Ординатура / Офтальмология / Английские материалы / Contact Lenses in Ophthalmic Practice_Mannis, Zadnik. Coral-Ghanem, Kara-Jose_2003

14. Pediatric Contact Lenses 131

process is similar to adults. The primary challenge in fitting a child is not due to physical differences. The most difficult aspects of fitting a child are overcoming the child’s stress, communicating with the child, and accommodating the rapid development of a young eye.

Despite many similarities between a child’s and an adult’s eye, a child’s palpebral fissure is generally smaller, which makes it more difficult to insert and remove contact lenses. This difficulty is exacerbated when the child is crying. The aqueous component of the tear film is generally increased in children. Since the concentration of lipids and proteins in the tears are reduced in children, they rarely have problems with contact lens deposits, except with contact lenses made of silicone elastomers, on which lipid deposits may accumulate quickly. The curvature of the cornea decreases over the first 2 years of age from approximately 45 D to 43 D, and the corneal diameter increases from approximately 10 mm at birth to 11.5 mm by 3 or 4 years of age.

3.What contact lenses are utilized in children?

Children can wear rigid gas permeable contact lenses or soft contact lenses. The indication for contact lens wear and the parents’ experience with contact lenses should be considered when determining the most appropriate type of contact lens.

Soft contact lenses are most commonly fitted in children. Parents are more likely to have experience with soft contact lenses than with rigid contact lenses, and soft contact lenses may be prescribed in a frequent replacement program so that spare lenses are readily available. However, it is difficult to find soft contact lenses with pediatric parameters. They require more dexterity in handling than rigid gas permeable contact lenses, and they pose a greater risk of infection than rigid contact lenses, especially with extended wear.

Rigid gas permeable contact lenses are frequently well tolerated by children, and they are more practical in terms of maintenance and care. These lenses have excellent oxygen permeability, they correct irregular astigmatism, and they can be custom made to fit children’s eyes. However, rigid contact lenses may be less comfortable initially, they are more likely to dislocate or be lost than soft contact lenses, and they are not available in multipacks.

4. How does one fit the child?

Some professionals use general anesthesia to fit a contact lens in an infant. This will certainly facilitate the measurement of the ocular parameters, refractive power, and evaluation of the contact lens on the eye, but there are serious potential risks associated with general anesthesia. Contact lens fitting under general anesthesia should be restricted to those children who are impossible to examine and fit appropriately in the office. When fitting the contact lenses in the operating room, the main priority is to determine the appropriate power of the

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contact lens. The best method to determine the power is to place a contact lens on the eye that approximates the resulting refractive error of the child (approximately 35 D). Retinoscopy should be performed over this contact lens using refractive trial lenses to determine the most appropriate power. Placing a high plus contact lens on the eye reduces the error potentially induced by the variable working distance of a high plus refractive trial lens. It may be necessary to stand on a stool or a short ladder in order to achieve the appropriate working distance for a child lying on an operating room table.

A toddler fitted in the office may need to be restrained, which can be accomplished by having the parent hold the child, by wrapping a sheet around the child, or by straddling the child while he or she is lying on the floor. At least one extra pair of hands is necessary to conduct the fitting.

An eye care practitioner may consider having an office assistant insert the contact lens in the child’s eye. Children may not trust the person who inserts the first contact lens for some time thereafter, so evaluation of the contact lens prescription may become very difficult. Once the child calms down, the eye care practitioner should evaluate the prescription and fit of the contact lens.

5.How does one examine the lens–cornea relationship in a child?

Children 5 years and older can typically be examined using a slit-lamp biomicroscope with fluorescein and a cobalt blue filter. Small children may need to sit on their knees and hold the slit lamp ‘‘like a motorcycle’’ in order for them to reach the chin rest and for them to be interested enough to sit still for 1 to 2 minutes. If a child cannot be examined with a slit lamp in the office, then a hand-hold Burton lamp with fluorescein can be used. Portable slit lamps and a direct ophthalmoscope/20 D lens combination works when other methods are not available.

When evaluating a contact lens fit, the key fitting criteria are similar to those looked for in the adult. One should check the movement, centration, and fluorescein pattern of a rigid contact lens, and the movement and centration of a soft contact lens. Determination of whether the power of the contact lens is appropriate is also necessary in all contact lens fittings.

