The next patient sitting in your chair may have narrow angles.
Patients with narrow angles can present along a wide spectrum of angle closure, from anatomically narrow angles with no glaucomatous damage to an acute angle closure attack.
Proper gonioscopy can guide management direction and have a significant long-term impact on visual outcome in these patients.
Looking at narrow angles
Glaucoma is the leading cause of irreversible blindness worldwide.1 Angle closure is the underlying mechanism in one-third of primary glaucomas, and it is responsible for half of all glaucoma blindness worldwide.2-4
Primary-angle closure glaucoma (PACG) is a leading cause of bilateral blindness worldwide, estimated to affect between 16 and 20 million people.4,5 Although angle-closure glaucoma (ACG) is less prevalent than open-angle glaucoma, it may blind a higher proportion of individuals due to the underlying nature of the disease.6
Angle closure results from appositional closure of the anterior chamber angle and can be divided into primary and secondary classifications, with the former indicating no detectable cause besides anatomical predisposition and the latter arising from a known pathology.
Angle closure disease can be categorized as primary angle-closure suspect, primary angle closure, and angle-closure glaucoma.7-9
A narrow-angle diagnosis is typically defined an anatomical disposition in which the trabecular meshwork cannot be seen in more than 180 degrees.10 An angle-closure suspect has narrow angles or approximately 180 degrees of iridotrabecular apposition without other glaucomatous associations.
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Primary angle-closure patients will have a narrow or closed angle with an elevated intraocular pressure (IOP). In some cases, there may also be peripheral anterior synechiae present, resulting from long-term iridotrabecular contact.7,11,12 Patients with ACG will have a closed angle and glaucomatous damage evidenced by visual field, nerve fiber layer, or optic nerve damage with or without peripheral anterior synechiae.5
Angle closure risk factors
Demographics at risk for angle closure include female gender; advanced age; and Asian, Indian, or Inuit descent.4,10,11 Ocular risk factors include smaller eyes (shorter axial length, smaller corneal diameter), narrow angles, shallower anterior chamber depth, thicker and/or anteriorly displaced lens, and hyperopic refractive error.10
Patients are typically asymptomatic due to the slow nature of closure unless undergoing an acute angle closure attack, in which the symptoms may range from pain, nausea, and vision loss to redness and halos around lights.
The American Academy of Ophthalmology Preferred Practice Patterns and the American Optometric Association Clinical Practice Guidelines agree for both primary open-angle glaucoma and PACG that gonioscopy is an essential part of the evaluation of glaucoma patients, yet recent studies suggest that gonioscopy is likely underperformed in these patients.7
Gonioscopy was performed in fewer than 50 percent of patients in the five years preceding glaucoma surgery.7,13
In an open angle, the most posterior structure visible is the ciliary body and appears as a grayish-brown structure next to the iris root. Moving anteriorly, the next most posterior structure is the scleral spur. This structure is often white in appearance but can also appear light gray in some individuals. The next structure is the trabecular meshwork, which can be subdivided into anterior and posterior. The posterior portion of the trabecular meshwork filters aqueous into Schlemm’s canal. The amount of pigment visible in the trabecular meshwork can increase over time, darkening its initial light gray color. The most anterior structure in the angle is Schwalbe’s line, which may also be light gray with pigment.
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Various classification systems exist to describe the angle appearance; however, they are not uniform in their designations and may cause confusion if not accurately interpreted. Some require estimation or measurement of the degrees of angle opening, with an angle measuring 10 to 20 degrees defined as narrow.4 The most common classification is to identify the most posterior structure seen for all angles, noting any iris abnormalities (synechiae, approach).
Types of angle closure
The most common form of primary angle closure is thought to arise from pupillary block11 in which aqueous forces the pupil forward. In this scenario, apposition of the lens and the posterior iris at the pupil leads to blockage of the aqueous flow from the posterior chamber to the anterior chamber. As the pressure in the posterior chamber increases, the peripheral and midperipheral iris is pushed forward, blocking trabecular meshwork drainage.14
Another mechanism of primary angle closure is plateau iris in which the iris root is displaced anteriorly, creating a fold in the angle and displacing the peripheral iris into the trabecular meshwork.
