New Surgical Techniques

The surgical options for glaucoma are expanding with a growing body of evidence of the short- and longer-term results. This chapter will focus on description of newer surgical techniques that hold promise in the treatment of glaucoma. The ExPRESS Mini-shunt (Optonol Ltd., Neve Ilan, Israel/Alcon, Fort Worth, TX) has emerged as a device used to help standardize one part of the trabeculectomy filtering procedure. This biocompatible, stainless-steel device, which measure 400 microns wide by 3 mm long, contains a 50-micron non-valved opening to enable filtration for the treatment of glaucoma (Fig. 14.1) Currently recommended for use underneath a partial-thickness scleral flap • Using a standard fornix- or limbus-based conjunctival flap, and after application of antimetabolites, this device is placed underneath a partial-thickness scleral flap, fashioned identically to a trabeculectomy procedure. • A 26-gauge needle or commercially available Sapphire blade is used to enter the anterior chamber under the scleral flap at the color transition from clear cornea at an angle parallel to iris plane. • Using a preloaded injector, the device is placed into the anterior chamber through the previously fashioned tract so that the plate is flush with the bed of the sclera flap. • The desired position of the device under the sclera flap is into the anterior chamber with distance from the corneal endothelium. • The flap is then sutured as is typical for a trabeculectomy, titrating tightness of sutures to desired amounts of flow. These sutures can, as with a trabeculectomy, be released or lysed with laser subsequently depending on the suture technique. • An iridotomy is not performed with this procedure. Therefore, this procedure represents a modification of a guarded filtration procedure using a device with a standardized ostium size to replace the sclerostomy and iridotomy portions of the trabeculectomy procedure. • By eliminating the sclerostomy, the rate of aqueous egress from the 50-micron opening into the subconjunctival/sub-Tenon’s plane is reportedly more standardized in comparison to trabeculectomy. • Although there are reports suggesting a lower incidence of hypotony with the ExPRESS in the immediate postoperative period as compared to trabeculectomy, the rate of flow in both ExPRESS use and trabeculectomy is critically determined by the tension of the sutures at the scleral flap, which was not standardized among the two groups.

Management of Surgical Complications

•Glaucoma filtration surgery (GFS) has been associated with higher long-term failure rates and a substantially higher risk profile than most other ophthalmic surgeries. •Identifying and properly managing complications associated with GFS is essential in ensuring the best possible outcome. •Infection is a devastating complication of GFS that must be considered in a separate category (please see Chapter 7 for blebitis and bleb-related endophthalmitis). •Complications unique to glaucoma drainage devices (GDD; see Chapter 12) will be discussed at the end of the chapter. •One simple way to diagnose a complication resulting from GFS is to subcategorize possibilities according to the IOP and anterior chamber (AC) depth. •Table 13.1 shows the four potential outcomes after GFS, and the text below provides additional details about each potential complication. •Usually occurs in the first few months after surgery. •The most common complication of trabeculectomy. •Due to progressive episcleral fibrosis and blockage under the scleral flap. •Incidence has decreased due to intraoperative use of antifibrotics. •Bleb appears constricted, shallow, or flat with increased vascularity and loss of microcysts. •Negative Seidel test. •Gonioscopy reveals an open sclerostomy site, which is essential to differentiate from an inadequate fistula or fistula blockage from iris, blood, fibrin, or vitreous. •Anterior segment optical coherence tomography (AS-OCT) and ultrasound biomicroscopy (UBM) may reveal adherence of Tenon’s capsule and conjunctiva to underlying sclera. •Approached in a stepwise fashion. • Decreases rate of episcleral fibrosis in hopes of rescuing the function of the bleb.•Prednisolone acetate 1% every 2 hours for first 1 to 2 weeks, then taper slowly over 2 to 3 months. •Administered if early signs of bleb failure/episcleral fibrosis are present. •Technique •Instill topical anesthesia followed by direct application of a cottontipped pledget approximately 90 to 180 degrees away from the bleb. •Use a 30-gauge needle on a tuberculin syringe to inject 5 mg (0.1 cc) of undiluted 5-fluorouracil (5-FU; available in a concentration of 50 ug/mL) under the conjunctiva at the anesthetized site. •Avoid areas of bleb elevation and areas that show increased conjunctival vascularity.

