Ординатура / Офтальмология / Английские материалы / Pediatric Ophthalmology for Primary Care 3rd edition_Wright, Farzavandi_2008
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Contributors |
Jeff Yuan, MD
Fellow—Pediatrics
Cedars-Sinai Medical Center
Los Angeles, CA
Section on Alagille syndrome
Clinical Editor
Sonal Farzavandi, FRCS(Edin)
Senior Consultant
Pediatric Ophthalmology and Strabismus Service
Singapore National Eye Centre
Table of Contents
Chapter 1 Ocular Anatomy and Physiology . . . . . . . . . . . . . . . . . . . . . . . . . 1 Chapter 2 Amblyopia and Strabismus . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21 Chapter 3 Ocular Examination and Vision Screening . . . . . . . . . . . . . . . 35 Chapter 4 Common Forms of Strabismus. . . . . . . . . . . . . . . . . . . . . . . . . . 49 Chapter 5 Refractive Errors and Spectacles in Children . . . . . . . . . . . . . . 71 Chapter 6 Neonatal and Infantile Blindness—
“My Baby Doesn’t See” . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 77 Chapter 7 Acquired Visual Loss in Childhood. . . . . . . . . . . . . . . . . . . . . . 89 Chapter 8 Nystagmus (Oscillating Eyes) . . . . . . . . . . . . . . . . . . . . . . . . . . 113 Chapter 9 Abnormal Optic Discs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 119 Chapter 10 Ocular Torticollis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 131 Chapter 11 Pupil and Iris Abnormalities. . . . . . . . . . . . . . . . . . . . . . . . . . . 135 Chapter 12 Tearing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 145 Chapter 13 Pediatric “Pink Eye” . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 159 Chapter 14 Ocular Inflammation and Uveitis. . . . . . . . . . . . . . . . . . . . . . . 189 Chapter 15 Corneal Abnormalities. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 207
Chapter 16 Eyelid and Orbital Masses . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 223 Chapter 17 Eyelid Disorders . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 243 Chapter 18 Subluxated Lens (Ectopia Lentis) . . . . . . . . . . . . . . . . . . . . . . . 253 Chapter 19 Retinopathy of Prematurity. . . . . . . . . . . . . . . . . . . . . . . . . . . . 259 Chapter 20 Dyslexia and Learning Disabilities. . . . . . . . . . . . . . . . . . . . . . 275 Chapter 21 Ocular Pigmentation Abnormalities . . . . . . . . . . . . . . . . . . . . 279 Chapter 22 Leukocoria: Cataracts, Retinal Tumors,
and Coats Disease . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 285 Chapter 23 Ocular Trauma . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 311
Chapter 24 Pediatric Ophthalmology Syndromes . . . . . . . . . . . . . . . . . . . 333 Index . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 369
Chapter 1
Ocular Anatomy
and Physiology
The eye is a delicate structure protected by the bony orbit and cushioned by the surrounding orbital fat (Figure 1 1). It is a fluid filled sphere whose outer wall consists of the optically clear cornea anteriorly and the white sclera posteriorly. The cornea and sclera have different radius of curvature,
with the cornea representing a smaller sphere than the sclera. Consequently, it is a misconception that the eye is spherical. The junction between the cor nea and the sclera takes on a bluish appearance, and is termed the limbus.
Figure 1 1.
Sagittal section of the eyebrow, upper and lower eyelid, as well as the globe and the extraocular muscles within the orbit. SR, superior rectus; LR, lateral rectus; IR, inferior rectus.
