Ophthalmology

19 Ophthalmology



Infants and children may be affected by conditions not seen in adults, and the examination techniques and treatments that they may need frequently require subspecialty care. More than 50 years ago pediatric ophthalmology became established as a distinct subspecialty of Ophthalmology. Common problems include refractive errors, strabismus, amblyopia, infections, and trauma. Other problems encountered include ocular complications of systemic disease, developmental and genetic conditions, and neoplasms affecting the globe and orbits.



Anatomy of the Visual System


The visual system is conveniently separated into three principal parts: the globe and surrounding structures (Fig. 19-1), the visual pathways, and the visual or calcarine cortex.



The eyelids provide protection for the globe and assist in even distribution of the tear film over the cornea to provide a clear, undistorted optical surface. The crystalline lens complements the cornea’s refracting power with its ability to adjust the focal length of the optical system so that incoming light from objects at any distance may be clearly imaged on the retina. During the first 2 to 3 months of life, children develop the ability to focus on images at any range (accommodation). Light is focused on the macula, the portion of the retina responsible for the central field of vision (Fig. 19-2). The retina contains the photoreceptors, rods and cones, which convert light energy into an electrical nerve response. The fovea centralis is the center of the macula; it has the greatest concentration of cones and is responsible for detailed, colored central visual acuity.



Nerve fibers emanate from the ganglion cell layer of the retina and coalesce to form the optic nerve. The right and left optic nerves pass from the orbits and join together to form the optic chiasm. Nerve fibers from the nasal retina decussate at the chiasm and are directed toward the contralateral side of the brain. Fibers from the temporal retina travel without crossing at the chiasm to the ipsilateral visual cortex (Fig. 19-3). From the optic chiasm the fibers form the optic tracts and synapse in the lateral geniculate nucleus in the midbrain. From there the optic radiations, one on each side of the brain, travel posteriorly to the visual cortex above the cerebellum.



The decussation of nerve fibers at the chiasm and integration in the visual cortex are responsible for binocular vision and the formation of the visual field. For example, if an object is seen off to the person’s left, the image is received by the nasal retina of the left eye and the temporal retina of the right eye. Similarly, if the object is off to the person’s right, the image falls on the nasal retina of the right eye and the temporal retina of the left eye. The temporal retina images objects in the contralateral visual field, and the nasal retina images objects in the ipsilateral visual field. Because of the decussation of nasal retinal fibers, the right visual cortex receives images from the left side of the visual field and the left visual cortex receives images from the right side of the visual field.


Lesions of the visual pathways produce predictable patterns of visual field loss; for example, a left homonymous hemianopsia (loss of the left side of the visual field) is produced by a lesion of the right occipital cortex. Detection of a visual field defect that respects or does not extend across the vertical midline of the visual field indicates pathology posterior to the optic chiasm (within the intracranial portion of the visual system). Visual field defects that involve both the right and left sides of the visual field in one or both eyes indicate either retinal or optic nerve pathology or lesions to both sides of the intracranial visual system. Because of the anatomy of the optic chiasm, compressive lesions of the chiasm (e.g., pituitary tumors) produce visual field defects involving the left side of the visual field of the left eye and the right side of the visual field of the right eye (bitemporal defects).


The visual field can be arbitrarily divided into the central field of vision and the peripheral field. The macula is responsible for the central field. A physiologic blind spot is found about 10 to 15 degrees temporal to central fixation (the fovea) and represents the area of the visual field that corresponds to the optic nerve head (optic disc). Precise measurement of the visual field of each eye can be obtained in a cooperative child or adult, using a Goldmann visual field perimeter or an automated visual field device. This test requires steady fixation and concentration. In young children, it is impractical to attempt this tedious measurement. In a patient unable to cooperate for a formal visual field test, the fields are assessed by observation of the child’s eyes fixating on small targets brought into the peripheral field of vision in each quadrant of the visual field. Visual fields may also be assessed by a confrontation method, in which the child fixates on the examiner’s nose and is asked to identify the examiner’s fingers as they are slowly brought into each quadrant of the visual field from the periphery.



Evaluation of Vision


Selection of a test to measure a patient’s visual acuity depends on the patient’s age, cooperation, and level of development. The evaluation of vision in a young infant or nonverbal patient requires the use of the fixation reflex. This reflex develops during the first month or two of life. Although almost all 2- to 3-month-old infants can fixate and follow a face or bright object quite well into all fields of gaze, it is not necessarily abnormal for this milestone not to be present until 6 months of age. The level of vision can be estimated by the quality and intensity of the fixation response. If the visual acuity is normal, central fixation is steady and maintained on objects. If visual acuity is profoundly decreased, the quality of fixation may be wandering in nature, poorly maintained, or eccentric. Central, steady, maintained fixation equates to visual acuity of 20/200 or better. Eyes with unsteady or wandering fixation usually have visual acuity decreased to the 20/800 range (Fig. 19-4).



