? Photographs in this presentation are courtesy of
Kanski's Clinical Ophthalmology.
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3Learning Objectives
At the end of the class, students shall be able to
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? Understand what is refraction.
? Have basic knowledge of hypermetropia and astigmatism
and their management.
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4
Question
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? A patient with a corneal scar is carefullyrefracted. Best corrected visual acuity is 6/12.
With a pinhole over his correction, his acuity
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improves to 6/6. The best explanation for this is
? a. spherical aberration.
? b. myopic astigmatism.
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? c. cataract.? d. irregular astigmatism.
5
What is Refraction
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? When rays of light traveling through air enter a
denser transparent medium, the speed of the
light is reduced and the light rays proceed at a
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different angle, i.e., they are refracted.? Except when the rays are normal
Refraction in Ophthalmology
? Methods for evaluating the optical and refractive
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state of the eye
6
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Emmetropia? Parallel light rays, from an object more than 6 m away, are
focused at the plane of the retina when accomodation is at
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rest.? Clear image of a distant object formed without any
internal adjustment of the optics of the eye.
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? Absence of emmetropia = Ametropia
7
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Refractive errors
Anomalies of the optical state of the eye
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? Myopia? Hypermetropia
? Astigmatism
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8
Hypermetropia
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Hypermetropia
? Refractive or Diopteric state of eye wherein
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incident parallel rays of light coming frominfinity are focused behind the retina with
accommodation being at rest.
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10
? Near images can be blurred unless there is
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sufficient accommodation, as in a child.? They have blurred images for distant objects also
? Most children are born about +3 D hyperopic,
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11
Types
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||
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|
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|Axial Curvature Index Positional Absence of lens
? Axial is the commonest form.
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? In this condition the total refractive power of eye isnormal but there is axial shortening of eye ball.
12
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? Each millimeter of shortening represents approximately
3D of refractive change and thus a hypermetropia of over
6D is uncommon.
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? Physiological: Infant, child.
? Pathological: Orbital tumour, or inflammatory mass may
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indent the posterior pole of the eye and flatten it13
? Curvature Hypermetropia : When the radius of
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curvature of any of the refracting surfaces is increased,? congenitally (cornea plana) or as a result of trauma
? Increase of 1 mm produces a hypermetropia of 6 D.
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14
? Index Hypermetropia : Usually manifests
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itself as a decrease in the effective refractivity ofthe lens and is responsible for the hypermetropia
which occurs physiologically in old age and
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pathologically in diabetes.
15
? Positional Hypermetropia : Posterior placed lens
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also produced hypermetropia whether it occurs as a
congenital anomaly or as a result of trauma and disease.
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? Aphakia : Surgical, posterior dislocation of lens16
Clinical Types:
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? Simple Hypermetropia : Commonest form.
? It results from normal biological variations in the
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development of eye e.g., axial and curvatural.? Pathological Hypermetropia : Either congenital or
acquired conditions of eyeball which are outside the normal
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biological variation of development? Example: index , positional (Aphakia).
? Functional Hypermetropia : Results from paralysis of
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accommodation as seen in patients with third nerve palsy.
17
Components of hypermetropia
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Total hypermetropia = Latent+manifest
(facultative + absolute)
Accommodation in Hypermetropia
? Contraction of ciliary muscle in the act of
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accommodation increases the refractive power of
the lens so that it corrects a certain amount of
hypermetropia.
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18? Normally there is an appreciable amount corrected by
contraction involved in physiological tone of ciliary muscle.
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? Consequently the full degree of hypermetropia is revealed
only when this muscle is paralysed by the use of a drug such
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as atropine.? This is called latent hypermetropia, normally 1D.
19
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Manifest Hypermetropia consists of:? Facultative Hypermetropia: Corrected by effort of
accomodation
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? Absolute Hypermetropia: Cannot be overcome by
effort of accomodation
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? As tone of ciliary muscle decreases with age, some latenthypermetropia becomes manifest
? As range of accomodation reduces with age, more
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facultative hypermetropia becomes absolute, all of it
after age 60.
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20Symptoms
? Vary with degree of hypermetropia and accomodative effort
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? Blurred vision: near>distant
? Accomodative asthenopia
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? Convergent squint due to continuous effort of accomodation,excess of convergence leads to dissociation of muscle balance
? Early onset of presbyopia
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21Signs
? Small eyeball
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? Smaller cornea
? Shallow anterior chamber predisposes to angle closure
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glaucoma since size of lens is normal? Apparent divergent squint
22
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? Retina : Has peculiar sheen : a reflex effect so
called "shot silk retina" on ophthalmoscopy.
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? Optic disc : Characteristic appearance whichmay resemble optic neuritis (Pseudopapillitis).
