Introduction
Refractive errors are common in children.[1] These refractive errors are expected to change with the increasing age of the subject.[2] While myopic powers may increase in early childhood and late teens, hyperopic powers usually decrease.[3]
Refractive errors result from the inability of the ocular refractive apparatus to sufficiently and accurately bend rays of light to a point focused on the retina. The prevalence of blurred vision precipitated by refractive errors amongst school-age children may reduce attention to detail, create a lack of interest in classwork and result in poor academic performance.[4] Uncorrected refractive errors in children may be correlated to higher child morbidity, poor academic accomplishment, and overall reduced educational opportunities.[5][6]
In some cases, significant refractive errors and spectacle use in parents may increase the likelihood of refractive errors in children being picked up earlier.[5][7]
Children possess an active and malleable accommodation, which is attributable to the elasticity of the crystalline lens, intact extrinsic properties of the crystalline lens fibers, and degree of aggregated lens fibers. Consequently, children are more prone to vergence and accommodative dysfunctions, giving rise to binocular vision anomalies. The amplitude of accommodation tends to gradually and progressively recede in flexibility and magnitude with age.[8]
The higher amounts of the amplitude of accommodation in children provided by the crystalline lens elasticity can mask a refractive error and bring parallel rays of light traveling from a distant object into focus on the retinal. This may grant the eye a pseudo-emmetropic status. This compensatory mechanism may break down with time resulting in fatigue and expressed symptoms. Children may have difficulty understanding their experience and relating their visual complaints and associated ocular discomfort to their parents and guardians.[9]
This necessitates visual screening. A thorough evaluation can identify potential vision problems and eye disorders. Visual screening of children and teenagers, which can be done formally and informally, can help identify refractive errors, thus, enabling prompt medical attention.[10]
In regions with limited resources, teachers can be trained to conduct vision screening.[11] Spectacles are the most common means to manage and address refractive errors.
Vision is commonly measured and recorded as visual acuity. Visual acuity is a measure of the resolving power of the human eye.[12] It is customary for clinicians to denote an individual's visual acuity using a fraction.[13] The upper value usually indicates the test distance, while the lower value indicates the size of the letter or optotype read. Visual acuity can also be measured by calculating the minimum angle of resolution (MAR). The MAR is usually the reciprocal of the visual acuity when written as a fraction, i.e., visual acuity of 20/80 corresponds to a MAR of 4. The logarithmic value of the MAR (logMAR) is also a good indicator of visual acuity.[13]
Function
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Function
Uncorrected refractive error constitutes a leading cause of preventable visual impairment and blindness, creating a significant public health burden with enormous economic implications. The overall public health impact of uncorrected refractive error and other causes of preventable visual impairment has increased appreciably as the population increases and ages thus, forms an important basis of eye care advocacy in public health policies.[14]
These policies tend to be targeted at facilitating early diagnosis and providing adequate management of refractive error. Various options are available for the management of refractive errors. However, spectacle correction is the most common option used in managing refractive errors in children. The prescribing philosophy of spectacle prescription in children is determined by the age of onset, magnitude and type of refractive error, accommodative anomalies, and the presence of latent and manifest deviation. Although most children have similar amounts of refractive errors in both eyes, anisometropia remains the most common cause of amblyopia among this group.[15]
Myopia is more prevalent in children who frequently engage in indoor activities and near work when compared to those children that tend to spend more time outdoors.[16] Geographically, the prevalence of myopia remains higher in Asia (60%) compared to Europe(40%).[16] Minus spherical prescriptions are used to correct myopic patients. The prevalence of myopia among school children reduces when a cycloplegic agent temporarily suspends accommodation.[16]
Hyperopia is a refractive abnormality in which parallel rays of light incident on the eye are brought to focus behind the retina.[17] A plus-powered spherical prescription is used to move the image from behind the eye and onto the retina. Uncorrected hyperopia in children can impair visual development, leading to amblyopia and strabismus.[18] This notion, however, has been questioned by several authors reported in the literature.[19]
Astigmatism is commonly encountered in prescription glasses for first-grade children.[20] Spherocylindrical prescriptions are used in astigmatic refractive errors. In correcting astigmatism, the spherical component of the sphero-cylindrical lens is used to place the circle of least confusion (an imaginary blur circle that lies mid-way in the interval of Sturm) on the retina. The cylindrical component is used to collapse the interval of Sturm onto the retina, thus providing a clear image.[21] Early correction of the refractive error enables the nascent visual system development and reinforces second and third-degree fusion.
Special charts may be needed for screening children for refractive errors before prescribing lenses.[22][23][24] Examples of charts are Lea symbol charts, HOTV, Snellen-E charts, and the e-MOVA test.[22][25][26][27] A clinician may opt to use Mohindra retinoscopy if the child is not attentive during standard retinoscopy or is too restless for autorefractometry.[28] It is usually advisable to book children in the mornings when they are still active. Examination sessions should not be excessively long, considering that children tend to be less collaborative if tired or bored.
Several pharmaceutical cycloplegic agents are available for cycloplegic refraction. Atropine drops provide the strongest cycloplegia, with effects that may last up to fourteen days. The cycloplegic effect of homatropine and scopolamine closely approximates each other and may last up to three days. Other drops like cyclopentolate and tropicamide may last from several hours to one day.
Although tropicamide exacts a more mydriatic effect, it's primarily used when weak cycloplegia is required, as in older children. Due to the sympathomimetic effects of cycloplegic agents, efficacy and safety must be considered before use. Studies based on efficacy and safety suggest using tropicamide 0.5% combined with phenylephrine 0.5% in older children.[29] Occlusion of the lacrimal punctum prevents or minimizes systemic absorption, thereby reducing systemic toxicity.