Medical Management for Glaucoma

When evaluating patients for glaucoma or ocular hypertension, the question remains whether or not the patient should be treated, and when treatment should be initiated. Treatment decisions are usually guided by risk factor assessment, and these include race, age, family history, medical history, IOP, central corneal thickness, and clinical examination, including optic nerve appearance and ancillary diagnostic testing. The information is compiled in each individual to determine the risk of significant visual loss in the patient’s lifetime. Numerous studies have demonstrated that lowering IOP slows progression of this disease. Most common current medical therapies are therefore ocular hypotensive medications. The armamentarium of medications has expanded over the past two decades in terms of number and classes. Future potential therapies may include those that provide neuroprotection, but the main focus of this chapter will be on medications most frequently used to treat glaucoma. The goal of therapy is to slow progression of disease with the fewest side effects and medications and the lowest doses and cost of therapy. Consideration of these issues maximizes compliance and effectiveness of therapy in long-term disease control. An effective medication lowers the IOP 20% to 30% from baseline. Figure 10.1 lists the most common classes of medications with mechanism of action and common side effects; sample bottles of medications are also shown. We will discuss each class of medications and offer clinical pearls. • Direct-acting: pilocarpine HCl, pilocarpine gel •Indirect-acting: echothiophate iodide, eserine sulfate ointment, demecarium bromide, isofluorophate •Affect the parasympathetic or cholinergic system through direct- or indirect-acting Agents •In addition to effects on ciliary muscle, parasympathomimetics stimulate muscarinic receptors of the iris sphincter to cause miosis. This may improve outflow facility in eyes with angle-closure glaucomas by relieving pupillary block or by changing the anatomy of the peripheral iris in the angle. •Miosis may cause dimness of vision, contraction of visual fields, and pinhole effect. •Patients may develop brow ache due to ciliary muscle spasm.

Management of Glaucoma Following Intraocular Procedures

The development of glaucoma can occur postoperatively from corneal/refractive, cataract, and vitreoretinal surgery. Additionally, glaucoma may be noted after clinical procedures have been performed, including injections and laser procedures. This chapter is organized into two basic sections: postoperative and post-procedure glaucoma. Background: Currently little is known about the effect of refractive surgery in glaucoma patients or about patients who undergo refractive procedures and may go on to develop glaucoma. •IOP measurement •Measurement of IOP after refractive surgery can be challenging. Corneal properties that are altered after refractive surgery include corneal thickness, corneal curvature, the structural integrity (stiffness or hysteresis), as well as the overlying tear film that interacts with instruments that measure IOP. Photorefractive keratectomy (PRK) additionally ablates portions of Bowman’s layer, which may change corneal resistance. Nomograms have been developed to adjust for IOP change after corneal alteration but usually take only corneak thickness into account, which has led to little success in their use. •Goldmann applanation tonometry (GAT) assumes corneal thickness = 520 microns. Thicker corneas will overestimate IOP and thinner corneas, which result from refractive procedures such as PRK and LASIK, will underestimate IOP. Therefore, GAT may have limited value in measuring true IOP following refractive surgery. Other tonometric devices, like Pascal dynamic contour tonometry, pneumatonometry, and the Reichert ocular response analyzer, may be more accurate. There does not appear to be any simple conversion table that can be referenced in correcting measured IOP after the cornea is altered surgically. Preoperative IOP is probably the most important variable that should be recorded. •The intraoperative pressure spike associated with LASIK may occur in select patients, leading to the development of glaucomatous optic neuropathy. • Pressure-induced stromal keratitis (PISK) is a condition related to steroid-induced elevated IOP that may occur after LASIK. The clinical appearance is similar to diffuse lamellar keratitis (DLK), where there is a diffuse interlamellar haze covering the flap. DLK is an inflamatory response where IOP is not elevated and requires topical steroid treatment for resolution.

Trauma and Glaucoma Emergencies

• A tear in the anterior face of the ciliary body, with damage to the major arterial circle of the iris, arterial branches to the ciliary body, or veins coursing between the ciliary body and episcleral venous plexus • In most cases, the hyphema clears in a few days, with the red blood cells exiting the eye through the trabecular meshwork • The size of initial hyphema has prognostic significance regarding final visual acuity. • 76% of subtotal hyphemas attain a visual acuity of 20/50 or better, whereas only 35% of total hyphemas attain a visual acuity of 20/50 or better. •Overall in literature: 3.5% to 38% • Scandinavian literature: 2% to 9% • Most studies in urban North American centers: 20% to 30% •Clot lysis and retraction from the traumatized vessel can lead to a rebleed. • Usually between the third and the fifth day Increase in the size of the hyphema, a layer of fresh blood over older blood, and dispersed erythrocytes over the clot once the blood has settled •Ocular hypotony, hypertension, use of aspirin, and African-American race • The incidence of rebleed does not seem to correlate with the size of hyphema. Therefore, the use of medications to prevent rebleed should not depend on the size of hyphema. • Approximately one third of all patients with hyphema have increased IOP. • Obstruction of the trabecular meshwork by erythrocytes and blood products or damage to the trabecular meshwork function • In larger hyphemas, pupillary block by a blood clot can also contribute to increase in IOP. • Peripheral anterior synechiae (PAS) •Persistence of hyphema for more than 1 week can result in the formation of PAS. •Approximately 6% of patients have optic atrophy, exhibited by optic nerve pallor. • Secondary to elevated IOP or optic nerve contusion •The risk of optic atrophy appears to be greater if the IOP is allowed to remain 50 mmHg or more for 5 days or 35 mmHg or more for 7 days in sickle cell-negative patients without prior optic nerve damage. •The incidence of corneal blood staining is between 2% and 11% and is much higher in patients with a total hyphema.