The visual pathways coalesce in the visual cortex. Electrical impulses in the visual cortex produced by light stimulation of the retina can be measured by placement of sensitive electrodes on the overlying scalp. This is termed the visual evoked potential or response (VEP or VER). The pattern visual evoked potential uses an alternating checkerboard stimulus, which can be controlled to produce a pattern of checks that may be increased or decreased in size. This test can be used to estimate visual acuity in preverbal or nonverbal children. Caution must be used in interpreting this test, however, because children and adults with known 20/20 vision can voluntarily suppress the visual evoked response. In addition, children who have significant decreases in their visual acuity may have a visual evoked response that overestimates the visual acuity.


Nonverbal infants or children may have their grating visual acuity measured with Teller Acuity Cards (Stereo Optical, Chicago, Ill.). This test is based on a child’s reflex to move the eyes or head toward a pattern of alternating black-and-white stripes of increasing frequency rather than neutral gray of the same brightness.


The Allen object recognition cards, simple pictures of common objects, are useful for assessing visual acuity in a 2- to image-year-old child who cannot comprehend the illiterate or tumbling E game or recognize Snellen letters. To perform this test, the child is taught what the pictures are, and then one eye is occluded and picture cards are individually presented at increasing distances until the patient recognizes the cards at 20 feet or fails to recognize the cards (Fig. 19-5). Recognition of the cards at a distance of 20 feet equates to a visual acuity of 20/30. The farthest distance at which the cards can be recognized is noted, and the visual acuity is quantitated as that distance over the denominator of 30 (e.g., 5/30, 15/30, 20/30). This is a measurement of recognition visual acuity. Although use of isolated targets is not ideal for detection of amblyopia, the test can be quickly and easily taught to apprehensive or shy young children and comparison of vision between the eyes detects most cases of amblyopia and other defects in visual acuity.



The LEA symbols are another set of object recognition visual acuity cards. These have the advantage of having five symbols on each card, and the child identifies the symbol in the middle of the card. Presentation of several letters at a time is a more accurate measurement of visual acuity, due to a phenomenon termed crowding. Amblyopic eyes recognize letters or symbols better if they are presented in isolation or one at a time rather than if four or more are presented together on lines above and below one another. The difference may be as much as one or two lines of visual acuity (e.g., 20/30 isolated symbol visual acuity reducing to 20/40 or 20/50 when measured with a Snellen letter chart). Many different visual acuity tests are calibrated using different letters and symbols or groups of symbols.


The Sheridan-Gardiner or HOTV visual acuity tests are easy to administer and more accurately measure visual acuity in 4- to 6-year-old children who are beginning to read letters. In the HOTV test the letters H, O, T, and V are individually presented on cards, and the child matches the letter with a corresponding letter on a card that is held on the lap (Fig. 19-6).



Another commonly used test to measure the visual acuity of image-year-old children is the “E game.” The child is presented with the letter E in decreasing sizes and rotated in an up, down, right, or left orientation, and the child indicates the direction of the crossbars of the E by pointing.


The gold standard for measurement of visual acuity is the presentation of a full line of letter optotypes. This presentation is best achieved with a wall chart or by projection of the letters onto a standardized reflective surface.


Discussion of visual acuity measurements should include whether the visual acuity has been measured without correction of refractive errors or whether any refractive error present has been corrected with glasses or contact lenses (best corrected visual acuity). To differentiate an organic problem of the visual system from simple refractive error, the best corrected visual acuity provides the most useful information. If correction of the patient’s refractive error with glasses is not available an approximation of corrected visual acuity may be made by having the patient look through a pinhole. The pinhole prevents indirect rays of light, which need to be refracted by the optics of the eye, from entering the eye, so that the effects of refractive errors in the eye are minimized. Patients demonstrate the pinhole effect when they squint in order to see better. If the patient’s visual acuity improves when looking through the pinhole a refractive error is present. If it does not improve then another cause for the decrease in vision is likely.


Normal values for best corrected visual acuity depend on the patient’s age. A child at 6 months of age should have a visual acuity of 20/60 to 20/100. A child who is 3 years old can be expected to have an acuity in the range of 20/25 or 20/30, using the E game or a recognition target test. With further maturation, a 5- to 7-year-old child should have visual acuity of 20/20 to 20/25 as tested with a full-line presentation of Snellen letters. If the best corrected visual acuity is less than 20/20 in a child older than 8 years of age, investigation for the cause of the decrease in visual acuity should be made.


It is recommended that vision screening be conducted as part of well-child care at regularly scheduled intervals in the pediatrician’s or family practitioner’s office. In infancy the fixation and following response of each eye to a fixation target should be recorded. Beginning at age 3, quantitation of visual acuity using Allen cards, the E game, an HOTV chart, or other preliterate vision test should be completed. Later, a Snellen or letter chart visual acuity test should be performed by the office staff or physician, and the results should be recorded as part of the patient’s medical record. Most importantly, the visual acuity should be equal in both eyes. Further evaluation of a young child is prompted if the patient is cooperating well and the visual acuity is less than 20/40 with letters, or less than 15/30 measured with Allen visual acuity cards, in either or both eyes.


