Ординатура / Офтальмология / Английские материалы / Pediatric Ophthalmology for Primary Care 3rd edition_Wright, Farzavandi_2008

Acquired Brown syndrome is usually caused by an inflammation around the superior oblique tendon and trochlea. There may be pain and tenderness in the superior nasal quadrant, with the condition often being intermittent. Treatment of inflammatory Brown syndrome is the use of oral nonsteroidal anti inflammatories (eg, ibuprofen) or in severe cases, local corticosteroid injections, but surgery is usually contraindicated. Other causes of acquired Brown syndrome or pseudo Brown syndrome include floor fracture, peritrochlear scarring or superior oblique tendon sheath syn drome, trochlear inflammation (rheumatoid arthritis), glaucoma implant under superior oblique tendon in the superior nasal quadrant, or fat adher ence syndrome. Virtually any periocular condition that results in limited elevation in adduction can look like Brown syndrome.

Double Elevator Palsy—rare

Double elevator palsy is the congenital limitation of elevation of one eye, occurring sporadically without an inheritance pattern. The term double elevator implies paresis of the superior rectus muscle and inferior oblique muscle. This, however, is a misnomer; in 70% of all cases the deficient eleva tion is due to restriction, secondary to a tight inferior rectus muscle. A better term, therefore, is monocular elevation deficit syndrome. Double elevator palsy may be mistaken for Brown syndrome, though the limited elevation in Brown syndrome is worse in adduction than abduction.

Congenital Fibrosis Syndrome—rare

Congenital fibrosis syndrome of the extraocular muscles is usually inherited as an autosomal dominant trait. The etiology is unknown, but the syndrome is associated with fibrotic replacement of extraocular muscle tissue.

Because of the tight fibrotic muscles, ductions are limited. The medial rectus muscle is most commonly affected, producing an esotropia, though the fibrosis can be generalized and affect virtually all of the rectus muscles. Treatment is surgical recession of the fibrotic muscles. These cases can be technically difficult because exposure of the muscle is limited, especially in cases with a fibrotic medial rectus muscle.

Graves Ophthalmopathy—rare in children

Graves ophthalmopathy is an autoimmune disease related to thyroid dys function, despite the fact that thyroid function studies may be normal. It is usually an adult disease, although it may be present in childhood. There is an initial acute inflammatory phase with lymphocytic infiltration of the

extraocular muscles, resulting in extraocular muscle enlargement and prop tosis (Figure 4 16). This active phase usually lasts several months to a year. Orbital imaging studies show thickened extraocular muscles, especially posteriorly. Later (6 months to a year after onset), there is a cicatricial phase with quiescence of inflammation and secondary contracture of the muscles. All extraocular muscles are usually involved, but the inferior rectus and medial rectus are most often affected (Figure 4 17). Strabismus develops

in the cicatricial phase, with a restric tive hypotropia and esotropia being the most common signs. The management of Graves ophthalmopathy is careful obser vation during the acute inflammatory phase. Treatment with systemic steroids and even external beam radiation may be indicated for severe cases where there are signs of optic nerve compression from inflamed extraocular muscles. Orbital decompression surgery is also useful

if vision is compromised or if there is severe proptosis. Treatment is rarely indi cated for children. After the inflamma tory phase has subsided and strabismus measurements have stabilized, strabis mus surgery may be considered.

Figure 4 17.

Computed tomography scan of thyroid myopathy. Note enlargement of all the extraocular muscles, especially the inferior and medial recti.

Bibliography

1.Archer SM, Sondhi N, Helveston EM. Strabismus in infancy. Ophthalmology. 1989;96:133–137

2.Crawford ML, von Noorden GK. Optically induced concomitant strabismus in monkeys.

