Ophthalmology



Ophthalmology


Michael X. Repka


Department of Ophthalmology and Pediatrics, Johns Hopkins University School of Medicine, Johns Hopkins Hospital, Baltimore, Maryland 21287.



The human visual system is an important yet often overlooked subject in a physician’s education. A large percentage of the afferent and efferent connections of the brain relate to the eye and its functions. This chapter imparts a basic understanding of the diagnosis and initial management of common ocular problems seen in children.


OCULAR DEVELOPMENT


Embryologic Development

The eye begins its development during the fourth week of pregnancy as a thickening of the neural tube called the optic placode. This evaginates from the prosencephalon to form the optic vesicle. During the fifth week, the optic vesicle invaginates to form the optic cup. This occurs at the same time that the branchial pouches are reaching the surface ectoderm. This temporal relation is important in understanding the frequent simultaneous occurrence of malformations of the globe and structures derived from the branchial arches. The classic example of this developmental malformation is the Goldenhar syndrome. This syndrome is also known as the oculoauriculvertebral syndrome. Other problems that result from defects in the structures derived from the branchial arches include ocular malformations (limbal choristomas), preauricular appendages or sinuses, hearing disorders, and vertebral defects.

The ocular lens forms during the sixth week of pregnancy. The optic nerve axons sprout from the retinal ganglion cells and enter the optic stalk during the seventh week. By the eighth week, retinal differentiation begins. At the ninth week, the recognizable eyeball is 1 mm in diameter.

The eyelids open and the retina completes vascular development and tissue differentiation during the eighth month. At full term, the fetus’ eye is 16 mm in diameter and the optic nerve is completing myelination. Children born prematurely experience delays in completing retinal differentiation and vascularization, presumably because of the arrest of growth for some period during the neonatal intensive care stay. Because of the anomalous influences of the preterm environment on the developing retina, retinopathy of prematurity can develop as discussed later in this chapter.


Postnatal Ocular System Development

At birth, an infant’s visual system is capable of formed vision. The retinal fovea is the central 1 mm portion of the retina that is used for straight-ahead vision. It completes development during the first year. The globe grows to 22 mm in diameter during the third year and to 24 mm in diameter by the end of adolescence. Most visual improvement noted by parents and clinicians during infancy and childhood is linked to the occipital cortex. This structure undergoes tremendous elaboration and growth during the first 7 years of life.


Visual Development

The development of vision is a dynamic process during childhood. For normal vision to develop, focused, clear visual input is required. If visual input is disrupted—for instance, by scarring, a cataract, or even a refractive error—normal vision does not develop.

Visual development begins shortly before term, proceeding rapidly through the first 2 years of life, then more slowly for the rest of the first decade. After this time, a child’s visual ability remains largely unchanged into adulthood. Thus, any injury or event that negatively affects visual input, even temporarily, has lifelong adverse consequences.



Amblyopia

Amblyopia, which occurs in 2% to 3% of the population, is a reduction in best-corrected visual acuity due to deprivation during the period of visual development. Amblyopia does not affect the retina, optic nerve, or lateral geniculate body in the thalamus. Nearly all the structural changes occur in the layers of gray matter in the occipital lobe. When the development of vision in one eye is deprived, the cells in the occipital lobe layers that receive information from that eye are markedly reduced in number and size, whereas the layers that correspond to the opposite eye that is functioning are enlarged.

Amblyopia is most often defined to be visual acuity less than 20/40 in the affected eye. Amblyopia may occur in one or both eyes. In many cases, the problem is not detected until the patient’s vision is tested upon entering school. At this late time, visual development is not often correctable with currently available interventions. Amblyopia is common following eye trauma in children, especially now that more sophisticated surgical techniques allow severely damaged eyes to have the chance for preserved visual function.

The treatment of amblyopia consists of clearing any obstruction to visual input and correcting any refractive error with glasses or contact lenses. Then, the patient must use the amblyopic eye. This is most commonly accomplished by occluding the sound eye with an adhesive patch. Other methods include using drops or glasses, which blur the vision in the sound eye. Such treatment may last for 1 year or longer. Treatment loses its effectiveness as the occipital cortex matures and is generally less effective after age 8 years.


DETERMINATION OF VISUAL ACUITY

The visual system accounts for a large proportion of the sensory input that the central nervous system receives. Furthermore, eliciting a response reveals much about other areas of the brain. The ability to quickly assess a patient’s visual function is an important part of physical diagnosis. The approach to measuring visual acuity differs based on the patient’s age.


