Error Of Refaction

Question 1

Type of errors of refraction

Answer 1

1 spherical errors (myopia and hypermetropia)

2 non spherical errors (astigmatism)

Question 2

MYOPIA Defination

Answer 2

: when the incident parallel rays come to focus in front of the retina ; when the
eye is at rest .i.e. no accommodation

Question 3

Type of myopia

Answer 3

1-Axial myopia
A ) simple b ) Developmental c ) pathological, progressive, degenerative
2 – Refractive myopia
A ) curvature b ) Index c ) Anterior dislocation of the lens

Question 4

Simple myopia :

Answer 4

The eye has axial length longer than normal , it’s the commonest type ,it start at puberty and then progress slowly till adulthood when it becomes stable .
It rarely exceed 6 diopters ,no degenerative changes in the fundus

Question 5

Pathological / progressive myopia :

Answer 5

it starts at 5-10 yrs and steadily progress up to 20 D or more
more common in females & strongly hereditary in nature , with marked degenerative changes in the fundus & more labial complication .

Question 6

Developmental myopia :

Answer 6

The child is born with abnormally long eye The refractive soon after birth is more than 6 and up to 10 diopters

Question 7

Refractive curvature myopia

Answer 7

1mm increasing the curvature leads to 6D myopia
1 ) Corneal causes : due to too strong curvature of the cornea
2 ) Lenticular causes : due to increase lens curvature which occurs in :
Spasm of accommodation , cyclitis , anterior dislocation of the lens & congenital spheroid

((type of refractive error that develops when the cornea is curved too much.))

Question 8

index myopia :

refractive index

Answer 8

due to increase in RI of the cornea , aqueous , the lens or low RI of the vitreous
The lens is the most important cause , it is either increase RI of the nucleus (nuclear cataract ) or low RI of the cortex

Question 9

Optical condition in myopia :

Answer 9

. incident parallel rays comes to focus infront of the retina with accommodation at rest
. rays emerging from retina will converge infront of the eye between the eye & infinity , this is called punctum remotum (far point )this point and that in the retina are two conjugate foci provided that accommodation is at rest
.this means that the myopic eye is focused for the divergent rays , so the principle of correcting myopia is by insertion infront of the eye biconcave lens whose principle focus coincide with the far point of the eye

Question 10

Symptoms of myopia :

Answer 10

blurred distant vision and in high myopia discomfort after near due to disproportion between convergence and accommodation
musca violantes , photopsia , scotoma (field defect) defective vision at night

Question 11

sign of myopia :

Answer 11

large prominent globe , big cornea and deep AC apparent convergent squint
true divergent squint

fundus changes :

1) myopia crescent & annular crescent
2) atropic chorioretinal degenerative white patches 3) tigroid fundus
4) fuchs fleck & CNV
5) lacquer crack
6) lattic retinal degeneration
7) retinal detachment
8) PVD
9) posterior staphyloma

Question 12

myopia crescent & annular crescent

Answer 12

is a moon-shaped feature that can develop at the temporal (lateral) border of disc (it rarely occurs at the nasal border) of myopic eyes. It is primarily caused by atrophic changes

Question 13

atropic chorioretinal degenerative white patches

Answer 13

Chorioretinal Atrophy is a condition of the eye where both the choroid and retina are damaged.

Question 14

tigroid fundus

Answer 14

the retinal pigment epithelium is not well pigmented, as in people with blond or red hair, then the underlying choroidal vessels may become strikingly visible

Question 15

fuchs fleck & CNV

Answer 15

هي تَنَكُّس بقعة الشبكية في حال قصر النظر. يتناسب حجم بُقع فوكس مع شدة مرضية قصر النظر.

Question 16

lacquer crack

Answer 16

are breaks in Bruch’s membrane frequently observed in the posterior pole of a highly myopic eye

Question 17

lattic retinal degeneration

Answer 17

It when peripheral retina becomes atrophy and develop tears and may detachment of a retinal

Question 18

posterior staphyloma

Answer 18

a localized defect in the eye wall with protrusion of uveal tissue due to alterations in scleral thickness and structure

Question 19

Complication of myopia :

Answer 19

Complicated cataract (PSC)
Pigmentary glaucoma
Consecutive optic atrophy

Question 20

Treatment of myopia :

Answer 20

1) glasses with concave lens
2) contact lens
3) surgical treatment :
a) radial keratotomy (1-4 Diopters)
b) photorefractive keratectomy (PRK) correct up to 6 diopters c) laser in situ kerato mileusis (LASIK) correct up to 12 diopters
4) Phakic intraocular lens : correct up to 20D
5) combined phakic IOL & LASIK 6) clear lens extraction

Question 21

Hypermetropia Definition:

Answer 21

: it is the dioptric condition of the accommodation at rest ; the incident parallel rays come to focus behind the retina .

