This document provides an overview of refractive errors, including emmetropia, ametropia, and various types of refractive errors such as hyperopia, myopia, astigmatism, aphakia, and pseudophakia. It discusses the optical conditions and clinical features of each type of refractive error, as well as their causes, treatment options, and potential complications. Key information covered includes the definition of emmetropia as the eye's ability to focus light correctly on the retina, the various causes and classifications of refractive errors, and management approaches for different refractive conditions including optical corrections and refractive surgery.

1. REFRACTIVE ERRORS
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2. EMMETROPIA
 The parallel rays of light coming from infinity are focused at
sensitive layer of retina with the accommodation at being at
rest
 Good visual acuity (6/6 or better) at 6 m testing distance
 If accommodation amplitude is adequate ,equally good visual
acuity at the near testing distance of 40 cm
 Axial length =24mm
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3. CONT
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4. Refractive sate of eye
 Corneal refractive power
 Anterior chamber depth
 Lens refracting power
 Axial length
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5. AMETROPIA
 The parallel rays of light coming from infinity are focused
either in front or behind the sensitive layer of retina in one or
both meridian when accommodation at rest
 Refractive Status And Aging
o Hyperopic (infant)
o Emmetropic (10 years old)
o Myopic (25 years old)
o Hyperopic (60 years old)
o Less hyperopic (80 years
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6. TYPES OF REFRACTIVE ERRORS
Hypermetropia
Myopia
Astigmatism
Aphakia
pseudophakia
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7. HYPERMETROPIA
 The parallel rays of light coming from infinity are focused
behind the sensitive layer of retina with accommodation
being at rest
 Back focal point is behind retina
 It is also called far/long sightedness
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8. AETIOLOGY
Axial hypermetropia:-the antero-posterior diameter of
eye is too short & retina is too near to optical system,1mm-3D
Curvature hypermetropia:-curvature of cornea or
lens may be too small,1mm-6D
Index hypermetropia:- due to change in refractive
index of lens ,aqueous humour ,vitreous humour or diabetes
Positional hypermetropia:-if the crystalline lens is
dislocated backwards
Absence of crystalline lens:- aphakia
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9. CLINICAL TYPES
simple hypermetropia:- normal biological variations in
development of eyeball
Pathological hypermetropia:-outside biological
variations of development ,include:-
 Senile :- curvature &index
 Positional
 Aphakia
Functional hypermetropia:-paralysis of
accommodation -third nerve paralysis &internal
ophthaloplegia
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10. OPTICAL CONDITION
 Parallel rays of light come to a behind the retina
 Parallel rays of light are brought to a focus upon the
retina by increasing the refractivity by
accommodation .the normal lens becomes more
convex
 Parallel rays of light are brought to a focus upon the
retina by increasing refractivity by a convex
spectacles lens .the degree of hypermetropia is given
by power lens
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11. ACCOMMODATION IN HP
 Latent hypermetropia (LH):-
 This is a condition in which all or part of hypermetropia is compensated or corrected by
the tonicity of the ciliary muscle.
 Latent hypermetropia becomes manifest when the amplitude of accommodation
decreased significantly.
 Manifest hypermetropia (MH): It has two parts.
 Facultative hypermetropia (fH) – The amount of hypermetrropia that can be
corrected by the effort of accommodation.
 Absolute hypermetropia (aH) – T he amount of hypermetropia that can not be
corrected by the effort of accommodation.
 Thus the total amount of hypermetropia (tH) is the sum of
latent and manifest hypermetropia.
tH=LH+MH=LH+(fH+aH).
