Glaucoma is a disorder characterized by damage to the optic nerve that, if untreated, leads to progressive loss of vision. In children it is almost always caused by increased intraocular pressure (IOP). Glaucoma is one of the leading causes of visual loss in adults, but is rare in children. Estimates of the incidence of primary infantile glaucoma range from 1 in 2,500 to 1 in 22,000.

Glaucoma may be classified as primary or secondary. Primary glaucoma is caused by an underlying disorder of aqueous fluid outflow from the eye. Secondary glaucoma occurs due to a variety of ocular defects that lead to increased IOP.

Glaucoma may also be classified as open angle or closed angle (Figure 32–1). This refers to whether or not the trabecular meshwork is visible when viewed with a goniolens, an instrument that allows the examiner to visualize the fluid outflow pathways. Open angle glaucoma is much more common. In this condition, the pressure increases due to resistance within the outflow pathways, usually caused by microscopic alterations within the trabecular meshwork. In closed-angle glaucoma, access to the trabecular meshwork is blocked. This is usually caused by forward movement of the iris. This may occur for a variety of reasons, including a mass growing behind the iris (e.g., retinoblastoma), scarring of the pupil margin causing fluid to build up behind the iris and push it forward (as may occur in iritis), or in patients with very small eyes (nanophthalmos).

Normal ocular pressure is maintained by a balance of fluid (aqueous humor) production by the ciliary body and fluid outflow through the trabecular meshwork (Figures 32–2 and 32–3A and B). Glaucoma virtually always results from obstructed outflow, rather than fluid overproduction. When the IOP is elevated, the optic nerve is damaged by compression against the sclera, resulting in loss of the ganglion cells that form the optic nerve. This initially affects the upper and lower fibers on the lateral side of the optic nerve, causing loss of vision in an arcuate pattern above and below the center of vision. If untreated, progressive constriction of the visual field occurs, ultimately affecting central vision late in the disease. Patients may not notice the peripheral loss initially, and therefore they may remain asymptomatic until substantial damage has occurred.

One of the main differences between adults and children with glaucoma is due to decreased scleral rigidity in children. In adults the sclera is rigid and nondistensible. Therefore, the effect of pressure is entirely directed to the optic nerve, and changes in the nerve may be the only visible sign of the disorder. In infants and young children, however, the sclera can enlarge. This may produce visible abnormal growth of the eye (buphthalmos) and enlargement of the cornea (Figure 32–4). Tears in Descemet’s membrane (Haab stria) may develop due to the stretching (Figure 32–5), leading to edema of the cornea. The corneal edema is the cause of the epiphora and light sensitivity frequently seen in infants with glaucoma. The beneficial effect of scleral distensibility is that improvement in optic nerve cupping may be seen in infants with successful treatment (Figure 32–6A and B), whereas the cupping never improves in adults, even if the IOP is lowered.

In primary glaucoma, there is an underlying defect of the trabecular meshwork that inhibits normal outflow of fluid, with a resultant increase in pressure. Secondary glaucoma may occur as a result of other ocular defects. Examples include blockage of the normal outflow due to forward displacement of the iris from a retinal tumor, or abnormal resistance to outflow due to vascular abnormalities in patients with Sturge-Weber syndrome (SWS).

Primary infantile glaucoma is usually sporadic, but can be inherited in an autosomal recessive pattern. Mutations of the CYP1B1 gene on chromosome 2p21 have been identified as a cause of this disorder. Other genetic abnormalities associated with glaucoma include mutations of the MYOC gene in autosomal dominant juvenile glaucoma, and mutations of the PITX2 and FOXC1 genes in patients with anterior segment dysgenesis syndromes.

Glaucoma may occur acutely, subacutely, or insidiously, depending on how rapidly the pressure rises. Most infants with glaucoma present subacutely. Increased pressure in the eye produces a variety of effects, some of which are visible and some of which are not. In infants and young children, the entire eye enlarges (buphthalmos, from the Greek “ox eye”). This enlargement is most noticeable if only one eye is affected, because of the contrast with the normal eye (Figure 32–4). The eye appears to bulge from the orbit, and the space between the eyelids may appear larger than normal. Enlargement of the cornea increases the portion of the cornea visible between the eyelids. In severe cases the cornea may fill the entire space between the eyelids (Figure 32–7).