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The interior of the eye consists of the lens, the anterior and posterior chambers, and the vitreous cavity. The lens is suspended behind the pupil by cord like structures called zonules. Zonules are attached to the ciliary body, a muscle that controls lens focusing. The cornea and lens are the refractive elements of the eye. The cornea is a strong, fixed focus lens structure, while the crystalline lens is less powerful but is able to change focus to fine tune image clarity and provide near focusing. The anterior chamber is the space between the iris and cornea and the posterior chamber is the thin space between the lens and the back of the iris. The anterior and posterior cham bers are in front of the lens and are filled with a clear nutrient fluid called the aqueous humor or “aqueous.” Aqueous humor circulates around the lens and the posterior aspect of the cornea providing nutrition and oxygen to these avascular tissues. Behind the lens is the vitreous cavity, a large cavity filled with a clear gel called the vitreous humor or “vitreous” (Figure 1 2).
Figure 1 2.
Drawing of the eye showing important anatomic structures of the eye.
Ocular Anatomy and Physiology |
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The shape of the globe is maintained by the rigidity of the corneal scleral wall and by aqueous fluid pressure of approximately 10 to 20 mm Hg. Epithelium lining the ciliary body produces aqueous to maintain intraocu lar pressure. Aqueous passes from the ciliary body, around the lens, and through the pupil and exits at the anterior chamber angle through a filter like membrane called the trabecular meshwork (Figure 1 3). After pass ing through the trabecular meshwork, the aqueous enters Schlemm canal, which in turn feeds aqueous veins that connect with systemic veins. Glau coma is increased intraocular pressure (usually >22 mm Hg) resulting from abnormalities in the drainage of aqueous that damages the optic nerve and can cause blindness.
Figure 1 3.
Aqueous humor production and flow: Aqueous humor is produced by the ciliary body and released into the posterior chamber. In the normal eye, aqueous humor flows from the posterior chamber, between the lens and the iris, through the pupil, and into the anterior chamber. Most of the aqueous humor outflow is through the trabecular meshwork (conventional outflow pathway).
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Eyeball Growth
Eyeball growth is most dramatic during the first 2 years of life, and the eye is essentially adult size by 10 to 13 years of age (Gordon RA et al). Table 1 1 shows normal growth of the globe diameter (axial length) from birth to adulthood.
In addition to eyeball enlargement, there is also an increase in thickness and rigidity of the scleral wall with age. Scleral thickness in childhood is approximately 0.5 mm compared with 1 mm in adults. Children, especially infants, have elastic sclera that tends to collapse when intraocular pressure is low, and will stretch secondary to high intraocular pressure. This is why chil dren with congenital glaucoma have large eyes.
Cornea
The cornea is an amazing biological structure because of its optical clarity, allowing for clear transmission and focusing of light onto the retina. Optical clarity is a result of relatively acellular tissue that consists of a dense, regular collagen matrix. Hydration of this collagen matrix is highly regulated and an increase in hydration results in corneal edema and loss of clarity. Because the normally transparent cornea does not contain blood vessels, it receives oxygen and nutrients from the aqueous humor and from tears. It also receives ambient oxygen from its surface. Because the central cornea is avas cular, it tends to heal very slowly. Therefore, sutures used to repair a corneal laceration must be left in place for several months while the cornea heals.
Table 1-1. Axial Length Growth (Gordon and Donzis, 1985)
Age |
Axial Length |
|
|
Birth |
15 mm |
|
|
1 y |
17 mm |
|
|
2 y |
20 mm |
|
|
3 y |
21 mm |
|
|
4 y |
21.5 mm |
|
|
5 y |
22 mm |
|
|
6 y |
23 mm |
|
|
Adult |
24 mm |
|
|
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At birth, the cornea averages 9.8 mm in diameter and increases to 11 to 12 mm by 1 year of age. Corneas in infants measuring less than 9 mm in
diameter (microcornea) and corneas greater than 11 mm in diameter (meg alocornea) should be considered abnormal (see Chapter 15). In childhood, corneas smaller than 10 mm in diameter and corneas larger than 13 mm in diameter are also considered abnormal and may be an indication of congeni tal glaucoma.
On cross section of the cornea, 3 major corneal structures can be identi fied: surface epithelium, stroma, and endothelium (Figure 1 4).
