Managing Young Children in Contact Lenses

BY BRUCE MOORE, O.D., F.A.A.O.
MAY 1996

Understanding how infants and young children differ from teens and adults in ocular surface configuration and physiology will help you adapt contact lens fitting and follow-up care to meet their special needs.

The primary reasons for prescribing contact lenses for infants or children younger than five years old are to allow more normal development of visual acuity and visual motor and perceptual skills, and to prevent or minimize amblyopia. Contact lenses should be used only when the degree of refractive error is enough to potentially disrupt normal visual development and result in amblyopia. Other less common uses of contact lenses for infants or very young children are nystagmus, corneal masking and corneal bandaging (Table 1).

TABLE 1: INDICATIONS FOR PEDIATRIC CONTACT LENSES High Myopia Moderate to High Hyperopia Aphakia Moderate to High Anisometropia Amblyopia Nystagmus Corneal Masking Corneal Bandaging

REFRACTIVE CORRECTION

Although eyeglasses can be used for refractive correction, it may be difficult to keep them on infants or very young children, especially if there are craniofacial anomalies or behavioral problems. With moderate or high refractive errors, peripheral distortions of spectacle lenses and image size changes may create problems. Anisometropic refractive errors, when corrected with eyeglasses, usually produce more aniseikonia and induced prismatic imbalance than when corrected with contact lenses.

Infants or very young children with moderate or high hyperopia may develop accommodative esotropia unless the refractive error is corrected. There is evidence that contact lenses are more effective than spectacles because they eliminate the base-out prismatic effect caused by plus spectacle lenses and decrease of accommodative demand. This may apparently decrease the AC/A ratio and reduce esotropia.

Children between six months and 30 months old normally have very variable astigmatic power and axis. This variable astigmatism does not cause vision problems unless associated with high spherical refractive errors, and the astigmatism does not have to be corrected unless associated with strabismus or amblyopia. In fact, inappropriate optical correction may actually interfere with emmetropization, leading to significant refractive error later.

APHAKIA

Cataracts are uncommon in infants and very young children, but they are a large part of pediatric contact lens practice. The prognosis for good vision depends upon the time of onset, cataract density, whether unilateral or bilateral, and the timeliness of surgical intervention and optical correction.

For a favorable prognosis with congenital or very early developing cataracts, surgical and optical correction combined with aggressive amblyopia therapy must occur before a child is six months old. Cataracts that develop after this critical period of visual development do not have as much impact on visual acuity unless they are not removed for a long time. Spectacle lens correction in a typical pediatric aphakic power increases image size about 20 percent to 30 percent, while contact lens correction increases image size about eight percent to 12 percent. Image size is almost normal with intraocular lens implants, but they should be reserved for those few infants or very young children who cannot wear spectacles or contact lenses but who tolerate patching for amblyopia. Managing pediatric aphakes in contact lenses is an ongoing process because lenses must be changed to compensate for refractive and ocular changes. Constant attention to amblyopia is a major part of the treatment (Fig. 1).

FIG. 1: CHILD WHO HAD SURGERY FOR A CONGENITAL CATARACT IN THE RIGHT EYE WEARING A SILSOFT APHAKIC CONTACT LENS.

AMBLYOPIA

There are two ways to treat amblyopia with contact lenses. If the amblyopia is not too deep, a patient can wear high plus lenses over the normal eye to blur the image quality below that of the amblyopic eye. Surprisingly, in many patients treated for early onset cataracts and dense amblyopia, the degree of optical blur achieved with even a +30D contact lens over the normal eye may not be sufficient to induce the child to use the amblyopic eye. High plus lenses may be more useful in patients with milder strabismic or refractive amblyopia.

Many amblyopic patients, including those with congenital and acquired cataracts and strabismic and refractive amblyopia, can be treated with black occluder soft contact lenses. These lenses are most effective in patients who are already using a contact lens for optical purposes since the patient and the parents do not have to adapt to new handling and care techniques. Patients without previous contact lens experience may also do well if the parents are highly motivated. Many young patients object more to the feel of a patch on their face than to the effects of the patch on their vision. Some young patients accept an occluder lens without behavioral problems but object strenuously when a patch is applied over that eye with the occluder lens still in place. When using an occluder lens, remember that there is a slight risk that a serious problem such as corneal infection may develop in the normal eye. A few children become adept at manipulating the lens off the cornea by hand or by blinking, thus reducing the effectiveness of the treatment. To fit an occluder lens, first determine the optimal fit with a clear lens of the same parameters as those of the opaque lens. The lens can then be ordered in opaque form from the supplier (Figs. 2 & 3).