The increased IOP also causes dysfunction of the corneal endothelium, resulting in thickening and edema that creates a cloudy or ground-glass corneal appearance. Curvilinear Haab stria may sometimes be seen with a penlight, but usually a slit lamp is required for visualization (Figure 32–5). In severe cases of infantile glaucoma, the lens zonules stretch, and subluxation of the lens may occur.

The end result of glaucoma is damage to the optic nerve, which can be visualized with an ophthalmoscope as an increase in the cup:disc ratio. Abnormal growth of the eye in children with glaucoma may also cause myopia (nearsightedness) due to an increase in the length of the eye. In the typical subacute presentation of infants, most children will have light sensitivity (photophobia), excess tearing (epiphora), and squeezing of the eyelids (blepharospasm) due to corneal irritation. Decreased vision and nystagmus may be noted in severe bilateral cases.

Acute presentations of glaucoma occur if the rise in IOP is marked and rapid. Approximately 25% of infants with primary infantile glaucoma are born with enlarged and cloudy corneas. The prognosis in such infants is poor. In older children, most cases of acute glaucoma are secondary to other ocular problems, such as trauma or ocular tumors. If the pressure rises rapidly to high levels (usually >40 mm Hg), the eye becomes acutely painful, the cornea becomes cloudy, the conjunctiva is usually injected, and the vision is decreased (Figure 32–8). Nausea and vomiting frequently develop when the pressure is this high.

Glaucoma in older children and adults often presents insidiously. If the pressure is not high enough to produce symptoms of acute glaucoma, but is high enough to cause damage to the optic nerve, patients are often initially asymptomatic. The nerve damage first affects the peripheral vision, which may go unnoticed until it progresses to near the center of vision. This is why glaucoma, particularly in adults, is sometimes referred to as “the sneak thief of sight.” On examination, the IOP is elevated, and the cup:disc ratios are enlarged. Formal visual field testing shows peripheral loss in an arcuate pattern (Figure 32–9). This testing is often not possible in children due to the degree of cooperation and concentration required.

The diagnosis of glaucoma requires a detailed ophthalmic examination. Vision is assessed in the standard fashion for children. In infants and young children, the remainder of the assessment often necessitates examination under anesthesia. Elevated IOP is the underlying final common pathway for almost all glaucoma in children. Normal IOP in infants is around 12 mm Hg. This increases with age, and by late childhood and adulthood normal pressure is 10-20 mm Hg.

In practice, measurement of IOP in infants and young children often cannot be performed accurately when they are awake. Although the measurements are taken after use of topical anesthetic drops, the proximity of the instrument to the eye usually provokes anxiety. When the children forcefully close their eyes, this squeezing artificially raises the IOP. Therefore, most young children with glaucoma (or in whom glaucoma is suspected) require examination under anesthesia to measure the IOP and perform other portions of the examination that cannot be performed accurately with the patient awake. When the pressure is measured under anesthesia, there is also a potential for inaccurate readings due to effects of anesthetic agents on the IOP. Therefore, the pressure is measured as soon as the child is adequately sedated, preferably before placement of an endotracheal tube or laryngeal mask.

Other features of the glaucoma evaluation include measurement of the corneal diameter, assessment of corneal clarity, and slit lamp examination. Measurement of the refractive error may reveal abnormal myopia (nearsightedness) due to enlargement of the eye.

The anterior chamber angle is not visible directly, but can be viewed with a goniolens. This is a mirrored lens that is placed directly on the cornea. By coupling the lens to the cornea via the tear film, the angle becomes visible (Figure 32–10A and B). Gonioscopy allows assessment of the anatomic configuration of the angle. This can differentiate between open-angle and closed-angle glaucoma. In infantile glaucoma, a membrane-like structure (Barkan’s membrane) is sometimes visible overlying the trabecular meshwork (Figure 32–11).