Indications for surgery

Published on 08/03/2015 by admin

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Last modified 08/03/2015

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CHAPTER 34 Indications for surgery


Glaucoma is the leading cause of irreversible blindness worldwide, affecting an estimated 60 million people in 20101. More than 50% of sufferers in developed countries are unaware of their condition and this figure increases to over 90% in the developing world. The economic burden is substantial at almost $3 billion in the US in 20042. A recent estimate of the risk of progressing to blindness in patients with diagnosed glaucoma attending a specialist glaucoma clinic in the US is around 14% for unilateral blindness and 6% for bilateral blindness after 15 years3.

Glaucoma results in visual loss due to a progressive loss of retinal ganglion cells (RGC) with corresponding visual field loss and a characteristic ‘cupped’ appearance at the optic nerve head. Visual field loss usually begins peripherally, but sometimes affects the central visual field first. The only modifiable risk factor for glaucoma at present is the intraocular pressure (IOP) and the only proven method to delay or prevent glaucomatous optic neuropathy is IOP lowering. This may be achieved by medication, laser, or surgery.

Surgery for primary open angle glaucoma (POAG) has evolved in the past 50 years from full-thickness filtration surgery, in which a hole in the scleral wall at the corneo-scleral limbus drained aqueous from the anterior chamber to a subconjunctival ‘drainage bleb’. As this procedure carried a high risk of ocular hypotony, and bleb-related endophthalmitis4,5, it evolved to a partial-thickness scleral flap which provided an extra flow resistor (Fig. 34.1)6, prevented hypotony, and consequently lowered aqueous pressure within the subconjunctival drainage bleb lowering the risk of conjunctival breakdown and infection.

As a guarded filtration procedure, trabeculectomy was safer than the full-thickness procedure. However, as satisfactory long-term IOP control could not be achieved in a significant proportion of patients, pharmacological enhancement with anti-proliferative agents (e.g. 5-fluorouracil (5FU)7 and later, mitomycin C (MMC)) was introduced in the late 1980s. While these improved success rates some safety concerns, previously reduced by the evolution of trabeculectomy from full-thickness filtration surgery, reappeared8,9. The main concerns are hypotony10 and infection, especially as trabeculectomy-related infection has a predilection for more aggressive organisms than do other types of intraocular infections11. The alteration in conjunctival surface healing that resulted from the use of 5FU, and especially MMC, also resulted in prominent drainage blebs that could cause chronic discomfort or dysesthesia12. These and a higher incidence of cataract after trabeculectomy have promoted further evolution in glaucoma surgical techniques in four main directions.

General considerations

Purpose of glaucoma treatment and surgery

The overall purpose of glaucoma treatment is to maintain visual function and related quality of life at a sustainable cost. Glaucoma surgery aims for a prolonged IOP reduction without complications. Generally, medical treatment is considered first, followed by laser. Surgery is considered later because medical treatment is sufficient to control IOP in most patients; the inconvenience of lifelong eye drops is considered a smaller imposition than risks of surgery. Often medical treatment is thought to be ‘sufficient’. Many glaucoma patients are managed by general ophthalmologists who may not perform glaucoma surgery regularly. These factors all favor later surgery.

Although the aim of surgery is usually to preserve vision by lowering IOP, sometimes the primary aim may be to reduce pain in a poorly sighted eye, to correct an anatomic abnormality, e.g. peripheral iridotomy/iridectomy, to relieve pupil block, lens extraction in primary angle closure, removal of subluxated lens in secondary angle closure, or vitrectomy in aqueous misdirection.

These goals can be achieved by proper patient selection and choice of the most appropriate technique. As surgery always involves some risk, a careful assessment of risk versus the potential benefit is needed; this amounts to the risk of not operating. This must be considered and discussed in full. The factors that determine the level of treatment aggression depend on the severity of disease at presentation (i.e. the location and extent of visual field defects), the patient’s life expectancy, and the degree of IOP elevation. Other factors that play a role include the type of glaucoma, unilateral or bilateral disease, the family history, and a previous history of intraocular or conjunctival surgery.

Medical versus surgical treatment

While medical and laser treatment are usually the first lines of therapy, there are some situations where early surgery is advisable. Surgery is the principal treatment for angle closure, developmental glaucomas, and a number of secondary glaucomas. Surgery is recommended for POAG in three circumstances (Box 34.1):

In the developing world, medication is often unaffordable, and surgery may be indicated as an opportunity to prevent progression with one intervention alone. However, the barrier to treatment of glaucoma in the developing world is often lack of awareness or understanding of the nature of the condition or that preventive treatment is important. Few therefore opt for treatment even when it is available or affordable.

The term maximal-tolerable medical therapy (MTMT) is often used to indicate the level of medical therapy above which there is likely to be no further benefit in terms of IOP-lowering, or above which the patient’s ability to tolerate the regimen is likely to diminish because of increasing side effects. The term is of limited usefulness: first it takes no account of an individual patient’s ability to sustain the maximal level of medication. This term usually denotes the maximal level of medication that a patient can tolerate at any one time, which is often higher than the level tolerated in the longer term. Second, the implication, perhaps unintended, is that it is in the patient’s best interest to take as many medications as possible before even considering surgery. This is inaccurate for the following reasons:

On which eye to operate first?

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