 1994.
- 2. Grant WM, Schuman JS. The angle of the anterior chamber. In: Epstein DL, Allingham RR, Schuman JS, editors. Chandler and Grant's Glaucoma. Baltimore, USA: Williams and Wilkins; 1997. p 51-83.
- 3. Pamberg P. Gonioscopy. In: Ritch R, Sheilds MR, Krupin T, editors. The Glaucomas. St. Louis, USA: Mosby; 1996. Vol 1. p 455-69.
Thomas R, George T, Braganza A, Muliyil J The flashlight test and Van Herick's test are poor predictors for occludable angles. Aust NZ J Ophthalmol
[Figure - 1], [Figure - 2], [Figure - 3], [Figure - 4], [Figure - 5], [Figure - 6], [Figure - 7], [Figure - 8], [Figure - 9], [Figure - 10], [Figure - 11], [Figure - 12], [Figure - 13], [Figure - 14], [Figure - 15]
[Table - 1], [Table - 2]