BY.DR.HAMMID, HOUSE OFFICER IN EYE UNIT TWO,MAYO HOSPITAL, LAHORE

1. Errors of Refraction
Dr.Hamid Yaqoob
House Officer
Eye Unit-2 MHL

2. Refraction
Refractionof light occurs when light passes from one medium
to another of different refractive index(i.e density)
 Refractive Components:
1. Cornea: responsible for the majority of the refractive power of
eye(40D).
2.Lens: 20 D of refractive power, changes with accommodation.
3.Axial Length :At birth apiroxmately 17mm and 24-25mm at
adulthood.

3. Refractive Physiology
• Light rays are focused on Retina because they are refracted by
passing through the cornea and lens(Snell’s law).
• Corneal refractive power is constant.
• Lens refractive power is modifiable with accommodation.
• Axial length of eye is constant except under certain conditions.

4. Emmetropia and Ametropia
Emmetropia:
• Adequate correlation between axial length and refractive power.
• Parallel light rays fall on the retina(no accommodation).
Ametropia:
• Mismatch between axial length and refractive power.
• Parallel light rays don’t fall on retina(no accommodation)
• TYPES
Myopia
(Nearsightedness
)
Hyperopia
(Farsightedness)
Presbyopia
Astigmatism

5. Types of Ametropia

8. Myopia
• Parallel rays converge at a focal point anterior to retina while
accommodation at rest.
Etiology: not clear , genetic factor.
Causes :
• Excessive long globe (axial myopia)
• Excessive refractive power (refractive myopia)
• Increase in the curvature of cornea or the surfaces of crystalline
lens

9. Types of Myopia
Simple Degenerative Congenital
1. commonest common rare
2. Starts around Puberty Starts in children Dated since birth
3. Stops at 21-25 years Progresses till age 31-35
years
4. Usually less than -7D May be up to -30D About -10D
5.No degeneration Degenerations are common
leading to blinding
complications(malignant
myopia)
Degeneration may or may
not occur

10. Simple Myopia
Signs
1.Defective far vision
2.Normal ant.and post.
segment of eye
3.myopia<-7D on
retinoscopy
Complications
. 1 Eye ache and
referred headache
2. Red eyes
3.Recurrent stye and
blepharitis
4.Transient diplopia
s
Symptoms
1.Indistinct far
vision

11. Correction of Simple Myopia
Concave Lenses: We use minus(concave) lenses
Glasses or Contact lenses
Refractive Surgery
1. Radial Keratotomy(obsolete)
2. Excimer Laser
PRK(Photo-refractive Keratectomy)
LASIK(Laser Assisted in situ Keratomilleusis)
 LASEK (Laser Assisted Epithelial Keratoplasty)

12. PRK

13. LASIK

14. Degenerative Myopia
Optical Symptoms:( improved by glasses)
Defective far vision
Non-Optical Symptoms:(Not improved by glasses)
Musca volitans(Opaque cell faregments) due to either
vitreous degeneration
or retinal tear).
Sudden central scotoma(Partial LOV or blind spot)
due to macular hemorrhage
(fuch’s spot)
Acute drop of vision due to RD
Gradual drop of vision due to either complicated
cataract or macular degeneration

15. Signs of Degenerative Myopia
• A. Retinoscopy shows myopia more than >-7D.
• B.External appearance
Apparent Exophthalmos
Apparent convergent squint
• C. Anterior Segment
1.Large size cornea
2.Deep anterior chamber
3.Large sluggish pupil
4.Tremulous(shaking) iris due to lack of support of the iris by the lens
because the posterior chamber is deep
5.Thin bluish sclera

16. Signs of Degenerative myopia
• D.Posterior segment
1.Tigroid fundus (Tes-sellated fundus) :(increase visibility of choroidal vasculature)
2.Temporal myopic crescent:it is whitish crescent at the temporal side of optic disc.
3. Posteiror staphyloma :abnormal protrusion of the uveal tissue through a weak point in the
eyeball as detected by fundus examination
4. Large atrophic patches of chorioretinal atrophy they appear white.
5. Peripheral retinal degeneration that is predispose to retinal tear and retinal detachment .
6. Fuch’S Spot:A neovascular membrane grows from the choroid underneath the macula,it
causes sudden hemorrhage that is felt by the patient as a sudden central positive
scotoma(blind spot).Finally the blood is absorbed leaving a hyperpigmented macular scar
known as ‘’Fuchs spot”
7. Vitreous is degenerated and fluidy causing musca volitians, also it helps the
pathogenesis of RD.

19. Complications of degenerative myopia
• 1.Divergent squint
• 2.Complicated cataract either Nuclear or posterior Subcapsular.
• 3.Marked increase in incidence of Primary Open Angle Glaucoma.
• 4.Macular degeneration and Fuchs spot leading to permanent loss of central
vision and very poor visual acuity.
• 5.RD due to either a peripheral break atrophy.