FIG. 2A: CHILD WHO HAD A TRAUMATIC CATARACT AND SUBSEQUENT SURGERY

FIG. 2B: SAME CHILD FITTED WITH A PROSTHETIC SOFT CONTACT LENS.

FIG. 3: COSMETIC AND PROSTHETIC SOFT LENSES. (COURTESY OF ADVENTURES IN COLOR, GOLDEN, COLO.)

OTHER CONDITIONS

Cosmetic opaque contact lenses can mask a disfigured non-seeing eye. Corneal masking is also helpful for patients with severe photophobia, such as those who have iris coloboma, aniridia, albinism, and especially achromatopsia. Heavily tinted lenses that filter significant ambient light may improve comfort and vision (Fig. 4).

FIG. 4: CHILD WEARING AN APHAKIC SOFT CONTACT LENS OD AND AN OCCLUDER SOFT CONTACT LENS OS.

Patients with marked nystagmus and high refractive error may obtain poor optical correction with spectacles because the visual axis is only intermittently aligned with the optical center of the lens, which induces distortions and prismatic effects. A contact lens will move with the visual axis, reducing these effects. Contact lenses may also reduce the optical blur sufficiently to improve visual acuity and decrease the magnitude of the nystagmus in cases of sensory nystagmus. There have been anecdotal reports of a dampening effect on the nystagmus by two other mechanisms. One is simply from the weight of the lens acting as an anchor; the other is caused by the lenses dampening nystagmus through a sensory feedback mechanism due to movement of the lens on the eye resulting in increased awareness that the eye is moving. Neither mechanism has been confirmed, however.

Bandage soft lenses may benefit young children as well as adults. A bandage lens may aid healing of epithelial abrasions secondary to trauma. There are several rare pediatric dystrophic corneal syndromes that may also be aided by the use of bandage contact lenses.

SURFACE CONFIGURATION & PHYSIOLOGY

The eyes of infants and very young children are more than just smaller versions of adult eyes. Unfortunately, almost all pediatric contact lenses are designed based upon adult eyes, and they are often inappropriate for the ocular surface of pediatric eyes (Table 2).

TABLE 2: OCULAR SURFACE CONFIGURATION, PHYSIOLOGY & CHANGES DURING CHILDHOOD Precorneal fluid has reduced protein and lipid, increased aqueous. Palpebral aperture is small. Lids are tight lids when child is awake, loose when asleep. Pupillary diameter is 2mm-3mm in room light. Corneal diameter is about 10mm at birth. Corneal diameter is about 11.5mm at age three or four. Corneal curvature is quite steep (e.g. 47 to 49D) at birth. Corneal curvature flattens to normal (e.g. 43.5D) by age four.

 

Infants and very young children rarely have problems with proteinaceous or lipid deposits on contact lenses (except for silicone elastomer lenses which may have severe lipid buildup). The high aqueous component of the precorneal fluid may enhance oxygen supply to the cornea, and it maintains well-lubricated lenses and ocular surfaces. Patients who have had radiation therapy to the head for cancer may have dry eyes due to decreased lacrimal gland function, corneal integrity or regularity. These patients have a high probability of developing cataracts.

The small palpebral aperture of infants and very young children makes contact lens insertion and removal difficult. This is exacerbated with crying and the accompanying tight lid closure. Manually forcing the lids open may cause lid eversion.

Corneal diameter increases rapidly in the first year of life and more slowly over the next few years until it reaches the average adult diameter of 11.5mm to 12.0mm. Infants with microphthalmia, congenital cataracts or persistent hyperplastic primary vitreous may have corneal diameters of only six to seven millimeters, and the rate of growth of these eyes is usually slower than normal. Microcornea or microphthalmia does not always have a prognosis for poor visual acuity. Megalocornea at birth should arouse a suspicion of congenital glaucoma, although there are less serious causes for megalocornea. Patients with Marfan's syndrome may have 14mm to 15mm corneal diameters and high myopia.

