Ординатура / Офтальмология / Английские материалы / Pediatric Ophthalmology Current Thought and A Practical Guide_Wilson, Saunders, Trivedi_2008

after 2 years of age, albeit at a slower pace, such that most eyes are nearly emmetropic by 6−8 years of age. In some children, emmetropization fails and results in significant hyperopia, while in others emmetropia is overshot and myopia is the result.

It appears that emmetropization is guided by genetics but is modified by environmental influences.

Support for genetically guided processes comes from fraternal and identical twin cohort studies, as well as from differences in refractive errors observed in prevalence studies of pediatric populations in different countries. Direct comparison of these prevalence studies is complicated by differences in methodology and definitions, but still, general patterns have emerged. It appears that there is a bias toward myopia in eastern Asian populations, particularly among the urban Chinese (as high as 75% in some studies). In comparison, Chilean children have an increased prevalence (14.5%) of significant hyperopia. Australian children of Caucasian origin also seem to have an increased prevalence of hyperopia, though not as dramatic as demonstrated in the Chilean study. In addition to hyperopia or myopia, certain populations seem to have an increased prevalence of astigmatism significant enough to cause ametropic amblyopia [1].

Genetic biases are further supported by studies that demonstrate a predictive effect of parental myopia upon the development of myopia in their offspring. The COMET study reported that children who developed high myopia during 7 years of post-study fol- low-up were younger and had more myopia at base-

line. Children who developed high myopia were also more likely to have two myopic parents [2].

Studies of environmental influences on the development of refractive errors have primarily focused on the development of myopia, and some of the potential aggravating factors identified include sustained near work, accommodative variability, accommodative lag, and decreased time spent outdoors [3]. Urban environment [4] and increased night-time ambient lighting [5] may also have an effect on the development of myopia. In one recent report [6], parental cigarette smoking was associated with less prevalent myopia and a more hyperopic mean refraction with both prenatal and childhood exposure to tobacco smoke. Thus, the eventual refractive state of the eye depends upon both genetic and environmental influences. In addition, certain ocular and systemic disorders are commonly associated with ametropia (Table 2.1).

2.2Examination

2.2.1Refraction Prior to Cycloplegia

Accurate refraction of the pediatric patient is an essential element of the ophthalmic examination of the child, not only to determine the need for glasses, but also to aid in diagnosis and treatment of a variety of systemic and ocular disorders. Cycloplegic retinos-

In order to stimulate accommodation, it is necessary to use letters (Fig. 2.1a) or an age-appropriate picture (Fig. 2.1b) of interest to the child with little delay. When using a small picture, the author finds it helpful to pose a playful, but argumentative, ques-

Fig. 2.1  Dynamic retinoscopy with a the doctor holding a lettered target close to the peephole of the retinoscope, and stimulating accommodation by moving close to the teenager and asking her to read the letters. b The patient’s view of the retinoscope and a cartoon figure target

tion requiring the child’s observation of small details on the target. Most children will quickly and gleefully respond in order to correct the mistake. Pictures, rather than letters, are also of great value when evaluating the child with difficulty reading, or presumed non-physiologic visual complaints, as the child rarely suspects that the cartoon figure is being used as an evaluation of their ability to see at near. An infant’s accommodation can usually be stimulated by drawing their attention to a small toy held adjacent to the peephole of the retinoscope, sometimes using internal illumination in the base of the figure. Most infants can only be tested at near, as they are often inattentive for distance fixation.

Except for patients with moderate to large angle strabismus, both eyes of most children can be evaluated nearly simultaneously. If refractive correction has been prescribed, it should be worn during testing. With the child attentive to a distance fixation object, and with the peephole as close to the line of sight as possible (to avoid off-axis errors), the reflex is observed in the vertical meridian of each eye, and then rotated to assess the horizontal meridian of each eye. The reflexes in the two meridians should be approximately the same width, and a difference in width of the reflex indicates that astigmatism is present. A small amount of “with” motion should be observed when the patient is in focus at distance. Larger amounts of “with” motion indicate a significant residual hyperopic error, while “against” motion indicates myopia. Next, the patient is instructed to observe details on the near target as shown in Fig. 2.1a, and the observer should see the “with” motion neutralize rapidly as accommodation brings the far point to the peephole of the retinoscope. Failure to neutralize the reflex indicates an accommodative insufficiency and/ or a significant amount of hyperopia.