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12. CLINICAL PATHOLOGY
 Cornea is small, AC shallow ,closed –angle glaucoma
 Administration of dilated drugs to dilate pupil
 Developmental aberrations such as colobomata
,microphthalmos
 The retina appears to have peculiar sheen, optic neuritis,
vascular reflex
 Face asymmetrical ,dislocation of macula, divergent squint
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13. CLINICAL FEATURES
 SYMPTOMS:-
 Asymtomatic
 Asthenopic :-tiredness, frontal or frontotemporal headache, watering, mild
photophobia
 Defective vision with asthenopic symptoms
 Defective vision only
 The effect of ageing on vision
 Intermitted sudden blurring of vision
 Crossed – eye sensation
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14. CONT
Signs:-
 Size of eyeball may be normal or small as whole
 Cornea may smaller than normal
 Variation in visual acuity
 Abnormal branching of vessels , swelling of disc, retinal shine is
more than normal
 A –scan ultrasonography may reveal a short anteroposterior length
of eyeball
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15. COMPLICATION
Recurrent styes, blepharitis or chalazia
Accommodative convergent squint
Amblyopia
Predisposition to develop primary narrow
angle glaucoma
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16. TREATMENT
OPTICAL TREATMENT:-CONVEX(PLUS) LENS
 Total amount of HP-complete cycloplegic
 Manifest refractive error is small-1D or less
 Astigmatism should be fully corrected
 Exophoria -1-2D less
 Accommodative convergent squint /amblyopia-full correction
Surgery for Hp:-
 Thermokeratoplasty
 The use of excimer &Holmium lasers is under investigation
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17. APHAKIA
 Condition in which absence of crystaline lens from
pupillary area of eye
CAUSES:-
 Congenital absence of lens
 Surgical aphakia occurring after removal of lens
 Aphakia due to absorption of lens matter
 Traumatic extrusion of lens
 Posterior dislocation of lens in vitreous
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18. OPTICS OF APHAKIA
 Changes in cardinal data of the eye
 Image formation in the aphakic eye
 Visual acuity in aphakia
 Accommodation in aphakia
 Binocular vision
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19. CLINICAL FEATURES
SYMPTOMS:-
 Defective vision for near & distance
 Erythropsia and cyanopsia – due to entry of infrared and ultraviolet rays in
the absence of the crystalline lens
SIGNS:-
 Limbal scar in case of surgical aphakia
 Deep anterior chamber
 Iridodonesis – tremulousness of the iris due to loss of support of
lens
 Jet Black pupil
 Loss of 3rd and 4th purkinje images
 Fundus examination reveals a small hypermetropic fundus
 Retinoscopy shows high hypermetropia
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20. TREATMENT
SPECTACLES:-
 Spectacles should be prescribed with about +10D lens for
correction of aphakia
 It should also include correction for surgical astigmatism and
+3-4D for near vision
 Nowadays spectacles are not preferred for use in aphakia due
to its many disadvantage
 Advantages of using spectacles in aphakia
• Easy to use
• No complications
• cheap
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21. CONT…..
 Disadvantages
The images are magnified – about 30% – hence not useful in unilateral
aphakia as it causes diplopia
• The field of vision in decreased considerably
• Spherical and chromatic aberration of high power lenses
• Roving ring scotoma (Jack in the box phenomenon)
• Prismatic effect of the thick lenses
• High power are cosmetically not acceptable
Contact lenses
Advantages over spectacles:
• Produces less magnification
• Better field of vision
• Less chromatic and spherical aberration
• No prismatic effect
• Cosmetically more acceptable
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22. CONT……
Intraocular lens implantation
• The lens can be implanted in the capsular bag or in the anterior chamber
• It eliminates most of the disadvantages associated with the use of spectacles
or contact lenses
• Disadvantage include the complications associated with surgery
Refractive surgery
 Keratophakia
– a lenticule prepared from the donor cornea is placed within the
lamellae of the patient’s cornea
 Epikeratophakia
– a lenticule prepared form the donor cornea is stitched to the
patients cornea after removing the epithelium
 Hyperopic Lasik
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23. PSEUDOPHAKIA
 The condition of aphakia when corrected with
implantation of an IOL
Refractive status:-
 Emmetropia
 Consective myopia
 Consective ypermetropia
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24. SIGNS
 Surgical limbal scar may be seen
 Anterior chamber is slightly deeper than normal
 Mild iridodonesis of iris may be demonstrated
 Purkinje image test shows fours images
 Pupil is blackish in colour but when light thrown in pupillary
area shining reflexes are observed
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25. MYOPIA
 Shortsightness
 Lengthening of posterior part of eye