Much of the flattening of the very steep central corneal curvature at birth occurs during the first six months of life. There are some indications that the peripheral cornea is flatter at birth and steepens during the first year. These changes of central and peripheral corneal curvature affect contact lens fit, and often require a steeper fitting lens after a child is six months old.

LENS DESIGN & MATERIALS

Table 3 outlines the general pediatric design characteristics recommended for soft, RGP and silicone elastomer contact lenses. Because soft lenses are easier to fit and more comfortable, they are preferred for infants and young children. Their major disadvantage is that they are more difficult for parents to handle compared to RGP or silicone elastomer lenses. Soft lenses are also relatively fragile and prone to deposition; they can be rubbed out of eyes and they carry a somewhat greater risk of infection from poor compliance. Infection is more common with extended wear, which generally should be discouraged. Soft lenses in pediatric parameters may be available only on a custom basis.

TABLE 3: CONTACT LENS CHARACTERISTICS FOR YOUNG CHILDREN Lens Diameters Smaller Soft lenses: about 12.5mm to 13.0 mm RGP lenses: about 9.0 mm - 9.5 mm Silicone elastomer lenses: about 11.3 mm Base Curve Radii and Sagitta Steeper Soft & silicone elastomer: one step flatter than steepest available RGP: 0.10mm to 0.20 mm steeper than usual Center Thickness Standard to thick Thin lenses should be avoided Tints Visibility/handling tints are useful Ultraviolet filter desirable for aphakics Oxygen Transmission Sufficient to allow safe napping

RGP lenses are easier for parents to handle and care for, are readily available in the required pediatric lens parameters, can have excellent oxygen permeability and are often well-tolerated by the moist eyes of young patients. The major disadvantage of RGP lenses is that they are difficult to fit to very young children. Other disadvantages are poorer initial comfort, greater probability of lens ejection or dislodgment, and corneal insult from eye-rubbing by the child or rough insertion or removal by the parent.

Silicone elastomer lenses (B&L Silsoft) are available only for pediatric aphakia. They have enormous permeability to oxygen, but tend to coat with lipids easily. They may be the only safe extended wear lenses.

FITTING PROCEDURES

Some pediatric contact lens practitioners use general anesthesia for very young children. This facilitates determination of ocular measurements, refractive power and contact lens fit evaluation. Unfortunately, there are some potential problems associated with general anesthesia:

• Although rare, general anesthesia may precipitate a serious medical emergency.
• General anesthesia is expensive.
• Measurements of ocular characteristics may be anomalous as lid forces are different in the prone position, lacrimation is virtually absent, and the cornea is desensitized.
• Intraocular pressure may be greatly decreased, and this may temporarily change corneal shape.

Because of these factors, contact lens fitting under general anesthesia should be restricted to instances when a child would be undergoing general anesthesia for other reasons or when it is impossible to perform proper evaluation and fitting in a conventional office setting because of medical or behavioral reasons.

There are six general steps in the office fitting of infants or very young children.

1. Perform a thorough eye exam to ensure that the eye is ready to be fit with a contact lens. If cataract surgery was performed, consult the child's surgeon to confirm that the eye is healed and ready for a lens.

2. Determine parameters for the first trial lens. Estimate corneal diameter and determine the initial lens diameter. The base curve of a soft or silicone elastomer trial lens should be one step flatter than the steepest lens available in that design. RGP lens base curves can be estimated from keratometry readings and trial lens fitting. The hand-held Alcon autokeratometer makes it easy to measure corneal curvature, even in infants.

3. Approximate the lens power. Add about two to three diopters more plus power than the mean refractive error for the age of the child as a starting point for the power of an aphakic lens (6 months, +30D; 1 year, +27D; 2 years, +23D; 3 years, +21D). If the child is nonaphakic, perform retinoscopy with trial lenses and convert for the vertex distance at the corneal plane for a starting point of the lens power.