Some state laws require that vision screenings be performed in school at 1- to 2-year intervals. In a child 6 years of age or more, referral to an ophthalmologist is indicated if the vision is less than 20/30 in either eye. If appropriate vision screenings are passed in the primary care physician’s office, school, or preschool, and there is no family history of hereditary eye disease or other suspicion or risk factor for eye disease present, comprehensive examination of the child’s eyes by an optometrist or ophthalmologist is not necessary.



Refractive Errors


Decreased visual acuity is most commonly the result of a refractive error in the eye. This may be due to variation in the curvature of the cornea or lens or variation in the axial length of the eye. Determination of the refractive state of the eye is part of a comprehensive ophthalmic evaluation. In children, an objective measurement of the refractive error is best obtained by using eyedrops that temporarily inhibit accommodation (cycloplegia) and cause pupillary dilation (mydriasis). Cycloplegic–mydriatic agents such as cyclopentolate or tropicamide are instilled, and 30 minutes later accommodation is temporarily paralyzed and the pupil is dilated. A retinoscope is used to project a beam of light into the eye and illuminate the retina. The light is then reflected back to the examiner through the patient’s pupil and optical system. The focus of the reflected light is neutralized by placement of appropriate lenses in front of the eye, and the refractive error of the eye is accurately and objectively measured (Fig. 19-7).



Low levels of hyperopia (farsightedness) in the range of +1.50 to +2.00 diopters are normal during childhood and are easily compensated for by the focusing mechanism of the lens (accommodation), so glasses are not necessary. The amount of hyperopia normally increases until 5 years of age and then decreases. Under normal circumstances, emmetropia, or no refractive error, is achieved around adolescence. If excessive axial growth, that is, elongation, of the eye occurs, myopia (nearsightedness) develops. A patient’s refractive error is for the most part genetically predetermined. The effect that environment has on refractive error is not completely understood.


The optical image formed by a hyperopic eye is in focus behind the retina (Fig. 19-8, C). By changing the shape of the lens with accommodation, the image can be brought into focus on the retina and glasses may not be required. If a large amount of hyperopia is present (+4.00 diopters or more), fatigue; headaches; asthenopia; and blurring of vision, especially at near, may occur. Hyperopia greater than +5.00 or +6.00 diopters may cause ametropic amblyopia. When this occurs, glasses are prescribed to correct the child’s refractive error so that focused images stimulate the development of normal vision. If large hyperopic refractive errors are not treated by 6 to 8 years of age, the resultant amblyopia may be irreversible. The optic discs in eyes with large degrees of hyperopia may have an appearance simulating papilledema (pseudopapilledema) (Fig. 19-9).




Myopia is most commonly caused by an increase in axial length of the eye with respect to the optical power of the eye (see Fig. 19-8, B). Children who are myopic can see near objects clearly; objects at distance are blurred and cannot be brought into focus without the aid of glasses or a contact lens. Wearing glasses for myopia does not change the growth of the eye and, contrary to popular belief, does not promote the resolution or progression of the myopia. Bifocals and cycloplegics may have a small effect on slowing the progression of myopia, but no treatment is currently available to reverse or stop the progression of myopia.


Myopia may be present at birth but usually develops with growth spurts that occur between 8 and 10 years of age. The amount of myopia present usually increases until growth is completed after adolescence.


High degrees of myopia ranging from −8.00 to −20.00 diopters may be associated with systemic conditions such as Stickler and Ehlers-Danlos syndromes, which are associated with connective tissue defects and increased axial length of the eye. Myopia is inherited as a multifactorial trait. High myopia with extreme lengthening of the globe may be associated with retinal thinning, peripapillary pigment crescents, staphylomas (a focal area of bulging of the posterior globe wall), and decreased macular function with poor visual acuity. The optic nerve may appear to enter the eye at an angle (Fig. 19-10). High myopia has an increased incidence of retinal detachment, especially after direct trauma to the eye or concussive head trauma.



In astigmatism the refractive power of the eye is different in different meridians (see Fig. 19-8, D). This produces a blurred retinal image for objects at both distance and near. Astigmatism occurs when the cornea, lens, or retinal surface has a toric shape rather than a spherical one. This may be likened to the two different radii of curvature that give a football its characteristic shape. Bulky masses in the lids such as chalazions or hemangiomas may compress the cornea and induce astigmatic refractive errors.