6.When should contact lenses be fitted in an aphakic child, and what is the visual prognosis?

The developing visual system of an infant requires clear vision in order to achieve maximum visual potential. As little as 1 to 2 weeks of constant visual deprivation can result in amblyopia. When possible, a contact lens should be fitted immediately after surgery or within 1 week. Fitting the child with a contact lens while he or she is still on the operating table eliminates the potential need for a second dose of general

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corneal abrasions and ulcers, but these are more rare. By far, the most commonly encountered complication is contact lens loss or breakage.

10.What is the social responsibility of the eye doctor?

In the case of a child with a congenital cataract, if surgery is indicated, the eye care practitioner must be concerned that the family’s socioeconomic and psychological condition can support the long treatment that will be necessary. On the other hand, it is possible to create false expectations and anxiety in the family that has already been assaulted by the child’s disease. It is necessary that the parents understand the proposed objectives for treatment and the potential benefits and risks. They must be aware of the duration of the treatment as well as the expenses that will be incurred. On the other hand, they must also understand that only their initiative will allow the child to develop better vision.

Selected References

Donzis PB, Weissman BA, Demer JL. Pediatric contact lens care. In: Bennett ES, Weissman BA, eds. Clinical Contact Lens Practice, Philadelphia: JB Lippincott, 1994: Chapter 51, pp. 1–8.

Matsumoto ER, Murphree L. The use of silicone elastomer lenses in aphakic pediatric patients. Int Eyecare. 1986; 2:214–217.

Moore B. Managing young children in contact lens. Contact Lens Spectrum. 1996; 34–38.

Pe’er J, Rose L, Cohen E, Benezra D. Hard and soft contact lens fitting in infants. CLAO J. 1987; 13:46–49.

Stenson SM. Pediatric contact lens fitting. In: Kastl PR, ed. Contact Lenses—The CLAO Guide to Basic Science and Clinical Practice, Vol 3. Iowa: Kendall/Hunt Publishing, 1995:179–195.

15

Fitting Contact Lenses After

Refractive Surgery

Kaaryn Pederson and

Cleusa Coral-Ghanem

The fitting of contact lenses after refractive surgery is a challenge for the majority of eye care professionals. Not only are there problems because of limited designs for oblate corneas but in addition many patients opt for refractive surgery in the first place due to contact lens intolerance. In such cases, patients require encouragement and psychological support during the process of fitting.1

Incisional techniques such as radial and astigmatic keratotomy cause corneal alterations that are different from those techniques in which tissue is removed, such as photorefractive keratectomy (PRK) and laser in situ keratomeleusis (LASIK). For this reason, the fitting of contact lenses in each of these classes of surgery is detailed separately.

1.What are the indications for fitting contact lenses after radial keratotomy?

●Undercorrection

●Overcorrection

●Irregular astigmatism

●Anisometropia

●Progressive hyperopic shift

●Glare

●Fluctuating vision

The optical complications most commonly encountered after radial keratotomy are undercorrection, overcorrection and induced astigmatism (regular or irregular) that can result in anisometropia and subsequent aniseikonia. The results of the Prospective Evaluation of Radial Keratotomy (PERK) Study2 showed that 28% of subjects were undercorrected by more than 1.00 D and 17% were overcorrected by more than 1.00 D after 4 years.3,4 After 10 years, the PERK Study Group found that 26% of subjects were more than 0.50 D undercorrected and 36%

15. Fitting Contact Lenses After Refractive Surgery 137

were more than 0.50 D overcorrected, indicating the need for optical correction after many years.5 Other problems after radial keratotomy (RK) include disabling glare, difficulty with vision in low illumination, monocular diplopia, and fluctuating vision.2–9

Irregular astigmatism is caused by differential scarring of the various incisions, inadvertent placement of an incision in the visual axis, a decentered optical zone, and microor macroperforations. Anisometropia, which may be the result of residual refractive error, results in retinal images of different sizes and may necessitate contact lenses, since glasses are intolerable.2–9

