Ординатура / Офтальмология / Английские материалы / Shields Textbook of Glaucoma, 6th edition_Allingham, Damji, Freedman_2010

Figure 13.13 Reversal of cupping. This 14-year-old girl with endstage juvenile open-angle glaucoma and total cupping of her right optic nerve (A) showed some reversal of cupping (B) (although no improvement in arcuate scotomas on visual field testing) 2 years after trabeculectomy with mitomycin C and a reduction in IOP from 30 mm Hg to about 10 mm Hg.

Other Useful Diagnostic Tests Refraction

Refractive error determination cannot only suggest possible glaucoma (as when a myopic shift occurs rapidly after cataract removal, or asymmetric relative myopia occurs in the eye with higher IOP) but also serve a critical function in maximizing the visual function of the child with glaucoma, in whom high myopia, astigmatism, or anisometropia, singly or in combination, may result from IOP-induced corneal scarring or ocular enlargement.

The enlargement of the globe with elevated IOP in the first 3 years of life creates a myopic shift in the refractive error, which may lead to amblyopia if significant anisometropia is present. The presence of Haab striae often produces significant

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astigmatism, which also contributes to amblyopia, especially in unilateral or asymmetric cases. Children between 3 and 10 years of age with elevated IOP may develop progressive myopia and astigmatism, despite a stable corneal diameter. These refractive changes have been attributed to continued scleral stretching (3). Myopia is also commonly associated with forms of juvenile glaucoma (35), although it may be unclear whether glaucoma or myopia was the primary event.

Ultrasonography

Measurement of the axial length (by using ultrasonography, preferably by immersion technique, during examination under anesthesia) serves as an adjunct to serial corneal diameter determination for infants and young children being treated for glaucoma, because stabilization and even reduction in axial length can occur in the enlarged eye with stable IOP reduction (9). This axial length change may be evident within days after a significant IOP reduction, especially in aphakic eyes of infants after filtration surgery or implantation of a glaucoma drainage device (Freedman S, personal experience). Ultrasonography may also be helpful when glaucoma drainage-device surgery is being contemplated, because the size of the proposed implant reservoir may be limited by the globe size (see Chapter 40). B-scan ultrasonography helps confirm retinal status in eyes with opaque media and often aids in assessing the patency of a glaucoma drainage device when the bleb itself cannot be well seen (see Chapter 39). Anterior segment ultrasonography also plays a useful role in surgical management for selected patients in whom opaque media precludes adequate assessment of the anterior chamber and associated anterior segment structures (e.g., a demonstrated deep anterior chamber may allow glaucoma drainage-device placement, or congenital aphakia may allow endoscopic laser cycloablation; see also Chapter 40).

Central Corneal Thickness Measurement

Ultrasonic pachymetry (to measure the central corneal thickness) has become standard in the evaluation of adults with chronic open-angle glaucoma, because this variable seems to affect not only the accuracy of the measured IOP by applanation tonometry (elevated by an unusually thick central cornea, and vice versa) but also the potential susceptibility of an eye to glaucomatous vision loss at elevated IOP (36, 37, 38 and 39). In children, the reported central corneal thickness ranges from roughly 540 µm at 6 to 23 months of age to approximately 550 to 560 µm for ol der children, with thinner central corneal thickness reported in white compared with black children (40, 41, 42, 43, 44, 45 and 46), and stable measurements over at least 1 year in healthy eyes and those controlled on glaucoma medication (47). Central corneal thickness is thinner in children with congenital glaucoma than in other children, and this is probably a function of the larger, stretched corneas in the eyes of many of the children with congenital glaucoma (41). By contrast, eyes with aniridia have thickerthanaverage central corneas (48), as do eyes with aphakia and particularly those with aphakic glaucoma (47, 49, 50, 51 and 52); this is perhaps an acquired rather than a congenital feature (49).

The importance of central corneal thickness in the evaluation and management of children with glaucoma currently remains undetermined, and although this feature is worthwhile to measure and consider when setting the target IOP, the clinician should avoid “adjusting” the measured IOP on the basis of the pachymetry results. It may be reasonable to make a downward adjustment in the target IOP for those eyes with thinner-than-normal central corneas.

