Chapter 590. Anterior Segment Disorders

The anterior segment of the eye consists of the cornea, the anterior chamber, the iris, the pupil, and the lens, which anatomically divides the anterior segment of the eye from its posterior segment. The posterior segment includes the vitreous gel, the retina, the optic nerve, and the choroid. This is a useful clinical division, because many diseases of the eye predominantly affect the anterior or posterior segment and are usefully differentiated from conditions (eg, endophthalmitis) that affect the whole eye. Casual inspection of the eye (the globe) is inevitably an assessment of the anterior segment structures and offers very little information about the internal, more posterior ocular structures. A checklist of anterior segment findings that may be recognized by the pediatrician would include cornea size and transparency; iris color (eg, heterochromia); pupil size, shape, position, and reaction to light; lens clarity (eg, cataract) and position (eg, dislocation/subluxation); and signs of elevated eye pressure.

Transparency of the cornea can be judged by how well the iris can be visualized and by noting the appearance of the normally black pupil. Comparing the patient’s cornea with those of a sibling or parent can be helpful. A cloudy cornea (Fig. 590-1) is always a significant clinical observation and has many pathological causes (Table 590-1). Corneal transparency is essential for normal vision, and its loss is an important cause of childhood blindness. Corneal opacification or change in the cornea’s size are essential signs of both systemic and ocular disease. Some corneal conditions that cause cloudiness are best treated promptly, such as glaucoma and corneal keratitis (inflammation or infection of the cornea). Glaucoma in young children causes corneal cloudiness and enlargement (Fig. 590-1), as well as optic neuropathy, potentially associated with permanent vision loss.

The corneas are normally transparent and equal in diameter. Rapid growth occurs in infancy, reaching adult size of 10 to 13 mm in horizontal diameter by 12 to 81 months of life. A cornea with a diameter greater than 13 mm is considered enlarged, and a diameter less than 10 mm is considered small.1 These abnormalities are more easily appreciated when the two corneas differ is size; this is always abnormal and requires immediate investigation (Table 590-2).

Symptoms of corneal disease vary considerably. Acquired defects of the corneal epithelium produce intense pain associated with photophobia and tearing. Corneal tears secondary to continued corneal stretching from elevated intraocular pressure are associated with intense photophobia and discomfort. Systemic diseases associated with cornea deposits of storage material are typically asymptomatic. Corneal enlargement secondary to glaucoma can also be asymptomatic.

The anterior chamber is filled with aqueous humor, which is optically clear. This space is delineated anteriorly by the back surface of the cornea and posteriorly by the iris and the front surface of the lens. It is best examined with a slit beam of light, which is a routine component of ophthalmologic examinations. The slit beam from an ophthalmoscope or a handheld slit can be substituted when children are examined. Common abnormalities of the anterior chamber are shown in Table 590-3.

Abnormalities of the iris and pupil are listed in Table 590-4. The iris (from Greek, iris means “rainbow”) is normally easily seen through the clear cornea and anterior chamber. It is variably colored from blue to dark brown, depending on the amount of melanin present. This pigmentation is normally uniform and approximately equal bilaterally. The architecture of the iris stroma making up the body of the iris is highly variable and is studied carefully by ophthalmologists for evidence of intraocular disease.

The pupils are usually approximately equal in size; they enlarge (dilate) in reduced illumination and constrict in response to increased light or with accommodation. Careful assessment of pupillary reactivity to a light stimulus is an important test of ocular and optic nerve function as well as a test of third nerve function. If pupil size is asymmetric, it is important to determine which is the abnormal pupil. If the relative disparity increases in bright light, the larger pupil is abnormal (ie, not constricting properly). If the disparity increases in dim light, the smaller pupil is abnormal (ie, not dilating properly). If the relative disparity is maintained regardless of the illumination, the child has physiological anisocoria, a finding seen in approximately 20% of the normal population. Examination of old photographs may be useful in establishing the congenital nature of this minor anomaly.

Arguably the most important pediatric pupillary eye sign is leukocoria, the white pupillary reflex, also referred to as the cat’s eye reflex (Fig. 590-2). This defect is caused by the reflection of light from a white cataract or from a white structure in the posterior segment. Many defects produce this reflex, including cataract, retinoblastoma, and retinal detachment. The expected “red reflex” is the normal reflection from the vascular choroid underlying the retina. It is rarely actually red but more often a combination of yellow, pink, and orange. Most importantly, it is symmetric between the two eyes. An absent red reflex (“black reflex”) is also a sign of intraocular disease, indicating an obstruction in the ability of light to reach and reflect back from the inner eye. Possible causes include cataract and presence of blood, but it is commonly merely the result of miosis (small pupils); pharmacological dilation of the pupils may reveal a normal red reflex and obviate the need for referral. An absent reflex or leukocoria should prompt urgent referral for ophthalmology consultation.

The most important and vision-threatening diseases of the anterior segment are keratitis, glaucoma, and cataracts. Both glaucoma and cataracts may be inherited, are associated with many pediatric systemic conditions, and can be secondary to other eye conditions such as trauma or chronic ocular inflammation. In developed nations, they are the most important causes of preventable and treatable blindness.

Childhood Glaucoma

Childhood glaucoma is an uncommon eye disease but an important cause of blindness.2 Potential causes fall into one of two categories: primary (isolated) glaucoma or secondary to some other ocular disease (Table 590-5). Primary congenital glaucoma is caused by abnormal development of the aqueous humor drainage system.3 It occurs in about 1 in 10,000 births in the United States and is the most common form of glaucoma in infants. Secondary glaucoma results from other disorders of the eye and may or may not be genetic; these include cataract surgery, trauma, or uveitis. Both types may be associated with other medical conditions. Ten percent of primary congenital glaucoma is present at birth, and 80% is diagnosed during the first year of life. The first signs of glaucoma include clouding or enlargement of the cornea (Fig. 590-1). The elevated intraocular pressure can cause the eyeball to enlarge, with injury to the inner layers of the cornea (Haab stria). Important early symptoms of glaucoma in infants and children are poor vision, light sensitivity, and tearing. The prognosis for vision is directly related to early recognition and treatment and to the severity at presentation.

