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myopia
Myopia, or nearsightedness, is a refractive error where light rays focus in front of the retina when the eye is at rest. It can be classified as simple myopia, pathological myopia, or acquired myopia. Simple myopia is usually not associated with eye disease and typically does not exceed -6 to -8 diopters. Pathological myopia is a rapidly progressive form that can lead to high myopia over -10D and degenerative changes in the retina and choroid. Treatment includes optical correction with glasses or contacts, and refractive surgery such as LASIK for higher degrees of myopia. Prognosis is generally good for simple myopia but guarded for pathological myopia due to risk of vision
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myopia
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- 2. SOURCES 2 • Theory andpractice of optics and refraction by AK Khurana • Borish’s clinical refraction • Strabismus simplified,Pradeep Sharma • Parsons’ Diseases of the Eye - 22nd Edition, 2015
- 3. OUTLINE • Optics ofmyopia • Classification • Treatment of myopia • Complications • Prognosis
- 4. MYOPIA • Derived fromtwo Greek root words (Greek: μυωπία, muōpia, from myein "to shut" - ops (gen. opos) "eye“) • Myopia or shortsightedness is a type of refractive error in which parallel rays of light coming from infinity are focused in front of retina when the accommodation is at rest
- 5. Image formation • Inmyopia image formed in front of retina 5
- 6. Optics of myopia •The optical system is too powerful for its axial length • Image of distant object on retina is made up of circle of diffusion formed by divergent beam since the parallel rays of light coming from the infinity are focused in front of the retina • Far point is finite point in front of eye 6
- 7. Optics of myopia •Nodal point is further away from retina • Accommodation in uncorrected myopes is not developed normally, they may suffer from convergence insufficiency, exophoria,and early presbyopia
- 8. TYPES OF MYOPIA 8 •Etiologically • Axial myopia :result from increase in anterioposterior length of eyeball • Curvatural myopia :occurs due to increased curvature of cornea or lens or both • Index myopia :increase in refractive index of crystalline lens associated with nuclear sclerosis • Myopia due to excessive accommodation :occurs in patients with spasm of accommodation • Positional myopia
- 9. TYPES OF MYOPIA •Clinically, • congenital myopia • simple or developmental myopia • pathological or degenerative myopia • acquired myopia 9
- 10. TYPES OF MYOPIA According to degree: Classically: Very low : upto – 1.00D Low : –(1.00-3.00)D Medium : –(3.00-6.00)D High : –(6.00-10.00)D Very high : above –10.00D
- 11. Congenital myopia • Seenmore frequently in children who were born prematurely or with various birth defects • Usually error is about 8-10D, which mostly remains constant • Most of the times the error manifests as anisometropia • May sometimes be associated with other congenital anomalies such as cataract, microphthalmos, aniridia, megalocornea 11
- 12. Congenital myopia • Earlycorrection is desirable to help the children to develop normal distance vision • Full cycloplegic refractive error including any astigmatic correction should be prescribed 12
- 13. Simple myopia • Alsoknown as physiological or school myopia • Physiological error not associated with any disease of eye • Etiology: result from normal biological variation in the development of eye 14
- 14. Simple myopia Aetiology AxialPhysiological variation in the length of the eyeball Curvatural Underdevelopment of eyeball. -------- Role of diet in early childhood. -------- Theory of excessive near work. 15
- 15. Simple myopia Symptoms: . Poorvision for distance • Asthenopic symptoms • eye strain due to dissociation between convergence and accommodation • May develop convergence weakness and exophoria and supression in one eye. • Change in psychological outlook 16
- 16. Degree of myopiaVisual acuity -0.50 6/9-6/12 -1.00 6/18 -1.50 6/24 -2.00 6/36 -3.00 6/60 -4.00 4/60 -5.00 3/60 -6.00 2/60 17 Degree of myopia Rough estimate of visual acuity
- 17. Simple myopia: SIGNS •Eyes are large and prominent • Slight deep anterior chamber • Fundus is normal;rarely temporal myopic crescents may be seen • Usually error does not exceed 6-8D 18
- 18. Simple myopia :diagnosis •Confirmed by performing retinoscopy 19
- 19. Pathological myopia • Rapidlyprogressive error resulting in high myopia usually apparent during 1st decade of life • Etiology: 1)Heredity 2)General growth process 20
- 20. Pathological myopia • Highmyopia is considered to be sex linked recessive inherited disorder • It is said that increased axial length, degenerative changes in retina and vitreous, and pathological complications are determined by different genes. • Inheritance can be AD, AR ,X-LINKED 21
- 21. 22 Genetic factors Generalgrowth (play major role) ↓ More growth of retina ↓ Stretching of sclera ↓ Increased axial length ↓ Degeneration of choroid ↓ Degeneration of retina ↓ Degeneration of vitreous Features of pathological myopia etiological hypothesis for pathological myopia (Plays minor role) Elongation of the eyeball posterior to equator in pathological myopia.