 The parallel rays of light coming from infinity are focused in
front of sensitive layer of retina when accommodation is at
rest
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26. AETIOLOGY
Axial myopia:-the antero-posterior diameter of eye is too
long & retina is too far from optical system
Curvature myopia:-the curvature of cornea or lens may
be too great
Positional myopia:-if lens is dislocated forwards
Index myopia:-R.i of aqueous is too high ,vitreous is too
low or lens is too high
 Myopia due to excessive accommodation occurs in patients
with spasm of accommodation
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27. OPTICS OF MYOPIA
 Optical system of a myopic eye is too powerful for its axial length
 Image of distance object on retina is made up of circles of diffusion
formed by divergent beam
 Far point of the myopic eye is a finite point in front of the eye
 Nodal point in myopic eye is further away from retina
 Angle alpha of eye may be negative
 Accommodation in uncorrected myopes is not developed normally
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28. CLINICAL VARIETIES OF MYOPIA
 Congenital myopia
 Simple or developmental myopia
 Pathological or degenerative myopia
 Acquired myopia
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29. CONGENTICAL MYOPIA
The child is born with elongated eyes
The refraction may be upto -10D
Typical fundus changes are seen
Progression is rare
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30. SIMPLE MYOPIA
 Commonest clinical type
 Does not progress much after the adolescence
 May be upto -5 to -6D
 No degenerative changes are seen in the fundus, although
peripheral retinal degeneration may be seen in later life
 Associated with good vision with a good prognosis
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31. PATHOLOGICAL MYOPIA
 It is also called progressive or degenerative myopia
 Myopia appears in childhood &increasing steadily with age upto 25
years or beyond
 The final amount of myopia may be -15Dto -25D or more
 There are typical degenerative changes in the fundus
 Strongly hereditary & more common in female
 Prognosis is usually poor
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32. ACQUIRED MYOPIA
CAUSES :-
 Index myopia
 Curvatural myopia
 Positional myopia
 Consecutive myopia
 Pseudomyopia
 Space myopia
 Night myopia
 Drug –induced myopia
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33. CLINICAL FEATURS
SYMPTOMS:-
 Impaired distance vision
 Eye –strain
 Exophoria or divergent squint
 Delayed dark adaptation
 Sudden loss of vision
 Black floaters
SIGNS:-
 Prominent eyeball, large cornea, deep anterior chamber& a
large pupil, apparent convergent squint, degeneration of
vitreous
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34. COMPLICATION OF MYOPIA
Retinal tear –vitreous haemorrhage
Retinal detachment degeneration of the
vitreous
Primary open –angle glaucoma
Posterior cortical cataract
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35. TREATMENT
Divergent or minus lenses in spectacles or
contact lenses
Cycloplegics
Surgery
Refractive surgery
General hygiene
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36. ASTIGMATISM
 Condition of refraction wherein a point focus of light cannot
be formed upon the retina
 Caused by unequal refraction of light in different meridians
 Curvatures of both axes are unequal & too small is HM ASG &
both unequal & too great is MP ASG
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37. AETIOLOGY
Corneal astigmastism :-abnormalites of curvature of
cornea
Lenticular astigmatism:-
• Small amount of curvature astigmatism due to congenital abnormalities of
curvature of lens
• Position astigmatism due to congenital or traumatic subluxation of lens
• Refractive index of lens in different median
Retinal astigmatism due to oblique placement
of macula
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38. TYPES OF ASTIGMATISM
REGULAR ASTIGMASTIM:-Axis & angle
 With –the –rule :-two principal meridian are placed at right
angles to one another but vertical meridian is more curve
than horizontal
 Against –the rule :-horizontal meridian is more curved than
vertical meridian
 Oblique:-two principal meridian are not horizontal & vertical
@ right angle to one another
 Bi-oblique:-two principal meridian are not @ right angle to
each other
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39. CONT..
REGULAR ASTIGMATISM:-REFRACTIVE TYPES
 Simple:-one meridian focus in front & other behind retina
 Compound :-ray of light in both meridian are focused either
in front or behind retina
 Mixed:-rays of light in one meridian are focused in front &
other behind retina
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40. OPTICS OF REGULAR ASTIGMATISM
 Parallel rays of light are not focused on a point but form two
focal lines
 The configuration of rays refracted through astigmatism
surface is called sturm’s conoid& distance between two lines
is called focal interval of sturm
 The length of this focal interval is a measure of degree of
astigmatism
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