Imaging Techniques: Fundus Photography, Optical Coherence Tomography

Fundus photography of the optic nerve head has long been a mainstay in the evaluation of adults with

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Shields > SECTION II - The Clinical Forms of Glaucoma >

14 - Childhood Glaucomas: Clinical Presentation

Authors: Allingham, R. Rand

Title: Shields Textbook of Glaucoma, 6th Edition Copyright ©2011 Lippincott Williams & Wilkins

> Table of Contents > SECTION II - The Clinical Forms of Glaucoma > 14 - Childhood Glaucomas: Clinical Presentation

14

Childhood Glaucomas: Clinical Presentation

Childhood glaucomas constitute a heterogenous group of disorders affecting the pediatric age-group. The previous chapter (Chapter 13) considered the general classification of these diseases, and provided a general approach to the infant or child with glaucoma. In this chapter, we highlight important features of the more common types of primary, and a few of the secondary, pediatric glaucomas, with attention to those features specific to children (since some of the secondary glaucomas also affect adults) (Table 13.1). Recall that the primary pediatric glaucomas can be broadly divided into (a) those with an isolated aqueous outflow abnormality and (b) those with associated ocular abnormalities, systemic abnormalities, or both. The former group can be further divided into (a) those presenting in the first 3 years of life (primary congenital/infantile glaucoma [PCG]) and (b) those presenting after that period but before adulthood (juvenile open-angle glaucoma [JOAG]). The latter group, often termed developmental glaucomas, comprises many different disorders, a few of which will be included in more detail in this chapter.

The secondary pediatric glaucomas are caused by a preceding process in the eye, and many are common to both adults and children, although some seem specific to children (such as glaucoma after removal of congenital cataracts). In addition, the mechanism of glaucoma in selected developmental cases (see Table 13.1) may be secondary rather than strictly primary.

PRIMARY CONGENITAL GLAUCOMAS Classification

When they occur without a consistent association with other ocular or systemic anomalies (in other words, they seem primary), congenital glaucomas have traditionally been called PCG or primary congenital open-angle glaucoma (1). In this chapter, we will refrain from referring to other birthor infancy-onset childhood glaucomas as PCG unless the outflow pathway defect and resultant elevated intraocular pressure (IOP) occur in apparent isolation. Newborn glaucoma, the most severe form of PCG, is apparent at birth, whereas infantile glaucoma refers to cases of PCG with clinical onset after

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birth but in the first 3 years of life (2). In general, the terms PCG and primary infantile glaucoma may be used interchangeably. Although PCG has also been called buphthalmos (i.e., cow's eye) or hydrophthalmia, referring to the enlargement of the eye that may occur with this condition (3), these terms should not be used as synonyms for PCG because enlargement of the globe is seen with other childhood glaucomas if they occur early enough in life.

Primary congenital glaucoma has also been referred to as isolated trabeculodysgenesis or goniodysgenesis, to indicate that the iris and cornea are morphologically normal. Newborn glaucoma, a severe variant of PCG present at birth, is also considered by some as iridotrabeculodysgenesis (Table 13.1). PCG can therefore be considered as one form of anterior segment dysgenesis.

When primary glaucoma appears later in childhood or early adulthood, it is sometimes referred to as juvenile glaucoma (also JOAG) (4). Three years of age is generally taken as the division between PCG and JOAG, because it is at approximately this age that the eye no longer expands in response to elevated IOP (1, 4). Others prefer a broader definition for juvenile glaucoma that includes all forms of open-angle glaucoma diagnosed between the ages of 10 and 35 years (5) (see JOAG, Chapter 11).

General Features Demographic Features

The most common of the primary pediatric glaucomas, PCG has an estimated incidence of 1 in 10,000 to 20,000 live births in Western countries, while it presents more frequently in the Middle East and among the Roma population of Slovakia, where parental consanguinity may play a role in the increased incidence (6). Lacking clear sex or racial-ethnic predilection (except where consanguinity or small population may play a role), most PCG cases (65% to 80%) are bilateral, and greater than 75% present in the first year of life. About 25% of patients with PCG present initially as newborns, and more than 60% of PCG diagnoses are made in infants younger than 6 months of age (7). Nonetheless, this condition occurs much less frequently than the open-angle and angle-closure glaucomas seen in adults, and it has been estimated that the average ophthalmic practice encounters one new case of congenital glaucoma every 5 years.

