Ординатура / Офтальмология / Английские материалы / Ophthalmology A Short Textbook_Lang_2000

10.5 Childhood Glaucomas 273

Treatment of secondary glaucomas:

Medical therapy of secondary glaucomas is usually identical to the treatment of primary chronic open angle glaucoma.

Secondary glaucomas may be caused by many different factors, and the angle may be open or closed. Therefore, treatment will depend on the etiology of the glaucoma. The underlying disorder is best treated first. Glaucomas with uveitis (such as iritis or iridocyclitis) initially are treated conservatively with anti-inflammatory and antiglaucoma agents. Surgery is indicated where conservative treatment is not sufficient.

The prognosis for secondary glaucomas is generally worse than for primary glaucomas.

10.5Childhood Glaucomas

Definition

Any abnormal increase in intraocular pressure during the first years of life will cause dilatation of the wall of the globe, and especially of the cornea. The result is a characteristic, abnormally large eye (buphthalmos) with a progressive increase in corneal diameter. This is also referred to as hydrophthalmos or hydrophthalmia.

Epidemiology: Glaucomas in children occur once every 12000–18000 births and account for about 1% of all glaucomas. Primary congenital glaucoma is an inherited autosomal recessive disorder. It is bilateral in approximately 70% of all cases; boys are affected in approximately 70% of all cases; and glaucoma manifests itself before the age of six months in approximately 70% of all cases.

Today there is widespread public awareness of glaucoma in adults. Unfortunately, this does not yet apply to glaucoma in children.

Etiology: (See also physiology and pathophysiology of aqueous humor circulation): The iris inserts anteriorly far in the trabecular meshwork (Fig. 10.2). Embryonic mesodermal tissue in the form of a thin transparent membrane (Barkan’s membrane) covers the trabecular meshwork and impedes the flow of aqueous humor into the canal of Schlemm. Other abnormal ocular or systemic findings are lacking.

Aside from isolated buphthalmos, other ocular changes can lead to secondary hydrophthalmos. These include:

Hydrophthalmia with ocular developmental anomalies.

Hydrophthalmia with systemic disease.

Secondary buphthalmos resulting from acquired eye disorders.

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Regardless of the cause of the increase in intraocular pressure, the objective signs and clinical symptoms of childhood forms of glaucoma are identical and should be apparent to any examining physician.

Symptoms: Classic signs include photophobia, epiphora, corneal opacification, and unilateral or bilateral enlargement of the cornea. These changes may be present from birth (in congenital glaucoma) or may develop shortly after birth or during the first few years of life.

Children with this disorder are irritable, poor eaters, and rub their eyes often. The behavior of some children may lead one to suspect mental retardation.

Physicians should be alert to parents who boast about their child’s “big beautiful eyes” and should measure intraocular pressure.

It is essential to diagnose the disorder as early in the child’s life as possible to minimize the risk of loss of or irreparable damage to the child’s vision.

Diagnostic considerations: These examinations may be performed without general anesthesia in many children. However, general anesthesia will occasionally be necessary to confirm the diagnosis especially in older children (Fig. 10.21).

Congenital glaucoma.

Fig. 10.21 Examination of a three- month-old infant with buphthalmos under general anesthesia. Findings include a corneal diameter of 14.0 mm (normal diameter is approximately 9.5 mm) and stromal opacification.

10.5 Childhood Glaucomas 275

Measurement of intraocular pressure. One should generally attempt to measure intraocular pressure by applanation tonometry (tonometry with a hand-held tonometer).

Measurement is facilitated by giving the hungry infant a bottle during the examination. Feeding distracts the baby, and a measurement usually can be obtained easily. Such a measurement is usually far more accurate than one obtained under general anesthesia as narcotics, especially barbiturates and halothane, reduce intraocular pressure.

Optic disk ophthalmoscopy. The optic cup is a very sensitive indicator of intraocular pressure, particularly in the phase in which permanent visual field defects occurs. Asymmetry in the optic cup can be helpful in diagnosing the disorder and in follow-up.

Special considerations: A glaucomatous optic cup in children may well be reversible. Often it will be significantly smaller within several hours of a successful trabeculotomy.