Preverbal Children

Acuity in children during the first year of life is assessed in terms of corrected age. Visual development is not accelerated by preterm delivery. Acuity testing of young, preverbal children is performed at a distance of 0.5 m using an attractive, colorful toy. A handlight is not used because it is an aversive stimulus for some patients and a too easily seen stimulus for others. Testing is performed monocularly, securely covering the opposite eye with a patch, hand, or a piece of 2-in. tape. By 6 weeks of life, an infant should fixate the target quickly. By 3 months, the patient should be able to follow the target as it moves before the eyes in a 40-degree arc. Many infants can perform these tasks even earlier. Visual function that does not meet these guidelines requires a thorough evaluation. Abnormalities may be present anywhere within the visual system from eye to occipital lobe. A few children have primary delayed visual maturation and eventually become normal. Children with cortical visual impairment respond more favorably to brightly colored objects rather than black and white targets. They may also adopt unusual head positions to place their remaining visual field in the forward direction.

The evaluation of a toddler’s vision should include an assessment of behavior during unstructured play as well as visual function when patched. Children with normal vision appear unimpaired when using either eye after a few moments of distress from the patch. Children who have impaired vision often cry uncontrollably or become withdrawn when trying to use an impaired eye.


Verbal Children


Visual Acuity

Around the age of 3 years, children can read one of the pediatric eye charts. These tests involve picture recognition or detection of the orientation of a test figure (e.g., tumbling “E”). Although such testing is best performed using a distance target, pediatric near cards are useful for inpatient and intensive care situations. In the United States, acuity is reported as a Snellen fraction, with 20 as the numerator. A denominator of 30 or less indicates normal acuity. Denominators greater than 30 denote impaired vision. Any child found to have vision less than 20/30 needs an ophthalmologic examination.


Visual Fields

An important part of the examination of visual function is an assessment of the peripheral visual field. Such fields are difficult in this age group. It is possible with young children to assess fields by observing the patient’s behavior. A neurosurgical patient with hemianopia will ignore the corresponding portion of the visual environment.


THE RED EYE

After refraction, the most common reason that a child seeks ophthalmologic consultation is for a red eye. The redness is caused by dilated vessels in both the conjunctiva and deeper ocular tissues. There may or may not be associated pain. The causes of a red eye include conjunctivitis, iritis, glaucoma, corneal exposure, corneal abrasion, and endophthalmitis. The evaluation includes the amount and type of ocular discharge, pain, shape and clarity of the iris, the quality of the red reflex, the presence of fluorescein staining of the cornea, and the visual acuity.



Conjunctivitis

Conjunctivitis is the most common cause of a red eye in the pediatric patient. Pain is usually mild. Conjunctivitis, unlike other causes of red eye, is associated with copious discharge. Health care providers are often the unwitting vector of epidemics of viral conjunctivitis. Following contact with a patient who has a red eye, hands must be washed and the areas of the office or clinic visited by the patient must also be thoroughly disinfected.

The most common cause of conjunctivitis is viral. These cases are termed pink eye by families. Many viruses are implicated, but the most common are the adenoviruses. These are responsible for numerous outbreaks in the spring and summer. The conjunctiva is pink and slightly thickened, especially the palpebral conjunctiva. This tissue loses its smooth surface, becoming bumpy and resembling a cobblestone road. There is intense photophobia. The discharge is copious and clear, and there is a prominent painless preauricular lymph node.

Although many cases of conjunctivitis are isolated, some types are associated with fever, pharyngitis, and other symptoms of an upper respiratory infection (pharyngeal conjunctival fever). The disease is self-limited, resolving in 7 to 10 days. Cultures are usually not necessary.

Supportive therapy includes cool compresses, artificial tears, topical and systemic antihistamines, and topical mast-cell stabilizers (e.g., ketorolac, levocabastine, lodoxamide). Topical corticosteroids should not be used without ophthalmologist supervision because these drugs adversely affect a herpetic infection.

The first exposure to herpes simplex virus produces a viral conjunctivitis indistinguishable from any other type of viral conjunctivitis. This infection is self-limited. The presence of clear vesicles on the eyelids is usually secondary to a herpes simplex infection and confirms the diagnosis without the need for culture.