- 22. Pathological myopia 23 • Symptoms •defective vision • muscae volitantes • night blindness
- 23. Pathological myopia • Signs: •Eyes are prominent, appearing elongated, and even stimulating an exophthalmos • Cornea is large and anterior chamber is deep • Pupils are larger • Refractive error: increase by as much as 4D yearly stabilizes at about the age of 20 but occasionally may progress until mid 30s frequently result in myopia of 10-20D 24
- 24. 25 Retinal changes inpathological myopia Optic disc: • appears large and pale • at temporal edge a characteristic myopic crescent present Degenerative changes: • in retina and choroid are common. • occurs tigroid appearance of fundus due to diffuse attenuation of the RPE with visibility of large choroidal vessels
- 26. Retinal changes inpathological myopia • Foster- Fuchs spot may be present at macula • Cystoid degeneration may be seen at the periphery • In advanced cases there occurs Focal chorio-retinal atrophy which is characterized by visibility of the larger choroidal vessels and eventually the sclera, total retinal atrophy, particularly at central area 27
- 27. Retinal changes inpathological myopia • There may be associated lattice degeneration and or snail track lesions • Retinal tears, haemorrhage , retinal detachment may be seen • A posterior staphyloma due to ectasia or bulging of sclera at posterior pole due to focal expansion and thinning .
- 28. Retinal changes inpathological myopia • It occurs in about a third of eyes with pathological myopia, and is virtually always peripapillary or involves the macula.Staphyloma development can be associated with macular hole formation • Degenerative changes of vitreous include: liquefaction, vitreous opacities, PVD • Visual field shows contraction and sometimes ring scotoma may be seen. 29
- 29. 30 Fundus changes inmyopia Foster-Fuch’s spot Peripapilary and macular degeneration
- 30. 31 Choroidal neovascularization associated with alacquer crack and high myopia. Peripheral retinal degernerations : A:Lattice degeneration, B:Snail track degeneration C:Acquired retinoschisis D:white-with-pressure E:Focal pigment clumps F:Diffuse chorioretinal degeneration G:Peripheral cystoid degeneration
- 31. 32 Pathological myopia :complications •Rhegmatogenous retinal detachment (RD) • Foveal retinoschisis and macular retinal detachment without macular hole formation may occur in highly myopic eyes with posterior staphyloma, probably as a result of vitreous traction
- 32. Pathological myopia :complications •Complicated cataract which may be either posterior subcapsular or early onset nuclear sclerotic • Nuclear sclerosis • Vitreous haemorrhage • Choroidal haemorrhage and thrombosis
- 33. 34 High myopia canbe seen in these syndromes • Down syndrome • Stickler syndrome • Marfan’s syndrome • Prematurity • Noonan syndrome • Ehlers–Danlos syndrome • Pierre–Robin syndrome
- 34. 35 Acquired myopia • Causes: •Index myopia : nuclear sclerosis incipient cataract . Curvatural myopia increase of corneal curvature in diseased conditions like corneal ectasias, and conical cornea • Positional myopia
- 35. 36 Acquired myopia • consecutivemyopia surgical overcorrection of hypermetropia pseudophakia with overcorrecting IOL. • Pseudomyopia • Space myopia –Experienced when the individual has no stimulation for distance fixation It is never more than 0.75-1.5D
- 36. Acquired myopia • Nightmyopia or twilight myopia 37 The emmetropic eye ,if accomodated for the middle range of visusal spectrum,will be slightrly myopic for the shorter wavelengths. Increased sensitivity to shorter wavelength of light Shift from photopic to scotopic vision at twilight
- 37. 38 Acquired myopia • Druginduced myopia -Cholinergic -Steroid induced -Sulphonamides
- 38. TREATMENT OF MYOPIA 39 •Optical treatment • Surgical treatment • General measures • Visual hygiene • Low-vision aids
- 39. Optical treatment 40 Guidelines forcorrecting low degree of myopia upto -6D Children younger than 8yr should be fully corrected and instructed to use their glasses constantly Adult younger than 30 yrs: usually accept their full correction. Older than 30 yrs: not able to tolerate a full correction over 3D if they have never worn glasses before. prescribe less than full correction with which the patient has comfortable.