Anisometropia refers to the condition in which one eye has a different refractive error than the other. Usually the eye with the least amount of hyperopia or refractive error is the dominant or preferred eye. The fellow eye may be suppressed and develop amblyopia because the development of the visual system is being stimulated by a sharp focused image from one eye and a less focused image from the other eye. The magnitude of the amblyopia depends on the magnitude of the anisometropia and the age at which it developed. Anisometropia may occur with hyperopia, myopia, astigmatism, or a combination of these refractive errors. If the degree of anisometropia is large, the optical properties of the required correcting lenses produce a difference in image size between the two eyes, aniseikonia, which may be difficult for the patient to tolerate.



Strabismus


Misalignment of the visual axes is referred to as strabismus. Strabismus occurs in 1% to 4% of the population and may be congenital or acquired. It may occur on a hereditary basis, most commonly without a clearly defined inheritance pattern. In the majority of childhood strabismus the misalignment of the eyes is not caused by a specific cranial nerve or extraocular muscle dysfunction. In some cases, strabismus may be caused by cranial nerve paralysis or neuromuscular disorders (myasthenia gravis).


Voluntary and reflex movement of the eyes is mediated via the extraocular muscles. These muscles are coordinated in their saccadic and pursuit movements by centers in the frontal and occipital areas of the cerebral cortex with modification by the cerebellum. Saccades are voluntary movements used to move the eyes to the object of regard. These are rapid eye movements. Pursuit or following movements are used to track or follow moving objects. These are slow eye movements.


The third, fourth, and sixth cranial nerve nuclei, located in the brainstem, are the centers responsible for innervating the extraocular muscles. In addition to innervation of the inferior oblique, medial, inferior, and superior recti, the third cranial nerve is responsible for innervation of the levator muscle, pupillary constriction, and accommodation of the lens. The fourth cranial nerve provides innervation to the superior oblique muscle, and the sixth cranial nerve supplies the lateral rectus muscle (Fig. 19-11). When one or more of the cranial nerves are paretic, the action of the innervated muscle is decreased, leading to a deficit in the duction or movement of the eye into the field of action of the muscle. The muscle having a function of movement in the opposite direction is no longer balanced, producing strabismus.



An abnormal head posture may be a sign of strabismus in patients with cranial nerve dysfunction or nystagmus. These postures are observed in children who have good binocular function. Head postures are used to compensate for double vision caused by horizontal, vertical, or cyclovertical muscle palsies. For example, in a patient with a right sixth nerve palsy the abduction of the right eye is deficient. The adducting force of the medial rectus is not balanced, and the eye is in a relatively adducted or esotropic position. The patient then manifests a head turn to the right to allow the right eye to be in a position where less abducting force is required, allowing both eyes to fixate together. In a patient with nystagmus, a head posture may be used to place the eyes at the null point, or direction of gaze where the amplitude of nystagmus is the least. In cases of torticollis, if the head posture is present while the patient is sleeping, the cause of the head posture is unlikely to be ophthalmologic in nature. Conversely, if a patient’s head posture goes away when either eye is occluded, it suggests that the cause of the head tilt or turn may be related to a problem of ocular alignment or strabismus. Head turns may sometimes be seen when the vision in one eye is much worse than the other.




Phorias and Tropias


If strabismus is present, it may be manifest (i.e., a tropia) or held latent by sensory fusion (i.e., a phoria). When the fusion of a patient with a phoria is interrupted by placing an occluder in front of one eye, the eye seeks its position of rest and deviates so that the visual axes of the two eyes are no longer both aligned on the point of fixation. When the eye is uncovered and binocular vision is re-established, the fusion response assists in the realignment of the eyes on the object of regard. A phoria may produce symptoms of fatigue, blurring, or movement of objects. When a phoria breaks down into an intermittent tropia, there may be a symptom of intermittent double vision or diplopia. Phorias, especially if large, may become symptomatic at times of fatigue, stress, or illness.


A tropia is a constant or intermittently present ocular deviation. The fusion mechanism is unable to maintain alignment of the eyes on an object of fixation. Young children with tropias develop suppression of the tropic eye as a natural response to avoid diplopia. Older children or adults who acquire a tropia (e.g., from an acquired cranial nerve palsy) have diplopia as a symptom of the misalignment of their visual axes. The deviation present in a tropia may occur in one or all positions of gaze, depending on the cause of the tropia.


Phorias and tropias are classified according to the pattern of the eye deviation. The prefixes eso– and exo– classify horizontal strabismus. Hyper– and hypo– are used for vertical deviations, and incyclo– and excyclo– for torsional deviations.



Esodeviations


An esodeviation is a convergent deviation of the eyes. The deviation may be latent, a phoria (esophoria), or it may occur as a manifest deviation, a tropia (esotropia). Common esodeviations seen in children are infantile esotropia, accommodative esotropia, esotropia resulting from sixth cranial nerve palsy, and Duane syndrome.