23
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Treatment? In young children below the age of 6-7 years:
some degree of hypermetropia is physiological
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and a correction need be given only if the error ishigh or if strabismus is present.
? In those between 6 and 16 years:
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smaller error may require correction.24
? Refractive correction is required
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? in middle aged patients? in high hypermetropia
? and if patient is symptomatic
? Optical:
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Glasses
Contact lens
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? Convex lenses prescribed after full cycloplegicrefraction, particularly in children
? Child with convergent squint may need "full
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atropine correction"
? Contact lens power is a little more than spectacle
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power26
Surgical Options
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? Conductive keratoplasty.
? Non contact Holmium YAG laser thermokeratoplasty
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for lower hypermetropia (+1D ? 2.5 D).? Phakic Intraocular lens (+6D ? +10 D)
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27Astigmatism
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Astigmatism
? Astigmatism is a type of refractive error wherein
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the refraction varies in different meridia.? Consequently rays of light entering the eye
cannot converge to a point focus, but form focal
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lines.Astigmatism
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RegularIrregular
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Astigmatism? Light rays passing through a steep meridian are
deflected more than those passing through a
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flatter meridian.30
1. Corneal Astigmatism e.g. keratoconus
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2. Lenticular Astigmatism
(i) Curvatural ? e.g. lenticonus
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(ii) Positional ? subluxation(iii) Index ? cataract
3. Retinal astigmatism ? due to oblique placement of macula.
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31Types of Regular Astigmatism
1. With the rule astigmatism : The two principal meridia
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are placed at right angles to one another but the vertical
meridian is more curved than horizontal meridian
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(most common type)2. Against the rule astigmatism : Horizontal meridian is
more curved than the vertical meridian.
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3. Oblique astigmatism : Is a type of regular astigmatism
where the two principal meridia are not horizontal and
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vertical , though they are at right angles to one another(45 and 135 deg)
32
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Oblique astigmatism :
aCy
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saxi lr
s in
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m l
eqa
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e S:t
du y
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ri
enir(i
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s )mm
cal
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ed et
rical
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in both eyes.in
30o
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a r
t equiCy
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rl led Com
i
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enn
s d
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rip:ca(i
l l i)
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ementary
one eye and at 150o in the other eye.
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4. Bi-oblique astigmatism : In this type of regularastigmatism the two principal meridia are not at
right angles to each other, one eye at 30o and other
at 100o.
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33
? Optics of regular astigmatism : In regular
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astigmatism the parallel rays of light are not focused on a
point but form two focal lines ? Sturm's conoid
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34Refractive types of Regular astigmatism
? Depending upon the position of
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two focal lines in relation to retina,
regular astigmatism is further
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classified? Simple : Where one focus falls
upon retina, the other focus may
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fall in front of or behind, so that
one meridian is emmetropic the
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other is either hypermetropic ormyopic.
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35Compound : Where neither of two
foci lie upon retina but both are
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placed in front or behind it.The state of the refraction is then
entirely hypermetropic or entirely
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myopic. The former is known ascompound hypermetropic, the latter
as compound myopic astigmatism.
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3. Mixed : Where one focus is in front of and other behind
retina so that the refraction is hypermetropic in one
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direction and myopic in the other.37
? Irregular Astigmatism : Refraction in different
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meridia are irregular.Etiological types:
1. Curvatural irregular astigmatism: irregular healing of
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cornea after trauma and inflammation (particularly
ulceration & keratoconus)
2. Index irregular astigmatism : incipient cataract
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38
Symptoms
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1. Defective vision2. Blurring of objects
3. Asthenopic symptoms - eyeache and headache
4. Running of lines
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Treatment
? Optical ? Spectacles with cylindrical lenses, Contact lens
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(Toric contact lenses with prism ballast)? Surgical
1. Astigmatic keratotomy: Limbal Relaxing Incision,
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arcuate keratectomy, removal of sutures
2. Photo-astigmatic refractive keratotomy (PARK)
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3. Laser: Excimer laser: LASIK or Femtosecond laser40
Guidelines for Optical treatment
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1. If the patient does not complain of asthenopic
symptoms small astigmatic errors (0.5 D or less)
generally do not require correction
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2. If asthenopic symptoms are present , error should be
corrected by cylindrical lenses.
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3. Undercorrect the error initially4. At a later date, full correction may be worn comfortably.
41
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Question? In a patient with astigmatism, all of the following are
true of myopia and hyperopia except
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? a. In simple myopic astigmatism, one focal line lies in
front of the retina and the other is on the retina.
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? b. In compound myopic astigmatism, both focal lines liein front of the retina.
? c. In simple hyperopic astigmatism, both focal lines lie
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behind the retina.
? d. In mixed astigmatism, one focal line lies in front of the
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retina and one lies behind the retina.42
Thank you
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