Prescription of glasses in children

Basics

1. Prescription Of Glasses In Children Eranda Wannigama

2. Objectives Definition of terms.(Refractive errors) Developmental aspects. Refraction in children: What should I prescribe? Guidelines for prescribing Glasses in children. What is Amblyopia ? How to Manage Anisometropic Amblyopia ?

3. Emmetropia Is the refractive state in which parallel rays of light from a distant object are brought to focus on the retina in the nonaccommodating eye The far point of the emmetropic eye is at infinity, and infinity is conjugate with the retina.

4. Ametropia Ametropia refers to the absence of emmetropia and can be classified by presumptive etiology Axial Refractive . Eyeball is either unusually long (myopia) Eyeball is either unusually Short ( hyperopia ) length of the eye is statistically normal, Refractive power of the eye (cornea and/or lens) excessive (myopia) Refractive power of the eye (cornea and/or lens) deficient (hyperopia).

5. Myopia Myopia with accommodation relaxed. Parallel light rays from infinity focus to a point anterior to the retina, forming a blurred image on the retina. Light rays emanating from a point on the retina focus to a far point in front of the eye , between optical infinity and the cornea.

6. Hyperopia Hyperopia with accommodation relaxed. Parallel light rays from infinity focus to a point posterior to the retina , forming a blurred image on the retina. Light rays emanating from a point on the retina are divergent as they exit the eye, appearing to have come from a virtual far point behind the eye.

7. Divide in to several parts based on ability of eye to cope up with the refractive error. Total hyperopia =full amount of hyperopia Latent hyperopia =potion of total error can over come with accommodation. Attempt to correct this will result in blurring of vision. Absolute hyperopia =potion can’t be corrected by accommodation. Total hyperopia = Latent + Absolute Hyperopia

8. Astigmatism Astigmatism [A ~ without, stigmos ~ point] is an optical condition of the eye in which light rays from an object do not focus to a Single point. because of variations in the curvature of the cornea or lens at different meridians . Instead, there is a set of 2 focal lines. Each astigmatic eye can be classified by the orientations and relative positions of these focal lines

9. If principal meridians (or axis) of astigmatism have constant orientation at every point across the pupil, and if the amount of astigmatism is the same at every point, it is known as Regular astigmatism - is corrected by cylindrical spectacle lenses. Regular astigmatism may itself be classified into with-the-rule and against the-rule astigmatism In Irregular astigmatism, the orientation of the principal meridians or the amount of astigmatism changes from point to point across the pupil. Eg .. Keratocornus Astigmatism… ctd

10. Oblique astigmatism =principal meridian at 45 o or 135 In with -the-rule astigmatism the vertical meridian is steepest (resembling an American football lying on its side), correcting minus cylinder should be used at or near axis 180°. In against-the-rule astigmatism the horizontal meridian is steepest (resembling a football standing on its end), and a correcting minus cylinder should be used at or near axis 90°

11. Definition of terms Spherical equivalent is the algebraic sum of the spherical component and half of the astigmatic component. Eg.+3.00DS-1.00DC x 90 –SE=+2.50 Anisometropia refers to any difference in the spherical equivalents between the 2 eyes. Aniseikonia - binocular condition in which the apparent sizes of the images seen with the two eyes are unequal.

12. Developmental aspects….. An interplay among corneal power, lens power, AC depth, and AL determines an individual's refractive status. All 4 elements change continuously as the eye grows. On average, babies are born with about 3-8 D of hyperopia. In the 1 st few months of life, this hyperopia may increase slightly, but it then declines to an average of about 1.0 D of hyperopia by age 1 year. Up to 7 years slightly hyperopic. 7 to 8 years myopic shift towards Plano. After 14 years eye become Emmetropic.

13. Prescribing for Children In adults, the correction of refractive errors has one measurable endpoint: the best-corrected visual acuity.(BCVA) Prescribing visual correction for children often has 2 goals: 1. providing a focused retinal image. 2.Achieving the optimal balance between accommodation and convergence.

