In the name of ALLAH, most gracious, most merciful

MYOPIA BY: SUMAYYA NASEEM Internee Optometrist

AIMS & OBJECTIVES OF TODAY’S LECTURE

• Myopia and its etiology• Mechanisms of production• Clinical types• Signs & symptoms• Complications• Diagnosis• Correction• Prevention

HUMAN EYE:OPTICAL CONDITIONS

Emmetropia Ametropia

Index

Axial

Curvature

Myopia

Presbyopia

AstigmatismHyperopia

Parallel incident light is focused in front of the retina

Parallel incident light is focused behind the

retina

We get 2 focal points

• EMMETROPIA

Parallel incident rays come to a

focus on the retina when the

accomodation is fully relaxed so far

point is at infinity.

OPTICS OF EMMETROPIA

• AMMETROPIA

Parallel incident rays do not come to a

focus on the retina when the

accomodation is fully relaxed so far point

is not at infinity.

MYOPIA (short sightedness, hypometropia)

A type of refractive error in which Parallel incident light is brought to a focus in front of the retina when eye is at rest. So far point is at finite distance.

AETIOLOGY

• Hereditary (Genetic Factor)

• Role of diet• Theory of excessive near work• Reading posture• Racial (Chinese and Japanese highest)• Environmental Factors

MECHANISMS OF PRODUCTION

1. Axial myopia • Increased length of eyeball• 1mm=3D

2. Curvature myopia• Increased curve of cornea e.g. conical

cornea• Increased curve of lens e.g. lenticonus• 1mm=6D

3. Positional myopia• Anterior displacement of lens e.g. trauma

4. Index myopia• Increase in ref index of lens e.g. nuclear

sclerosis in diabetes• Increase in ref index of aqueous humor• Decrease in ref index of vitreous humor e.g.

vitreous liquefication

5. Myopia due to excessive accomodation• Patients with excessive accomodation

MYOPIA: REFRACTIVE vs AXIALRefractive Myopia

(Optics of the eye too strong)

Axial Myopia

(Eye too long)

Image of distant object & near object

CLINICAL VARIETIES OF MYOPIA

1.Congenital myopia

2.Simple or developmental myopia

3.Pathological or degenerative myopia

4.Acquired myopia

CLINICAL VARIETIES OF MYOPIA

1. Congenital myopia• Present since birth• Diagnosed at 2-3 years• Common in children born with Marfan’s

syndrome• Mostly unilateral and anisometropic• Rarely bilateral• Usually 8-10 D and constant• May be associated with aniridia,

megalocornea and congenital separation of retina

2. Simple myopia• Commonest• Not associated with any eye disease• Error usually does not exceed 6D• Usually begins at age of 7 to 10 years• Stabilizes around midteens

CLINICAL PICTURE Symptoms• Poor vision for distance

• Asthenopic symptoms (due to dissociation b/w accomodation

and convergence)

• Change in physiological outlook of children

SIGNS• Myopic eyes are large• Anterior chamber is deeper than normal• Pupil is dilated and sluggish• Fundus is normal• Does not exceed 6D• Normal near vision • Defective distant vision

3. PATHOLOGICAL MYOPIA

• Rapidly progressing error• Associated with degenerative changes in

posterior segment• Rapid axial growth of eyeball• Usually Hereditary in nature• Can exceed till 30 D• Ref error increases 4D yearly• Also known as degenerative myopia.

CLINICAL PICTURE

Symptoms• Defective distant vision• Defective near vision if degeneration starts• Muscae volitantes (Flying Flies)• Night blindness

MUSCAE VOLITANTES

SIGNS

• Prominent eyes• Proptosis if error exceeds 20D• Cornea large• a/c deep• Pupil large and sluggish• Sclera is thin

Idiopathic Retinal

Detachment

Open-Angle Glaucoma

Chorioretinal Degeneration

Posterior Subcapsular Cataract

OPHTHALMOSCOPICALLY

Changes in vitreous

• Liquefication• Floaters• Vitreous detachment

POSTERIOR VITREOUS DETACHMENT

VITREOUS DETACHMENT

CHOROIDAL AND RETINAL CHANGES

• Degeneration of choroid• Choroidal hemorrhage• White atrophic patches• Tilted disc• Posterior staphyloma• Myopic crescent (temporally)

