Download MBBS Ophthalmology PPT 9 Refraction I 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 myopia and its management.

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

4

What is Refraction

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

? 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

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

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

? Except when the rays are normal

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

Refraction in Ophthalmology
? Methods for evaluating the optical and refractive

state of the eye
5

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

Emmetropia

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

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

focused at the plane of the retina when accomodation is at
rest.

? Clear image of a distant object formed without any

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

internal adjustment of the optics of the eye.

? Absence of emmetropia = Ametropia

6

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

Progress of refractive state of eye

? Birth : +2 to +3 D

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

? 90% of children at age 5 yrs are Hypermetropic

? 50% of children at age 16 yrs are Hypermetropic

? After the period of growth has passed the refractive state

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

tends to remain stationary, until in old age a further
tendency of hypermetropia is evident.

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

7

Refractive data in adult

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

? Normal axial length 24 mm
? Change in axial length by 1mm = ?3D

? Refraction at corneal surface= +40 to 45(+43)D

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

? Change in Corneal Curvature by 1mm = ?6D

? Refraction by unaccomodated lens= +16 to

20(+17)D

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

8

Angle kappa ()

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

? M = Macula

? D= Centre of pupil, on cornea

? N = Nodal point

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

M

Optic axis

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

D

N

(

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

B

FD = Pupillary line

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

F

FNM = Visual axis

= "Between the visual axis and pupillary line, hence roughly corresponds to

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

angle ".


9

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

Anisometropia

? Anisometropia is a state in which there is a difference in

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

the refractive errors of the two eyes, i.e., one eye is
myopic and the other hyperopic, or both are hyperopic or
myopic but to different degrees.

? This condition may be congenital or acquired due to

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

asymmetric age changes or disease.

10

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

Refractive errors

Anomalies of the optical state of the eye

? Myopia

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

? Hypermetropia

? Astigmatism

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

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

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

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

11

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

What is Myopia ?

? Diopteric condition of the eye

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

where parallel incident rays from

optical infinity

focus anterior to light sensitive layers

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

of retina

when accomodation is at rest

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

12

Myopia ? Optics

Emmetropia

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

Diverging lens
13

Optics of Myopic eye

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

? Far point is at a finite distance inversely proportional to

the degree of myopia

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

? Weakest concave lens that diverges rays just sufficiently

to focus them at the retina is to be used

? Poor visual acuity is compensated to some extent by

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

enlarged image size due to the nodal point being further

from the retina

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

14

Causes of Myopia

? The causes of myopia are not known.

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

? Epidemiological correlation suggest...

lengthy periods of close work are probably a

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

contributory factor

there is some genetic predisposition to myopia and its

severity

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

15

Types of myopia

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

? Axial

? Curvature

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

? Index

? Positional

16

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

Axial Myopia

? AP diameter increased to 25.5 to 32.5 mm

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

? 90-95% cases

? There may be...

pseudoproptosis resulting from the abnormally large

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

anterior segment,

a peripapillary myopic crescent from an exaggerated

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

scleral ring,

posterior staphyloma
17

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

Curvature Myopia

? Corneal curvature steeper than average, e.g.,

keratoconus,

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

? Radius <7-8.5 mm (normal); 1 mm=6 D

? Lens curvature is increased
? moderate to severe hyperglycemia (intumescence)

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

lenticonus (ant/post)

spasm of accomodation
spherophakia

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

18

Index Myopia

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

? Increased index of refraction in early to moderate

nuclear sclerotic cataracts in the elderly.

? Many people find themselves ultimately able to read

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

without glasses or having gained "second sight."

? Decrease in refractive index of cortex ? diabetic

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

myopia


19

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

Positional Myopia

? Anterior movement of the lens is often seen after

glaucoma surgery and will increase the myopic error in

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

the eye.

? Axial myopia of buphthalmos is countered to a large

extent due to posterior displacement of lens-iris

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

diaphragm and flattening of the cornea

20

Clinical course

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

?

Simple

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

?

Pathological
21

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

Simple Myopia

? Rarely present at birth, but often begins to

develop as the child grows.

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

? Usually detected by age 9 or 10 years in the

school vision tests

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

? May increase during the years of growth,

stabilizing around the mid-teens, usually at

about 5 D or less.

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

22

Pathological Myopia

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

? 2-3% population

? Increases by as much as 4 D/yr

? Usually stabilizes at about age 20 years and frequently

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

results in myopia ? 10 to 20 D.

? If progress is rapid from age 15-20, likely to reach 20-30

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

dioptres

? Commoner in women, Jews and Japanese
23

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

Pathological Myopia-Etiology

? Developmental defect affecting posterior segment

? Retina grows extensively stretching sclera

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

? Adjuvants- growth influences during puberty and

physical debility

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

? Excessive convergence- stretching

24

Pathological Myopia

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

? Associated vitreous floaters, liquefaction, posterior

staphyloma and chorioretinal changes.

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

? Degeneration is not necessarily comparable with degree

of myopia

? Genetic predisposition in offspring as per laws of

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

recessive Mendelian inheritance ? if both parents
affected, close supervision needed

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

25

School/ Physiologic/Pseudo-Myopia

? 2D

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

? Excessive near work causing accomodative

spasm

? Inherited predisposition-more in Orientals and

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

Jews

26

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

Clinical features of Myopia
27

Symptoms

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

1. Blurred distance vision.

2. Squinting to sharpen distance vision by attempting a

pinhole effect through narrowing of the palpebral

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

fissures.