Secondary angle closure may arise from pathological enlargement and anterior displacement of the lens, pushing the iris forward to narrow the angles in phacomorphic glaucoma.14,15 Other etiologies include neovascularization, membrane obstruction of the angle, and developmental abnormalities.14
Another contribution to recognize in the development of narrow or closed angles is the role of prescription and over-the-counter medications. Many widely prescribed and readily available antidepressants and antihistamines can increase the risk of ACG by inducing iris dilation or anteriorly displace the lens-iris diaphragm.16
One medication to note is topiramate (Topamax, Janssen), used in the treatment and management of epilepsy and migraines and more recently for weight loss, along with many off-label uses. Topiramate can cause swelling of the ciliary body and lens, as well as uveitis, myopia, and bilateral angle closure.14,16,17 The management of topiramate-induced angle closure consists of immediate discontinuation of the medication along with medical IOP reduction.16,17
Although it is difficult to be precise about the mechanism of narrow angle in all eyes,15 it is important to recognize it may be the result of a combination of a number of factors.
Gonioscopy is the standard for visualizing and diagnosing angle closure. It is important to evaluate all angles carefully. If the most posterior structure visible is the posterior trabecular meshwork, the angle is described as narrow. If only the anterior trabecular meshwork is visible, the angle is typically open 10 degrees or less and is likely to close. If greater than 180 degrees of the angle is found to be narrow, that patient is considered to be at risk for angle closure.
When performing gonioscopy as an initial assessment, it is important to balance the pressure of the lens and not inadvertently perform indentation gonioscopy. In that case, a narrow or closed angle may be mistakenly perceived as open.
Additional factors when performing gonioscopy include the level of illumination, both in the exam room and the light entering the pupil from the slit lamp.18 Illumination from a computer screen or eyechart may cause the pupil to constrict, thereby pulling the iris out of the angle. In addition, using a small parallelepiped square to assess the inferior angle first will allow for a more accurate assessment. The lack of a fixation target will serve to reduce the role of accommodation in pupil constriction, although it may create some additional complications when the lens is first applied.
As mentioned, it is important to assess all angles because peripheral anterior synechiae may be more likely to develop earlier in the superior and temporal angles due to anatomical structure.
Angle OCT and ultrasound biomicroscopy are useful adjunct imaging tools but may not reveal important characteristics such as peripheral anterior synechiae and should not replace gonioscopic evaluation. Note that these adjunct tests do not yield information about the amount of pigment in the trabecular meshwork.
Angle OCT imaging is also helpful in monitoring angle position status post treatment as well as for patient education.
Treatment and management
In cases of identified acute angle closure, the first line of treatment is to reduce IOP in order to prevent glaucomatous optic neuropathy. This may be accomplished by using fast-acting topical glaucoma medications such as beta blockers, alpha agonists, carbonic anhydrase inhibitors, and pilocarpine.11
With the exception of pilocarpine, these medications work to reduce the aqueous production quickly—pilocarpine constricts the pupil and helps widen the angle. It should be noted that if a secondary angle closure such as phacomorphic glaucoma is suspected, pilocarpine should not be used because it may narrow the angle further. Pilocarpine may also worsen an angle closure due to uveal effusion because it facilitates vascular permeability. Prostaglandins may not be as effective in immediate IOP reduction but should be used if no alternative or additional medications are available.
The medications may be instilled every 10 to 30 minutes and should be continued until the IOP has been reduced to under 30 mm Hg. As with any treatment, optometrists should be aware of systemic conditions and potential contraindications with these medications. These include but are not limited to asthma, chronic obstructive pulmonary disease (COPD), kidney disease, and allergies.
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In urgent or nonresponsive IOP, systemic carbonic anhydrase inhibitors (two 250-mg tablets po in one dose) may be given but are contraindicated in secondary angle closure induced by topiramate.14
If secondary inflammation is present, topical steroids should be initiated.
Indentation gonioscopy may also be performed with a smaller lens such as a four-mirror lens. Applying pressure to the central cornea may drive the iris posteriorly, allowing the angle to open.
