Download MBBS Ophthalmology PPT 10 Refraction II Lecture Notes

Department of Ophthalmology

--- Content provided by FirstRanker.com ---

2

Acknowledgement

? Photographs in this presentation are courtesy of

--- Content provided by FirstRanker.com ---

Kanski's Clinical Ophthalmology.
3

Learning Objectives

--- Content provided by FirstRanker.com ---

At the end of the class, students shall be able to

? Understand what is refraction.
? Have basic knowledge of hypermetropia and astigmatism

--- Content provided by FirstRanker.com ---

and their management.

4

--- Content provided by FirstRanker.com ---

What is Refraction

? When rays of light traveling through air enter a

denser transparent medium, the speed of the

--- Content provided by FirstRanker.com ---

light is reduced and the light rays proceed at a

different angle, i.e., they are refracted.

--- Content provided by FirstRanker.com ---

? Except when the rays are normal

Refraction in Ophthalmology
? Methods for evaluating the optical and refractive

--- Content provided by FirstRanker.com ---

state of the eye


5

--- Content provided by FirstRanker.com ---

Emmetropia

? Parallel light rays, from an object more than 6 m away, are

focused at the plane of the retina when accomodation is at

--- Content provided by FirstRanker.com ---

rest.

? Clear image of a distant object formed without any

internal adjustment of the optics of the eye.

--- Content provided by FirstRanker.com ---

? Absence of emmetropia = Ametropia

6

--- Content provided by FirstRanker.com ---

Refractive errors

Anomalies of the optical state of the eye

? Myopia

--- Content provided by FirstRanker.com ---

? Hypermetropia

? Astigmatism
7

--- Content provided by FirstRanker.com ---

Hypermetropia

8

--- Content provided by FirstRanker.com ---

Hypermetropia

? Refractive or Diopteric state of eye wherein

incident parallel rays of light coming from

--- Content provided by FirstRanker.com ---

infinity are focused behind the retina with

accommodation being at rest.

--- Content provided by FirstRanker.com ---

? Near images can be blurred unless there is

sufficient accommodation, as in a child.

? They have blurred images for distant objects also

--- Content provided by FirstRanker.com ---

? Most children are born about +3 D hyperopic,

but this usually resolves by age 12 years.

--- Content provided by FirstRanker.com ---

--- Content provided by FirstRanker.com ---

9

--- Content provided by FirstRanker.com ---

Types

|

|

--- Content provided by FirstRanker.com ---

|

|

--- Content provided by FirstRanker.com ---

|

|

Axial Curvature Index Positional Absence of lens

--- Content provided by FirstRanker.com ---

? Axial is the commonest form.
? In this condition the total refractive power of eye is

normal but there is axial shortening of eye wall.

--- Content provided by FirstRanker.com ---

10

? Each millimeter of shortening represents approximately

--- Content provided by FirstRanker.com ---

3D of refractive change and thus a hypermetropia of over
6D is uncommon.

? Physiological: Infant, child.

--- Content provided by FirstRanker.com ---

? Pathological: Orbital tumour, or inflammatory mass may

indent the posterior pole of the eye and flatten it
11

--- Content provided by FirstRanker.com ---

? Curvature Hypermetropia : When the radius of

curvature of any of the refracting surfaces is increased,

? congenitally (cornea plana) or as a result of trauma

--- Content provided by FirstRanker.com ---

? Increase of 1 mm produces a hypermetropia of 6 D.

? Index Hypermetropia : Usually manifests itself as a

--- Content provided by FirstRanker.com ---

decrease in the effective refractivity of the lens and is
responsible for the hypermetropia which occurs
physiologically in old age and pathologically in diabetes.

12

--- Content provided by FirstRanker.com ---

? Positional Hypermetropia : Posterior placed lens

also produced hypermetropia whether it occurs as a
congenital anomaly or as a result of trauma and disease.

--- Content provided by FirstRanker.com ---

? Aphakia : Surgical, posterior dislocation of lens
13

Clinical Types:

--- Content provided by FirstRanker.com ---

? Simple Hypermetropia : Commonest form.
? It results from normal biological variations in the

development of eye e.g., axial and curvatural.

--- Content provided by FirstRanker.com ---

? Pathological Hypermetropia : Either congenital or

acquired conditions of eyeball which are outside the

--- Content provided by FirstRanker.com ---

normal biological variation of development e.g.

? index , positional (Aphakia).

? Functional Hypermetropia : Results from paralysis

--- Content provided by FirstRanker.com ---

of accommodation as seen in patients with third nerve

palsy.

