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

38 Pediatric Ophthalmology for Primary Care

*If patient’s vision does not meet these standards, then an ophthalmology referral is indicated.

blind. Also, use a compelling target. In infants, the human face is probably the most compelling target, while in toddlers and young children, a small toy or a finger puppet is a good target. Observe for central fixation with the presence of accurate smooth pursuit. Central fixation means that the patient looks directly at the target, not off center, and will smoothly and accurately follow the target. If the patient has trouble locking on the target and appears to be looking off center, this indicates poor fixation and poor vision (Figure 3 3).

Verbal Children

By 2½ to 3 years of age, most children should be able to cooperate with opto type visual acuity testing using a picture (E game, Wright figures) or Snel len letters. It is important to test each eye separately and make sure that the occluded eye is truly covered. Many examiners prefer occluding one eye with an adhesive patch, rather than a paddle occluder, to prevent the child from peeking. Most vision charts are calibrated at 10 or 20 feet from the patient. Examine patients with their customary eyeglasses or contact lenses. Not

all child visual acuity figures accurately diagnose amblyopia. Comparison of Wright figures to Allen figures for diagnosing amblyopia showed Allen figures underdiagnose amblyopia and Wright figures accurately diagnose amblyopia in children (Mocan et al).

Figure 3 3.

A child being tested for central fixation right eye. Check for accurate and smooth pursuit eye movements. Does the patient lock on the target? Test each eye individually by covering the opposite eye.

Pinholes

If a patient forgets his or her corrective lenses, you can use a pinhole to esti mate what the patient’s vision would be with correction. First test the vision without correction, then retest using a pinhole. Pinholes are commercially available; however, you can make your own pinhole by taking a 3"× 5" card and placing several small pinholes in the card. If the patient’s visual acuity improves after viewing through the pinhole, this indicates that a refractive error is the cause of the decreased vision. A pinhole will correct virtually any refractive error (need for glasses). A pinhole will improve vision to around 20/30, even when patients have large refractive errors.

Measuring Poor Vision

In children with very poor vision, visual acuity is measured by the ability to (1) count fingers at 1 to 2 feet, (2) see hand motions at 1 foot, or (3) per ceive any light. The ability to see light is called light perception and no light

vision is called no light perception. Most states define legal blindness as 20/200 or worse visual acuity.

Criterion for Referral

If a 3 to 5 year old has a visual acuity of 20/50 or worse, or greater than 2 Snellen lines’ difference between fellow eyes, this patient should be referred. Children 6 years or older should be referred if visual acuity is 20/40 or worse or if there is greater than 2 lines’ difference between fellow eyes (Table 3 3). Many young children will give inconsistent responses; in these cases, visual acuity should be retested or the patient referred for a complete ophthalmic examination.

Red Reflex Test

The red reflex test is the most important part of the vision screening examination for infants and young children. It is best performed using the Bruckner modification, which is simply a simultaneous bilateral red reflex. Use the direct ophthalmoscope and view the patient’s eyes at a distance of approximately 2 feet. Use a broad beam so that both eyes are

illuminated at the same time. Have the child look directly into the ophthal moscope light and dim the room lights. Start with the ophthalmoscope on low illumination, then slowly increase the illumination until a red reflex

is seen. You will observe a red reflex that fills the pupil and a small (approx imately 1 mm) white light reflex that appears to reflect off the cornea

(Figure 3 4). The light reflex is actually a reflex coming from just behind the pupil; however, it is commonly called the corneal light reflex or the Hirschberg reflex. Thus, the Bruckner test will give a red reflex and the corneal light reflex simultaneously.

An opacity in the optical media or large area of retinal pathology will result in an abnormal red reflex (Figures 3 5 A through D). A cataract can either block the red reflex or reflect light to give a white reflex (Figure 3 5A). Retinoblastoma has a yellowish white color and will produce a

yellow reflex (Figure 3 5B). Anisometropia (ie, asymmetric refractive error) will result in an unequal red reflex (Figure 3 5C). Strabismus will cause a brighter red reflex in the deviated eye and the corneal light reflex will be decentered (Figure 3 5D). The key sign of a normal examination is sym metry. Asymmetry or an abnormality of the reflex indicates a need for an immediate ophthalmology referral (Table 3 4).

Figure 3 4.

Normal Bruckner test with symmetric red reflexes and centered corneal light reflexes.

Figure 3 5.

Abnormal reflex. A, Cataract and esotro- pia—left eye. B, Retinoblastoma—left eye. C, Anisometropia—brighter reflex right eye. D, Strabismus—esotropia with brighter reflex from deviated left eye (Note this is the author’s youngest son. The author subsequently performed strabismus surgery and is happy to report the eyes have remained straight.)

42 Pediatric Ophthalmology for Primary Care

Table 3-4. Abnormal Red Reflex (Asymmetry Indicates Pathology)

Use of Mydriatic Drops

Some physicians have recommended the use of mydriatics for vision screening examinations. This author suggests testing the red reflex without mydriatics, but using low room light illumination and low ophthalmoscope illumination to keep the pupil dilated. If dilation is desired, Mydriacyl 1% or cyclopentolate ½% with phenylephrine 2.5% may be used. For infants younger than 1 year, ½% Mydriacyl or Cyclomydril, which is a low concen tration of Cyclogyl and phenylephrine, can be used.