Unlike the other causes of viral conjunctivitis, this virus becomes latent in the trigeminal nerve ganglion. Once there, the herpes simplex virus is responsible for recurrent conjunctivitis and keratitis, the latter a major cause of blindness in the United States. The recurrent inflammation and ulceration of the cornea leads to scarring and vascularization. These changes in the cornea reduce clarity and eventually reduce vision. Many patients eventually require corneal transplantation to restore vision.

When the diagnosis of a herpes simplex infection—whether primary or secondary—is made, a topical antiviral agent is administered (e.g., trifluridine). Most clinicians suggest systemic acyclovir for treating infant herpetic ocular disease or any case involving the eyelids or cornea because of the high frequency of systemic infection.

Patients with herpetic disease or its history should be treated cautiously with topical steroids because they can cause the disease to dramatically worsen. Such a deleterious effect may also be seen with the use of systemic corticosteroids. For this reason, the use of steroids should be avoided by nonophthalmologists in treating conjunctivitis and all other causes of a red eye.

The signs of bacterial conjunctivitis include an injected conjunctiva, both bulbar and palpebral, associated with a purulent discharge. There is no preauricular lymphadenopathy. The causative organisms include Neisseria, Haemophilus, Staphylococcus, and Streptococcus. A Gram stain and culture should be performed to assist in selecting the appropriate antibiotic therapy. A broad-spectrum topical agent (e.g., a combination of trimethoprim and polymyxin B sulfate) is used initially if the Gram stain does not suggest Neisseria gonorrhea. Pseudomonas can have a devastating effect on the cornea in patients using contact lenses due to its quick invasion, and sometimes even perforation, of the cornea. Redness or pain in a contact lens wearing patient should elicit emergent ophthalmologic consultation, removal of the lens, and culture of any discharge. Many organisms are resistant to common topical antimicrobials. Quinolone antibiotics have become the drug of choice for initial therapy of these ulcers.

Conjunctival infection and destruction with subsequent corneal scarring from chlamydia is one of the most common causes of blindness in the world. This blinding form of chlamydia is trachoma. In the United States, chlamydia presents as either neonatal or inclusion conjunctivitis. These forms of the disease are not associated with visual loss.

Inclusion conjunctivitis presents as a prolonged follicular conjunctivitis with mild mucopurulent discharge. The diagnosis is made by Giemsa stain, culture, or most rapidly by fluorescent antibody test of conjunctival swab. The diagnosis of chlamydia in older children suggests child abuse and should be appropriately reported. Therapy for all forms of the disease is systemic.

Ophthalmia neonatorum is conjunctivitis seen in the first 2 weeks after birth due to chemical irritation, bacteria, chlamydia, or herpes simplex. With the discontinuation of silver nitrate drops, the single topical application of erythromycin or tetracycline ointment has replaced silver nitrate in the delivery room as prophylaxsis. A diluted solution of povidone-iodine has been found very effective in clinical trials.

One of the common causes of ophthalmia neonatorum is N. gonorrheae. Although the incidence has been reduced through the use of postnatal prophylaxis, the disease occurs and can lead to blindness if untreated. Unlike other bacteria that require an epithelial defect to infect the cornea, N. gonorrheae may invade through an intact epithelium. Infections with this pathogen must be treated with systemic antibiotics, usually ceftriaxone. Topical therapy, such as erythromycin ointment, may be used but is much less important to the success of the therapy.

Chlamydia trachomatis conjunctivitis is probably the most common cause of neonatal conjunctivitis, occurring in 4 of every 1,000 births. It involves a moderate
mucopurulent conjunctivitis with onset 7 to 14 days after vaginal delivery. Diagnosis is made with a fluorescent antibody test or a Giemsa stain of a conjunctival swab. Cultures can also be obtained. Treatment is a 10-day course of oral erythromycin. Topical agents are not necessary.


Glaucoma

Glaucoma, a disease characterized by elevated intraocular pressure, is an infrequent cause of a red eye in childhood. Compared with conjunctivitis, an eye with glaucoma is minimally injected, but much more painful. The triad of ocular signs that should alert the physician to the diagnosis of congenital or infantile glaucoma include red conjunctiva of the bulbar surface, enlarged and cloudy cornea, and tearing. There may also be photophobia and blepharospasm. Older children may present with pain in the eye and vomiting.