Infantile Esotropia


The most common cause for an esodeviation presenting in infancy is infantile, or congenital, esotropia (Fig. 19-12). In this condition the esotropia is seen at birth or very early in infancy. On occasion a family history of infantile esotropia exists. The angle of esodeviation is large and constant. Abduction may be deficient due to contraction of the medial rectus muscles, and differentiation from sixth nerve palsy may be difficult. Cross-fixation is usually present, with the adducted right eye used for vision to the left and the adducted left eye used for vision to the right. Abduction of an eye is checked by occluding the contralateral eye and quickly encouraging fixation movements while holding the head. Doll’s head maneuvers may also be used to test abduction of the eyes. Children with this condition usually do not develop much amblyopia and maintain good visual acuity in both eyes whether they are treated or not. There are no associated neurologic or systemic abnormalities.



The esodeviation present in infantile esotropia requires surgical correction. After correction, the ocular alignment is frequently unstable, with further surgery commonly required later in life no matter how early surgery is performed or how well aligned the eyes are after surgery. Inferior oblique overaction and dissociated vertical deviations frequently develop later in childhood or adolescence. Inferior oblique overaction is seen as an elevation of one or both eyes in adduction. Dissociated vertical deviation (DVD) (Fig. 19-13) is an upward and outward “floating” movement of one or both eyes that becomes more prominent with fatigue or inattention. A DVD may be elicited on examination by covering one eye and watching its position as the eye is covered. These patients do not experience diplopia. Patients with infantile esotropia also commonly develop accommodative esotropia, with a need for glasses later in childhood. While excellent visual acuity and alignment of the eyes are most commonly achieved with treatment, the development of high levels of binocular function (stereopsis) is usually not obtained.




Accommodative Esotropia


Accommodative esotropia most commonly presents as an acquired strabismus at image to 5 years of age. Family histories of hypertropia, anisometropia, esotropia, and amblyopia are very common. The presence of uncorrected hyperopia causes the patient to accommodate or focus to obtain clear visual acuity. With accommodation, the synkinetic near response, which includes miosis, accommodation, and convergence of the eyes, occurs. If the fusion mechanism is unable to diverge the eyes to compensate for the excessive convergence accompanying the need to accommodate to correct for the patient’s hyperopia, esotropia results.


If an esodeviation is associated with a modest degree of farsightedness, treatment of the hyperopia optically with glasses is indicated. In patients with purely accommodative esotropia, this measure alone may completely correct the deviation (Fig. 19-14). Frequently, especially if the esodeviation has been left untreated for a long period of time, a residual esodeviation will remain. This is a partially accommodative esotropia. Surgical correction may be recommended for these patients. Some patients have straight eyes for some time with their glasses in place and decompensate to partially accommodative or nonaccommodative esodeviations later.



In patients with accommodative esotropia, the eyes are straight with their glasses on and esotropic when they are removed. Frequently, if the patient is only moderately hyperopic in the preferred fixating eye, the patient will say that he or she can see just as well or perhaps better without their glasses. The glasses are not prescribed necessarily to improve visual acuity; rather, the glasses are intended to decrease the accommodative effort and to decrease the esotropia.


In another form of accommodative esotropia, the ratio between accommodative convergence and accommodation (AC/A ratio) may be abnormally high, producing excessive convergence when focusing on near objects. In high AC/A ratio accommodative esotropia, the esodeviation with near vision is greater in magnitude than it is with distance vision (Fig. 19-15). These patients may be treated with a bifocal, which gives them additional hyperopic correction for near, decreasing their accommodative effort at near and decreasing the near esodeviation.




Nonaccommodative Esotropia


Children may develop an esodeviation that is present without any relationship to the patient’s refractive error (Fig. 19-16). Correction of the hyperopia with glasses does not improve the esotropia in these patients. These nonaccommodative esodeviations may be associated with poor vision, trauma, prematurity, aphakia, or high myopia. Nonaccommodative esotropia may also develop when accommodative esotropias are left untreated.




Other Causes of Esotropia


Unilateral or bilateral sixth cranial nerve palsy causes deficient abduction and an esodeviation. In sixth nerve palsy the esotropia increases with gaze directed toward the side of the palsy (gaze incomitance). Other signs of the nerve paralysis that may be more difficult to detect include the extent and speed of abduction of the eye. Patients may display a head turn toward the side of the palsy to hold the involved eye in adduction and maintain binocular vision. Sixth cranial nerve palsies in children may be associated with increased intracranial pressure, trauma, tumor, or antecedent viral illness. In benign or “postviral” and traumatic cases the lateral rectus function may return gradually and fully over a 6-month period. In idiopathic cases, if improvement does not occur, if the deviation increases, or if a gaze palsy develops, suspicion should be raised that a tumor, most commonly pontine glioma, may be the cause for the sixth nerve paralysis.


Duane syndrome is a congenital unilateral or bilateral defect characterized by inability to abduct an eye. This may be accompanied by an up or down shoot of the eye and narrowing of the lid fissure on attempted adduction. In attempted abduction the palpebral fissure widens. Duane syndrome is caused by a malformation of the cranial nerve nuclei producing co-innervation of the medial and lateral rectus muscles. The lateral rectus muscle does not contract with abduction and paradoxically co-contracts along with the medial rectus on adduction. The co-contraction with adduction causes a retraction of the globe and the lid fissure narrowing. Patients with Duane syndrome may be esotropic and have a head turn toward the involved side analogous to those seen with a sixth cranial nerve palsy. The changes in lid position and vertical deviations help to differentiate the two conditions (Fig. 19-17).





