Primary surgical treatment for developmental glaucomas

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CHAPTER 42 Primary surgical treatment for developmental glaucomas

Introduction

After Otto Barkan described the use of goniotomy as a primary treatment for congenital glaucoma in 1942, the prognosis for infantile glaucoma was markedly improved1,2. Barkan’s method of using a goniolens for incisional angle surgery under direct visualization continues to be useful with little modification. Trabeculotomy is an alternative approach that was independently described by Burian and Smith in 196034. This procedure involves canulation of Schlemm’s canal through a scleral incision with a trabeculotome, which is then rotated to rupture the trabecular meshwork. More recently, some glaucoma surgeons have utilized combined trabeculotomy and trabeculectomy as a primary procedure in patients judged to have a poor prognosis for success with initial goniotomy or trabeculotomy. This approach has been used most commonly in infants in the Middle East and India as well as in patients over 2 to 3 years of age.

Epidemiologic considerations and terminology

Developmental glaucoma refers to glaucoma associated with developmental anomalies of the eye present at birth. This broad term encompasses the majority of glaucomas occurring in infants and children. Primary developmental glaucoma describes glaucoma that results from maldevelopment of the aqueous outflow system. Secondary developmental glaucoma indicates that damage to the aqueous outflow system is due to maldevelopment of some other portion of the eye.

Primary congenital glaucoma is the most common form of glaucoma in children, occurring in approximately 1 in 10 000 births in western developed countries5. This condition results from an isolated maldevelopment of the trabecular meshwork (trabeculodysgenesis) and is not associated with other developmental ocular anomalies or ocular disease. Typically, it manifests at birth or early childhood, before age 3 years. The majority of patients are diagnosed by age 6 months, and 80% are diagnosed within the first year of life.

Secondary congenital glaucoma is characterized by increased intraocular pressure (IOP) in patients with developmental defects of the anterior chamber angle associated with ocular and sometimes systemic abnormalities. The genetic basis for these disorders may be known, and the condition is usually bilateral. Examples of anomalies often associated with glaucoma include Axenfeld–Rieger syndrome, Peters’ anomaly, aniridia, and the phacomatoses (e.g., Sturge–Weber syndrome). Metabolic diseases, persistent fetal vasculature, retinopathy of prematurity, and chromosomal anomalies are also often associated with secondary developmental glaucoma. Finally, aphakia/pseudophakia and uveitis are important causes of glaucoma in infants and young children.

Clinical features, diagnosis, and differential diagnosis

Primary congenital glaucoma presents classically with a triad of symptoms: epiphora, photophobia, and blepharospasm6. These symptoms arise due to corneal irritation accompanying corneal epithelial edema, which is secondary to increased intraocular pressure. Patients may also present with a ‘red eye’ that mimics conjunctivitis7.

Several clinical signs may be evident in primary congenital glaucoma. Ocular enlargement (buphthalmos) may occur under the influence of increased intraocular pressure, with the major enlargement occurring at the corneo-scleral junction68. The cornea may appear hazy or opacified, and breaks in Descemet’s membrane (Haab’s striae) may be present. Finally, optic nerve cupping can occur rapidly and early in infants with primary congenital glaucoma. Cupping of the optic nerve head may be reversible with normalization of the intraocular pressure in infants9. This finding is uncommon in an adult with glaucomatous optic nerve head damage.

Many of the clinical features of primary congenital glaucoma can be found in other conditions and must be considered in the differential diagnosis2. Other conditions may cause red eye, corneal enlargement, corneal edema, and optic nerve abnormalities. However, these clinical entities cannot be completely characterized by photophobia, tearing, blepharospasm, increased intraocular pressure, and generalized ocular enlargement with optic nerve cupping. Recognition of the type of glaucoma present in a pediatric patient often requires experience and knowledge.

Anatomic considerations

The anterior chamber angle exhibits characteristic ultrastructural changes in eyes with primary congenital glaucoma. Anterior iris insertion is accompanied by compact trabecular beams containing excessive extracellular matrix material. Proliferation of fibrous tissue at the inner wall of Schlemm’s canal has also been described10,11. These findings are consistent with non-differentiation of the trabecular meshwork and persistence of embryonic characteristics. Secondary forms of congenital glaucoma may demonstrate additional anomalies of the iris, cornea, and lens. Pigmentation of the trabecular meshwork is acquired with age; therefore, recognition of the lightly or non-pigmented trabecular meshwork in an infant may be difficult. Severe ocular enlargement, sclerocornea, and other abnormalities may render external landmarks for internal structures unreliable. In these instances, imaging techniques such as ultrasound and optical coherence tomography (OCT) or endoscopic techniques may be helpful.

Fundamental principles

Surgical intervention provides the most effective and definitive treatment for most developmental glaucomas. Medical therapy may serve a supportive role in temporarily reducing intraocular pressure and clearing the cornea until surgery can be performed. A minority of patients with congenital glaucoma may respond to medical therapy alone12. Some secondary glaucomas may respond to medical therapy, such as glaucoma associated with aphakia or pseudophakia. Commonly used glaucoma medications in pediatric patients include topical beta-blockers, carbonic anhydrase inhibitors, and prostaglandin analogs. Oral acetazolamide elixir (5–15 mg/kg/day) may also be administered. Alpha-2-agonists are avoided in young children due to problems with sedation and other untoward side effects.

Indications for surgery

The primary developmental glaucomas are highly responsive to both goniotomy and trabeculotomy. Goniotomy is the classic procedure for primary congenital glaucoma and can be useful in cases of uveitic glaucoma as well as to prevent glaucoma development in patients with aniridia1315. It requires a clear or nearly clear cornea and gonioscopy surgical skills. Trabeculotomy is an alternative to goniotomy which is particularly useful in eyes with cloudy corneas that preclude a gonioscopic view of the angle. In recent years, combined trabeculotomy and trabeculectomy has been advocated as an alternative approach in refractory cases. When extensive iris structural defects accompany the trabeculodysgenesis, careful examination of the angle is important. In aniridia, for example, peripheral anterior synechiae formation and anterior stromal insertion add complexity to surgical decisions.

Preoperative assessment

For most pediatric patients under the age of 5, an exam under anesthesia (EUA) is the most accurate way to diagnose and monitor glaucoma. In most patients, a thorough examination under anesthesia is performed prior to surgical treatment. Key elements of the exam are:

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