Attention is then directed again to the distance object, and “with” movement should be seen. Finally, attention is redirected to the near target, and the child is queried about the details of the target as the retinoscopist observes for and accurate and sustained accommodative response. The retinoscope and target are moved as a unit, and as they are moved toward the child, accommodation is further stimulated. The child should be able to sustain the accommodative effort and maintain neutralization easily as the target is studied for several seconds. When accommodation is normal, the results can be described as “rapid,

complete, and steady OU”. When accommodation is abnormal, either the reflex will fail to neutralize completely or the patient will be unable to sustain the effort over time. The speed, symmetry, and sustainability of the accommodative effort should be recorded in the patient’s chart. If abnormal accommodation is detected, the amount of near correction required can be determined by holding plus lenses in front of the patient and reassessing the retinoscopic reflexes at near. If dynamic retinoscopy is routinely performed on new patients and those at risk for accommodative insufficiency prior to cycloplegia, a post-cycloplegic evaluation can be avoided.

Dynamic retinoscopy can be used to evaluate how much hyperopia to correct in a patient with normal alignment and high hyperopia, and to assure that enough residual accommodation is available for near work. In a patient with strabismus that is large enough to cause off-axis errors in the retinoscopic evaluation of the non-fixating eye, it is necessary to test each eye separately and occlude the eye not being examined.

Monocular evaluation is also useful in the evaluation of amblyopic eyes that are not improving with treatment of the amblyopia. Some amblyopic eyes have deficient accommodation and may require correction for near in order for amblyopia treatment to succeed.

Finally, dynamic retinoscopy is quite useful in the evaluation of the pediatric patient with complaints that may be non-physiologic in nature. Taken in conjunction with the history, other objective findings (normal papillary reactions, structural examination, and cycloplegic refraction), good stereopsis, and non-physiologic responses to stereo and color vision testing, dynamic retinoscopy can help to reassure the ophthalmologist when the findings are normal.

2.2.4Assessment of Current Spectacles

Current spectacle correction should be measured at each visit to avoid surprise and confusion. It is always important to check that the lenses were made properly and that if the lenses have fallen out, they have been properly replaced. Sometimes children present for examination wearing old correction, a sibling’s correction, or wearing glasses where the

lenses have been switched. Attention to accurate measurement of current spectacles is important for ophthalmologists who prescribe using the technique of over-refraction.

Ophthalmologists who write prescriptions in plus cylinder notation should instruct their staff to be vigilant about measuring cylinder axis, as transposition errors made by opticians can result in 90° axis errors.

Opticians routinely transpose prescriptions written in plus cylinder notation to minus cylinder, since lenses are manufactured with cylinder correction on the posterior surface of the lens (minus cylinder).

The accurate measurement of bifocal power, especially in hyperopic correction, should be measured with the temples oriented toward the practitioner, in contrast to typical clinical practice. The distance correction is measured first (using the least hyperopic meridian if cylinder is present), and then measuring the power in the same meridian through the near segment. The bifocal power is the difference between the two.

Some children require large astigmatic corrections, and proper cylinder axis is essential, particularly for children with amblyopia. ANSI Z80.1-2005 standards [12] require that cylinder powers 0.50-D cylinder power be dispensed within ± 7°, 0.75 diopters cylinder must be within 5° the prescribed axis, correction > 0.75 to ≤ 1.50-D cylinder within ± 3°, and for greater cylinder powers its axis tolerance is ± 2°.

Attention should also be given to the general location of the optical center of the lenses relative to the interpupillary distance, especially when a new or unexpected ocular deviation is present. Some frame designs have round or oval lens apertures, and the lenses can be placed in the frame with astigmatic correction attheproperaxisbutlocatedtemporallyintheeyewire relative to its proper placement (Fig. 2.2). In a patient with high hyperopia and previously well-controlled accommodative esotropia, temporal displacement of the optical centers produces base-out prism, and can cause an exodeviation.Aquick way to locate the optical centers of a lens while in the exam lane is to hold the lens below a ceiling spotlight and align the reflections of the light from the front and rear surfaces of the lens (Fig. 2.3). If a problem with the optical center of the lens is suspected based on the rapid chair-side assessment, the precise location of the optical center can be confirmed with a lens meter.

