Download MBBS Ophthalmology PPT 49 Refraction I Lecture Notes

2

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

Acknowledgement

? Photographs : Courtesy of

Kanski's Clinical Ophthalmology.

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

3

Learning Objectives

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

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

? Understand what is refraction.
? Have basic knowledge of myopia and its management.

4

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

Question

? You have gone fishing and see a fish in the water.

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

You do not have a fishing rod. The only

equipment that you have is a spear to catch the

fish. Where do you throw the spear?

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

a. in front of the fish.
b. behind the fish.
c. directly at the fish.
d. It is not possible to hit the fish as it is a virtual

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

image.
5

What is Refraction

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

? When rays of light traveling through air enter a

denser transparent medium, the speed of light is
reduced and the light rays proceed at a different

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

angle, i.e., they are refracted.

? Except when the rays are normal
Refraction in Ophthalmology
? Methods for evaluating optical and refractive

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

state of the eye

6

--- 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
7

Progress of refractive state of eye

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

? Birth : +2 to +3 D

? 90% of children at age 5 yrs are Hypermetropic

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

? 50% of children at age 16 yrs are Hypermetropic

? After the period of growth has passed , refractive state

tends to remain stationary, until in old age a further

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

tendency of hypermetropia is evident.

8

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 ---

9

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

Angle kappa ()

? M = Macula

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

? D= Centre of pupil, on cornea

? N = Nodal point

M

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

Optic axis

D

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

N

(

B

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

FD = Pupillary line

F

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

FNM = Visual axis

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

angle ".

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

10

Anisometropia

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

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

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.

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

? This condition may be congenital or acquired due to

asymmetric age changes or disease.

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

11

Refractive errors

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

Anomalies of the optical state of the eye

? Myopia

? Hypermetropia

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

? Astigmatism

12

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

What is Myopia ?

? Diopteric condition of the eye

where parallel incident rays from

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

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 ---

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

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

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

13

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

Myopia ? Optics

Emmetropia

Diverging lens

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

14

Optics of Myopic eye

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

? Far point is at a finite distance inversely proportional to

the degree of myopia

? Weakest concave lens that diverges rays just sufficiently

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

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


15

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

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

contributory factor

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

there is some genetic predisposition to myopia and its

severity

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

16

Types of myopia

? Axial

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

? Curvature

? Index

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

? Positional
17

Axial Myopia

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

? AP diameter increased to 25.5 to 32.5 mm

? 90-95% cases

? There may be...

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

pseudoproptosis resulting from the abnormally large

anterior segment,

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

a peripapillary myopic crescent from an exaggerated

scleral ring,

posterior staphyloma

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

18

Curvature Myopia

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

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

keratoconus,

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

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

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

lenticonus (anterior/posterior)

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

spasm of accomodation
spherophakia
19

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

Index Myopia

? Increased index of refraction in early to moderate

nuclear sclerotic cataracts in the elderly.

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

? Many people find themselves ultimately able to read

without glasses or having gained "second sight."

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

? Decrease in refractive index of cortex ? diabetic

myopia

20

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

Positional Myopia

? Anterior movement of the lens is often seen after

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

glaucoma surgery and will increase the myopic error in
the eye.

? Axial myopia of buphthalmos is countered to a large

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

extent due to posterior displacement of lens-iris
diaphragm and flattening of the cornea


21

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

Clinical course

?

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

Simple

?

Pathological

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

22

Simple Myopia

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

? Rarely present at birth, but often begins to

develop as the child grows.

? Usually detected by age 9 or 10 years in school

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

vision tests

? May increase during years of growth, stabilizing

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

around the mid-teens, usually at about 5 D or
less.
23

Pathological Myopia

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

? 2-3% population

? Increases by as much as 4 D/yr

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

? Usually stabilizes at about age 20 years and frequently

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

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

24

Pathological Myopia-Etiology

? Developmental defect affecting posterior segment

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

? Retina grows extensively stretching sclera

? Adjuvants- growth influences during puberty and

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

physical debility

? Excessive convergence- stretching
25

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

Pathological Myopia

? Associated vitreous floaters, liquefaction, posterior

staphyloma and chorioretinal changes.

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

? Degeneration is not necessarily comparable with degree

of myopia

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

? Genetic predisposition in offspring as per laws of

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

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

26

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


27

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

Clinical features of Myopia

28

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

Symptoms

1. Blurred distance vision.

2. Squinting to sharpen distance vision by

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

attempting a pinhole effect through narrowing of

palpebral fissures.