4. Evaluate the fitting characteristics of the first trial lenses. Insert lenses of appropriate power and base curve for that design. Evaluate the position and movement of the lens after it has stabilized on the eye. Soft or silicone elastomer lenses should position centrally over the cornea, with slightly less movement than preferred for adults. The lens should not decenter more than slightly on the blink or after a finger push on the child's eyelid. If it does, choose a steeper base curve, a different diameter, or a lens configuration with a larger corneal vault or sagitta. If this lens design does not fit properly, you may need a different design or material. RGP lenses should position slightly superiorly and show an acceptable fluorescein pattern.

5. Determine the final lens power. After determining the appropriate material and base curve, perform careful retinoscopy with hand-held lenses over a contact lens as close to the correct power and configuration as possible. For aphakes, order the lens power approximately +2.50D to +3.00D greater than the actual refractive error to provide for focusing at the near and intermediate distances (a prime concern for young children). Use standard methods to determine the power of a nonaphakic lens.

6. Confirm the correct fit of the lens. Check the lens several times to ensure proper fit and power. Change lens design or parameters to achieve the ideal fit. Have the child rub his eyes to be certain that the lens does not decenter or pop out easily. Pediatric lenses should fit more tightly than lenses for adults to minimize the risk of ejection, but be certain that the parents are able to remove the lenses easily.

INSTRUCTION & FOLLOW-UP

Communication with parents is critical. Parents must fully understand the objectives of the proposed treatment and the potential benefits and risks. They must understand the likely day-to-day difficulties, the long duration of care and use of the lenses, and the expenses involved. They must also understand that through their efforts their children should be able to see better. Confidence must be enhanced and expectations must be realistic. They must be taught the skills needed to help in their child's treatment.

Parents are initially apprehensive about inserting and removing lenses, but with proper instruction, encouragement and patience, most do surprisingly well. Initially, most parents find lens removal easier than insertion. Be sure parents are at least reasonably adept at lens insertion and removal before dispensing lenses.

Many children are able to remove and sometimes insert lenses by five to six years of age. Encourage them to learn these techniques as soon as possible. If a lens becomes uncomfortable while they are in school, they can simply remove it without becoming upset or injuring the eye. This also gives the child some control over the situation, which makes parents, children and school personnel more comfortable.

Simplicity, safety and efficacy of contact lens care systems are important, and "all-in-one" systems are preferred. Instruct parents in the proper use of lens care products and provide simple, clearly written instruction sheets as a home resource. If children are in daycare or preschool programs, parents should inform personnel that the child is wearing contact lenses and provide instructions and a lens care kit.

Frequent follow-up visits will ensure that the lenses are performing well and the therapy is proceeding. This frequency is determined by the diagnosis, the child's age, the parent's level of competency, how far away the family lives, and the rate of progress of the treatment.

Measure vision at each visit. You can measure the visual acuity of young children by visual evoked potentials, the preferential looking procedure or other behavioral tests. Teller Acuity Cards are preferred for use on the younger age groups. Test older children by recognition acuity procedures such as HOTV cards, LEA cards, Broken Wheel cards or Snellen letters. An assessment of monocular visual acuity is essential to evaluate the efficacy of amblyopia treatment. Measuring visual acuity also provides valuable feedback for parents. They can easily see the improvement in their child's vision from visit to visit when the patching is going well, and decreases in acuity when the patching is lax.

Evaluate the lens fit on each follow-up visit. Changes in the shape of the eye and the refractive error occur rapidly in infants, which affects the efficacy and fit of the lens. Change lenses promptly to maintain optimal fit and optical correction. You may need to do this a number of times in the first year. Assess ocular health on each visit using a hand-held slit lamp or loupes and penlight to inspect the anterior segment.

Continue the combination of contact lens wear and amblyopia therapy until the possibility of regression of acuity is past, usually sometime between ages six and nine. After age five, the amount of patching is usually decreased to maintain the acuity level.

OLDER CHILDREN

Contact lens care for children over five years old is similar to that for adults in terms of conditions amenable to treatment, configuration and physiology of the ocular surface, options of lens materials and designs, and techniques of fitting and follow-up. Differences are maturity level, type of activity involvement and psychological effect of contact lens wear.