Heredity

PCG occurs in both sporadic and familial patterns. Inheritance is usually autosomal recessive in familial cases, and hence, there is increased incidence with consanguinity. Three genetic loci— GLC3A,

GLC3B, and GLC3C (Table 8.1)—have been identified b y linkage analysis in large pedigrees with multiple affected individuals (8, 9). The presence of additional loci has also been suggested (10). Thus far, two main causative genes have been reported—th e CYP1B1 gene, on the GLC3A locus, and the LTBP2 gene, possibly on the GLC3C locus (9, 10, 11 and 12). The MYOC gene has also been implicated in rare cases of PCG (13, 14 and 15).

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The CYP1B1 gene (Online Mendelian Inheritance in Man [OMIM] number, 601771) was the first reported PCG-causing gene (9, 16). It is located on chromosome 2p22-p21 on the GLC3A locus. It belongs to the cytochrome P450 superfamily of enzymes and oxidizes several compounds important to eye structure and function, including steroids, retinoids, arachidonate, and melatonin (17, 18, 19, 20, 21 and 22). The CYP1B1 enzyme is thought to participate in the metabolism of an unknown molecule that is important to eye development and therefore plays an important role in the development of PCG. Studies have demonstrated its expression in fetal and adult ciliary body and neuroepithelium (23). Since the CYP1B1 gene's discovery, many PCG cohorts have been screened for CYP1B1 sequence variants. Several CYP1B1 sequence variants have been determined to cause PCG (24). The proportion of PCG patients whose disease is due to CYP1B1 mutations varies with ethnicity, ranging from 100% in the Roma population of Slovakia to 20% in Japan (25, 26).

The MYOC gene (OMIM 601652) has been associated with juvenile and adult forms of open-angle glaucoma and a few rare cases of PCG (13, 15, 16). It is located on chromosome 1q24.3-q25.2 (27). MYOC or myocilin is also known as trabecular meshwork-induced glucocorticoid-response protein (TIGR). As its name implies, treatment of trabecular meshwork cells with glucocorticoids results in the

induction of MYOC (28). It is speculated that MYOC obstructs trabecular meshwork outflow and thus causes increased IOP (27). Increased IOP may also be caused by changes in the ciliary body secondary to MYOC. Studies have revealed expression of MYOC in both the trabecular meshwork and ciliary body (29). Diseasecausing MYOC sequence variants, both with and without CYP1B1 alterations, have been reported in families with earlyonset open-angle glaucoma, including PCG (13, 14 and 15). LTBP2 (OMIM 602091) is the most recent gene to be associated with PCG (11, 12, 16). LTBP2, or latent transforming growth factor beta binding protein 2, is located on chromosome 14q24 (30). Its location is 1.5 Mb from the GLC3C locus. Whether LTBP2 and GLC3C represent the same genetic component remains to be determined. In nonocular tissues, LTBP2 functions in tissue repair and cell adhesion (31, 32, 33 and 34). The role LTBP2 plays in PCG is still unknown. Ocular expression of LTBP2 has been demonstrated in the trabecular meshwork and ciliary processes (35). Null mutations of LTBP2 have been found in consanguineous Pakistani and Iranian families, as well as Slovakian Roma, with PCG (11, 12).

All siblings of any child with PCG (or early-onset JOAG) should be examined carefully; infants should be followed up closely, especially during the first year of life, to exclude this disease. A discussion of the risk of having additional children with PCG should be carried out with parents, either with the ophthalmologist or a genetic counselor.

Clinical Features

PCG is bilateral in 65% to 80% of cases (3, 36), although a significant IOP elevation may occur in only one eye in 25% to 30% of the cases. Several ocular features, with the possible exception of gonioscopic findings, are not unique to the PCG, but they may be a part of any childhood glaucoma during the first few years of life. The neonatal globe is distensible and often greatly enlarges with exposure to elevated IOP. Stretching of the infant eye is not limited to the cornea and may involve the anterior chamber angle structures, sclera, optic nerve, scleral canal, and lamina cribrosa (7) (see also Chapter 13).