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

3. Eye strain seen in patients with uncorrected low

myopic errors
29

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

Symptoms

4. Closer working distance at near that typically

gets closer and closer as the person sustains

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

working at near.

5. Delayed dark adaptation

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

6. Floaters, photopsiae

7. Visual deterioration

30

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

Clinical Signs ?

Apparent convergent squint

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

? The problem begins at near and spreads to distance

leading to a cascade of changes in the findings over time

? Results usually in apparent convergent squint due

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

to excess convergence
31

Clinical Signs ?

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

True divergent squint

? Excess convergence for near work disorients

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

accommodation which may increase causing ciliary

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

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

relied upon for vision while the other deviates outwards

causing true divergent squint

32

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

Clinical Signs

? 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 ---

33

Fundus

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

? Atrophy of retina and choroid ?

depigmentation

? Tigroid fundus with prominent

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

choroidal vessels

? Patches of choroidal atrophy

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

surrounded by pigment associated

with haemorrhages

? Atrophic patch at macula

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

associated with loss of central

vision

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

34

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


35

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

Macular haemorrhage

36

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

Posterior staphyloma

? Herniation of posterior pole

? Crescentric shadow 2-3 DD temporal to disc,

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

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

? Gross atrophy

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

37

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

Peripheral

Degenerations

Not requiring

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

prophylaxis:

Paving stone

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

38

Predisposing Degenerations

Lattice, snailtrack, retinoschisis, white without

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

pressure

Snailtrack

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

Retinoschisis


39

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

Lattice degeneration

Figure:

40

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

Complications

? Atrophy ? scotomata

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

? macular most incapacitating

Horseshoe Tear

? Vitreous degeneration + floaters

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

? Tears + haemorrhages
? Detachment ? post traumatic or spontaneous

associated with peripheral degenerations due to

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

vitreous adhesion

? Lenticular opacities, esp. posterior cortical
? Open angle glaucoma

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

41

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 ---

42

Treatment

1. Optical correction after subjective and objective

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

refraction

Spectacles

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

Contact lens (including Orthokeratology)

2. Visual hygiene
3. Refractive surgery

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

LASIK

o

LASEK

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

Wavefront Lasik

o

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

Clear lens Extraction

Phakic IOL

o

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

ICRS

4. Pharmacological intervention

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

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

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

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

43

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

Optical correction

44

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

Myopia ? Optics

Diverging lens
45

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

Cycloplegic Refraction

? Cycloplegia is the employment of pharmaceutical

agents to paralyze the ciliary muscle temporarily

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

to stabilize the accommodative reflex of the eye

so that a definitive end point may be measured.

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

? Benefit of relaxing the accommodative tone is

especially important in young individuals.

? Cycloplegic + Mydriatic = Relaxes accomodation

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

+ dilates pupil for better reflex

46

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

Cycloplegic Refraction

Drug

Actions

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

Onset

Duration

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

Remarks

Atropine

Strong

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

6 ? 24 hr

10 ? 15 days

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

Slow,

Prolonged

Homatropine

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

Weak

1 hr

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

1 ? 2 days

Weak,

Prolonged

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

Phenylephrine

Mydriatic

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

Tropicamide

Weak

20 ? 30 min

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

4 ? 10 hr

Fast, Short

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

Cyclopentolate

Weak

10 ? 30 min

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

12 ? 24 hr

Fast,

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

intermediate


47

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

Visual Hygiene

? Proper illumination
? Proper posture
? Clear print

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

? Better contrast

48

Visual Hygiene

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

? Avoid ocular fatigue
? Proper occupation in case of degenerative

myopia

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

? May need special institutions if low vision

dictates
49

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

Summary

? Refraction is a method for evaluating optical and

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

refractive state of the eye.

? Myopia is a diopteric condition of the eye

where parallel incident rays from optical infinity

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

focus anterior to light sensitive layers of retina
when accomodation is at rest.

? Myopia is corrected by concave lenses prescribed

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

after cycloplegic refraction.

50

Question

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

? Which of the following drugs can cause acquired

myopia?

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

? a. chloroquine.
? b. sulfonamides.
? c. phenothiazines.
? d. benzodiazepines.
51

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

Question

? Which of the following is a cause of acquired

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

myopia?

? a. orbital tumor.
? b. central serous chorioretinopathy.
? c. intravitreal silicone oil.

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

? d. childhood glaucoma.

52

Thank you

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