- 40. Optical treatment 41 Include prescriptionof appropriate concave lens minimum acceptance providing maximum vision should be prescribed. never overcorrect myopia
- 41. Optical treatment 42 guidelinesfor correcting high myopia • full correction can rarely be tolerated • under correct as little is compatible with comfort for binocular near vision • under correction to the tune of 1-3D or even more may be required • under correction is always better to avoid the problem of near vision and minification of image.
- 42. 43 Modes of prescribingconcave lenses Spectacles Contact lenses
- 43. Surgical treatment: 44 – Radialkeratotomy • Making deep (90 percent thickness radial incision in the peripheral cornea leaving about 4mm central optical zone. • On healing flattens central cornea there by reducing refractive power|(refractive error between -1.5to -6D.
- 44. Photorefractive keratectomy Photorefractive keratectomy •Photoablation of excimer LASER – Which can accurately ablate corneal tissue to an exact depth with minimal distortion of normal tissues – Myopia is treated by ablating the central anterior corneal surface so that it becomes flatter – Approximately 10 micron of ablation corrects 1D of myopia.
- 45. 46 • LASIK • Laserin situ keratomileusis • Currently most frequent performed refractive procedure • Can correct myopia upto -10D • Automated microkeratome is used to raise corneal flap • Excimer laser applied to stromal bed and flap again repositioned
- 46. General measures: 47 – Balanceddiet rich in vitamins and proteins – Early management of associated debilitating diseases
- 47. Visual hygiene: 48 – toavoid asthenopic symptoms – adequate illumination during close work – clarity of print should be good to avoid undue ocular fatigue
- 48. Low vision aids: 49 –Indicated in patients of progressive myopia with advanced degenerative changes where useful vision cannot be obtained with spectacles and contact lenses
- 49. Prophylaxis 50 • genetic counselingfor people having pathological myopia, not to marry pathological myopic peoples
- 50. PROGNOSIS 51 Simple myopia – Prognosisis good. – Error usually does not progress beyond 6-8D – Stabilizes by the age of 21 Pathological myopia: – Visual prognosis is always guarded – Possibility of progressive visual loss due to degenerative changes and danger of complications such as retinal detachment should be borne in mind.
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Editor's Notes
- #7 The optical system is too powerful for its axial length Image of distant object on retina is made up of circle of diffusion formed by divergent beam since the parallel rays of light coming from the infinity are focused in front of the retina Far point is finite point in front of eye Therefore a near object placed at a far point is focussed without an effort of accomodation
- #8 Nodal point is further away from retina therefore the image formed will be larger than it would be in emmetropic eyes.(it is a point on principal axis of lens from where the rays go un deviated) Accommodation in uncorrected myopes is not developed normally, since they need not accommodate to see near objects for this reason they may suffer from convergence insufficiency, exophoria,and early presbyopia
- #9 Etiologically Axial myopia :result from increase in anterioposterior length of eyebal.it is the most commonest type Curvatural myopia :occurs due to increased curvature of cornea or lens or both Index myopia :increase in refractive index of crystalline lens associated with nuclear sclerosis Myopia due to excessive accommodation :occurs in patients with spasm of accommodation-pseudomyopia Positional myopia due to the anterior placement of lens in the eye
- #10 Degenerative-due to degenerative changes in the eye Induced-due to variations in bsl Noctrnal-due to excessive accomodation in dim illumination
- #12 Aetiologically-associated with an increase in the axial length of the eye and overall globe size.Seen more frequently in children who were born prematurely or with various birth defects. Associated with High degree of error.Usually error is about 8-10D, which mostly remains constant Most of the times the error manifests as anisometropia.rarely bilateral May sometimes be associated with other congenital anomalies such as cataract, microphthalmos, aniridia, megalocornea
- #13 Diagnosis-unilateral cong myopia is usually discovered during routine screening examination or after strabismus developes because of associated amlyopia. If bilateral the child may display some noticable difficulty in seeing didtanat objects and hold things very close for viewing. Treatment….Early correction is desirable to help the children to develop normal distance vision Full cycloplegic refractive error including any astigmatic correction should be prescribed. Prognosis-poor if anisometropia or myopia is severe. Myopia Age <1 yr: -4.00 or more Age 1-2yr: -3.00 or more Age2-3yrs: -3.00 or moreThreshold for correction of anisometropia should should be lower if the child has strabismus.the values represent the minimum difference in the magnitude of refractive error between eyes that would prompt refractive correction
- #14 Threshold for correction of anisometropia should should be lower if the child has strabismus.the values represent the minimum difference in the magnitude of refractive error between eyes that would prompt refractive correction
- #15 Onset occurs at school going age
- #16 Axial Physiological variation in the length of the eyeball Curvatural Underdevelopment of eyeball. -------- Role of diet in early childhood. -------- Theory of excessive near work. Role of genetics-play some role in biological variation of development of eye.if both parents myopic then 20 percent chance and if one parent myopic 10 percent.inheretence may be AD.however several reports claim that the inheretence is AR.