Invest Ophthalmol Vis Sci. 1980;19:1105–1109

3.Crawford ML, von Noorden GK. The effects of short term experimental strabismus on the visual system in Macaca mulatta. Invest Ophthalmol Vis Sci. 1979;18:496–505

4.Ing MR. Early surgical alignment for congenital esotropia. Ophthalmology. 1983;90:132–135

5.Pediatric Eye Disease Investigator Group. Spontaneous resolution of early onset esotropia: experience of the Congenital Esotropia Observational Study. Am J Ophthalmol. 2002;133: 109–118

6.Pediatric Eye Disease Investigator Group. The clinical spectrum of early onset esotropia: experience of the Congenital Esotropia Observational Study. Am J Ophthalmol. 2002;133: 102–108

7.Wright KW, Edelman PM, McVey JH, Terry AP, Lin M. High grade stereo acuity after early surgery for congenital esotropia. Arch Ophthalmol. 1994;112:913–919

Chapter 5

Refractive Errors and

Spectacles in Children

The Eye as an Optical System

The cornea and lens are the refractive elements of the eye. The cornea accounts for approximately two thirds of the optical power and the lens makes up the remaining third. Together, the combined power of the cornea and lens equals approximately 60 diopters. This strong “plus” lens converges light on the retina at a distance of about 23 mm from the cornea.

In contrast to the lens, the cornea cannot change refractive power or focus. The lens is secured to a sphincter type muscle called the ciliary body muscle. When this muscle contracts, the sphincter closes and slackens the tension of the lens’ zonules that connect to the lens. This results in the steep ening of the lens curvature and increases the lens power, which is called accommodation. The mechanism for increasing the lens power is used when focusing at near. Children have great accommodative amplitudes. These accommodative amplitudes, however, start decreasing at around

20 years of age. At age 10 years, the accommodative amplitude is approxi mately 14 diopters. By age 40 years, accommodative amplitudes are down to 4.5 diopters, and reading glasses may be needed for near vision. Large accommodative amplitudes are what allow children to see details on a penny at a distance of only a few centimeters. Accommodation is physiologically linked to pupillary miosis and ocular convergence (both eyes turning in toward midline). Thus the classic triad for near response is convergence, miosis, and accommodation.

If the eye is naturally in focus when accommodation is at rest, the retinal image will be in focus for distance, and this is called emmetropia (Figure 5 1). Emmetropia is the normal state and glasses are not required.

A refractive error is when the image is not in focus. A description of refrac tive errors including hypermetropia, myopia, astigmatism, and anisometro pia follows.

Figure 5 1.

Posterior focal length is approximately 23 mm. This drawing shows emmetropia with the parallel light focused on the retina.

Refractive Errors

Hypermetropia (Hyperopia)

Hypermetropia (farsightedness), or hyperopia as it is also termed, occurs when the cornea and lens power are not sufficient to bring the image clearly in focus on the retina because of the relatively short length of the eye. With hyperopia, the light theoretically focuses behind the retina (Figure 5 2 top). Small amounts of hypermetropia are normal in infants and young children (Figure 5 2 bottom). Children with small to moderate amounts of hyper opia have 20/20 vision for distance and near because they can correct for the refractive error by lens accommodation. Over time, the eye grows and the hyperopia improves. Most children, especially infants, are actually slightly farsighted at birth and become emmetropic as the eye grows.

Children with moderate hypermetropia (>3.00 diopters) can accommo date to keep retinal images clear, but this amount of accommodation often results in the eyes over converging (turning in) and can lead to accommo dative esotropia (see Chapter 4). Prescribing hyperopic spectacle correction relaxes accommodation and consequently relaxes convergence. In many cases, hyperopic spectacles will straighten the eyes without the need for eye muscle surgery. Large amounts of hyperopia (6.00 diopters) can result in

Figure 5 2.

Drawing of hyperopia. Top, Note that lens power is too weak for the relatively short length of the eye and parallel light rays entering the eye are focused behind the eye. Bottom, Note that the lens is steeper as the eye accommodates (focuses) to converge and focus the light rays on the retina.

bilateral amblyopia. This happens because infants cannot fully accommo date for high hypermetropia, which then results in bilateral blurred retinal images. Unilateral or asymmetric hyperopia is very amblyogenic, as the child accommodates for the eye with the lesser amount of hyperopia, thus leaving the more hyperopic eye constantly out of focus (anisometropic amblyopia).

Myopia

Myopia (nearsightedness) occurs when the cornea and lens power are too great for the length of the eye and light focuses in front of the retina.