Most childhood glaucoma presents within the first year of life. Ocular involvement is often bilateral. The congenital disease may present alone, as part of an ocular syndrome, or as part of a systemic syndrome. The systemic syndromes include aniridia, the congenital rubella syndrome (cataract, hearing, cardiac), Lowe syndrome (renal, cataract), Sturge-Weber syndrome, and neurofibromatosis type 1. Glaucoma may also occur following ocular injuries, especially blunt trauma to the eye, and as a postoperative complication following intraocular ophthalmologic surgery.

The elevated pressure within the eye that causes congenital, infantile, and juvenile forms of glaucoma is usually produced by impaired drainage of fluid from the eye. The pressure is responsible for producing the enlargement of the eye and the destruction of the optic nerve. Prompt institution of pressure-reducing treatment may prevent optic nerve damage. Emergent treatment includes acetazolamide, β-blockers, and filtration surgery. Therapy is needed for life, and many of these patients suffer severe visual impairment.






FIGURE 52-1. Anatomy of the lacrimal drainage system. Tears pass through the lacrimal puncta, located in both eyelids into the lacrimal canaliculi. Tears then pass into the lacrimal sac, move down into the nasolacrimal duct, and finally into the nasopharynx below the inferior turbinate.


Iritis

Childhood iritis, or inflammation of the iris, may follow trauma, be associated with juvenile rheumatoid arthritis, or be idiopathic. The most common cause is blunt trauma to the eye. The patient presents with a red eye, pain, photophobia, and reduced vision. Iritis is treated with cycloplegic and steroid drops.

Any patient with iritis in the absence of trauma should be tested for rheumatoid arthritis and antinuclear antibodies. Most cases are idiopathic, but a few patients have arthritis. The morphology of the inflammation may suggest the etiology. Patients with juvenile rheumatoid arthritis should be carefully followed for the development of glaucoma and cataract. Iritis may precede or follow the diagnosis of the arthritis. Once the diagnosis is made, ongoing ophthalmologic observation is recommended.


NASOLACRIMAL ABNORMALITIES

The lacrimal drainage system begins at the nasal aspect of the eyelids (Fig. 52-1). The small openings in the margins of the lids are the lacrimal puncta. These are situated about 3 mm from the medial canthus. Tears flow through these 0.5-mm openings into the canaliculi, which are 5-mm ducts leading to the lacrimal sac. The lacrimal sac is located between the lacrimal bone and the medial canthus and tendon of the eyelids. Tears drain from the lacrimal sac along the nasolacrimal duct into the nose beneath the inferior turbinate. The tears are then swallowed.

The most common congenital problem is simple obstruction. The nasolacrimal duct is blocked in about 10% of neonates. Tearing is the only symptom with either clear tears or mucopurulent discharge if secondarily infected. Many of these cases spontaneously remit, while others need surgical intervention at about 1 year of age.

Facial trauma to the eye, lids, or nasal bone is another important cause of blockage. Such an injury can easily
be overlooked when accompanied by more severe injuries and can go undiscovered for days or weeks. This problem is much easier to repair in the acute setting, however, when scarring of the damaged structures has not occurred. In addition, the physician should consider the possibility of globe injury in any patient who has sustained a facial injury. Ophthalmologic consultation is obtained to assure there has been no disruption to the eye, even if the patient is not sufficiently stable for lacrimal treatment. This can be done once the patient has been placed under general anesthesia for treatment of the major injury.


Diagnosis

Nasolacrimal blockage should be suspected in the presence of an unremitting ocular discharge despite the use of topical antibiotics and the absence of upper respiratory infection and congestion. An intermittent discharge likely represents a partial obstruction. This situation occurs when there is mild swelling of the nasal mucosa. The discharge can be clear or purulent. With growth, this problem generally disappears.

Simple testing of the patency of the drainage system may be performed with a dye disappearance test. This test is performed by adding a drop of 2% fluorescein to each eye. Normally, all traces of the dye in the tear film disappear in 5 minutes. If the dye remains in the tear film, this is confirmatory evidence of an obstruction. Comparison of the rate of dye disappearance between a symptomatic eye and an asymptomatic eye is very reliable. Alternatively, a cotton applicator can be placed under the inferior turbinate in the very cooperative patient. If the applicator is stained yellow from the dye, patency is confirmed.

More complex testing involves computed tomography (CT) views with contrast media placed in the tear film or injected into the lacrimal sac.

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Aug 25, 2016 | Posted by in PEDIATRICS | Comments Off on Ophthalmology
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