• Forster-Fuchs flecks (subretinal neovascularisation & pigmented lesion at or near the fovea)

POSTERIOR STAPHYLOMA

TILTED DISC

CHOROIDAL AND RETINAL DEGENERATIONS

MYOPIC CRESCENT

HIGHLY MYOPIC FUNDUS

COMPLICATIONS

• Retinal tears• Retinal detachment• Hemorrhages• Complicated cataract• Vitreous hemorrhage• Primary open angle glaucoma• Visual field shows contraction• Scotoma can be seen

RETINAL DETACHMENT

RETINAL DETACHMENT

VISUAL FIELD LOSS

4. ACQUIRED MYOPIA

Some causes are as follows:1. Index myopia (diabetic, nuclear sclerosis)

2. Curvature myopia (conical cornea & corneal ectasias)

3. Positional myopia (ant. Subluxation of lens)

4. Consecutive myopia (surgical overcorrection)

5. Night myopia (as pupil dilates)

6. Drug induced myopia (pilocarpine, steroids)

7. Pseudo myopia (excessive & spasm of accomodation)

REFRACTION PROCEDURE

• VA with and without correction monocularly• Pinhole VA• Cover test with and without correction• Quick ophthalmoscopy• Retinoscopy

Subjective verification:

• Duochrome test• Muscle balance- Maddox rod for distance

Bailey-Lovie ChartUniversity of Waterloo

distance VA chart

DISTANCE VA CHART

RETINOSCOPIC FINDINGSDuring retinoscopy of a myopic patient, ‘against’ movement of reflex is seen as compared to retinoscopic light or streak.

Against movement is neutralized by negative or concave lenses.

Reflex motion seen during retinoscopy

“w ith” “neutrality” “against”

Retinoscopy Reflex

RETINOSCOPY: SET-UP

DUOCHROME TEST

Letters Circles

COVER/UNCOVER TEST

MADDOX ROD

PHOROPTER (MANUAL REFRACTOR)

VISUAL FUNCTIONS ASSESSMENT

OPTICAL CORRECTION OF MYOPIAOptions are as follows:• Spectacles and LVD’s• Contact lenses• Refractive surgeries• LaserOthers:• Visual hygiene• Prophylaxis• General measures

SPECTACLES• Minus lenses (CONCAVE) are used to correct

myopia• In high numbers glasses are not cosmetically

attractive and minify actual pt eye size for others

• Myopes are usually kept under corrected so that there accomodation is not stimulated. Otherwise, they will complain of Asthenopic symptoms

EXTREME MYOPIA

CONTACT LENS

Contact lens is a better option for correction of high myopia both optically and cosmetically..

C/L INSERTION & REMOVAL

A SOFT C/L

LOW VISION DEVICES (LVD’s)READING GLASSES

HAND MAGNIFIERS & STAND MAGNIFIERS

DOME/PAPERWEIGHT MAGNIFIER

FILTERS

TELESCOPES

ORTHOKERATOLOGY

• Orthokeratology is defined as, the reduction, modification, or elimination of visual defect by the programmed application of contact lenses

• Orthokeratology uses hard Contact Lenses to remould the Cornea, to reduce or correct Myopic (short-sighted) and Astigmatic (irregular surface) errors of the eye.

• In some ways this is similar to the use of dental braces by an Orthodontist to straighten crooked teeth.

• The main difference is that if a tooth position is corrected for some months it will stay in the new position.   However the Cornea is highly elastic, and always returns to its original shape.

• For this reason the lenses are worn nightly or on alternate nights  after the ideal Corneal shape has been achieved and removed in the morning giving perfect vision without the need for spectacles or contact lenses.

• Once the desired level of V.A has been achieved a of retainer lens wear is initiated until cornea reaches the level of stability new shape cornea. Lens wear is then gradually reduced to the minimum, required to attain good functional vision through out the day.