Treatment of glaucoma in children is different from that in adults. Many patients will require surgery, with the goal of reducing pressure either by increasing the outflow of fluid from the eye or decreasing the production of fluid within the eye. Goniotomy or trabeculotomy are important surgical procedures that open the natural drainage mechanism (the trabecular meshwork) of the eye. Goniotomy is preferred, as it is less injurious to the eye tissues. Its rate of success is associated with the age of the child at the time of diagnosis, the type and severity of the glaucoma, and the surgery technique. Other surgical options are trabeculectomy and insertion of glaucoma drainage tubes, both of which create alternative means for fluid to escape from the eye.

Approximately 80% to 90% of babies who receive prompt surgical treatment, long-term care, and monitoring of their visual development will do well. If childhood glaucoma is not recognized and treatedpromptly, permanent visual loss will result. Unfortunately, primary and secondary congenital glaucoma still causes 2% to 15% of blindness in children.

Childhood Cataract

The natural lens of the eye anatomically forms the normally clear-transparent back wall of the anterior segment. It provides approximately 20% of the total focusing power of the eye with the remainder being supplied by the front surface of the cornea. Pathological lesions of the lens include opacification (cataract formation), dislocation or subluxation (ectopia lentis), and abnormalities of size. The lens is normally clear, but frequently small stable opacities can be identified; these are of no visual significance and do not require treatment. The lens is a highly cellular structure that continues to grow into adult years. It is metabolically active and at risk for the formation of cataracts related to many primary and secondary mechanisms (Table 590-6).

Cataracts in children are not rare, occurring with an incidence of approximately 1 per 4000 to 10,000 children. The red reflex test is an important screening tool to help recognize cataracts. Cataracts may be focal or total (Fig. 590-2), unilateral or bilateral, congenital or acquired and are an important cause of childhood blindness. Early recognition is essential to allow prompt intervention and optimal outcome for vision. Recognition of cataracts can be an important diagnostic aid in interpreting systemic inheritable diseases and acquired conditions.

Treatment of childhood cataracts that are visually significant requires their removal and correction of the resultant optical defect. Optical correction is accomplished with intraocular lenses, contact lenses, or spectacles; effects of these techniques on outcome for vision appear to be similar. Different centers may have different cutoffs for implanting an intraocular “plastic” lens, but in general, most centers will not do so until a child is 1 to 2 years old. Spectacles are quite thick and often cosmetically unsatisfactory, but in infancy or early childhood, when appearance is less of an issue, they can be well tolerated and result in excellent vision outcomes. For many years, contact lenses have been the “gold standard” for visual rehabilitation in infants who have had cataract surgery (these children are referred to as aphakes). The lenses are usually made of highly permeable silicone that can allow for some long-term use, but daily wear is preferred. Parents can become remarkably adept at contact lens insertion and removal. Limitations include cost, convenience, and availability from the manufacturers.

Lens dislocation/subluxation (ectopia lentis) may be an isolated defect but more frequently occurs in association with an ocular disease (eg, aniridia) or secondary to a systemic disease (eg, Marfan syndrome). Dislocation of the lens occurs in all instances due to loss of zonular integrity: secondary to a genetic defect or due to stretching in the case of an enlarged eye (eg, congenital glaucoma). A subluxed lens can cause high refractive defects, decreased vision, ocular inflammation (iritis), and glaucoma (Table 590-5). Early lens subluxation may require only optical correction (glasses or contact lenses), but when vision is more significantly affected, surgical removal of the lens may become indicated. Homocystinuria is a rare cause of ectopia lentis that must be ruled out by appropriate serum or urine testing prior to surgery in any child in whom another cause of the ectopia lentis cannot be confirmed. Children with homocystinuria have a platelet aggregation defect that can lead to thromboembolism during anesthesia.

Keratitis

Infection of the cornea is a serious vision-threatening disorder that requires urgent ophthalmology consultation, particularly if bacterial or herpetic infection is suspected. Bacterial ulcers appear as white areas overlying the iris or pupil. Patients usually have intense pain and photophobia. Bacterial infection is most common in contact lens wearers. For that reason, the pediatrician, faced with a child who presents with a red and painful eye and who wears contact lenses, should remove the contact lens; instilling a topical anesthetic such as tetracaine or proparacaine may facilitate removal. The child should be referred to an ophthalmologist urgently. The pediatrician should not put the child on antibiotics and should not apply a patch. The ophthalmologist will first determine if the symptoms and signs are due to infection or to other contact-lens-related issues (eg, overwear, contact lens solution allergy, tight fit). If an infectious corneal ulcer is present, direct culture may be required and an intense broad-spectrum antibiotic regime started. Contact lens wearers increase the risk for infection by overnight wear, poor hygiene, swimming in fresh water with contact lenses on, or using tap water for cleaning the lenses.

Herpetic infection can result from herpes simplex or varicella. Primary dermatologic infection is usually not associated with corneal involvement, but the presence of a red eye should prompt urgent ophthalmology consultation. Subsequent recurrence may be confined to the cornea with or without involvement of surrounding skin. Episodes are usually painful and almost always unilateral. Patients learn to recognize their symptoms and intensely red eye. Antiviral treatment should be prescribed only by an ophthalmologist, who will provide ongoing care. Scar formation may lead to vision loss, which may even require corneal transplantation.4