--- Content provided by FirstRanker.com ---

14

Components of hypermetropia

Total hypermetropia = Latent+manifest (facultative +

--- Content provided by FirstRanker.com ---

absolute

Accommodation in Hypermetropia

--- Content provided by FirstRanker.com ---

? Contraction of the ciliary muscle in the act of

accommodation increases the refractive power of the

lens so that it corrects a certain amount of

--- Content provided by FirstRanker.com ---

hypermetropia.

? Normally there is an appreciable amount corrected by

--- Content provided by FirstRanker.com ---

the contraction involved in the physiological tone of this

muscle.

? Consequently the full degree of hypermetropia is

--- Content provided by FirstRanker.com ---

revealed only when this muscle is paralysed by the use of

a drug such as atropine.

--- Content provided by FirstRanker.com ---

? This is called latent hypermetropia, normally 1D.
15

Manifest Hypermetropia consists of:

--- Content provided by FirstRanker.com ---

? Facultative Hypermetropia: Corrected by

the effort of accomodation

? Absolute Hypermetropia: Cannot be

--- Content provided by FirstRanker.com ---

overcome by effort of accomodation

? As tone of ciliary muscle decreases with age,

--- Content provided by FirstRanker.com ---

some latent hypermetropia becomes manifest

? As range of accomodation reduces with age,

more facultative hypermetropia becomes

--- Content provided by FirstRanker.com ---

absolute, all of it after age 60.

16

--- Content provided by FirstRanker.com ---

Symptoms

? Vary with degree of hypermetropia and accomodative

effort

--- Content provided by FirstRanker.com ---

? Blurred vision: near>distant

? Accomodative asthenopia

--- Content provided by FirstRanker.com ---

? Convergent squint due to continuous effort of

accomodation, excess of convergence leads to
dissociation of muscle balance

--- Content provided by FirstRanker.com ---

? Early onset of presbyopia
17

Signs

--- Content provided by FirstRanker.com ---

? Small eyeball

? Smaller cornea

? Shallow anterior chamber predisposes to angle closure

--- Content provided by FirstRanker.com ---

glaucoma since size of lens is normal

? Apparent divergent squint

--- Content provided by FirstRanker.com ---

18

? Retina : Have peculiar sheen : a reflex effect so

called "shot silk retina" on ophthalmoscopic

--- Content provided by FirstRanker.com ---

finding.

? Optic disc : Characteristic appearance which

may resemble an optic neuritis (Pseudopapillitis).

--- Content provided by FirstRanker.com ---

19

Treatment

? In young children below the age of 6-7 years, some

--- Content provided by FirstRanker.com ---

degree of hypermetropia is physiological and a

correction need be given only if the error is high or if

--- Content provided by FirstRanker.com ---

strabismus is present.

? In those between 6 and 16 years especially when they

are working strenuously at school smaller error may

--- Content provided by FirstRanker.com ---

require correction.

? Required in middle aged patient, in high

--- Content provided by FirstRanker.com ---

hypermetropia and if patient is having symptoms

? Optical:

Glasses

--- Content provided by FirstRanker.com ---

Contact lens

20

--- Content provided by FirstRanker.com ---

? Convex lenses prescribed after full cycloplegic

refraction, particularly in children

? Child with convergent squint may need "full

--- Content provided by FirstRanker.com ---

atropine correction"

? Contact lens power is a little more than spectacle

--- Content provided by FirstRanker.com ---

power
21

Surgical

--- Content provided by FirstRanker.com ---

? Conductive keratoplasty.
? Non contact Holmium YAG laser

thermokeratoplasty for lower hypermetropia
(+1D ? 2.5 D).

--- Content provided by FirstRanker.com ---

? Phakic Intraocular lens (+6D ? +10 D)

22

--- Content provided by FirstRanker.com ---

Astigmatism


23

--- Content provided by FirstRanker.com ---

Astigmatism

? Astigmatism is a type of refractive error where

in the refraction varies in the different meridia.

--- Content provided by FirstRanker.com ---

? Consequently the ray of light entering in the eye

cannot converge to a point focus but form focal

--- Content provided by FirstRanker.com ---

lines.

Astigmatism

|

--- Content provided by FirstRanker.com ---

|

|

--- Content provided by FirstRanker.com ---

Regular

Irregular

24

--- Content provided by FirstRanker.com ---

Astigmatism

? Light rays passing through a steep meridian are deflected

--- Content provided by FirstRanker.com ---

more than those passing through a flatter meridian.
25

1. Corneal Astigmatism e.g. keratoconus
2. Lenticular Astigmatism

--- Content provided by FirstRanker.com ---

(i) Curvatural ? e.g. lenticonus
(ii) Positional ? subluxation
(iii) Index ? cataract

--- Content provided by FirstRanker.com ---

3. Retinal astigmatism ? due to oblique placement of

macula.

