Examining the Visual System

chapter 8 Examining the Visual System





Because vision provides almost 80% of the sensory input during the first years of life, a faulty visual system can have a major effect on a youngster’s intellectual and physical development. In addition to conditions primarily affecting the eyes or parts of the visual system, many systemic diseases can manifest as ocular signs and visual symptoms, providing important clues to a timely diagnosis.


Performance of a reliable visual assessment does not require expensive equipment or prolonged practice. The first part of this chapter describes the normal visual system in infants and children and provides a glossary of terms used to describe the ophthalmologic findings and conditions that are commonly encountered; the second part describes examination techniques. Finally, some key questions required to evaluate particular ophthalmologic problems are described, along with the role of sequential diagnostic logic in elucidating etiologies.



Normal Visual System in Infants and Children


Although the gross anatomy of the eye is similar at all ages, important differences exist between the eye of a young child and an adult. For example, the volumetric relationship between the eye and the orbit is dramatically different in children.



In infants, the choroid gives a blue hue to the overlying thin sclera. In white persons, the iris is often poorly pigmented at birth, and the final eye color may not be established until at least 8 months of age. Examination by direct ophthalmoscopy shows the baby’s fundus to be pale, with the macula barely visible. As the child gets older, the fundus becomes darker, and the macula becomes darker than the surrounding retina. The macula then displays the easily recognized oval, bright reflection of the ophthalmoscope light, known as the macular umbo (Plate 8–1).


The birth process can be somewhat traumatic to the eyes. Many newborns sustain episcleral and retinal hemorrhages during vaginal delivery (see Fig. 4-14). These hemorrhages can be alarming to both parents and physicians but are harmless and usually disappear within 2 weeks. At birth, the nasolacrimal duct often is blocked at its junction with the nasal mucosa under the inferior turbinate. The blockage resolves spontaneously in more than 90% of cases, although it can remain until 1 year of age in some children, causing persistent tearing. A few affected children then need surgical treatment.


The process and rate of development of vision in infants are better understood than they were 10 years ago. Vision exists in several forms with different neuronal channels carrying specific visual functions, such as contrast sensitivity, orientation, movement, and hyperacuity. Each function develops at a different rate. For practical purposes, normal newborns can see a human face easily and demonstrate their visual ability by looking at it; they even follow the face with eye or head movement as it passes slowly before them at close range (Fig. 8-1). A baby’s ability to follow your face can be verified only when the baby is awake and alert, often just before or in the middle of a feeding session. This innate ability is paramount to the infant’s future development because few parents fail to form an emotional attachment to a little one who looks directly at them minutes after birth. By contrast, parents of a blind or strabismic infant who are unable to establish the interaction that comes with normal eye contact may have significantly greater difficulty developing the same level of emotional attachment to their offspring.



By 3 months of age, babies enjoy looking at the human mouth and eyes and at simple, colored toys. A 1-year-old toddler’s vision is about half as good as the best attainable adult score. Three-year-olds can see at least 6/9 (or 20/30 in the American system) in each eye, and their visual acuity can be tested with charts specially designed for them (see the section in this chapter on the LH test). The numerical ratio 20/30 actually indicates that a 3-year-old can see at 20 feet what the average adult sees at 30 feet.



Color vision is present from an early age. Newborns have color vision, although it is less sensitive than that of older infants. Newborns do not see faint colors well, if at all, but by 3 months of age, definite trichromatism is established. Babies of this age can differentiate between red, green, and yellow.


Binocularity, which confers the ability to see in three dimensions, has been proven to exist by 3 months of age, coinciding with the time the eyes finally maintain good alignment. This finding underlines the clinical significance of any persistent deviation of the eyes after age 3 months.


Eye movements may appear irregular, unbalanced, or disconjugate until the third month of life. Healthy newborns can display tonic movements of the eyes downward or upward. Sometimes, the eyes turn toward (esotropia) or away (exotropia) from each other.



Pupillary movements are limited in the newborn and are almost impossible to examine thoroughly at that age. A good pupillary examination in older children demands cooperation and patience, because children can rarely stare fixedly at a distant target while an observer tries to evaluate their pupils by shining a bright light in them. The children look either at the light or anywhere else and change their accommodation continuously, keeping their pupillary diameter in constant flux and possibly preventing adequate assessment of light-induced responses.


Accommodation in the newborn is limited. From a practical viewpoint, consider the newborn’s focus as stuck at an adult arm’s length. Within a few months after birth, focus improves, and the child’s accommodative amplitude soon reaches remarkable proportions. For example, a 5-year-old can clearly see a plane in the sky and then switch in a fraction of a second to look with great intensity at the details of a tiny spider close at hand. Unfortunately, this marvelous accommodative ability does not last forever.


Finally, a word on media transparency. The extraordinary transparency of all the optical parts of the child’s eye provides the observer with a crisp and bright image of the retina when viewed up close with the direct ophthalmoscope (a difficult but rewarding technique ). It also enables the clinician to critically assess the integrity of the eye with the very simple red pupillary image (reflex) test. In the right conditions, a bright coloration in the pupil provides a clear path for a light beam to enter the eye, hit the retina, and bounce back. This is the reason why photo shots can become prime screening tools to detect severe eye diseases.