Corneal Epithelium
Corneal epithelium consists of non keratinized, stratified, squamous epithe lium approximately 8 to 10 cells thick. It is attached to its basement mem brane by hemidesmosomes and provides a protective barrier against corneal infection. Traumatic removal of the corneal epithelium (corneal abrasion) is analogous to a tear of the skin. It causes extreme pain and provides an opportunity for corneal infection. Healing of a corneal epithelium abrasion first occurs by the sliding of adjacent corneal epithelium to fill the defect. Later, mitosis of basal epithelium cells replaces lost epithelium.
Corneal Stroma
Corneal stroma is made up of collagen fibers in a regular matrix with a uni form diameter. The few cells found within the corneal stroma are termed
’
’ 
’
’
Figure 1 4.
Diagrammatic representation of the corneal ultrastructure through all 5 layers.
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keratocytes. Keratocytes proliferate following corneal injury, and they secrete collagens and glycoproteins to repair the extracellular matrix. The new collagen matrix is disorganized and results in an opacification (corneal scar). Over several months to years, there is collagen remodeling and improved clarity, but the corneal scar almost always persists.
Corneal Endothelium
Corneal endothelium lines the interior surface of the cornea and consists of a single layer of hexagonal shaped cells (Figure 1 5). These endothelial cells play an important role in active transport to pump fluid out of the corneal stroma, thus maintaining the normal condition of deturgescence and corneal clarity. Injury to the endothelium from disease or trauma results in hydra tion of the cornea (corneal edema), disruption of the well organized corneal stromal collagen matrix, and opacification with the cornea appearing white. Unlike the corneal epithelium, the corneal endothelium is almost completely amitotic soon after birth, so endothelial cells do not regenerate. Loss of cor neal endothelial cells will not be replaced, but endothelial cells stretch and slide to cover defects. This process results in loss of the normal hexagonal cell morphology and decreased cell density, and eventually causes chronic corneal edema. The critical cell density, below which results in corneal
Figure 1 5.
Corneal endothelial pattern. A schematic drawing of the endothelial layer of the cornea demonstrating the hexagonal pattern of the cells, the slight difference in cell shape and size, and the continuous pattern of coverage.
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edema, is approximately 400 to 700 cells per square millimeter. Treatment for endothelial cell loss and corneal edema is to perform corneal transplan tation. Endothelial cell density and morphology are important indicators of the overall health of the cornea.
Uvea: Iris, Ciliary Body, Choroid
The uvea is a densely pigmented vascular layer between the sclera on the outside and the retina on the inside. Moving from the anterior to the pos terior, the uvea includes the iris, ciliary body, and choroid (figures 1 2 and 1 3).
The iris is the most anterior part of the uvea and consists of a densely pigmented layer on the inside and a lighter pigmented stroma on the sur face. The iris has 2 muscular layers: the iris sphincter near the pupil, and the dilator muscle toward the periphery of the iris. The iris sphincter muscle is innervated by parasympathetic fibers from the third cranial nerve, while the dilator muscle is innervated by sympathetic fibers from the superior cervical ganglion. Damage to the sympathetic innervation results in pupillary miosis (small pupil) called a Horner pupil. Damage to the fibers from the parasym pathetic third nerve results in pupillary mydriasis (dilation), causing the pupil to be unresponsive to light.
The ciliary body, a muscular structure located just posterior to the iris, consists of multiple radial folds called the ciliary processes. The ciliary body is covered with pigmented and non pigmented epithelium and it is this epi thelium that produces aqueous humor. Ciliary processes are connected to the lens by collagen fibers termed zonules. Ciliary muscle contractions cause the lens to change shape, which then changes the lens power, thus control ling lens focusing.
The choroid is a 0.25 mm–thick vascular structure with dense pigmen tation and a capillary network called the choriocapillaris. The choroid has a spongy black appearance that can be seen as a jet black tissue in a patient with a traumatic scleral rupture. This vascular tissue underlies the retina, providing oxygen and nutrients to the outer third of the retina. It has large capillaries that provide the highest perfusion rate of the body.