Exodeviations


When the visual axes are divergent, an exodeviation is present (Fig. 19-20). Many children with exodeviations have family histories of strabismus. Exodeviations may also occur with vision loss in one eye (sensory exotropia) and cranial nerve paralysis (third nerve palsy). An exodeviation may be controlled by fusion (exophoria), be manifest intermittently (intermittent exotropia), or be constant (exotropia).



Intermittent exodeviations become manifest with fatigue, daydreaming, or illness. Patients with exodeviations frequently squint one eye in bright light, but they typically do not experience diplopia. They may complain of images jumping as they switch fixation or of discomfort at night or when tired. Patients with intermittent exotropia usually do not have amblyopia, or it may only be mild. One third of cases improve spontaneously. Treatment of intermittent exotropia consists of glasses to correct refractive errors, patching, and surgery.


If there is poor vision in one eye, the decreased visual stimulation may produce a sensory deviation. Generally speaking, if the onset of decreased vision occurs after the age of 4 years, an exodeviation will occur; however, if sensory input to the eye is decreased before the age of 2 years, an esodeviation usually occurs. Because young children do not complain of monocular vision loss, especially if congenital or with onset during infancy, sensory strabismus is frequently the presenting sign of vision-limiting pathology of the retina or optic nerve.


Exodeviations may be simulated in patients with widely spaced eyes (hypertelorism) or in those whose maculae are temporally displaced, as may occur in retinopathy of prematurity. When the macula is displaced temporally, the eye rotates outward to align its visual axis on the fixation target. The term positive angle kappa is used to describe this condition (Fig. 19-21).






Vertical Deviations


Isolated vertical misalignment of the eyes is uncommon. Vertical deviations may occur in only one field of gaze, or they may be comitant and equal in all fields of gaze. Vertical deviations may have a cyclotorsional component and be associated with a head tilt or head posture to eliminate double vision. All patients with torticollis should be evaluated for cyclovertical muscle palsies.


The most common cyclovertical deviation is due to a palsy of the fourth cranial (trochlear) nerve (Fig. 19-24). Fourth nerve palsies in children occur congenitally or secondary to head trauma. The eye is excyclorotated, and the head is tilted to the shoulder opposite the side of the paretic nerve and superior oblique muscle. Other features are elevation of the eye and difficulty depressing the eye in adduction (Fig. 19-25). Patients with fourth nerve palsies have diplopia in the contralateral field of gaze, especially up and away from the paretic side. Patients with congenital palsies may not always recognize this diplopia. Some facial asymmetry, especially of the cheek and jaw line, is usually seen in congenital cases as the children age. Examination of candid photos will typically display head postures that usually are not noticed by family members.




Brown syndrome describes an isolated motility disorder in which there is an inability to elevate the eye when it is adducted (Fig. 19-26). This may be caused by a congenital anomaly of the superior oblique tendon, or it may be acquired as an idiopathic inflammation or tenosynovitis of the superior oblique tendon. Acquired cases may be persistent, resolve spontaneously (sometimes over many years), or respond to nonsteroidal antiinflammatory drugs.



Abnormalities of extraocular muscle innervation rarely cause vertical deviations. Double elevator palsy is an inherited unilateral or bilateral condition in which there is hypotropia and limitation of elevation of the involved eye. To achieve binocularity, patients tilt their chins up and position their heads back. Ptosis is frequently present.


Additional causes of vertical deviations include myasthenia gravis, thyroid ophthalmopathy, chronic progressive external ophthalmoplegia, orbital fractures with muscle entrapment (most commonly the inferior rectus entrapped within a blowout fracture of the orbital floor), and orbital disease with intraorbital masses.



Tests for Strabismus


Although gross observation may detect the majority of cases of strabismus, pseudostrabismus will lead frequently to unnecessary referrals. More significantly, smaller angle deviations may be missed, leading to delays in treatment if further tests for strabismus are not employed by the primary care physician.


The type and degree of ocular misalignment may be estimated using the corneal light reflex test, or Hirschberg method. The patient fixates on a penlight held at 1 m. Using the pupil edge as a point of reference, the light reflections between the two eyes are compared for symmetry; if the light reflex is displaced temporally in one eye compared with the reflex seen in the other eye, an esotropia is present. If the light reflex is displaced nasally in comparison with the other eye, an exodeviation is present (Fig. 19-27). Although observation of the corneal light reflexes is more sensitive and specific than gross observation alone, a more accurate method of detecting misalignment of the eyes is cover and uncover testing.