Another way to think of myopia is that the eye is too long for the relatively strong cornea lens power (Figure 5 3 top). Near objects, however, are natu rally in focus for a myopic eye, as near objects reflect divergent light that is focused more posteriorly (Figure 5 3 bottom). Thus, the layman uses the term nearsightedness for this refractive error because patients with myopia can see up close.

Figure 5 3.

Drawing of myopia. Top shows parallel light converging in front of the retina, as the eye is too long for the power of the cornea and lens. Bottom shows that an object close to the eye gives off divergent light that is focused more posteriorly on the retina.

Myopia runs in families and the inheritance pattern is variable, some being autosomal dominant or autosomal recessive and others apparently sporadic. Myopia tends to develop in school aged children and increase during the growth spurt period as the eye increases in size. In most cases, myopia will stabilize by the mid to late teenage years. Patients with myo pia usually do not have amblyopia, since myopia develops after the critical period of visual development. Because infants with myopia can see clearly up close, this provides clear retinal images necessary for normal visual development.

high plus, usually more than 10.00 diopters. Pseudophakia is the term for an intraocular lens that has been implanted to replace a cataract.

Correcting Refractive Errors

There are 2 ways to correct refractive errors in children: (1) the use of con tact lenses or (2) the use of spectacles. Spectacles have the advantage of being easy to use, providing protection for the eyes with no chance of corneal problems. Contact lenses, on the other hand, are cosmetically desirable and do not magnify or minify the image as glasses can. However, there is a risk of corneal infection, especially with soft contact lenses, and contact lenses can also be difficult for children to use. Contact lenses are very important

in the treatment of aphakia (patients without the natural lens) because they provide a constant, clear image without significant distortion or magnifica tion. Even infants can be fit with contact lenses if necessary.

Why Do We Use Cycloplegic Drops to Test for

Refractive Errors?

Because children have great accommodative amplitudes (ability to focus), they can greatly change focus during the refraction, thus giving variable measurements. Errors in focusing measurement results produce a myopic shift or the false appearance of astigmatism. Cycloplegic drops paralyze accommodation, allowing precise measurement of the refractive error.

A child who is emmetropic (no refractive error) can appear significantly myopic or astigmatic and a hypermetropic child can appear normal if the refraction is performed without cycloplegic drops. The best way to obtain an accurate refraction in children is to control accommodation by using cycloplegic drops.

Chapter 6

Neonatal and

Infantile Blindness—

“My Baby Doesn’t See”

Poor vision and lack of visual attentiveness in infancy is frightening for any parent. It is important to know that normal newborns have poor vision and only demonstrate sporadic fixation with relatively little visual behavior. By 2 months of age, smooth pursuit eye movements have usually developed and

visual acuity will have improved significantly. Two month old infants should show some visual attentiveness, and by 4 months of age, most normal infants will show visual behavior such as following mother’s face. Lack of visual attentiveness by 4 months of age requires an ophthalmology consultation.

As discussed in Chapter 3, all newborns should have a red reflex screen ing test as part of every well baby examination. The red reflex test is espe cially important if the baby demonstrates poor vision. Retinal and optic nerve disorders may or may not present with an abnormal red reflex. If there are large areas of pathology, such as in retinoblastoma or optic nerve coloboma, an abnormal red reflex occurs. Diseases that involve less disrup tion of retinal anatomy, such as retinal dystrophies and optic nerve hypo plasia, show a normal red reflex. Cortical blindness has a normal red reflex examination with no nystagmus. Poor visual fixation in infancy may also be because of a disorder in eye movements such as ocular motor apraxia. In this chapter, we cover those diseases that present with visual loss in infancy and a normal appearing eye to inspection. Disorders that are associated with a distinctly abnormal red reflex (eg, cataracts) are covered in Chapter 22.

Sensory Nystagmus

Children who are born bilaterally blind or develop blindness in the first few months of life will develop sensory nystagmus, except in cases of cortical blindness (cortical blindness from neonatal hypoxia, for example, will not have nystagmus). In this chapter, the author describes causes of bilateral neonatal blindness that are almost always associated with nystagmus. If the