Once the IOP is controlled, the next step is to reverse the mechanism of angle closure. Laser peripheral iridotomy (PI) has been the definitive treatment for ACG due to pupillary block as well as a preventative treatment in narrow angle suspects. A PI establishes an alternative route for aqueous flow between the anterior and posterior chambers and allows for the iris to return to a neutral position.
The PI may be placed superior, inferior, or at 3o’clock on the peripheral iris and is typically performed with a YAG laser. In some cases, the IOP remains elevated despite a patent PI, as seen with retro illumination. This is thought to be the result of prolonged irido-trabecular contact, resulting in long-term damage to the trabecular meshwork. Most patients who undergo PI will require additional intervention for either IOP lowering or improvement of visual acuity.5,10,11
Even though PI is a minimally invasive procedure, complications may develop as a result, although unlikely. These include the risk of cataract progression, hyphema, peaked pupil, monocular diplopia, retinal detachment, and permanent vision loss.5
An alternative approach for managing PACG is surgical lens extraction, as used in managing age-related cataracts. Age-related growth of the lens plays a major part in the mechanisms leading to primary angle-closure glaucoma, and lens extraction is used routinely in patients with coexisting cataract.10
The effectiveness of early lens extraction for the treatment of primary angle-closure glaucoma (EAGLE) study is a step in determining the efficacy and safety of this treatment in people with primary angle-closure glaucoma without cataract. The results, released in 2016, showed that the study has achieved its primary aim to demonstrate that initial clear-lens extraction would be associated with better quality of life, lower IOP, and less need for glaucoma surgery at 36 months than standard care.19
Despite these results, we still lack predictive factors that would better enable clinicians to identify individuals who are more likely to benefit from clear-lens extraction as a first line treatment. The decision should be made carefully after thorough evaluation and discussion with individual patients.
Narrow angle suspect
In cases of angle closure or ACG, the treatment and management process is relatively step-wise and direct—reduce the IOP and address the underlying cause.
What about the asymptomatic patient with anatomically narrow angles? If he has no history of intermittent attacks or optic disc damage, what is the best management? Not everyone with narrow angles will go on to develop angle closure.
Ultimately there is no one method of management in these scenarios. Careful and accurate gonioscopy is essential in correctly evaluating the angle and identifying additional risk factors such as peripheral anterior synechiae. If synechiae are present with no other findings, a PI may be warranted. Dilating these patients on a case by case basis due to their increased possibility of undiagnosed glaucoma is an important component of their ocular care. Avoid using combinations of drugs that stimulate both the dilator and sphincter muscles as these will maximize the pupil block. Monitoring post-dilation IOP for any changes greater than approximately 5 mm Hg will help proactively identify any pressure spikes and allow for timely treatment. An iatrogenic angle-closure attack occurring in a managed and well-controlled environment can actually be turned to the patient’s advantage. The likelihood of acute angle-closure producing visual debilitation is far greater when the attack is unsupervised, where there is an average delay of 3.5 days before patients present for attention.11 If no pressure spike or angle closure event occurs, consider having the patient return in a few weeks to repeat gonioscopy and/or additional imaging. Ultimately, educating the patient on signs and symptoms of angle closure will be your best tool going forward as well as discussing prophylactic options available for all narrow angle patients.
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16. Lachkar Y, Bouassida W. Drug-induced acute angle closure glaucoma. Curr Opin Ophthalmol. 2007 Mar;18(2):129-33.
17. Acharya N, Nithyanandam S, Kamat S. Topiramate-associated bilateral anterior uveitis and angle closure glaucoma. Indian J Ophthalmol. 2010 Nov-Dec;58(6):557-9.
18. Asrani SG, Foster PJ, Palmberg PF, Ritch R. MD Roundtable: Expert Tips for Assessing the Narrow Angle. Available at: https://www.aao.org/eyenet/article/md-roundtable-expert-tips-assessing-narrow-angle?january-2015. Accessed 8/25/17.
19. Chan P, Tham C. Commentary on effectiveness of early lens extraction for the treatment of primary angle-closure glaucoma (EAGLE). Annals Eye Science. Available at: http://aes.amegroups.com/article/view/3677. Accessed 12/15/17.