Figure 14.1 Infantile glaucoma, with asymmetric involvement. Note marked enlargement of the right, compared with the left, cornea. The IOP was higher in the right eye, where multiple Haab striae and corneal edema were present.

History

Infants with PCG usually present for ophthalmologic evaluation because the pediatrician or the parents have noticed something unusual about the appearance of the patient's eyes or behavior. Often, corneal opacification and enlargement (resulting from elevated IOP) are the signs that signal glaucoma in the infant (Figs. 14.1, 13.2, and 14.2). In other cases, the child's glaucoma manifests as one or more of the classic triad of findings, any one of which should arouse suspicion of glaucoma in an infant or young child: (a) epiphora (i.e., excessive tearing); (b) photophobia (i.e., hypersensitivity to light), which results from corneal edema and is manifested by the child hiding his or her face in bright lighting or even in ordinary lighting in severe cases; and (c) blepharospasm (i.e., squeezing the eyelids), which may be another manifestation of photophobia.

The severity of presenting signs and symptoms varies among infants with PCG, probably because of differences in

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the magnitude and duration of the IOP elevation. For example, newborn infants presenting with enlarged, very cloudy corneas presumably had elevated IOP in utero, whereas those with milder signs and symptoms might have experienced the IOP elevation beginning sometime after birth. Parents and healthcare providers have occasionally failed to recognize glaucoma in infants with clear but enlarged corneas (37) (Fig. 14.3). Some bilateral cases may manifest with such asymmetric signs and symptoms that glaucoma is initially suspected only in the more severely affected eye. In children with glaucoma onset after 1 year of age, fewer overt signs and symptoms may occur because of the decreased expansibility of the eye.

Figure 14.2 Corneal edema with a central Haab striae in the eye of a 5-month-old infant girl with PCG. IOP was 28 mm Hg on maximal tolerated medications at examination under anesthesia, several weeks after trabeculotomy was performed from the temporal limbus. Further angle surgery was planned. (See also Fig. 13.2.)

Figure 14.3 A child whose diagnosis of congenital glaucoma was delayed until 2.5 years of age. Corneal diameters were 15 mm OU. The IOP was 40 mm Hg, and the optic nerves showed total cupping; best vision was less than 20/400 OU. IOP control was achieved by using goniotomy and medications for 6 years; the patient then required trabeculectomy with use of mitomycin C for glaucoma control.

External Examination

The infant with PCG presents as an otherwise healthy child, without any systemic or facial features to suggest a different diagnosis. Often the examiner notes that the child is unusually photophobic and fussy, and parents frequently relate a history of eye rubbing.

Corneal Features

Corneal Diameter

The healthy newborn's cornea has a horizontal diameter ranging from 9.5 to 10.5 mm, which enlarges about 0.5 to 1.0 mm in the first year of life (38, 39 and 40) (Table 13.2). Distention of the globe in response to elevated IOP (buphthalmos) leads to additional enlargement of the cornea, especially at the corneoscleral junction. A corneal diameter larger than 12 mm in the first year of life is a highly suspect finding. Asymmetry in diameter between the two corneas or a corneal diameter of 13 mm or more at any age strongly suggests abnormality (7). Corneal enlargement is more obvious in asymmetric cases (Fig. 14.1). In one study, corneal diameter was found to be a more reliable guide than axial length in the assessment of congenital glaucoma (38).

Corneal Edema

Initially, corneal edema may be a direct result of the elevated IOP, producing a corneal haze that clears with normalization of the pressure. Often, there are underlying breaks in the Descemet membrane (Haab striae) that occur as the cornea stretches because of elevated IOP. These often appear acutely as areas of increased corneal edema and clouding; clinical onset may take only a matter of hours (7) (see Slitlamp section). In more advanced cases, a dense opacification of the corneal stroma may persist despite reduction of the IOP (Fig. 14.4). Results of one study suggest that the latter may result from reduced aqueous production with poor corneal nutrition (41).