Abstract
Purpose of review: The diagnosis and successful treatment of visually significant refractive errors in children are a subject of continued study and debate.
Recent findings: Treatment of significant refractive errors is widely accepted to reduce lifelong vision loss from amblyopia. Children aged 3–5 years may be screened for unexplained vision loss, refractive errors and amblyogenic factors using traditional eye charts as well as newer modalities such as autorefractors and photoscreeners. The accuracy of various screening methods is variable throughout the literature. Debate remains as to who is best suited to administer vision screening tests. Compliance with follow-up with an eye-care professional once a child is identified with an amblyogenic factor remains suboptimal. Treatment of significant refractive errors in certain populations of pediatric patients with refractive surgery shows promise but requires further study.
Summary: The timely diagnosis of significant refractive errors in children remains a significant challenge, especially for ages 3–5 years, but treatment may provide significant improvement of visual acuity and quality of life.
Abbreviation IOL: intraocular lens.
Introduction
Diagnosis of significant refractive errors in children remains a diagnostic and public health dilemma. Treatment of amblyogenic hyperopia, astigmatism, anisometropia and myopia can prevent legal blindness and vision loss. The difficulty remains how to screen large numbers of children in a timely and cost-efficient way. Traditional vision screening methods using eye charts in children aged 3–5 years requires their cooperation as well as proficiency in testing by the examiner. Alternative methods such as autorefraction and photoscreening have been developed to address the difficulties in screening young children. Treatment of refractive errors with spectacles alone can resolve refractive amblyopia in some cases. Refractive surgery to treat children with special needs that preclude spectacle or contact lens use shows promise but requires further long-term safety evaluation.
Epidemiology
Population-based studies attempt to determine the prevalence of untreated refractive error and its disability. In the United States, an estimated 5–7% of preschool children have significant refractive errors and 1–4% have amblyopia [1]. Recent studies have reported a substantial amount of refractive visual impairment in pediatric populations around the world, including 10.4% in a predominantly Caucasian Australian 12-year-old population, 11.2% in a rural Chinese population, 9.8% in an urban Chilean sample, and 20.2% and 21.3% in Malaysian and urban Chinese populations, respectively [2].
Diagnosis of refractive errors
Traditional vision screening with acuity charts and ocular alignment testing starting at the age of 3 is recommended by the American Academy of Pediatrics [3]. Many children do not receive proper vision screening due to inadequate training of office staff, time constraints and lack of confidence in screening results. Traditional vision screening methods for young children aged 3–5 years using eye charts such as the HOTV, Lea, Tumbling E's and Allen pictures as well as the Random Dot E or Titmus Fly stereoacuity tests require comprehension and cooperation. Newer techniques such as autorefraction and photoscreening attempt to remedy some of the difficulties faced when screening young children. Despite new techniques to screen young children, the accuracy of all methods is variable even among trained eye professionals [4].
The Vision in Preschoolers study found that two different autorefractors (Retinomax Autorefractor and Suresight Vision Screener) detected 15% more amblyogenic factors than photoscreeners (MTI and iScreen) with the same number of false positives when used by licensed eye-care professionals. Debate remains within the literature as to which method of screening in children aged 3–5 years old is most effective when performed by staff in the pediatrician's office. The Vision in Preschoolers Study Group [5] found that nurse and lay screeners using both autorefractors and conventional Lea symbols achieved similar detection rates in children aged 3–5 years needing comprehensive eye examinations due to the presence of amblyopia, strabismus, significant refractive error or unexplained reduced visual acuity. Autorefraction in a noncyclopleged state may result in overdiagnosing and treating myopia. Cycloplegia decreases the tendency for autorefractors to overestimate myopia, and more closely resembles the refractions determined by subjective refraction [6].
Higher order aberrations and their influence on the quality of vision remain a significant field of study. Refractive surgery in the adult population aims to address higher order aberrations to improve the postoperative outcome and vision quality. Wavefront sensors – aberrometers – have recently been developed and are used to identify higher order aberrations in addition to spherical and cylindrical errors. Their accuracy and applicability in the pediatric population were addressed in a study by Martinez et al. [7]. They found the Canon RK-F1 autorefractor (Canon Inc., Tokyo, Japan) and Complete Ophthalmic Analysis System G200 aberrometer (Wavefront Sciences Inc., Albuquerque, New Mexico, USA) were equivalent under cycloplegic conditions. This observation suggests that the aberrometer may be a reliable tool to screen children for significant refractive errors, but further study is required.
Cycloplegic refraction using retinoscopy and loose lenses remains the standard method of refraction in children. This can be difficult when a child becomes uncooperative when lenses are held close to the face. ‘Estimation retinoscopy’ performed using only a retinoscope – a scale dependent on the brand of retinoscope and the distance from the spectacle plane where neutrality is achieved – may be a useful technique in diagnosing low levels of myopia, hyperopia and astigmatism [8•]. The accuracy of estimation retinoscopy was equivalent to standard retinoscopy in patients with spherical equivalents of less than 4D myopia and less than 2D hyperopia in Wallace et al.'s [8•] study of 50 children. It seems that this technique would be best suited as a screening technique to determine whether amblyogenic refractive errors exist in poorly cooperative children such as those with autism or developmental delays. The disadvantage to this technique is that the scale for the retinoscope is not readily available, and even the authors reported that this technique does require practice.