14. Why it is difficult to prescribe? Challenges, especially while dealing with younger children, 1.lack of subjective response . inability to co-operate with subjective refraction techniques . 2. poor attention span 3.Need for good cycloplegia . optimal refraction in an infant or a small child (particularly with esotropia )requires the paralysis of accommodation with complete cycloplegia . Hence most guidelines for prescription of glasses in children are based on clinical experience rather than randomized, masked clinical trials.

15. Presentation Clinical presentation in refractive errors may vary from completely asymptomatic to strabismus . It is important to remember that, children, even those with severe visual impairment, rarely complain of poor vision.

16. Most children will report to ophthalmologist, 1 .If parents or teachers notice abnormal visual behavior. 2 .Some children may be picked up on failing routine school screening. 3 .Intermittent strabismus can also be a presenting complaint. 4. Recurrent styes or chalazions occurring in a child is an indirect pointer toward need for refraction. 5 .Older children may occasionally complain of symptoms of asthenopia such as headache and eye strain Presentation

17. Cycloplegia It is absolutely mandatory to relax accommodation before attempting refraction in children. Incomplete cycloplegia often leads to over- or underestimation of refractive errors. Choice of cycloplegic agent in most pediatric clinics would be cyclopentolate 1%.Two drops of cyclopentolate 1% are administered at 5 min intervals and refraction should done 30 min after 2 nd drop

18. Retinoscopy Manual retinoscopy is more reliable than autorefractometers . Autorefractometer tend to overestimate myopia because they induce proximal convergence and accommodation

19. Guidelines for prescribing glasses Three questions to be answered before prescribing: 1. Is this error amblyopiagenic? 2. Is this error significant for the visual needs of the child depending on his age? 3.Will this error cause any effect on the strabismus if present? With these three questions answered, it is possible to prescribe glasses even if there is no subjective response from the child. By general consensus, hyperopia of more than +4 D, myopia of more than -4 D and astigmatism of more than -1.5 D is considered as amblyopiagenic .

20. Myopia Myopia entails relatively less risk of amblyopia , and prescription for symmetric myopia should solely rest on visual needs of the patient depending on the age. Infants are not expected to view things in fine details or distant objects , hence low-to-moderate myopia may not need prescription. However, if myopia exceeds-4 D , then it is likely to cause visual blur and amblyopia hence needs prescription.

21. School-going children need full correction of myopia.There is no role oundercorrecting myopia or overcorrecting it. Overcorrecting myopia can be detrimental and may cause accommodative spasm leading to severe asthenopia and esotropia . Only one circumstance where over minused glasses may be prescribed is the presence of intermittent divergent strabismus.Minus glasses are used to induce accommodation and thus accommodative convergence to control exotropia . This can be a strategy to delay surgery in young children. These children need to be followed closely and should they develop esophoria minus glasses should be discontinued. Myopia

22. Hyperopia The appropriate correction of childhood hyperopia is more complex than that of myopia. 1 st , children who are Significantly hyperopic (>5 D) are more Visually impaired than their myopic counterparts, who can at least see clearly at near. 2 nd , childhood hyperopia is more frequently associated with strabismus and abnormalities of the accommodative convergence/accommodation (AC/ A) ratio .

23. following are general guidelines for correcting childhood hyperopia : Unless there is esodeviation or evidence of reduced vision. it is not necessary to correct low hyperopia . As with myopia, Significant astigmatic errors should be fully corrected. Hypermetropia is very common in infants and children, and requires a full correction in the presence of esophoria or esotropia . It is also wise to correct it if there is a family history of esotropia Hyperopia

24. Moderate or high degrees of hypermetropia require correction to achieve good visual acuity, And more than 1 D of hypermetropic anisometropia must be corrected to prevent refractive amblyopia in the more hypermetropic eye. Hyperopia

25. The uncorrected hypermetropic child overcomes some or all of his hypermetropia by exercising extra accommodation. When glasses are worn for the first time, the accommodation may not relax and the vision will be blurred. Usually the accommodation relaxes after a few days with the use of glasses. , but it is wise to warn the parents about this when the glasses are prescribed. Occasionally the accommodation fails to relax and the prescription needs to be reduced for a while, or a short course of cycloplegic drops may do the trick. Hyperopia

26. To summarize , Any child above 2 years of age who has hyperopia of more than 4 D needs prescription. If there is any coexisting esotropia or phoria , then full cycloplegic correction is mandatory. In older children who are capable of subjective response , post- mydriatic test (PMT) can be done to give optimal hyperopic correction for comfortable distance as well as near activities. Hyperopia

27. Astigmatism Mild-to-moderate meridional astigmatism of up to 1.5 D produces minimal degradation of visual acuity in children and may not be amblyogenic when symmetrical. Oblique astigmatism degrades visual acuity more and is more amblyopiagenic. Preverbal children with symmetric astigmatism 1.5 D typically do not need correction unless the astigmatism is associated with high myopia or high hyperopia.