Motility and Eye Alignment

Ocular motility is assessed by having the patient follow a target right, left, up, and down, observing for full ocular rotation. Patients with a muscle weakness show limited eye movement. If a limitation of eye movement is identified, an ophthalmology consultation is indicated.

Ocular alignment is best assessed by the use of the corneal light reflex or Hirschberg test. As described previously, the corneal light reflex can be obtained when performing the Bruckner test. Alternatively, any light source that produces a beam broad enough to illuminate both eyes can elicit a corneal light reflex. Proper procedure is to use a muscle light or flashlight held at the examiner’s nose and pointed toward the patient’s nose, having the child look directly at the light (Figure 3 6). The light reflex should be symmetrically centered or slightly nasally deviated. The key is that the light reflex is symmetric. Displacement of the light reflex indicates strabismus. Examples of the Hirschberg test are shown in Figure 3 7 A through C. Make sure the patient maintains fixation on the light source; otherwise, the light will appear to be off center. Some authors have suggested the cover test be used to identify strabismus; however, this test is complex and even a

will constrict to a light shone in one eye. If there is an optic nerve lesion or a large retinal lesion in one eye, light directed toward that eye results in minimal pupillary reaction and both eyes remain dilated. When the light is

briskly moved to the fellow good eye, this results in increased pupillary reac tion and miosis. Moving the light back to the eye with the pathology results in pupillary dilatation. Patients with equal pupillary responses show little change in pupil size when the flashlight is moved from eye to eye (see also Chapter 11).

Fluorescein Staining

Fluorescein staining is used to identify a corneal or conjunctival epithelial defect. The corneal epithelium is only approximately 5 to 8 cell layers thick. A scratch or abrasion of the corneal epithelium results in positive staining by fluorescein (see Chapter 23). Use a premixed fluorescein solution, or use a fluorescein strip and add a drop of sterile saline or topical anesthetic to moisten the strip, and place a drop of fluorescein on the eye. Then have the patient blink several times and observe for a staining defect. Too much fluorescein will cloud the entire cornea and make identification of the stain ing defect very difficult. A Wood light or blue light causes the fluorescein to fluoresce and facilitates identification of the epithelial defect. A blue light, however, is not absolutely necessary, as one can often see the fluorescence even with natural white light.

Fundus Examination

Direct ophthalmoscopy (handheld ophthalmoscope) allows visualization of the optic nerve, retinal vessels, and fovea. The optic nerve will be visualized just nasal to the fovea. The fovea can be visualized by having the patient look directly into the light while direct ophthalmoscopy is performed. One can usually visualize a small reflex at the center of fixation, which is the foveal pit. The optic nerve should be pink with sharp margins. Blurred optic disc margins, especially if associated with hemorrhages, may indicate papille dema. The optic cup is the central area of the optic disc that is delineated

by the retinal vessels. In patients with glaucoma, the retinal vessels exit the optic nerve, separate, and are splayed out widely with an enlarged cup (see Chapter 12, Figure 8). The normal cup to disc ratio should be 0.3 or less (see Chapter 1, figures 1 8 and 1 9).

Automated Vision Screening

There are 2 major types of automated vision screening devices for preverbal children: automated refractors and photoscreeners. In general, these devices should not be used to replace a good clinical examination, but only as a supplement for early screening of preverbal children.

Automated Refractors

Automated refractors use infrared light to measure the optical power of the eye and identify refractive errors. Automated refractors are used in ophthal mology practice to prescribe glasses. The handheld versions of automated refractors have been used for vision screening (eg, SureSight by Welch Allyn). Clinical studies have shown that automated refractors are most sen sitive for detecting anisometropic amblyopia. Automated refractors have inherent limitations; they have a high rate of over referrals, do not test visual function, and do not identify strabismus because they test one eye at a time. Because automated refractors do not test visual function, they will not iden tify vision loss secondary to optic nerve lesions or retinal lesions. Despite these limitations, automated refractors have improved the early detection of anisometropic amblyopia. Use of an automated refractor should not replace the I ARM examination.

Photoscreening

Photoscreening uses a special linear streak of light that records a bilateral red reflex to screen for eye pathology. This method identifies large refractive errors, ocular opacities (eg, cataracts), and strabismus. Questions remain about their screening sensitivity and specificity in young children. Like automated refractors, photoscreeners do not test visual function. Photo screening will not identify patients with optic nerve or small retinal lesions that do not disrupt the red reflex. Photoscreening should not replace the I ARM examination (Schmidt et al).

Bibliography

1.Mocan MC, Najera Covarrubias M, Wright KW. Comparison of visual acuity levels in pediatric patients with amblyopia using Wright figures, Allen optotypes, and Snellen letters. J AAPOS. 2005;9:48–52

2.Schmidt P, Baumritter A, Ciner E, et al. Predictive value of photoscreening and traditional screening of preschool children. J AAPOS. 2006;10:377–378