Inspection of the cornea. The cornea will appear whitish and opacified due to epithelial edema. Breaks in Descemet’s membrane can exacerbate an epithelial or stromal edema. These lesions, known as Haab’s striae, will exhibit a typical horizontal or curvilinear configuration.

The enlarged corneal diameter is a characteristic finding. The cornea normally measures 9.5 mm on average in normal newborn infants. Enlargement to more than 10.5 mm suggests childhood glaucoma. Chronically elevated intraocular pressure in children under the age of three will lead to enlargement of the entire globe.

Gonioscopy of the angle of the anterior chamber. Examination of the angle of the anterior chamber provides crucial etiologic information. The angle will not be fully differentiated. Embryonic tissue will be seen to occlude the trabecular meshwork.

Differential diagnosis: Large eyes. A large corneal diameter can occur as a harmless anomaly (megalocornea).

Corneal opacification. Diffuse corneal opacification with epithelial edema occurs in congenital hereditary endothelial dystrophy. Opacification without epithelial edema occurs in mucopolysaccharidosis (Hurler’s syndrome, Scheie’s syndrome, Morquio’s syndrome, and Maroteaux-Lamy syndrome).

Striae in Descemet’s membrane. In contrast to the horizontal Haab’s striae in congenital glaucoma, endothelial breaks can also occur as a result of injury during a forceps delivery (vertical striae), in keratoconus, and in deep keratitis.

276 10 Glaucoma

None of these differential diagnoses are accompanied by elevated intraocular pressure.

Treatment: Childhood glaucomas are treated surgically. The prognosis improves the earlier surgery is performed.

Principle and procedure of goniotomy. With a gonioscope in place on the eye, the goniotomy scalpel is advanced through the anterior chamber to the trabecular meshwork. The trabecular meshwork can now be incised as far the canal of Schlemm over an arc of about 120 degrees to permit drainage of the aqueous humor. Often two or three goniotomies at different locations are required to control intraocular pressure. These operations can only be performed when the cornea is clear enough to allow visualization of the structures of the anterior chamber.

Principle and procedure of trabeculotomy. After a conjunctival flap and split-thickness scleral flap have been raised, access to the canal of Schlemm is gained through a radial incision, and the canal is probed with a trabeculotome. Then the trabeculotome is rotated into the anterior chamber (Fig. 10.22). This tears through the inner wall of the canal, the trabecular meshwork, and any embryonic tissue covering it to open a drainage route for the aqueous humor.

A higher rate of success is attributed to trabeculotomy when performed as an initial procedure. This operation can also be performed when the cornea is largely opacified.

Prognosis: Goniotomies and trabeculotomies are not always successful. Even after apparently successful initial trabecular surgery, these children

require a lifetime of follow-up examinations (initially several times a year and later once every year) as elevated intraocular pressure can recur, in which case repeat goniotomy or trabeculotomy is indicated.

279

11 Vitreous Body

Christoph W. Spraul and Gerhard K. Lang

11.1Basic Knowledge

Importance of the vitreous body for the eye: The vitreous body stabilizes the globe although the eye can remain intact without the vitreous body (see vitrectomy). It also prevents retinal detachment.

Embryology: The development of the vitreous body can be divided into three phases:

First phase (first month of pregnancy; fetus measures 5–13 mm cranium to coccyx): The primary vitreous forms during this period. This phase is characterized by the entry of mesenchyme into the optic cup through the embryonic choroidal fissure. The main function of the primary vitreous is to supply the developing lens with nourishment. In keeping with this function, it consists mainly of a vascular plexus, the anterior and posterior tunica vasculosa lentis, that covers the anterior and posterior surfaces of the lens. This vascular plexus is supplied by the hyaloid artery and its branches (Fig. 11.1). This vascular system and the primary vitreous regress as the posterior lens capsule develops at the end of the second month of pregnancy.

Second phase (second month of pregnancy; fetus measures 14–70 mm cranium to coccyx): The secondary vitreous forms during this period. This avascular vitreous body consisting of fine undulating collagen fibers develops from what later becomes the retina. In normal development it expands to compress the central primary vitreous into a residual central canal (hyaloid canal or Cloquet’s canal).

Third phase (third month of pregnancy; fetus measures 71–110 mm cranium to coccyx): The tertiary vitreous develops from existing structures in the secondary vitreous. The secondary vitreous remains. The zonule fibers that form the suspensory ligament of the lens develop during this period.