Intraocular Pressure Measurement

Intraocular pressure (IOP) measurement is a key test by which patients with glaucoma are clinically monitored. Clinical trials have demonstrated that a reduction in IOP results in a reduction in the risk of progression of glaucoma. Accordingly, measuring IOP with relative accuracy is very important in managing patients. There are multiple methods to measure IOP. The method used may depend on the particular clinical setting. All are surrogate measures in comparison to manometry (i.e., IOP measurement using an intracameral cannula), which is the most direct means to measure IOP. However, manometry is not practical for everyday clinical practice since it is invasive. This overview provides information about currently available methods to measure IOP and how they may be best applied. This section also outlines the advantages and disadvantages involved with these methods. Not all techniques are available to every practitioner, but knowing the principles behind these methods and the limitations should allow clinicians to more carefully interpret and reliably obtain IOP measurements using the techniques at their disposal. Goldmann applanation tonometry (GAT) is considered to be the standard by which IOP is measured for the average patient (i.e., average corneal thickness without apparent corneal abnormalities). GAT is also likely the measurement modality most readily available to practitioners. The Perkins tonometer is a handheld Goldmann applanation device (Fig. 1.1B). This is helpful when measuring IOP in children as it can be used in the upright or supine position and for patients unable to come to the slit lamp. Based on the Imbert-Fick principle Applanation diameter is 3.06 mm (not the size of the applanation tip, which is larger), so that 1 g of force represents 10 mmHg. Assumes the eye is a sphere, corneal thickness is estimated to be 0.52 mm, and volume displaced by contact is negligible Instill topical anesthetic and fluorescein dye. Clean tip (see recommended cleaning technique at end of this section). Position patient at slit lamp (for GAT). Set illumination to cobalt blue filter and set force knob/drum to 1 (which corresponds to 10 mmHg).

Optic Nerve Examination

•Small field of view but increased magnification •Significant degradation of the view from media opacities or small pupil •Lacks ability to perform stereoscopic examination •Useful when slit-lamp exam not possible •Most commonly used system •Variable magnification and field of view • Reasonable view through small pupil • Good stereoscopic view •Less degradation of view from media opacities than direct ophthalmoscope •The magnification and stereopsis obtained with a slit-lamp system is generally superior to that of a handheld or headlamp-based system. • Poor magnification, with wide field of view •Least degradation of view from media opacities •Value of stereopsis limited by poor magnification Fair to poor with small pupils •May be useful for bedside exam or in the operating room • The vertical diameter of the optic nerve can be easily estimated during a slit-lamp exam by the following method: 1. A thin slit beam is focused on the nerve through the lens of choice. 2. The vertical length of the beam is adjusted to match the height of the disc. 3. The length of the beam is read off the slit-lamp beam scale. 4. The scale reading is adjusted by the correction factor of the specific lens. •This estimation is reasonably accurate, but it tends to underestimate disc size in high levels of myopia, and overestimate in high hyperopia. • One can also use the scale projection of the direct ophthalmoscope to estimate nerve head size, with no correction factor needed. The small light cone of the direct ophthalmoscope subtends an angle of about 5 degrees, about the same size as an average optic disc, and can give a quick estimate of relative size. • Stereo-photographs are the most helpful but are more difficult to obtain in a reproducible manner. •Cameras with a prism-based fixed-angle method of taking simultaneous stereo-photos tend to produce more consistent results, but are more expensive. • While non-mydriatic cameras exist, images suffer when the pupil is smaller than 4 mm, and dilation is commonly employed to obtain the best images.

