MYOPIA

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MYOPIA

MANOJ ARYAL

B. Optometry IOM Maharajgunj Medical

Campus

PRESENTATION LAYOUT2

Introduction Optics of myopia Classification Treatment of myopia Prognosis

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EMMETROPIA

When parallel rays of light coming from infinity are focused in sensitive layer of retinawith accommodation being at rest.

Components that maintain emmetropization are

axial lengthAC depth

corneal curvature

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AMETROPIA

Parallel rays of light coming from infinity (with accommodation at rest) are focused either in front or behind retina.

Further classified into Myopia :where the parallel rays of light

coming from infinity are focused in front of retina.

Hypermetropia: where the parallel rays of light are focused behind the sensitive layer of retina.

Astigmatism :where the refraction varies in different meridia.

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TYPES OF AMETROPIA

myopiaastigmatism

hypermetropia

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Introduction

Derived from two 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 with the accommodation is at rest.

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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.

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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 as they grow.

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Image formation

In myopia image formed in front of eye which is corrected by placing the negative lenses.

TYPES OF MYOPIA10

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 assotiated with nuclear sclerosis.

myopia due to excessive accommodation :occurs in patients with spasm of accommodation.

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TYPES OF MYOPIA CONTD…

Clinically, congenital myopia. simple or developmental myopia. pathological or degenerative myopia. acquired myopia.

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Congenital myopia

Present since birth. Seen more frequently in children who were born

prematurely or with various birth defects. Usually error is about 8-10D, which mostly

remains constant. May sometimes be associated with other

congenital anomalies such as cataract, microphthalmos, aniridia, megalocornea.

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Congenital myopia contd..

Early correction is desirable to help the children to develop normal distance vision and perception of world.

Full cycloplegic refractive error including any astigmatic correction should be prescribed.

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Simple myopia

Aka physiological or school myopia. Physiological error not associated with any

disease of eye. Etiology:

result from normal biological variation in the development of eye.

Simple myopia etiology

Axial Physiological variation in the length of the eyeball.

Curvatural Underdevelopment of eyeball.

-------- Role of diet in early childhood.

-------- Theory of excessive near work.

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Simple myopia contd…

Clinical pictures:Symptoms:

Poor vision 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.

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Degree of myopia Visual 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

Degree of myopia Rough estimate of visual acuity

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Simple myopia: SIGNS

Eyes are large and prominent. Slight deep anterior chamber. Fundus is normal :rarely temporal myopic

cresents may be seen. Usually error does not exceed 6-8D

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Simple myopia :diagnosis

Confirmed by performing retinoscopy.

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Pathological myopia

Rapidly progressive error resulting in high myopia usually apparent during 1st decade of life characterized by increase in volume of posterior segment.

Etiology:

no satisfactory hypothesis has emerged to explain the etiology of pathological myopia.

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Pathological myopia contd

However it is confirmed that genetic factors play a major role.

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

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Genetic factors General growth(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 inpathological myopia.

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Pathological myopia contd…

Symptoms defective vision. muscae volitantes. night blindness.

Pathological myopia contd…

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 4.00D yearlystabilizes at about the age of 20

but occasionally may progress until mid 30s`` frequently result in myopia of 10-20D

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Retinal changes in pathological 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 choroidalvessels.

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Foster- Fuchs spot may be present at macula

It is a raised, circular, pigmented lesion developing after a subretinal haemorrhage has been absorbed .

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.

There may be associated lattice degeneration and or snail track lesions.

Retinal tears, haemorrhage , retinal detachment may be seen.

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A posterior staphyloma is an ectasia or bulging of the posterior sclera due to focal expansion and thinning . 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 appearing as weiss reflex.

Visual field shows contraction and sometimes ring scotoma may be seen.

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Fundus changes in myopia

Foster-Fuch’s spotPeripapilary and macular degeneration

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Choroidal neovascularization associated witha lacquer 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 degenerationG:Peripheral cystoid degeneration

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Pathological myopia :complications

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

Complicated cataract which may be either posterior subcapsular or early onset nuclear sclerotic.

Nuclear sclerosis. Vitreous haemorrhages. Choroidal haemorrhages and thrombosis. Primary open angle glaucoma.

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Systemic associations of high myopia

• Down syndrome• Stickler syndrome• Marfan’s syndrome• Prematurity• Noonan syndrome• Ehlers–Danlos syndrome• Pierre–Robin syndrome

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Acquired myopia

Causes: index myopia : seen in 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. positional myopia:

conditions producing anterior subluxation of lens.

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Acquired myopia contd..

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.

Acquired myopia contd…

Pseudo myopia correction Cycloplegic refraction

-always prescribe plus lenses.

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Acquired myopia contd..

space myopia

experienced when the individual has no stimulation for distance fixation.

never more than 0.75-1.50D

Acquired myopia contd…

Night myopia or twilight myopia36

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Acquired myopia contd…

drug induced myopia

cholinergic drugs such as pilocarpine, echothiopate, di-isopropyl fluorophosphate.

sulphonamides.

TYPES OF MYOPIA CONTD…

According to amount: 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

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TREATMENT OF MYOPIA

Optical treatment Surgical treatment General measures Visual hygiene Low-vision aids

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Optical treatment

Include prescription of appropriate concave lens

minimum acceptance providing maximum vision should be prescribed.

never overcorrect myopia

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Optical treatment CONTD…

Guidelines for correcting 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.

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Optical treatment CONTD…

guidelines for correcting high myopia full correction can rarely be tolerated. undercorrect as little is compatible with comfort

for binocular near vision.

undercorrection to the tune of 1-3D or even more may be required.

undercorrection is always better to avoid the problem of near vision and minification of image.

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Modes prescribing concave lenses

Spectacles Contact lenses

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TREATMENT OF MYOPIA

OPTICAL PRINCIPAL

UNCORRECTED

CORRECTED WITH GLASS

CORRECTED WITH CONTACT LENS

Prescription of appropriate CONCAVE LENSES .

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Surgical treatment:

Radial keratotomy 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.

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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 becomrs flatter.

Approximately 10 micron of ablation corrects 1D of myopia.

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LASIK Laser in situ keratomileusis Currently most frequent performed

refractive procedure. Can correct myopia upto -10D. Automated microkeratone is used to raise

corneal flap. Excimer laser applied to stromal bed and

flap again repositioned.

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General measures:

Balanced diet rich in vitamins and proteins Early management of associated debiliating

diseases.

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Visual hygienes:

to avoid asthenopic symptoms adequate illumination during close

work clarity of print should be good to

avoid undue ocular fatigue.

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Low vision aids:

Indicated in patients of progressive myopia with advanced degenerative changes where useful vision cannot be obtained with spectacles and contact lenses.

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Prophylaxis

genetic counseling for people having pathological myopia, not to marriage with pathological myopic peoples.

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PROGNOSIS

Simple myopia Prognosis is good. Error usually does not progress beyond 6-8D Stablizes by the age of 21

Pathological myopia: Visual prognosis is always guarded Possibility of progressiove visual loss due to

degenerative changes and danger of complications such as retinal detachment should be borne in mind.

References

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Theory and practice of optics and refraction by AK Khurana

Borish’s clinical refraction

Internet

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