The cover test requires vision in each eye and use of a target that stimulates accommodation. Cover testing is performed while the patient maintains fixation on targets at 6 m and at 1 m because some types of strabismus produce misalignment of the eyes that is present only at either distance or near. The cover–uncover test is used to detect phorias. This test is performed by placing a cover over one eye to disrupt fusion or binocularity. As the cover is removed, the previously covered eye is observed. If the eye does not move, both eyes are aligned on the object at that distance; orthophoria is present. If the eye deviates while covered and then moves to regain fusion and assumes fixation as the cover is removed, a phoria exists. The test is then repeated, covering and uncovering the other eye (Fig. 19-28).



The second component of the cover test is performed by covering one eye and observing the movement of the other eye. If neither eye moves as the eyes are alternately covered, the eyes are both aligned on the fixation target and the term orthophoria is used. No deviation is present in this case. If a tropia and a fixation preference are present, a fixation movement of the deviating uncovered eye occurs when the preferred fixating eye is covered; when the cover is transferred back, the previously deviating eye again deviates behind the cover (Fig. 19-29). If a deviation is well controlled by fusion (a phoria) and is small in size, it may be safely observed if there are no symptoms and the fundus is normal. When a tropia is present, either constantly or intermittently, after 3 months of age, the patient should be referred to an ophthalmologist. Ophthalmologists use prisms along with cover testing to measure the size of strabismic deviations.




Amblyopia


Amblyopia is present when there is a decrease in vision in one or both eyes and all potential organic causes (refractive errors, media opacities, structural abnormalities) for the decrease in vision have been corrected or excluded. Amblyopia may be caused by the absence of stimulation of the immature visual system by a focused retinal image or by strabismus and the resultant suppression of one eye. Visual deprivation amblyopia may be caused by a corneal opacity, a dense cataract, vitreous opacity (hemorrhage or inflammation), or high refractive error (Fig. 19-30).



In anisometropic amblyopia an image is clearly focused on the fovea of one eye, but in the other eye the image is out of focus. The blurred retinal image is suppressed by the child’s immature visual system, and that eye is affected by amblyopia. In anisometropic amblyopia, most commonly one eye is more hyperopic than the other. Because both eyes must accommodate the same amount, the less hyperopic eye is preferred and the more hyperopic eye has the blurred image and develops the amblyopia. With high hyperopia or astigmatism affecting both eyes, bilateral ametropic amblyopia may occur if the child does not or cannot accommodate to produce a focused retinal image to stimulate the visual system with either eye. These patients have decreased vision in both eyes. In children with strabismus, the image from the deviating eye is suppressed by the brain as an adaptation to avoid diplopia and the deviating eye develops strabismic amblyopia. Patients often have both strabismus and anisometropia simultaneously as causes for their amblyopia.


The severity of the visual loss produced by amblyopia is determined by the nature of the visual deprivation; the age at onset; and its consistency, severity, and duration. Amblyopia is treated by removing the cause of the amblyopia, if possible, and by forcing use of the affected eye to stimulate the development of the vision from that eye. In bilateral ametropic amblyopia, the appropriate glasses are given as treatment. In strabismic or anisometropic amblyopia, appropriate glasses are given, and the preferred, nonamblyopic eye is penalized to force the use of the amblyopic eye. An occlusion patch placed over the preferred fixating eye is commonly used as treatment.


Other methods of treatment are optical via the eyeglass prescription and pharmacologic, with atropine drops placed in the nonamblyopic eye to prevent accommodation in that eye. This forces the use of the amblyopic eye for reading and near vision.


Amblyopia responds most rapidly and completely to treatment begun early in life. The visual system has developmental phases and if certain levels of visual acuity are not reached early in life the amblyopia present is unlikely to respond completely to treatment. Treatment is more difficult and less effective after 8 years of age but remains possible in older children, especially if they have no history of previous treatment.



Diseases of the Eyes and Surrounding Structures



Eyelids and Adnexa—Anatomy of the Eyelid


The eyelid is composed of skin and its related appendages, glands that contribute to the tear film, and muscular structures permitting the eyelid to open and close (Fig. 19-31). Conditions affecting the eyelid are related to these anatomic structures.



Telecanthus refers to an increase in the distance between the inner canthus of each eye (Fig. 19-32). Telecanthus can be due to the hereditary transmission of facial features or midline embryonic defects, or it can be related to a syndrome such as blepharophimosis, or Komoto syndrome (Fig. 19-33). This inherited syndrome consists of telecanthus, epicanthus inversus (a skinfold projecting over the inner angle of the eye and covering part of the canthus, arising from the lower lid skin), blepharophimosis (horizontal shortening of the lid fissure), and ptosis. Hypertelorism refers to an increase in the distance between the nasal walls of the orbits. This is usually associated with telecanthus.