Composition of the vitreous body: The gelatinous vitreous body consists of 98% water and 2% collagen and hyaluronic acid. It fills the vitreous chamber, which accounts for approximately two-thirds of the total volume of the eye.

280 11 Vitreous Body

Transitory embryonic vascular supply.

Fig. 11.1 The anterior tunica vasculosa lentis (dark red) forms anastomoses with the posterior tunica vasculosa lentis (light red) through the iridohyaloid vessels.

Stabilization and confines of the vitreous body: With their high negative electrostatic potential, the hyaluronic acid molecules fill the three-dimen- sional collagen fiber network and provide mechanical stability. Condensation of peripheral collagen fibrils creates a boundary membrane (hyaloid membrane), which is not a basement membrane. It is attached to adjacent structures at the following locations (Fig. 11.2):

At the ligament of Wieger along the posterior capsule of the lens.

At the vitreous base at the ora serrata.

At the funnel of Martegiani (approximately 10 µm wide) surrounding the

periphery of the optic disk.

The connections between the vitreous body and retina are generally loose although there may be firm focal adhesions. These firmer focal attachments cause problems during vitreous detachment because they do not permit the vitreous body to become completely detached. The focal adhesions between the vitreous body and retina produce focal traction forces that act on the retina and can cause retinal tears and detachment.

11.2 Examination Methods 281

Attachments of the vitreous body and adjacent spaces.

Fig. 11.2 Attachments of the vitreous body are identified by thick red lines and listed on the left. Spaces adjacent to the vitreous body are shown in green and listed on the right.

Neurovascular supply: The vitreous body contains neither blood vessels nor nerves. As a result, pathogens can multiply undisturbed for a relatively long time before the onset of an immune response from adjacent structures.

11.2Examination Methods

The anterior third of the vitreous body can be readily examined with a slit lamp. An additional contact lens or hand-held condensing lens (+ 60, + 78, and + 90 diopters) is required to examine the posterior portions. Indirect ophthalmoscopy or retroillumination (Brückner’s test) is usually used to examine the vitreous body in its entirety. Opacities will appear as dark shadows. Ultrasound examination of the vitreous body is performed in cases such as a mature cataract where visualization by other methods is not possible.

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11.3Aging Changes

11.3.1Synchysis

The regular arrangement of collagen fibers gradually deteriorates in middle age. The fibers condense to flattened filamentous structures. This process, known as liquefaction, creates small fluid-filled lacunae in the central vitreous body that initially are largely asymptomatic (patients may report floaters). However, once liquefaction has progressed beyond a certain point, the vitreous body can collapse and detach from the retina.

11.3.2Vitreous Detachment

Definition

Complete or partial detachment of the vitreous body from its underlying tissue. The most common form is posterior vitreous detachment (see Fig. 11.3a); anterior or basal vitreous detachment is much rarer.

Epidemiology: Six percent of patients between the ages of 54 and 65 and 65% of all patients between the ages of 65 and 85 have posterior vitreous detachment. Patients with axial myopia have a predisposition to early vitreous detachment. Presumably the vitreous body collapses earlier in these patients because it must fill a “longer” eye with a larger volume.

Etiology: Liquefaction causes collapse of the vitreous body. This usually begins posteriorly where the attachments to the underlying tissue are least well developed. Detachment in the anterior region (anterior vitreous detachment) or in the region of the vitreous base (basal vitreous detachment) usually only occurs where strong forces act on the globe as in ocular trauma.

Symptoms and findings: Collapse of the vitreous body leads to vitreous densities that the patient perceives as mobile opacities. These floaters (also known as flies or cobwebs) may take the form of circular or serpentine lines or points. The vitreous body may detach partially or completely from the retina. An increased risk of retinal detachment is present only with partial vitreous detachment. In this case, the vitreous body and retina remain attached, with the result that eye movements in this region will place traction on the retina. The patient perceives this phenomenon as flashes of light. If the traction on the retina becomes too strong, it can tear (see retinal tears in posterior vitreous detachment, Fig. 11.3b – c). This increases the risk of retinal detachment and vitreous bleeding from injured vessels.

Floaters and especially flashes of light require thorough examination of the ocular fundus to exclude a retinal tear.