26

--- Content provided by FirstRanker.com ---

Types of Regular Astigmatism

1. With the rule astigmatism : The two principal meridia

--- Content provided by FirstRanker.com ---

are placed at right angles to one another but the vertical

meridian is more curved then horizontal- more common.

2. Against the rule astigmatism : Horizontal meridian is

--- Content provided by FirstRanker.com ---

more curved than the vertical meridian.

3. Oblique astigmatism : Is a type of regular astigmatism

--- Content provided by FirstRanker.com ---

where the two principal meridia are not horizontal and

vertical though they are at right angles to one another

(45 and 135 deg)

--- Content provided by FirstRanker.com ---

27

Oblique astigmatism :

--- Content provided by FirstRanker.com ---

aCy

sa

--- Content provided by FirstRanker.com ---

xi lr

s in

m l

--- Content provided by FirstRanker.com ---

eqa

e S:

--- Content provided by FirstRanker.com ---

t

du y

ri

--- Content provided by FirstRanker.com ---

enir(i

s )

--- Content provided by FirstRanker.com ---

mm

cal

ed et

--- Content provided by FirstRanker.com ---

rical

in both eyes.

--- Content provided by FirstRanker.com ---

in

30o

a r

--- Content provided by FirstRanker.com ---

t equiCy

rl l

--- Content provided by FirstRanker.com ---

ed Com

i

enn

--- Content provided by FirstRanker.com ---

s d

rip:

--- Content provided by FirstRanker.com ---

ca(i

l l i)

ementary

--- Content provided by FirstRanker.com ---

one eye and at 150o in the other eye.

4. Bi-oblique astigmatism : In this type of regular

--- Content provided by FirstRanker.com ---

astigmatism the two principal meridia are not at
right angles to each other, one eye at 30o and other
at 100o.

28

--- Content provided by FirstRanker.com ---

? Optics of regular astigmatism : In regular

astigmatism the parallel rays of light are not focused on a

--- Content provided by FirstRanker.com ---

point but form two focal lines ? Sturm's conoid


29

--- Content provided by FirstRanker.com ---

Refractive types of Regular

astigmatism

? Depending upon the position of

--- Content provided by FirstRanker.com ---

two focal lines in relation to retina,

regular astigmatism is further

--- Content provided by FirstRanker.com ---

classified

? Simple : Where one of the foci

falls upon retina, the other focus

--- Content provided by FirstRanker.com ---

may fall in front of or behind so

that one meridian is emmetropic

--- Content provided by FirstRanker.com ---

the other is either hypermetropic

or myopic.

30

--- Content provided by FirstRanker.com ---

2. Compound : Where neither of

two foci lie upon the retina but
both are placed in front or

--- Content provided by FirstRanker.com ---

behind it.

The state of the refraction is

then entirely hypermetropic or

--- Content provided by FirstRanker.com ---

entirely myopic. The former is
known as compound
hypermetropic, the latter as
compound myopic astigmatism.

--- Content provided by FirstRanker.com ---

31

3. Mixed : Where one focus is in front of and other behind the

--- Content provided by FirstRanker.com ---

retina so that the refraction is hypermetropic in one

direction and myopic in the other.

32

--- Content provided by FirstRanker.com ---

? Irregular Astigmatism : Refraction in different

meridia are irregular.

--- Content provided by FirstRanker.com ---

Etiological types:

1. Curvatural irregular astigmatism: irregular healing of

cornea after trauma and inflammation (particularly

--- Content provided by FirstRanker.com ---

ulceration & keratoconus)

2. Index irregular astigmatism : incipient cataract
33

--- Content provided by FirstRanker.com ---

Symptoms

1. Defective vision
2. Blurring of objects
3. Asthenopic symptoms - eyeache and headache

--- Content provided by FirstRanker.com ---

4. Running of lines

34

Treatment

--- Content provided by FirstRanker.com ---

? Optical ? Spectacles with cylindrical lenses, Contact lens

(Toric contact lenses with prism ballast)

--- Content provided by FirstRanker.com ---

? Surgical

1. Astigmatic keratotomy: Limbal Relaxing Incision,

arcuate keratectomy, removal of sutures

--- Content provided by FirstRanker.com ---

2. Photo-astigmatic refractive keratotomy (PARK)

3. Laser: Excimer laser: LASIK or Femtosecond laser
35

--- Content provided by FirstRanker.com ---

Guidelines for Optical treatment

1. If the patient does not complain of asthenopic

--- Content provided by FirstRanker.com ---

symptoms small astigmatic errors (0.5 D or less)
generally do not require correction

2. If asthenopic symptoms are there, error should be

--- Content provided by FirstRanker.com ---

corrected by cylindrical lenses.

3. Undercorrect the error initially

4. At a later date, full correction may be worn comfortably.

--- Content provided by FirstRanker.com ---