Photoscreening involves taking two Polaroid images of each eye with a portable camera such as the MTI photoscreener (Medical Technology Industries, LLC, Riviera Beach, Florida, USA). The photographs are then sent to an interpretation center where they are read by trained evaluators to detect amblyogenic factors, including high refractive errors, anisometropia, strabismus, eyelid ptosis and media opacities. Referral rates for possible amblyogenic factors have been reported as around 4%, follow-up rates of referred children around 80% and a positive predictive value of approximately 65% [9,10]. The disadvantage to photoscreening is that the interpretation of photographs requires training, feedback is not immediate, and the techniqie is more costly than traditional vision screening. Some studies [11] suggest that photoscreening is more likely to detect amblyogenic factors than traditional vision screening in 3–4-year-old children. Proper evaluation by an eye-care professional remains an obstacle to the diagnosis and treatment of possible amblyogenic factors no matter what the means of their identification. A large community-based preschool vision screening program [9] found only about 50% of children referred received follow-up care. Multiple issues including lack of insurance, eye-care provider availability and parental understanding negatively impact the likelihood of compliance with referrals [12•].
Treatment of refractive errors with corrective lenses
Treatment of refractive error is based on the degree of myopia, hyperopia, astigmatism and anisometropia. The age and visual demands of the individual patient should also be taken into account. There are no strict guidelines for prescribing glasses in children. Myopes with a visual acuity worse than 20/30 and hyperopes with a cycloplegic refractive error around +5 diopters (D) would probably benefit from corrective lenses. Patients with astigmatism of +1.50 to +2.0 D would also probably benefit from glasses. The full cycloplegic refraction need not be prescribed in hyperopic patients unless strabismus is present. Between 0.5 and 1 D may be subtracted from the cycloplegic refraction. Myopes should be prescribed their full correction. Anisometropic amblyopia is an indication to prescribe glasses. The condition often results when there is more than 1 D of difference between the two eyes. The amount of anisometropia and the age of the individual affect the magnitude of amblyopia. A study by Donahue [13•] of preschool children with anisometropia detected by photoscreening found that only 14% of children aged 1 year or younger with anisometropia had amblyopia, whereas 40% of 2-year-olds and 65% of 3-year-olds had amblyopia. He also found that the depth of amblyopia increased in severity with age. Moderate amblyopia prevalence was 2% up to 1 year of age, 17% for 2-year-olds, and 45% for ages up to 6–7 years. Severe amblyopia was rare in children up to the age of 3 years, 9% at age 4 years, and 14% at age 5 years.
Refractive amblyopia and glasses
Treatment of refractive amblyopia first requires corrective lenses and compliance with spectacle wear. Amblyopia studies indicate that a fair number of children will have improvement or even resolution of their amblyopia with spectacle correction alone [14]. A study by the Pediatric Eye Disease Investigator Group [15•] found that anisometropic amblyopia in children aged 3 to less than 7 years improved at least two lines in 77% of patients and resolved in 27% with spectacle correction alone. Some children will require further amblyopia treatment, which can include patching the sound eye several hours a day while wearing their glasses. Patching the sound eye 2 h a day for moderate amblyopia has been shown to be effective [16]. Atropine penalization of the sound eye has been shown to be equally effective in treating amblyopia in hyperopic children. Cost–utility analysis for amblyopia therapy suggests that it is cost-effective compared with other interventions in healthcare [17].
Medications and refractive error
There have been numerous studies that try to determine what may help decrease the magnitude of myopic progression and axial elongation in children. Topical atropine has shown some modest benefit in decreasing myopic progression and axial elongation. A 2-year study by Chua et al. [18•] found that treating myopic Asian children with atropine decreased the mean progression of myopia and axial elongation. The treatment group had a myopic progression of -0.28 ± 0.92 D and essentially unchanged axial lengths (-0.02 ± 0.35 mm). The placebo group had a myopic progression and axial elongation of -1.20 ± 0.69 D and 0.38 ± 0.38 mm, respectively. Pirenzepine is another medication that has been used in clinical trials to decrease myopic progression and has been found to have modest success [19,20].
Refractive surgery
Refractive surgery for children with significant refractive errors remains a field of investigation. Surgical intervention is often reserved for children with severe and refractory amblyopia secondary to high anisometropia, high myopia and poor compliance with conventional spectacle and/or contact lens correction and amblyopia therapy. Patients with significant developmental delay or behavior abnormalities that preclude the use of glasses or contact lenses are also potential candidates for refractive surgery. Procedures under investigation to treat these patients include clear lens exchange, phakic intraocular lens (IOL) and corneal ablation procedures such as laser-assisted subepithelial keratectomy and laser-assisted in-situ keratomileusis. All procedures require general anesthesia.