3. Eye strain seen in patients with uncorrected low

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

myopic errors

4. Closer working distance at near that typically gets

closer and closer as the person sustains working at

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

near.

5. Delayed dark adaptation

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

6. Floaters, photopsiae

7. Visual deterioration

28

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

Signs

? Small eyeball

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

? Smaller cornea

? Shallow anterior chamber predisposes to angle closure

glaucoma since size of lens is normal

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

? Apparent divergent squint
29

Clinical Signs ?

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

Apparent convergent squint

? The problem begins at near and spreads to distance

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

leading to a cascade of changes in the findings over time

? Results usually in apparent convergent squint due

to excess convergence

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

30

Clinical Signs ?

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

True divergent squint

? Excess convergence for near work disorients

accommodation which may increase causing ciliary

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

spasm or

? more frequently, attempt at convergence is given up, its

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

latent insufficiency causing muscular imbalance till

? advantage of binocular vision is given up, one eye is

relied upon for vision while the other deviates outwards

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

causing true divergent squint


31

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

Pathology

? Eye appears large and prominent ? pseudoproptosis

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

? Deep anterior chamber

? Large, sluggish pupil

? Post segment sclera is thinned up to 25% of normal

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

? Post vitreous detachment ? Weiss ring

? Liquefaction ? muscae volitantes, large floaters

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

32

Fundus

? Atrophy of retina and choroid ?

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

depigmentation

? Tigroid fundus with prominent

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

choroidal vessels

? Patches of choroidal atrophy

surrounded by pigment associated

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

with haemorrhages

? Atrophic patch at macula

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

associated with loss of central

vision

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

33

Fundus

? Appearance of dark pigmented area at macula-Foster-

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

Fuch's fleck ? rare, sudden, proliferation of pigmentary

epithelium with intra-choroidal haemorrhage or

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

thrombosis

? Macular bunches of dilated capillaries or aneurysms

? Myopic crescent ? temporal or annular

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

? Nasal supertraction crescent

34

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

Macular haemorrhage

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

35

Posterior staphyloma

? Herniation of posterior pole

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

? Crescentric shadow 2-3 DD temporal to disc,

? Sudden kinking of retinal vessels as they dip over the edges,

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

? Gross atrophy

36

Peripheral

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

Degenerations

Not requiring

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

prophylaxis:

Paving stone

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

37

Predisposing Degenerations

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

Lattice, snailtrack, retinoschisis, white without

pressure

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

Snailtrack

Retinoschisis

38

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

Lattice degeneration

Figure:

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

39

Complications

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

? Atrophy ? scotomata

? macular most incapacitating

Horseshoe Tear

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

? Vitreous degeneration + floaters
? Tears + haemorrhages
? Detachment ? post traumatic or spontaneous

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

associated with peripheral degenerations due to

vitreous adhesion

? Lenticular opacities, esp. posterior cortical

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

? Open angle glaucoma

40

Night myopia

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

?

Manifest in reduced illumination

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

?

~ 0.5 D

?

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

Cone-rod shift in retina, pupillary dilatation,

ciliary muscle activity

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

?

If night vision appears seriously impaired,

appropriate correction may be given

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

41

Treatment

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

1. Optical correction after subjective and objective

refraction

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

Spectacles

Contact lens (including Orthokeratology)

2. Visual hygiene

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

3. Refractive surgery

LASIK

o

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

LASEK

Wavefront Lasik

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

o

Clear lens Extraction

Phakic IOL

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

o

ICRS

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

4. Pharmacological intervention

42

Optical correction

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

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

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

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

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

43

Myopia ? Optics

Diverging lens

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

44

Cycloplegic Refraction

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

? Cycloplegia is the employment of pharmaceutical

agents to paralyze the ciliary muscle temporarily

to stabilize the accommodative reflex of the eye

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

so that a definitive end point may be measured.

? Benefit of relaxing the accommodative tone is

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

especially important in young individuals.

? Cycloplegic + Mydriatic = Relaxes accomodation

+ dilates pupil for better reflex

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

45

Cycloplegic Refraction

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

Drug

Actions

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

Onset

Duration

Remarks

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

Atropine

Strong

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

6 ? 24 hr

10 ? 15 days

Slow,

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

Prolonged

Homatropine

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

Weak

1 hr

1 ? 2 days

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

Weak,

Prolonged

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

Phenylephrine

Mydriatic

Tropicamide

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

Weak

20 ? 30 min

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

4 ? 10 hr

Fast, Short

Cyclopentolate

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

Weak

10 ? 30 min

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

12 ? 24 hr

Fast,

intermediate

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

46

Visual Hygiene

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

? Proper illumination
? Proper posture
? Clear print
? Better contrast
? Avoid ocular fatigue

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

? Proper occupation in case of degenerative

myopia

? May need special institutions if low vision

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

dictates
47

Summary

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

? Refraction is a method for evaluating the optical

and refractive state of the eye.

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

? Myopia is a diopteric condition of the eye

where parallel incident rays from optical infinity
focus anterior to light sensitive layers of retina
when accomodation is at rest.

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

? Myopia is corrected by concave lenses prescribed

after cycloplegic refraction.