Fig. 2.3a–c Reflections from the front and rear surfaces of a spectacle lens can be used to quickly locate the optical center of a lens. a,b The reflections from the front and rear surfaces are separated. c The reflections are superimposed over the optical center of the lens

2.2.5Subjective Refraction

Subjective refraction of teens and older children is a useful adjunct to cycloplegic retinoscopy and can be particularly helpful in children with large amounts of cylinder where very small errors in cylinder axis can make a significant difference in visual acuity.

Subjective refraction can be performed either using a phoropter or in trial frames. Some children will readily accept either technique, but the author usually prefers trial frames in order to be able to watch the child’s facial expressions during the refraction. A rapid and succinct subjective technique is especially important for children who may have a short attention span or who may lack self confidence when responding to the examiner. The rapidity of the response from the child is often a good indicator of her confidence in the answer: a rapid response in the anticipated

direction is usually a good indication of a reliable response. It is also helpful to have a quiet examination room, free from distraction by active siblings or a well-intentioned parent. Retinoscopic findings are usually the most efficient starting point and allow the examiner to guard against accommodation when the refraction is performed without cycloplegia. Subjective refinement of cycloplegic retinoscopic findings can help to refine axis and power.

Most children have large accommodative reserves, so special attention to control of accommodation is needed during non-cycloplegic refraction. During subjective non-cycloplegic refraction, “pushing plus” and making the child demonstrate the anticipated improvement in acuity with added minus (or reduced plus) correction can help guard against stimulating accommodation – about a line of improvement should be expected with each 0.25 diopters in the minus direction. Control of accommodation can be confirmed while performing interocular balancing in most children who are cooperative with non-cycloplegic subjective refraction using the red-green (douchrome, bichrome) test.

Subjective refinement of static retinoscopic findings prior to dilation and cycloplegia is particularly important for older children with lenticular dislocation (e.g., Marfan syndrome or ectopia lentis) or corectopia (e.g., Rieger anomaly/syndrome or after trauma). After dilation, it is difficult or impossible to tell what portion of the cornea, pupil, and lens the eye habitually uses for viewing in eyes with these disorders, so refraction with the lens and pupil in their natural positions is important.

with dark irides. In cases where cyclopentolate does not produce adequate cycloplegia in the office, an atropine refraction may be needed. A common regimen is atropine 1% twice a day for 2 days prior to the examination, and again on the morning of the examination. Parents should be instructed to wash their hands after instilling the eye drops in their children to avoid inadvertent self-administration of the drug.

Some pediatric ophthalmologists recommend the use of a topical anesthetic prior to the instillation of the cycloplegic drops, as the anesthetic promotes penetration of the cycloplegic agent into the eye and reduces the stinging of the cycloplegic drops. Other pediatric ophthalmologists find that the instillation of an additional set of drops is not needed, and that since the anesthetic drops sting, they feel that the extra step does not contribute to a more positive office visit.

2.2.7Vertex Distance

Vertex distance, the distance from the cornea to the posterior surface of the refractive correction, is clinically significant for refractive errors greater than 5 diopters − a common finding in a pediatric ophthalmology practice. Vertex distance is most easily measured with a Distometer (Haag-Streit Services, Waldwick, New Jersey) and trial frames (Fig. 2.4) or the child’s

2.2.6Cycloplegia

Cycloplegia is essential for accurate refraction in young children. Due to their large accommodative amplitudes, a strong cycloplegic agent is indicated in the pediatric ophthalmic evaluation. Cyclopentolate is the most commonly used medication in the United States because of its rapid onset, relatively adequate cycloplegia, and short duration (compared with atropine). Cyclopentolate 1% is the most frequent strength used, and it is often combined with phenylephrine and/or tropicamide for pediatric patients

Fig. 2.4  A Distometer (Haag-Streit Services, Waldwick, N.J.) is used to measure the vertex distance in a patient with high hyperopia while wearing trial frames

current correction. Practically speaking, however, it is nearly impossible to measure vertex distance in most younger children. For children with refractive errors greater than 5 diopters, refraction over the current spectacle correction is the most accurate way to control for errors that result from vertex distance. Refractive findings can be added to the current spectacle correction (mathematically, or measured through a lensmeter) and the optician instructed to duplicate the vertex distance of the current correction. The optician will not be able to measure and duplicate the vertex distance exactly, but the optician can fit the frames so that the vertex distance of the new correction closely approximates that of the old one.