Evidence-Based Guidelines in Management of Glaucoma

Early detection and treatment of primary open-angle glaucoma (POAG) are important to reduce the burden of blindness and its economic impact on society. This chapter will address the evidence-based guidelines for treating POAG. POAG is defined as an optic neuropathy with associated visual field loss for which elevated IOP is a major risk factor. To date, most of our treatment strategies are directed at reducing IOP, either with medical therapy, laser surgery, or incisional surgery, with medical therapy being the most common initial course of treatment. Three important questions often confront a glaucoma specialist when initiating therapy: Who needs to be treated?, how should a patient be treated, and to what extent? The Ocular Hypertension Study (OHTS) has provided insightful information to guide us in treatment of ocular hypertensives who may present with some risk factors and clinical findings but not others. OHTS demonstrated that reducing IOP by 20% with medical therapy in patients with ocular hypertension reduced the risk of developing glaucoma to 4.4% in the treated group versus 9.5% in the observation group at 5–year follow-up. •This clinical trial not only established the efficacy of lowering IOP with medical therapy but also identified the risk factors for developing glaucoma in these patients. •Older age, higher IOP, larger cup-disc diameter, higher pattern standard deviation, and thin central corneal thickness were determined to be significant risk factors by multivariate analysis. •Although family history and race were not found to be independent risk factors in OHTS, their association with glaucoma has been well established with other large population-based studies, such as the Baltimore Eye Survey. • Of note, a majority of untreated patients (nearly 90%) in the first phase of OHTS did not show any evidence of progression, a finding that emphasized the need to individualize therapy based on assessing risk factors and clinical findings in a given patient.

Visual Field Testing

• Glaucoma results in progressive visual field deterioration, and detecting changes or recording stability in the visual field is important in the management of glaucoma. • Visual field testing is a highly subjective and operator-dependent test. • In patients with glaucoma, the visual field is tested in monocular fashion. •The boundaries of the visual field (in a well-lit environment with an easily visible target) are grossly 60 degrees superiorly, 75 degrees inferiorly, 100 degrees temporally, and 60 degrees nasally. • Basic concept in determination of visual field is “threshold” •Definition of “threshold”: weakest test stimulus that is just visible in a particular location (stimulus intensity at which the patient responds 50% of the time) •Types of visual field testing strategies •Confrontation •Spot testing •Kinetic spot testing •Static spot testing •An initial screening tool to look for large and dense visual field defects that may be present in very advanced glaucoma •Both hands should be used in the testing processed. The patient should occlude the untested eye with the palm of the hand. •If the visual acuity will allow the finger counting technique, all four quadrants may be tested at 3 to 4 feet from the patient at an approximate 45-degree angle holding up either one or two fingers, or a whole hand. • If the visual acuity is HM or LP, then test for light perception in the respective 4 quadrants. • It is important that the patient be able to tell you where the light is located in the field of vision, not simply the presence of light. • Factors that affect the visibility of the spot • Size Intensity • Background illumination Others: color, movement, duration of presentation, attentiveness of the patient, and refractive state of the eye • Kinetic • Usually Goldmann perimetry (though some of the automated machines such as the Octopus will perform kinetic perimetry) • The perimetrist may adjust the location, size, and intensity of the stimulus throughout the test. •Useful in the following cases: Those who need coaching and an altered pace of testing (e.g., elderly, wheelchair-bound, or limited concentration)

Gonioscopy

Gonioscopy allows visualization of the anterior chamber angle using special lenses. The anterior chamber angle cannot be visualized by direct observation because of its position in the angle recess and the phenomenon of total internal reflection of the light caused by the cornea. Goniolenses with appropriate optical properties and mirrors or prisms allow adequate visualization of its structures through a “periscope effect” and provide a more favourable reflection angle. Clinical circumstances where gonioscopy is essential or helpful in the diagnosis and management of glaucoma are as follows: • To diagnose primary angle closure and to assess the results of medical, laser, or surgical treatment on angle configuration • The Van Herick method of estimating the peripheral anterior chamber depth with the slit lamp gives a useful but rough estimate and does not replace gonioscopy. It can give false-negative results in patients with plateau iris configuration and false-positive results in patients with moderate anterior chamber depth but an open angle. • To assess the risk of angle closure in patients with shallow anterior chambers before undergoing pupillary dilation • To diagnose and follow treatment of acute angle-closure glaucoma attacks To establish the diagnosis of secondary angle-closure glaucoma • To determine precise anatomic landmarks for accurate laser application during trabeculoplasty • For the evaluation and follow-up of congenital or acquired abnormalities of the anterior chamber angle • To detect and evaluate mass lesions that affect the anterior chamber angle • To evaluate the anatomic angle changes and patency of the ostium after trabeculectomy • To visualize the angle during “angle surgery” • Such as goniotomy, trabectome surgery,or trabecular micro-bypass stent •During laser trabeculoplasty and after laser iridoplasty Three goniolens prototypes have been most used in the past and represent the precursors of newer lenses Their main features are displayed on Table 2.1. Explain the procedure to the patient and its purpose. Reassure him or her that with the use of topical anesthetic the test will not be painful, and request cooperation in terms of avoiding lid squeezing and excessive eye movement during the exam.