• The amount of ametropia that can be corrected using orthokeratology is: –1 to –6 D myopia with 1.5 D of WTR astigmatism and 0.75 D of ATR astigmatism.

ORTHOKERATOLOGY CONTACT LENS

SURGERYClear lens extraction:• For myopia of greater than 15-20 D,

cataract surgical procedure is applied and non-cataractous lens is removed and intra ocular lens of calculated power is inserted.

Phakic IOL:

• IOL is also placed in A/C or P/C of phakic eyes to correct the refractive error.

CATARACT SURGICAL PROCEDURE

LASER AND SURGERIES

Photorefractive keratectomy PRK:• Uses Excimer laser to change ant. curvature

of cornea.• Tissue is ablated centrally 3.5-4mm and

surface curvature is reduced.• After scarring, haloes, glare and reduction of

best VA are the complaints of patient.

PHOTOREFRACTIVE KERATECTOMY PRK

• A mechanical keratotome is used to dissect through the superficial corneal stroma and fashion a lamellar circular flap of uniform thickness.

• The bared corneal stroma is reshaped using Excimer laser and hinged flap is replaced.

• Better than PRK because of little scarring and better correction predictability.

LASER ASSISTED IN SITU LASER ASSISTED IN SITU KERATOMILEUSIS KERATOMILEUSIS LASIK

LASER ASSISTED IN SITU LASER ASSISTED IN SITU KERATOMILEUSIS KERATOMILEUSIS LASIK

Flap creation

Laser interventionFlap repositioning

CORRECTION WITH LASIK & PRK

Myopia•-1D to -6D --------- PRK•-6D to -12D -------- LASIK

(better to wait till the patient reaches the age of 21 years)

EXCIMER SYSTEM

LASIK

EPIKERATOPHAKIA

• This uncommon surgical technique creates a new corneal surface with a different surface curvature by attaching a lenticule of pre- shaped donor corneal stroma to the surface of host cornea.

• The eye is not entered and procedure is easily reversed by removal of lenticule.

EPIKERATOPHAKIA

KERATOMILEUSIS

• It is the use of microkeratotome to remove lamella of ant. corneal stroma which is then reshaped on a cryolathe before being replaced.

• High degrees of myopia till 15D can be corrected in this way.

• Keratophakia is developed as a modification of keratomileusis and is used for aphakia.

KERATOMILEUSIS

PREVENTION & CONTROL OF MYOPIA

• Many people believe that too much close work, such as reading or sitting too close to the television, causes nearsightedness. But there was little evidence to support this belief. However, one study suggested that people in professions that involve extensive reading have higher degrees of nearsightedness.

• With regular instillation, topical 0.05% atropine is an effective agent for controlling myopia progression in a majority of school aged children.

• Nutritional Factors

• Since the eye has a collagenous structure, it seems likely that the same nutrients which strengthen collagen might also be helpful in keeping the eye from becoming elongated.  Calcium, magnesium, boron, silica, selenium, manganese and vitamin D all come to mind, as well as vitamin C.  A strong ocular structure would likely be less prone to becoming elongated, as occurs in myopia. Low levels of calcium, fluoride and selenium were found to be related to increased risk of progressive myopia in an exploratory study.

• Vitamin E, can slow the progression of myopia in children.  Myopia in children was also significantly related to lower consumption of protein, fat, vitamins B1, B2 and C, phosphorus, iron, and cholesterol.

• We should insist that our children use good lighting and good posture when reading, take frequent eye rest breaks during long study periods, and encourage them to be physically active.

• Environmental visual stress may be lessened by taking these precautions while reading: frequently stretching and moving the eyes and looking away from the reading material at distant objects, removing distance eyewear(-) or using reading glasses for near tasks.

• As it is usually hereditary in nature, so family marriages should be avoided.

VISUAL HYGEINE

REFERENCES• Theory and practice of optics and

refraction by A K Khurana• Duke Elder's Practice of refraction

(Tenth edition)• Clinical Optics by Elkington, Frank and

Greaney (Third edition)• www.visionlaser.com• www.orthokeratology.com

and many other websites.