Vertex distance is very important in contact lens fitting for aphakic infants. Consider the following example of a typical aphakic infant. If the refraction with measured with retinoscopy and loose lenses is + 22.00 + 2.00 × 80, what should the contact lens power be? If fitting a soft contact lens, the refraction is converted to its spherical equivalent: + 23.00. It is difficult, if not impossible, to measure vertex distance in a squirming infant, but if a 10-mm vertex distance is assumed, the contact lens power needed would be + 29.9 diopters. If a 12-mm vertex distance is assumed instead, the contact lens power needed increases to + 31.8 diopters. Note the large (2 diopters) variation in calculated lens power depending on the vertex distance. It is easy to see how small differences in vertex distance could make a significant difference in the measured refraction. The examiner should select a contact lens with a power within several diopters of the calculated power, and the refraction should be repeated and refined with the contact lens in place.

portion of the pupil that the child has been observed to use while awake. In children without corectopia, it is helpful to place the first Purkinje-Sanson image (the corneal light reflex) in a physiologic position, just nasal of the geometric center of the pupil. As a practical point, finding the position yielding the most plus (or least minus) refraction is “on-axis”. Off-axis refraction will reduce the measured plus sphere (or increase the amount of minus sphere), will cause cylinder power and/or axis errors in the refraction of an astigmatic eye, or will produce an astigmatic refraction in an eye with a spherical refractive error. Care should also be taken to maintain an appropriate vertex distance, especially with larger refractive errors.

In children with difficult media and a poor retinoscopic reflex, it is often necessary to move closer to the eye to “enhance” the reflex. An assistant should measure the working distance while the doctor performs the refraction, and the working distance (in diopters) is subtracted from the retinoscopic findings.A useful distance is 20 cm, or 5 diopters from the eye.

For instance, an eye with a retinoscopic reflex that is neutralized with + 9.50 sphere at a working distance of 20 cm (5 diopters) would require distance-refrac- tive correction of + 4.50. It is important to measure an intentionally short working distance accurately, as small changes in a short working distance translate to larger dioptric changes in working distance compared with typical working distances.

2.2.9Estimation Retinoscopy

Estimation retinoscopy (using sleeve position to vary the vergence of light leaving the retinoscope and estimate refractive error based on sleeve position) is a

Children who are refracted in the operating room while anesthetized should have cycloplegic drops instilled at an appropriate interval prior to the refraction if the eyes are phakic. Anesthesia per se does not produce cycloplegia, and accommodation may occur spontaneously. When performing retinoscopy under anesthesia, it is important to pay special attention to the eye’s visual axis, and to refract that

able to cooperate with accurate measurement of refractive error using loose lenses. Wallace et al. demonstrated the accuracy of estimation retinoscopy in the evaluation errors less than 4 diopters of myopia and 2 diopters of hyperopia [13]. Uncooperative children with larger suspected refractive errors detected by estimation retinoscopy may warrant examination under anesthesia if accurate measurements cannot be obtained in the clinic setting.

2.3Prescribing and Dispensing

2.3.1Prescribing

The prescription of eyeglasses in the pediatric population is more difficult than in adults, where a prescription is usually given as a result of a visual complaint – asthenopia or blurred vision at near and/or distance. Usually, an improvement in visual acuity with correction warrants a prescription for refractive correction. While older children may present with blurred vision, younger children usually offer no subjective complaints. Prescribing for refractive errors in children is further complicated by the fact that many parents are resistant to their young child wearing glasses at all, and that children anisometropia and good uncorrected vision in the better eye may not appreciate an improvement with correction. Glasses for children are the most commonly prescribed treatment for vision disorders in children, and they can cause vision loss if improperly prescribed or can be a significant financial burden for families if not truly needed. The American Academy of Ophthalmology Pediatric Eye Evaluations Preferred Practice Pattern summarizes suggested guidelines for prescribing, and is reproduced in Table 2.2.

Table 2.2  The AAO PPP consensus guidelines for prescribing spectacles in children

The unit of measure is diopters

2.3.1.1Prescribing for Myopia: School-aged Child

Myopia is common in the school-aged population, and the prevalence in the United States and western Europe increases gradually in childhood such that about 25% of the adult population is myopic. In some clinical situations, the indications for glasses are straightforward: the school-age child with moderate myopic astigmatism that is having trouble seeing the board should receive full correction of the myopic and astigmatic error. For younger children and those needing smaller corrections, many practitioners use uncorrected distance acuity of worse that 20/40 as the threshold for prescribing; however, some children are symptomatic with better acuity, and correction should be offered for these children.