Glare may be caused from aberrations induced by incisions in the visual axis, scarring, or irregular astigmatism. Although most wavefront aberrations are a result of astigmatism or defocus, significant higher order aberrations have been found after radial keratotomy.8 Glare, light sensitivity, and poor vision in low illumination appear to be related to a small optical zone, a large pupillary diameter, and wide corneal scars. Symptoms are generally more intense in the first postoperative months and diminish proportionally with the decrease in the density of the scars. However, when persistent, glare can be made less problematic with a contact lens.9

Fluctuating vision is a problem secondary to incomplete healing of the corneal incisions. The cornea remains flexible after radial keratotomy, and abnormal collagen fibers are found within the incisions on histopathologic examination.2,10 The clinical manifestation of a flexible cornea is a diurnal variation in refraction. Some authors have suggested a relationship between this refractive instability and the alteration in corneal curvature. The corneal radius steepens throughout the day, resulting in a gradual myopic shift in power.11–15 Others suggest that the diurnal fluctuation is the result of stromal hydration and lid pressure. After RK, corneal thickness swells 4% to 5% more than the normal cornea after overnight lid closure, leading to a different refractive error in the morning for these patients.4,14–16 Lastly, others have found that intraocular pressure contributes to the diurnal change in visual acuity after RK. Higher intraocular pressures in the morning exert force on the cornea, allowing peripheral corneal steepening with central flattening as compared to the reduced intraocular pressures in the afternoon.7,17 Nonetheless, it is well known that, after RK, eyes measured in the morning show a flatter overall corneal shape, a more hyperopic refractive error, higher intraocular pressure, and increased corneal thickness compared to the same measures in the afternoon. In a study of 20 patients post-RK, two-thirds experienced fluctuating vision not related to the size of the optical zone. The refractive changes were present in 40% of patients two years after surgery. Fourteen percent of these required contact lens correction for part of the day, and 26% required lens wear all of the time.1 The most recent results from the PERK Study Group showed that diurnal fluctuation in refraction and visual acuity persists for at least 11 years after surgery.15 In practice, a significant number of patients after radial keratotomy demonstrate progressive

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hyperopia, and in many cases anisometropia and irregular astigmatism that are not amenable to spectacle correction.

2.When can a contact lens be fitted after radial keratotomy?

Ideally, contact lens fitting can be undertaken when topography and refraction appear stable. For this reason, one should wait at least 3 months, the minimal time necessary for the disappearance of peripheral corneal edema, stabilization of the scarring, and, as such, a decrease in the likelihood of contact lens–related complications.18–21 Extended wear and long wearing hours are discouraged to reduce contact lens– related diurnal fluctuation in vision and the risk of edema.

3.What are the contact lens options after radial keratotomy?

●Spherical rigid gas permeable contact lenses with high oxygen permeability (Dk).

●Hydrophilic contact lenses

●Special designs (both hydrophilic and rigid gas permeable lenses)

●Piggyback systems

●Hybrid contact lenses (Softperm )

The first choice of treatment should be a rigid gas permeable (RGP) contact lens. This lens, supported on the mid-peripheral cornea, stabilizes vision by creating a smooth and consistent optical surface. An ideal lens of this type is one made of fluorosilicone acrylate because of its high oxygen permeability. It permits better oxygen transmission to the cornea with less risk of complications compared to polymethylmethacrylate (PMMA), RGP lenses with a lower Dk, and hydrophilic lenses.

Soft hydrophilic contact lenses do not offer the benefit of stable and clear visual acuity because of the flexible nature of the material. In addition, because of lower oxygen permeability, they may increase the risk of corneal neovascularization to the incision scars.

A piggyback system—the combination of a soft lens under an RGP lens—is an option for patients with RGP intolerance. However, even with the advent of silicone extended wear disposable soft lenses, this system has the disadvantage of being more expensive, less convenient, and less healthy for the cornea than a RGP lens alone.

A hybrid lens offers greater convenience than piggyback systems but is more expensive and offers less oxygen transmissibility to the cornea. Both the rigid center and the soft skirt have a low Dk, which may lead to hypoxic conditions. This is complicated by the fact that these lenses tend to tighten on the eye, further increasing the risk of neovascularization and corneal edema. Both piggyback and hybrid options should therefore be avoided unless no other successful alternatives are available.