Blepharoptosis, or ptosis, is a unilateral or bilateral decrease in the vertical distance between the upper and lower eyelids (palpebral fissure) because of dysfunction of the levator muscle (Fig. 19-34). Congenital blepharoptosis is frequently transmitted as an autosomal dominant trait with variable penetrance. Congenital ptosis may be either unilateral or bilateral. Other causes for blepharoptosis include ocular inflammation, chronic irritation of the anterior segment of the eye, chronic use of topical steroid eye drops, third nerve palsy, and trauma. Ptosis may be severe enough to cause visual deprivation and amblyopia if the visual axis is occluded. Children with even mild degrees of congenital ptosis should be referred for evaluation because they have a higher than normal incidence of strabismus and anisometropic amblyopia than the general population. In congenital ptosis the eyelid position may improve somewhat from that observed early in infancy, but after that it tends to remain stable or worsen only slightly over time.



The Marcus Gunn, or jaw-winking, phenomenon is caused by a misdirection of the motor division of the fifth cranial nerve to the ipsilateral levator muscle of the eyelid (Fig. 19-35). With jaw movement to the ipsilateral side the eyelid droops, and when the jaw is moved to the contralateral side, the eyelid elevates. The eyelid winks with chewing or feeding. This is a benign phenomenon and no further neurologic or systemic evaluation is required. Surgical treatment is not indicated unless the associated ptosis warrants it. Most patients learn to control the winking by avoiding the inciting jaw movement.



Trichiasis is the term used to describe misdirected eyelashes that irritate the cornea or conjunctiva. It can be caused by chronic inflammation of the eyelids, entropion (inturning of the eyelid), eyelid trauma, or inflammatory conditions with scarring of the conjunctiva such as Stevens-Johnson syndrome.


Districhiasis describes a condition in which there is an accessory row of eyelashes (cilia) along the posterior border of the eyelid (Fig. 19-36). Eyelid eversion or ectropion frequently coexists because of defects in the tarsal plate. This condition is inherited as an autosomal dominant condition, but it may also be a sequela of severe ocular inflammation.



Entropion is an inverted eyelid with the lashes rubbing against the conjunctiva or cornea. This may be present at birth or occur with severe blepharospasm, inflammation, or trauma. If severe, abrasion of the cornea by the lashes can cause permanent corneal scarring (Fig. 19-37).



In epiblepharon a skinfold extends over the lid margin and presses the lashes against the globe. It is commonly observed during the first year of life (Fig. 19-38). The lower lid is more commonly affected in the white population, and both the upper and lower lids may be affected in Asian infants. This defect usually corrects itself spontaneously by 1 year of age. In Asians the problem may be persistent. Corneal abrasion usually does not occur because of the soft texture of the infant’s eyelashes or when it is the shaft of the eyelash rather than the tip of the lash that touches the cornea. However, surgical correction may be required if it is persistent and causing corneal abrasion; conjunctival injection, epiphora, and photosensitivity are symptoms in more significant cases.



Ectropion is an outward rotation of the eyelid margin. If severe, ectropion can lead to problems of corneal exposure. Ectropion may be congenital or caused by any condition (trauma, scleroderma), causing the eyelid skin to contract and evert the eyelid (Fig. 19-39). Ectropion may occur after seventh cranial nerve palsy with paralysis of the facial musculature.



Congenital eyelid colobomas are defects or notches in the eyelid margin caused by failed fusion of embryonic fissures early in development. These may be isolated defects or associated with conditions such as Goldenhar syndrome (Fig. 19-40). Goldenhar syndrome consists of eyelid colobomas, corneal–limbal dermoids, vertebral anomalies, and preauricular skin tags.



Ankyloblepharon is a fusion of the upper and lower eyelid margins. This may range from a few thin strands of tissue to complete fusion of the lids. The majority of cases are mild, isolated anomalies and no further evaluation is required. Treatment is by separating the lids, by simple eyelid opening if only threadlike strands are present, or with scissors if necessary.


Children may frequently have a low-grade inflammation of the eyelid margin, chronic blepharitis, caused by Staphylococcus infection of the oil glands of the lid margin. Blepharitis may be associated with seborrhea or allergies and occurs commonly in children with Down syndrome. Symptoms include crusting of the lashes, itching, light sensitivity, and irritation of the lids. The lashes may be matted and adherent in the morning. If the condition is chronic and severe, thickening of the eyelid and misdirection of the eyelashes to such a point that they may invert and irritate the cornea or conjunctiva may occur (Fig. 19-41). Complications include ulceration of the lid margin, abscess or hordeolum formation, chronic conjunctivitis, and keratitis (corneal irritation and inflammation).



A hordeolum is an inflamed gland of Zeis at the base of the cilia (Fig. 19-42). This produces painful swelling and erythema of the eyelid. These lesions are commonly called styes. Infection, frequently with Staphylococcus, may occur. Some discharge may be seen. Rarely, preseptal cellulitis may occur as a complication.


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Jul 11, 2016 | Posted by in PEDIATRICS | Comments Off on Ophthalmology
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