Some ophthalmologists have historically offered to undercorrect the myopic portion of the refractive error in the hope of slowing myopic progression; however, a recent study in school-aged children by

Chung et al. [14] demonstrated that the myopia progression actually increased when myopia is intentionally under-corrected by 0.75 diopters. Adler and

Millodot [15] undercorrected myopia by 0.5 diopters and demonstrated a slight increase in myopic progression, but the increase was not statistically significant. Thus, undercorrection of a myopic student will lead to blurred vision at distance, and may increase myopic progression, and should be avoided.

Some parents are especially concerned about myopic progression and will ask if anything can be done to slow progression in their child. The Correction of Myopia Evaluation Trial (COMET) studied the effect of progressive addition lenses versus single vision lenses on the progression of myopia in children during a 3-year randomized clinical trial. Although the trial did show a small, statistically significant reduction in myopic progression during the first year of correction only (and none during the subsequent years), the progressive addition lenses only resulted in a mean 0.2-D difference in myopia at the end of the 3-year trial [16]. Progressive addition lenses add significant cost to the spectacle correction and result in a clinically insignificant reduction in myopic progression. Thus, progressive addition lenses do not seem to be indicated in the correction of most myopic children; however, there may be some benefit for a

limited number of myopic children who have an esophoria at near, accommodative lag, or a combination of the two in association with myopia [17].

Rigid contact lenses have been proposed as a treatment for the progression of myopia, and the Contact Lenses and Myopia Progression (CLAMP) study [18] reported that rigid gas permeable contact lenses slowed myopic progression in young children when compared with soft contact lens wear. The difference in myopia progression between the rigid and the soft contact lens wearers was 0.63 diopters, but there was no difference in axial growth between the two groups. The investigators reported that the rigid contact lenses kept the cornea from changing shape more than soft contact lenses, and hypothesized that the effect of rigid lenses on myopia progression may not be permanent.

2.3.1.2Prescribing for Myopia: Infant and Preschool Child

Myopia in infancy and the preschool years should be treated if it is of a magnitude that it is likely to cause amblyopia through large amounts of isoametropia or more modest amounts of anisomyopia. An infant and toddler’s world is at near, and a younger child with symmetric amounts of mild to moderate myopia can be safely observed without correction. Miller and

Harvey [19] surveyedAAPOS members and reported a prescribing threshold of 5 diopters of myopia for infants less than 1 year old, decreasing to a threshold of 3 diopters of myopia for children 2−3 years old.

When anisomyopia of 2 or more diopters is present, glasses should be considered.

2.3.1.3Prescribing for Astigmatism

Evidence-based guidelines for prescribing for infants and toddlers do not exist, but Harvey et al. [20] reported the prescribing habits of AAPOS members for astigmatism. The American Academy of Ophthalmology’s Pediatric Eye Evaluations Preferred Practice Pattern [21] suggests prescribing for 3 diopters of astigmatism in a child less than 1 year old, but AAPOS members have been reported to have slightly higher thresholds for prescribing in infants and toddlers. Infants and preschoolers who require glasses for isoametropia and/or astigmatism should always receive their full astigmatic correction at the correct axis. Children do not complain about meridional distortion, and failure to fully correct astigmatic errors at the correct axis may cause amblyopia or hinder its treatment.

2.3.1.4Prescribing for Anisometropia

Amblyopic children with anisometropia should receive balance correction of the error. If hyperopia and esotropia are present, the full hyperopic and anisometropic correction should be prescribed. In the absence of an esodeviation, hyperopia should be corrected according to the guidelines below, with symmetric reduction of the error in each eye. The recommendations for anisometropic children without amblyopia are less clear, but Donahue [22] has nicely summarized the evidence and uncertainties surrounding the correction of anisometropia in the absence of definite amblyopia. He recommended a threshold of 1−1.5 diopters of anisometropia; however, abnormal ocular findings and/or family history of amblyopia could lower threshold for spectacle prescription.