Most ocular parameters reach adult dimensions by about age four. Increase of myopia or decrease of hyperopia often occurs throughout childhood, although hyperopia usually remains fairly stable for accommodative esotropes. There are typically only small changes of astigmatic power and axis after about age five. The amount of precorneal fluid is greater during childhood, and there is a reduced lipid and mucin content as compared with aqueous. Children's lid forces and pupil size are greater than for adults. Contact lens treatment of acquired aphakia in older children is usually less difficult because deprivation amblyopia is not a factor; but there is invariably some refractive, anisometropic or strabismic amblyopia that results from childhood cataract. Practitioners should be alert to development of this amblyopia, which can be treated with orthoptic eye patches or occluder soft contact lenses.

Adults and children do not necessarily use contact lenses under the same conditions and in the same manner. Young children tend to nap, and contact lens oxygen permeability should be sufficient to allow this. Children are usually more active than adults, so their contact lenses should be more positionally stable on the eye. Pediatric lenses should be durable and easy to handle. CLS

Dr. Moore is a clinical assistant in ophthalmology at Harvard Medical School, an associate professor of optometry at The New England College of Optometry, and director of contact lens service and staff optometrist at Children's Hospital, Boston.

References are available from: Dr. Paul White, The New England College of Optometry, 424 Beacon St., Boston, MA 02115

 

 

QUESTIONS

1. Prescribing contact lenses for children under five may allow better development of:

a. visual acuity

b. visual motor skills

c. visual perceptual skills

d. all of the above

2. Between the ages of six months and 24 months:

a. astigmatic power is very variable

b. astigmatic power is very stable

c. astigmatic axis is very stable

d. both "a" and "c"

3. With congenital or very early developing cataracts, removal and treatment should be by age:

a. 6 months

b. 12 months

c. 18 months

d. 24 months

4. High plus lenses to blur the image of the non-amblyopic eye are more successful with:

a. milder strabismic amblyopia

b. milder refractive amblyopia

c. both "a" and "b"

d. neither "a" nor "b"

5. Opaque lenses for corneal masking help patients with:

a. iris coloboma

b. aniridia

c. achromatopsia

d. all of the above

6. Contact lens mechanisms that might help a nystagmoid patient are:

a. more consistent alignment with visual axis

b. weight of contact lens

c. sensory feedback mechanism

d. all of the above

7. Which precorneal fluid component is greater with infants and very young children?

a. lipid

b. aqueous

c. protein

d. both "a" and "b"

8. Average corneal diameter at birth is about:

a. 9 mm

b. 10 mm

c. 11 mm

d. 12mm

9. Average central corneal curvature at birth is about:

a. 41 to 43 D

b. 44 to 46 D

c. 47 to 49 D

d. 50 to 52 D

10. Soft contact lens diameter for very young children should be:

a. 12.5 to 13.0 mm

b. 13.5 to 14.0 mm

c. 14.5 to 15.0 mm

d. 15.5 to 16.0 mm

11. The major disadvantage of RGPs for very young children is:

a. good parameter availability

b. difficulty in fitting

c. poor oxygen permeability

d. poor ocular toleration

12. Problems with general anesthesia for contact lens fitting are:

a. precipitation of serious medical problem

b. intraocular pressure decreases

c. great expense

d. all of the above

13. For very young aphakes, prescribed contact lens power should be in terms of mean refractive error:

a. two to three diopters greater

b. four to five diopters greater

c. two to three diopters less

d. four to five diopters less

14. Parents of young contact lens wearers should understand:

a. goals and objectives of treatment

b. potential benefits and risks

c. long duration of care

d. all of the above

15. Many children are able to remove and sometimes insert contact lenses by age:

a. 6

b. 4

c. 3

d. 2

16. Which procedure should be used to evaluate the visual acuity of older children?

a. visual evoked potentials

b. preferential looking

c. recognition acuity charts

d. all of the above

17. Patching for amblyopia is usually decreased after about age:

a. five

b. four

c. three

d. two

18. Most ocular parameters reach adult dimensions by about age:

a. eight

b. six

c. four

d. two

19. Contact lens treatment of acquired aphakia in older children is usually less difficult because:

a. there is no refractive amblyopia

b. deprivation amblyopia is not a factor

c. there is no anisometropic amblyopia

d. there is no strabismic amblyopia

20. Pediatric contact lenses should be:

a. positionally stable

b. durable

c. easy to handle

d. all of the above