Definition of terms


As an aid to diagnosis, this section contains a brief glossary of diagnostic terms that summarize the features to look for in children with eye problems. Box 8-1 and Figure 8-2 show the tools used to examine the eyes; Table 8-1 lists definitions and acronyms.




Table 8-1 Ophthalmologic Shorthand*





































































Abbreviation/Acronym Definition
Alt Alternating strabismus; in almost all cases of strabismus, fixation (use of the eye to look at something) is with at least one eye at a time; if there is equal vision, the eyes will alternate fixation
APD Afferent pupillary defect
CD Corneal diameter
C/D ratio Cup/disc ratio (cup size can be enlarged in persons with glaucoma)
CL Contact lens
Comit Comitant
E Esophoria; the eye turns in only when there is interference with binocular vision (as with covering)
ET Esotropia; one eye is turned in spontaneously
E(T) Intermittent esotropia; the eye turns in only occasionally
IOL Intra-ocular lens
IOP Intra-ocular pressure
OD Oculus dexter (Latin); right eye (English)
OS Oculus sinister (Latin); left eye (English)
OU Oculus uterque (Latin); each eye (English)
PERLA Pupils equally reactive to light and accommodation
SLE Slit-lamp examination
VA cc Visual acuity with correction (with glasses or contact lens[es])
VA sc Visual acuity without correction
X Exophoria
XT Exotropia; one eye turns out (exodeviation)
X(T) Intermittent exotropia; the eye turns out only occasionally

* For example, a diagnosis of strabismus could be written as “Alt Comit X(T),” which would mean “alternating comitant intermittent exotropia.”





Cataracts


Cataracts are an important cause of leukocoria (white pupil, from the Greek; see Plate 8–2). Causes of pediatric cataracts include congenital rubella, metabolic disorders, and chromosomal anomalies. Cataracts can result from ocular inflammation (uveitis) or may accompany other ocular malformations. Many idiopathic cataracts are sporadic, but some are genetic. Some systemically administered medications cause cataracts. Steroids are common culprits, and they can cause glaucoma as well. Amblyopia in a child with a cataract is severe; therefore, cataracts in infants need immediate attention. Postoperative optical correction may require the use of contact lenses in infants, although intraocular lenses are becoming more popular in children older than 2 years.



Coloboma


A defect of closure of the embryonic fissure of the eye; hence, its inferonasal location in the eye. In mild form, only the iris is involved; in more severe cases, the choroid and the optic nerve can be involved (Plate 8–3). With optic nerve involvement, central nervous system (CNS) midline defects should be suspected, as in optic nerve hypoplasia (see definition of this term).








Hemangioma (orbital, capillary)


Benign congenital tumors that grow rapidly when a child is between 1 and 6 months of age but tend to regress spontaneously later (Plate 8–4). Benign congenital tumors may cause severe amblyopia by pupillary obstruction, high astigmatism, or both. Early treatment is essential to preserve vision. Injection of steroids into the tumor, systemic treatment, glasses, and patching of the sound eye all may be necessary.




Hyphema


Bleeding into the eye’s anterior chamber (Plate 8–5). A trauma severe enough to cause a hyphema can involve other eye structures, leading to retinal detachment or injuring the trabecular meshwork of the iridocorneal angle and thereby causing glaucoma. Hyphema is the principal diagnosis in one third of eye traumas and is a major cause of ocular morbidity in children. Hyphemas rebleed in 6% of cases within 5 days of onset, causing further complications, but it may be possible to prevent rebleeding by decreasing physical activity and, in very selected cases, by administering systemic antifibrinolytic agents.





Leukocoria


A white pupil (Plate 8–2). This finding has major clinical implications. The differential diagnosis includes retinoblastoma and cataract. Delaying treatment of the former leads to death; delaying treatment of a cataract causes permanent loss of vision.




Myelinated nerve fiber layer


Abnormal presence of myelin around the superficial nerve fibers of the retina near the optic disc (Plate 8–6). It can be so extensive that the pupillary red reflex can be made to appear white (leukocoria). The vision is generally normal except when the macula is heavily involved.







Periorbital cellulitis


Any inflammation around the orbit is cause for concern, and the differential diagnosis should include rhabdomyosarcoma (see later definition). When the orbital content is involved, ocular motility is decreased and the patient is at imminent risk of loss of vision. Haemophilus influenzae meningitis is an early complication in children younger than 5 years. Periorbital cellulitis (Plate 8–8) is most often associated with ethmoiditis in children who do not have a clear history of skin trauma or infection around the eye, and both computed tomography scanning and magnetic resonance imaging are invaluable for a clear evaluation of the best therapeutic regimen. This condition is far less common in areas of the world where Haemophilus influenzae B vaccine is used. Most cases of periorbital cellulitis require systemic antibiotic therapy.







Retinoblastoma


The most important cause of unilateral or bilateral leukocoria, retinoblastoma occurs in 1 in 15,000 births and often is also present with a strabismus or a red eye (Plate 8–10). The gene for this condition is located on the long arm of chromosome 13. Retinoblastoma is most curable if diagnosed early. Later death from a second malignancy is a major concern in bilateral and autosomal dominant familial cases.




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Jul 3, 2016 | Posted by in PEDIATRICS | Comments Off on Examining the Visual System

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