2.3.1.5Prescribing for Hyperopia

Mild to moderate levels of astigmatism < 1.5 diopters decrease visual acuity only slightly, and do not require correction in younger children unless accompanied by a significant myopic or hyperopic error. School-aged children have greater visual demands and may require correction for astigmatism if it is causing blurred vision at distance. Comparison of best-corrected and uncorrected visual acuity can guide the decision of whether to prescribe for an isolated astigmatic error.

Uncorrected hyperopia is associated with isoametropic amblyopia, accommodative amblyopia, and strabismic amblyopia. Whether to prescribe correction for hyperopia is complicated by the consideration that most young children are mildly hyperopic, and the observation that not all children with moderate levels of hyperopia develop amblyopia and/or strabismus. Atkinson [23] and colleagues have carefully studied the effects of infant hyperopia and its correction in a series of studies, summarized in a 2007

publication. The authors report that the prevalence of ≥4 diopters of hyperopia in 8- to 9-month-old Caucasian infants is around 5%. Infant hypermetropia was associated with increased strabismus and poor acuity at 4 years of age, and spectacle wear produced better visual outcome than no glasses. The prescription of glasses did not affect emmetropization. The hyperopic patients demonstrated poorer overall performance compared with emmetropic controls on visuoperceptual, cognitive, motor, and attention tests.

This work was corroborated in a study [24] of 3- to

5-year-olds with a similar degree of ametropia, and the ametropic children scored significantly lower on test of visual-motor function.

Despite emerging evidence that moderate levels of uncorrected hyperopia in infancy can negatively affect ocular health and cognitive development, ophthalmologists have historically had a higher threshold for prescribing in hyperopic children without strabismus. Miller and Harvey reported that 50% of pediatric ophthalmologists would prescribe glasses for children less than 2 years old with 5 diopters of hyperopia, and the threshold decreased to 4 diopters for children older than 2 years. The AAO PPP Pediatric Eye Evaluation suggests a threshold of 6 diopters of hyperopia for infants less than 1 year old, 5 diopters for 1−2 years old, and 4.50 diopters for 2- to

3-year-olds without concurrent strabismus. When an esotropia is present, the threshold suggested by the AAO PPP changes to 3 diopters of hyperopia for infants < 1 year old, 2 diopters for 1−2 years old, and

1.50 diopters for 2- to 3-year-olds.

Once a decision is made that correction is needed for hyperopia, how much of the hyperopia should be corrected? When an esotropia is present, the full hyperopic correction should be given. Children who have difficulty adjusting to their hypermetropic glasses can benefit from “pharmacologic encouragement” – one drop of atropine in both eyes daily for 5 days helps most children to accept the glasses. Children with a residual esodeviation after correction of their full hyperopic error should be refracted again to check for residual hyperopia or an increase in the error. Bifocals are indicated for children with a high clinical accommodative convergence/accommodation ratio and should be fit with the top of the segment bisecting the pupil.

In children with significant hyperopia with normal ocular alignment, most pediatric ophthalmolo-

gists will reduce the correction by a symmetric amount – typically 1.5 diopters, unless there is a family history of accommodative esotropia or evidence of accommodative insufficiency. When parents seem to resist correction of hyperopia, it can be useful to “demonstrate” the hyperopic state by putting up minus lenses in front of the parent, and directing their attention to a distance and then near target to stress their accommodation. Parents should be warned that they may begin to see an esodeviation without correction after hyperopic spectacle correction is instituted.

2.4Dispensing Recommendations: Tints

Parents of children with albinism, aniridia, colobomata, corneal scarring, treated ROP, or other diseases associated with photophobia should be carefully questioned about light sensitivity. Children with photophobia can benefit from dark tints (80−90% tint /10−20% transmission) for outdoors, and lesser tints for indoors (20−30% tint / 70−80% transmission). Opaque side shields may be needed for children with more severe photophobia, particularly those with oculocutaneous albinism. The amount of tint desired should be specified on the prescription so that the tint density will be properly made; it is unambiguous to specify both transmission and blockage percentages as noted above. A special note for the tinted lenses may be needed for school. Hats with wide brims for outdoors can also help with photophobia.

2.5Dispensing Recommendations: Protective Eyewear

and Monocular Patients

Patients with unilateral vision impairment have an increased risk of vision loss in the better eye due to disease or injury. Thus, patients who are functionally monocular (best corrected acuity in the poorly seeing eye less than 20/40) should wear protective eyewear at all times, even if refractive correction is not in-