Issues of Concern
Suppression is usually a manifest secondary adaptation used by the visual system to overcome diplopia in children. Suppression is usually detected using first or second-degree fusion tests such as the Maddox rod and Worth four-dot test. This test accesses the presence or absence of suppression via the temporary disruption of fusion. Clinically, this is achieved by presenting dissimilar images or objects of contrasting characteristics to each eye. Uncorrected refractive error in children may therefore be a risk for suppression as unequal amounts of ametropia may result in dissimilar images reaching the retina.
Individuals with significant differences in refractive error between both eyes may also suffer unequal retinal images due to the magnification (or minification) properties of spectacles. The amount of anisometropia that may trigger a breakdown of binocular vision is still up for debate.[30] This condition, called aniseikonia, is another risk factor for suppression.[31]
Aniseikonia can be corrected by dispensing iseikonic lenses. However, these spectacles tend to be very expensive and are not easily available. Contact lenses have also shown promise in mitigating the occurrence of aniseikonia.[32] Suppression, in turn, is a precursor for manifest deviations (strabismus).[33] Common symptoms of a child with aniseikonia include complaints of double vision, drowsiness on near work, and gaze imbalance.[34]
Strabismus is easily identified by an inward (eso) or outward (exo) turning of one or both eyes. Refractive amblyopia, a term used to describe vision loss secondary to uncorrected refractive error, is most commonly associated with anisometropia.[35] Early diagnosis and prompt management are of utmost importance in addressing this public health concern.
Clinical Significance
The development of the visual system during the age of active neural plasticity depends on several factors, including the quality of the visual stimulus, the integrity of the visual pathway, and the child's general health status.[36]
The quality of the visual stimulus sent to the cortex is further determined by the accurate bending of rays of light entering the eye to focus on the retina. In the presence of a refractive abnormality, parallel rays of light incident on the anterior refractive apparatus of the eye are refracted incorrectly. Therefore, the refracted light rays fall in front of or behind the retina. In astigmatism, refracted rays form a two-point focus due to the meridional difference in the refractive structures of the eye.
Accommodation is the ability of the eye to exact a given dioptric change in power with respect to a change in viewing distance to keep the retinal image clear. The stimulus to accommodation is a blurred retinal image. The increased crystalline elasticity and amplitude of accommodation, which is common in this young age group, tend to predispose children to slightly overestimated myopia when objective refraction is done without cycloplegia.[37] Non-cycloplegic auto-refraction is mostly inaccurate for determining the type and magnitude of refractive error in children.[38]
Refractive error determined by Mohindra retinoscopy is comparable to static retinoscopy when the accommodative tonus is eliminated by a cycloplegic agent.[39] The choice of preferred retinoscopy procedure depends on the preference of the clinician. Adequate spherical and cylindrical correction ensures that visual stimulus of satisfactory quality is achieved, thereby enabling normal visual development. Care is necessary when examining children with acute visual symptoms and loss of visual acuity, which may be caused by underlying morbid conditions that could mimic uncorrected refractive error symptoms.[40][41]
Other Issues
Stigmatization of Glasses Among Children
There is still considerable stigmatization of children wearing glasses, especially in public, among children with big or high-powered lenses.[42] Children may be wary of wearing a pair of frames that may make them look different from their classmates. However, they may also be motivated to use them regularly if a good example is set by close friends that use spectacles. A trip to the school to meet with the classroom teacher can be useful in convincing the child to use spectacles regularly at school. Studies have reported that children tend to associate wearing glasses with smartness and excellence in sports.[43]
Older children are more likely to be embarrassed among peers when compared to younger age groups.[44] Broken and lost glasses are other reasons that limit regular spectacle use among children.[45] Studies have reported less spectacle use in rural areas, which may be because children from rural areas are screened three times less than their metropolitan counterparts.[46]
Economic shortages, beliefs that children will "outgrow" the need for glasses, and reduced staff are a few factors responsible for the disparity in screening rates.
Cosmesis and Frame/Lens Materials
The selection of spectacle frames for a child involves standard measurements similar to those for adults. With children, however, it is essential to assess the fit and stability of the spectacles on the child's face. It is important to address the child's preferences when choosing the right glasses, which can help accept and collaborate the regular spectacle use. Red-colored plastic frames were found to be a favorite among children.[47]
Rectangular glasses and spectacles with straight earpieces are also popular choices.[47] A good practice is allowing children to be actively involved in selecting frames for the glasses.
Enhancing Healthcare Team Outcomes
Prescribing glasses for children is a responsibility that starts at the homefront, even before it gets to the clinic. Parents must be observant of tell-tale signs of poor vision. Children with visual problems tend to sit relatively close to the television or hold books close to their eyes to read. Some children may complain of asthenopic symptoms, while preverbal toddlers may have difficulty reaching for objects. These signs may be helpful to parents in seeking early vision testing to screen for uncorrected refractive errors. When spectacles are prescribed for children, parents can also be influenced by the price, quality, and type of frames (Level 3).[47]
It is advisable to book children for morning appointments at the clinic when they will be more alert compared to evenings. Weekend appointments may also be better compared to weekdays, considering that school can make children tired and less collaborative. Numerous clinics have a child-friendly section that helps children relax during eye examinations and improves cooperation. The clinician must be efficient and thorough when examining children, considering that these age groups tend to bore easily and be less cooperative if not properly stimulated.[48]
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