Acknowledgement
? Photographs in this presentation are courtesy of
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Kanski's Clinical Ophthalmology.
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Learning Objectives
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At the end of the class, students shall be able to
? Understand what is refraction.
? Have basic knowledge of hypermetropia and astigmatism
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and their management.
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What is Refraction? When rays of light traveling through air enter a
denser transparent medium, the speed of the
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light is reduced and the light rays proceed at a
different angle, i.e., they are refracted.
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? Except when the rays are normalRefraction in Ophthalmology
? Methods for evaluating the optical and refractive
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state of the eye5
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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
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Refractive errorsAnomalies of the optical state of the eye
? Myopia
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? Hypermetropia
? Astigmatism
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Hypermetropia
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Hypermetropia? Refractive or Diopteric state of eye wherein
incident parallel rays of light coming from
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infinity are focused behind the retina with
accommodation being at rest.
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? Near images can be blurred unless there issufficient accommodation, as in a child.
? They have blurred images for distant objects also
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? Most children are born about +3 D hyperopic,but this usually resolves by age 12 years.
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Types|
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Axial Curvature Index Positional Absence of lens
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? Axial is the commonest form.
? In this condition the total refractive power of eye is
normal but there is axial shortening of eye wall.
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? Each millimeter of shortening represents approximately
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3D of refractive change and thus a hypermetropia of over6D is uncommon.
? Physiological: Infant, child.
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? Pathological: Orbital tumour, or inflammatory mass mayindent the posterior pole of the eye and flatten it
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? Curvature Hypermetropia : When the radius ofcurvature of any of the refracting surfaces is increased,
? congenitally (cornea plana) or as a result of trauma
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? Increase of 1 mm produces a hypermetropia of 6 D.
? Index Hypermetropia : Usually manifests itself as a
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decrease in the effective refractivity of the lens and isresponsible for the hypermetropia which occurs
physiologically in old age and pathologically in diabetes.
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? Positional Hypermetropia : Posterior placed lens
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 lens
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Clinical Types:
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? Simple Hypermetropia : Commonest form.
? It results from normal biological variations in the
development of eye e.g., axial and curvatural.
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? Pathological Hypermetropia : Either congenital or
acquired conditions of eyeball which are outside the
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normal biological variation of development e.g.? index , positional (Aphakia).
? Functional Hypermetropia : Results from paralysis
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of accommodation as seen in patients with third nerve
palsy.
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14Components of hypermetropia
Total hypermetropia = Latent+manifest (facultative +
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absolute
Accommodation in Hypermetropia
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? Contraction of the ciliary muscle in the act ofaccommodation increases the refractive power of the
lens so that it corrects a certain amount of
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hypermetropia.
? Normally there is an appreciable amount corrected by
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the contraction involved in the physiological tone of thismuscle.
? Consequently the full degree of hypermetropia is
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revealed only when this muscle is paralysed by the use of
a drug such as atropine.
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? This is called latent hypermetropia, normally 1D.15
Manifest Hypermetropia consists of:
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? Facultative Hypermetropia: Corrected bythe effort of accomodation
? Absolute Hypermetropia: Cannot be
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overcome by effort of accomodation
? As tone of ciliary muscle decreases with age,
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some latent hypermetropia becomes manifest? As range of accomodation reduces with age,
more facultative hypermetropia becomes
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absolute, all of it after age 60.
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Symptoms? 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 ofaccomodation, excess of convergence leads to
dissociation of muscle balance
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? Early onset of presbyopia17
Signs
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? Small eyeball? Smaller cornea
? Shallow anterior chamber predisposes to angle closure
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glaucoma since size of lens is normal
? Apparent divergent squint
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18? Retina : Have peculiar sheen : a reflex effect so
called "shot silk retina" on ophthalmoscopic
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finding.? Optic disc : Characteristic appearance which
may resemble an optic neuritis (Pseudopapillitis).
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19Treatment
? In young children below the age of 6-7 years, some
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degree of hypermetropia is physiological and a
correction need be given only if the error is high or if
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strabismus is present.? In those between 6 and 16 years especially when they
are working strenuously at school smaller error may
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require correction.
? Required in middle aged patient, in high
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hypermetropia and if patient is having symptoms? Optical:
Glasses
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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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power21
Surgical
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? Conductive keratoplasty.? Non contact Holmium YAG laser
thermokeratoplasty for lower hypermetropia
(+1D ? 2.5 D).
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? Phakic Intraocular lens (+6D ? +10 D)
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Astigmatism23
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Astigmatism? Astigmatism is a type of refractive error where
in the refraction varies in the different meridia.
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? Consequently the ray of light entering in 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
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more than those passing through a flatter meridian.25
1. Corneal Astigmatism e.g. keratoconus
2. Lenticular Astigmatism
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(i) Curvatural ? e.g. lenticonus
(ii) Positional ? subluxation
(iii) Index ? cataract
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3. Retinal astigmatism ? due to oblique placement ofmacula.
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Types 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 verticalmeridian is more curved then horizontal- more common.
2. Against the rule astigmatism : Horizontal meridian is
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more curved than the vertical meridian.
3. Oblique astigmatism : Is a type of regular astigmatism
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where the two principal meridia are not horizontal andvertical though they are at right angles to one another
(45 and 135 deg)
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Oblique astigmatism :
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aCy
sa
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xi lrs in
m l
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eqa
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tdu y
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enir(i
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mmcal
ed et
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rical
in both eyes.
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in30o
a r
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t equiCy
rl l
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ed Comi
enn
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s d
rip:
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ca(il l i)
ementary
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one eye and at 150o in the other eye.
4. Bi-oblique astigmatism : In this type of regular
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astigmatism the two principal meridia are not atright angles to each other, one eye at 30o and other
at 100o.
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? Optics of regular astigmatism : In regular
astigmatism the parallel rays of light are not focused on a
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point but form two focal lines ? Sturm's conoid29
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Refractive types of Regularastigmatism
? 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 of the foci
falls upon retina, the other focus
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may fall in front of or behind so
that one meridian is emmetropic
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the other is either hypermetropicor myopic.
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2. Compound : Where neither of
two foci lie upon the retina but
both are placed in front or
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behind it.The state of the refraction is
then entirely hypermetropic or
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entirely myopic. The former isknown as compound
hypermetropic, the latter as
compound myopic astigmatism.
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3. Mixed : Where one focus is in front of and other behind the
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retina so that the refraction is hypermetropic in onedirection and myopic in the other.
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? Irregular Astigmatism : Refraction in different
meridia are irregular.
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Etiological types:1. Curvatural irregular astigmatism: irregular healing of
cornea after trauma and inflammation (particularly
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ulceration & keratoconus)2. Index irregular astigmatism : incipient cataract
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Symptoms1. Defective vision
2. Blurring of objects
3. Asthenopic symptoms - eyeache and headache
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4. Running of lines34
Treatment
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? Optical ? Spectacles with cylindrical lenses, Contact lens
(Toric contact lenses with prism ballast)
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? Surgical1. Astigmatic keratotomy: Limbal Relaxing Incision,
arcuate keratectomy, removal of sutures
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2. Photo-astigmatic refractive keratotomy (PARK)
3. Laser: Excimer laser: LASIK or Femtosecond laser
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Guidelines for Optical treatment
1. If the patient does not complain of asthenopic
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symptoms small astigmatic errors (0.5 D or less)generally do not require correction
2. If asthenopic symptoms are there, error should be
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corrected by cylindrical lenses.3. Undercorrect the error initially
4. At a later date, full correction may be worn comfortably.
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