- #17 . Poor vision for distance Half shutting of eyes complained by parents. Asthenopic symptoms eye strain due to dissociation between convergence and accommodation Since myopes do not accommodate for near vision.May develop convergence weakness and exophoria and supression in one eye. Or While focussing at near objects the patients converge so there is excessive accomodation inducing ciliary spasm thus increasing the magnitude of myopia Change in psychological outlook
- #21 Rapidly progressive error resulting in high myopia usually apparent during 1st decade of life .results in high myopia during early adult life associated with degenerative changes in the eye.2-3 percent prevelence. High myopia is defined as the refractive error of atleast -6.00D or an axial length of 26.5mm or more. No satisfactory hypothesis to explain the etiology of myopia.however it is definitely linked with Etiology: 1)Heredity 2)General growth process
- #22 Familial more seen in chinese japanese arabs and jews
- #24 defective vision-uncorrectable vision loss may be there due to degenerative changes muscae volitantes-due to degenerated liquified vitereous night blindness may be reported in myopes having chorioretinal degenerative changes
- #28 Foster- Fuchs spot may be present at macula.dark red circular patch due to subretinal neovascularisation and choroidal haemorrage Cystoid degeeneration may be seen at the periphery In advanced cases there occurs Focal chorio-retinal atrophy which is characterized by visibility of the larger choroidal vessels and eventually the sclera, total retinal atrophy, particularly at central area
- #30 appearing as weiss reflex
- #33 Rhegmatogenous retinal detachment (RD) is much more common in high myopia, the pathogenesis including increased frequency of posterior vitreous detachment, lattice degeneration, asymptomatic atrophic holes, macular holes and occasionally giant retinal tears. Foveal retinoschisis and macular retinal detachment without macular hole formation may occur in highly myopic eyes with posterior staphyloma, probably as a result of vitreous traction
- #34 Complicated cataract which may be either posterior subcapsular or early onset nuclear sclerotic-due to abbresion in lenticular metabolism Nuclear sclerosis-common occurence and and leads to aggrevation of myopia Vitreous haemorrhage Choroidal haemorrhage and thrombosis -may lead to severe visual loss when involving foveal region
- #36 Causes: Index myopia : nuclear sclerosis incipient cataract diabetic myopia occurs due to decrease in refractive index of cortex . curvatural myopia increase of corneal curvature in diseased conditions like corneal ectasias, and conical cornea.associated with lenticonus positional myopia: conditions producing anterior subluxation of lens
- #37 consecutive myopia surgical overcorrection of hypermetropia pseudophakia with overcorrecting IOL. Pseudomyopia- also called artificial myopia. produced in a conditions such as excessive accommodation and spasm of accommodation may develop after too full a hypermetropic correction in children. Space myopia –Experienced when the individual has no stumilation for distance fixation. the eyes tend to choose a near fixation point which can be variable It is never more than 0.75-1.5D
- #39 -Cholinergic-pilocarpine,ecothiophate -Steroid induced-water metabolism changes involving crystalline lens -Sulphonamides –refractive changes in media
- #50 These are devices such as stands ,hand held magnifiers,strong magnifying reading glasses,loupes and telescopes