Clear lens extraction and refractive lens exchange
Treatment of significant refractive errors beyond the scope of corneal ablation procedures, laser-assisted in-situ keratomileusis or laser-assisted subepithelial keratectomy may benefit from clear lens exchange or extraction. Children with high myopia and neurobehavioral conditions that preclude spectacle or contact lens use pose a significant treatment challenge. Tychsen et al. [21••] published a series of 13 children (mean age 10.4 years, range 1–18 years) with neurobehavioral disorders, chronic noncompliance with spectacle wear and high myopia (-14.25 to -26.0 D, mean -19.1 D) treated with lensectomy in 10 eyes and treated with lensectomy and IOL implantation in 16 eyes. The target postoperative refraction was +1.0 D. The average postoperative myopia corrected by surgery was 19.9 D, 81% (21 eyes) were corrected within ± 2 D of the goal refraction and 19% (five eyes) within ± 4 D. Uncorrected visual acuity was reported to increase an average of two log units in all 26 eyes. Improvement in behavior and visual function was found in 14/16 children. Complications included myopic regression (average -0.16 D/year), capsular opacification requiring secondary membranectomy in 12 eyes (46%), and retinal detachment in one eye. Long-term safety has not been established in this population of patients that have a significant risk of retinal detachment and glaucoma. Close follow-up and further investigation are strongly recommended.
Phakic intraocular lens
A recent pilot clinical trial [22••] was the first US study to evaluate the benefits of a phakic anterior chamber IOL in children with unilateral high myopia and anisometropic amblyopia. Five children aged 6–10 years with high myopic anisometropia greater than 6 D, dense refractive amblyopia, and poor compliance with contact lens use were treated with phakic anterior chamber lens placement (Verisyse, AMO, Irvine, California, USA). After a postoperative follow-up of 6 months, three patients had significant improvement in their visual acuity of more than six lines (Allen/Snellen) and two patients had moderate improvement of more than four lines. No vision-threatening complications occurred. One complication found in adult patients treated in Europe with phakic IOLs for high myopia was cataract formation (prevalence 2% with anterior chamber lenses, 4–44% with posterior chamber lenses) [23–25]. Pigment dispersion and endothelial cell loss have been reported in Europe in children treated with phakic IOLs [26]. It has been suggested that implantation of a phakic IOL should be done only if the anterior chamber depth is greater than 3.2 mm in order to help minimize endothelial cell loss and cataract formation [27,28]. Eye rubbing can induce lens–IOL touch and can be difficult to prevent in the pediatric population. The long-term safety of these procedures performed in children remains undetermined.
Photorefractive keratectomy/laser-assisted in-situ keratomileusis/laser-assisted subepithelial keratectomy
Treatment of significant myopic refractive errors in children who are noncompliant with spectacles or contact lenses, and particularly in those with neurobehavioral problems, may benefit from corneal refractive procedures such as photorefractive keratectomy, laser-assisted in-situ keratomileusis or laser-assisted subepithelial keratectomy. Short-term complications of corneal ablation procedures in children include the relatively common occurrence of myopic regression and corneal haze. Long-term complications remain relatively unknown. A study by Paysse et al. [29••] examined the long-term outcome of 11 children, ages 2–11 years, treated with photorefractive keratectomy for severe anisometropic amblyopia. The mean follow-up period was 31 months. Regression over the first 12-month period for the myopic group was 2.50 ± 2.23 D, and was 1.10 ± 1.6 D for the hyperopic group. They reported that refractions stabilized 1 year after surgery. Regression rates (from 1 year after surgery to the last follow-up) of 0.50 ± 1.41 D (myopes) and 0.60 ± 0.57 D (hyperopes) were found. The best corrected visual acuity of the treated eyes improved in four of seven (57%) patients by at least two lines, one improving by seven lines. Stereoacuity improved in five of nine (55%) children. A study by Tychsen and Hoekel [30••] found that myopic regression in bilateral high myopes was greater in children treated with laser-assisted subepithelial keratectomy with a mean regression of -0.81 D/year versus -0.22 D/year for those treated with lens extraction. The authors recommended intentional overcorrection by 1–2 D in most children treated with corneal ablation procedures to compensate for myopic regression. Further long-term safety and efficacy studies are recommended.
Conclusion
Various methods are available to screen children for refractive errors and amblyogenic factors such as anisometropia. Traditional eye charts as well as newer methods including autorefractors and photoscreeners all have advantages and disadvantages. There is no consensus as to which method is the most likely to detect children at risk for vision loss from amblyogenic factors. Referral and compliance with follow-up with an eye-care professional remain obstacles to treatment no matter what screening method is used. Refractive surgery shows promise in treating certain cases of severe refractive amblyopia and in children with neurobehavioral disorders. The long-term safety of refractive surgery for children remains unknown and requires further study.
References and recommended reading
Papers of particular interest, published within the annual period of review, have been highlighted as:
• of special interest
•• of outstanding interest
Additional references related to this topic can also be found in the Current World Literature section in this issue (p. 435).
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Keywords: amblyopia; anisometropia; photoscreening; refractive errors; refractive surgery
Accession Number: 00055735-200709000-00006