20. Treatment of Degenerated Myopia
• A.Optical Correction;
• Aim is to bring the real point(P.R) at infinity .This is achived by:
• 1.Glasses using minus Concave lens
• 2.Contact lenses
• 3.Refractive surgery
 A.Lasik
 B.Implantation of a minus IOL in the anterior chamber
 C. Clear lens extraction can correct -24 D….However
accommodation is lost ,also it increases the risk of RD

21. Treatment of Degenerative Myopia
• B.Non Optical Treatment of High Myopia;
• 1. Instructions:
 Avoid head trauma and violent sports
 Avoid 2nd cousins marriage
 Routine periodic examination for early detection of
complication as retinal degenerations ,Tear and Glaucoma.
2.Treatment of complications of high myopia:
 Treatment of Primary Open Angle Glaucoma (Miotics should be
avoided because they cause contraction of the ciliary muscle
leading to traction on the retinal periphery causing retinal tear).

22. Treatment of Degenerative Myopia
• Treatment of complicated cataract by phacoemulsification (ICCE is
better to be avoided because it is usually complicated by retinal
detachment).
• RD Is treated by surgery
• Macular degeneration and optic atrophy are treated by low vision
aids as magnifying lenses.

23. Hyperopia
Parallel rays converge at a focal point posterior to retina
• Etiology: Not clear, Inherited
• Causes:
I. Excessive short globe(axial hyperopia):more common
II. Insufficient refractive power(refractive hyperopia)
III. Length of the eyeball is shorter than it should be..
IV. Hyperopia forms at stage in normal development of eyes- at birth eyes are
hypermetropic (2.5-3.0D)
V. When persists in adulthood it represents imperfectly developed eyes
VI. Lens changes(cataract)

24. Hyperopia
• Symptoms:
1) Distance vision is impaired in high refractive error(>3D) and in older patients
2) “Eye strain”(ciliary muscle is straining to maintain
accommodation)/watering/redness
3) Headaches in the later part of daytime
4) Young children with significant hypermetropia can also develop a convergent
squint
5) Hyperopia may be partially compensated for by using the eye accommodative
ability
6) When accommodative ability can not keep up with demand hyperopia is
manifest and images are blurred in the distance and for near.

25. Hyperopia
• Symptoms;
1. Visual acuity at near tends to blur relatively early
2. Nature of blur is vary from inability to read fine print ,to near is clear but suddenly and
intermittently blur
3. Blurred vision is more noticeable if person is tired, printing is weak or light inadequate
4. Asthenopic symptoms; eye pain, headache in frontal region, burning sensations in the eye
,blephroconjuctivitis
5. Accommodative esotropia;Because accommodation is linked to convergenceET
6. Amblyopia – Uncorrected hyperopia >5D
7. Fundus in axial hyperopia may reveal pseudooptic neuritis (Indistinct disc margin ,no
physiologic cup ,may elevate disc.
DDX from optic neuritic by >4D ,no enlarge blind spot, no passive congestion of vein.

26. Treatment of Hyperopia
Convex lenses ,
Keratorefreactive Surgery,
Refractive Lensectomy with IOL
Phakic IOL

27. Astigmatism
• Astigmatism >Parallel rays from infinity come to focus in 2 focal lines rather
than a single focal point
• Etiology; Heredity
• Cause; Refractive media is not sherical_>refract differently along one meridian
than along meridian perpendicular to it..>2 focal points (Punctiform object is
represent as 2 sharply defined lines).
• Classification
• 1.Regular astigmatism;
• Power and orientation of principle meridian are constant.
• With the rule astigmatism ,against the rule astigmatism,Oblique
astigmatism
• Simple or Compound myopic astigmatism,Mixed astigmatism.

28. Astigmatism
2.Irregular Astigmatism:
• Power and orientation of principle meridians change across the pupil.
Symptoms:
1. Asthenopic symptoms(headache, eye pain)
2. Blurred vision
3. Distortion of vision
4. Head tilting and turning
5. Amblyopia – uncontrolled astigmatism>1.5D

29. Astigmatism
Treatment:
 Regular Astigmatism:
Cylinder lenses with or without spherical lenses(convex or concave)
 Irregular Astigmatism:
Rigid CL, surgery
Pathologic Causes of Astigmatism:
Corneal:post surgical,traumatic,infectious
External pressure on cornea: lid masses
Lens: pressure on lens from tumors

30. Presbyopia
Physiologic loss of accommodation in advancing age
 Deposit of insoluble proteins in lens in advancing age elasticity of lens
progressively decreasedecrease accommodation
 Around 45 years of age , accommodation becomes less than 3D reading
is possible at 40-50cmdifficulty in reading fine print, headache,visual
fatigue
Treatment:
 Convex lenses in near vision
 Reading glasses
 Bifocal glasses
 Trifocal glasses
 Progressive power glasses

32. The End
Thanks