28. The Pediatric Preferred Practice Pattern for Children aged 2–3years suggests prescription if astigmatism exceeds 2D. School-going children with 1.0–1.5 D of astigmatism may benefit from correction, and a trial of spectacles is probably warranted for such children. In all such situations, one should prescribe the full cylinder that can be tolerated Astigmatism

29. Anisometropia can be a very powerful amblyogenic factor and almost always asymptomatic . Anisometropia is usually detected either on a routine eye examination or following a failed screening or is detected accidentally following trauma to better eye . The vision screening committee of AAPOS recommends that a difference of 1.5 D between two eyes is considered significant anisometropia . Anisometropia

30. Anisometropia . Contact lenses should be considered if there is significant anisometropia to cause aniseikonia . It must be said that children are able to tolerate aniseikonia much better than adults , and hence if there is intolerance to Contact lenses or socioeconomic factors preclude use of contact lens, give appropriate glasses in such situations.

31. What is Amblyopia? Early in life resulting from one of the following: 1. Strabismus(Commonest) 2.refractive ( Anisometropia or high bilateral refractive errors( isometropia ), 3. Stimulus deprivation Amblyopia is a unilateral , less commonly, bilateral reduction of best-corrected visual Acuity that cannot be attributed directly to the effect of any structural abnormality of the Eye or the posterior visual pathways . Amblyopia is caused by abnormal visual experience

32. How to Manage Anisometropic Amblyopia Prescribing the optimum refractive correction is the first step in the treatment of amblyopia . It provides a clear image to the fovea of the amblyopic eye. Not all degrees of refractive error are thought to induce amblyopia. 

33. Guidelines for the management of strabismus and amblyopia were published by the Royal College of Ophthalmologists • LogMAR tests of vision should be used where possible. • Amblyopia treatment should only be instituted for children whose vision falls below the normal range for age . • Significant refractive errors should be corrected. • Improvement in acuity following refractive correction should be allowed to plateau prior to treatment with occlusion or atropine – this may take 16 – 22 weeks • The choice of atropine or occlusion treatment should be discussed with parents

34. • 2 hours patching per day is effective for amblyopic defects from 0.2 to 0.6 LogMAR (6/9 to 6/24 Snellen ) • 6 hours patching per day is effective for acuities below 0.6 LogMAR (6/24 Snellen ) • Failure of acuity to improve with patching or atropine treatment should prompt re-refraction and re-examination of the fundus • Deterioration of acuity during treatment in the absence of an ocular cause should prompt consideration of neuroimaging Guidelines for the management of strabismus and amblyopia were published by the Royal College of Ophthalmologists

35. Special situations Children with refractive accommodative esotropia with high AC/A ratio require appropriate bifocal add for near should be given.

36. Special situations Certain clinical situations require out-of-box thinking; in these cases, it may not be enough to correct refractive error alone. Aphakic and psuedophakic children need correction for distance as well as for near. Infants who are aphakic need to be prescribed their near correction as a single-vision glasses to allow them to function optimally. As they grow older, bifocal glasses can be prescribed. Pseudophakic children need to be given full correction as there is no residual accommodation after cataract surgery. Near correction can be given as bifocals or progressive glasses. Photochromatic or tinted glasses need to be prescribed in children with Albinism and cone dystrophy.

37. Special situations One-eyed children should be given protective polycarbonate glasses even if there is no refractive error to prevent injury. Last but not the least, attention should be paid to fit and design of spectacle . Poorly fitting or ugly spectacle often means poor compliance. To summarize, Refraction is one of the simplest tests to be performed but highly rewarding to both patient and the physician.