Question 22

Optical condition in hypermetropia :

Answer 22

_ The hypermetropic pt must accommodate to see distant object , accommodation increase more as the object approximates from the eye , because light rays coming from near objet are divergent .i.e. hypermetropic pt accommodate more than emmetropia.
_ Rays coming from a point on the retina of emmetropia will emerge parallel , while in hypermetropoc will emerge divergent
_in hypermetropia wil lmeet behind the eye at the punctum remotum (is a virtual point behind the eye) the point on retina and punctum remotum are conjugate foci.

Question 23

Functional classification of hypermetropia :

Answer 23

1 latent hypermetropia
2 manifest
3-facultative
4 absolute

Question 24

latent hypermetropia :

Answer 24

is the part of hypermetropia corrected by ciliary muscle tone ,
usually 1D , it detected only after cycloplegia

Question 25

manifest {facultative & absolute } :

Answer 25

it’s equal to the strongest convex lens with which non atropinized eye see maximum .

Question 26

facultative :

Answer 26

it’s the part that corrected by accommodation . it’s the difference between the absolute & manifest hypermetropia

Question 27

absolute :

Answer 27

it is a part of hypermetropia which is not correct by accommodation , it’s known by the weakest convex lens with the eye sees maximum .

Question 28

Clinical picture of hypermetropia :

Answer 28

usually clear distant vision , blurred near vision (asthenopia).
true convergent squint in children b/c excessive accommodation . early presbyopia .
shallow AC & narrow angle predispose to acute congestive glaucoma . fundus picture :
bright retinal reflex .
pseudoneuritis like picture .
indistinct disc margin .
abnormal branching of retinal vessels .

Question 29

presbyopia

Answer 29

when your eyes gradually lose the ability to see things clearly up close

Question 30

treatment of hypermetropia :

Answer 30

Course : in children tend to diminish , but in adult it remains stationary , in old age
hypermetropia increase due to lens cortex change .
Treatment : by convex glass to improves vision , treat asthenopia & squint .

Question 31

strabismus

Answer 31

, is where the eyes point in different directions.

Question 32

Astigmatism is

Answer 32

Astigmatism
Is the radii of curvature of refractive surface are different in various meridians , comes to focus in two focal line separated from each other by focal interval or sternum

Question 33

Causes of astigmatism

Answer 33

:
A) Congenital : keratoconus
B) Acquired :
1- keratectasia following ulcer or wound
2- Corneal scar following inflammation or ulcer or trauma
3- Pressure on the globe by tumor or large chalazion
4- subluxation or titling lens

Question 34

Type of corneal astigmatism :

Answer 34

1) Regular astigmatism

2) irregular astigmatism

Question 35

Regular astigmatism :

Answer 35

in which two principle meridians are at right angle , this is the only
type susceptible to good correction
-when the two principle meridians are at 90 & 180 is termed straight regular astigmatism
-when the two principle meridians are at right angle but instead of being vertical or horizontal are incline in oblique direction is called Oblique

Question 36

Irregular astigmatism

Answer 36

: in which the meridians of the greatest and least refraction are not at right angle

Question 37

Classifications of Irregular astigmatism

Answer 37

1- simple
2-mixed
3-compounds

Question 38

Simple

Answer 38

: in which one meridian is normal and the other is myopic or hypermetropic

Question 39

Mixed

Answer 39

: in which one meridian is myopic and the other is hypermetropic

Question 40

Compound

Answer 40

: in which the principle two meridians of different dioptric values are

Question 41

Diagnosis of astigmatism :

Answer 41

• Decrease VA .
• Red reflex is oval/band shape .
• Retinoscopy :different dioptric power used for correction of principal meridian.
• Keratometer : it measure anterior corneal surface and its axial only (every step equal to 1D) .
• corneal topograghy .

Question 42

Treatment of astigmatism simple

Answer 42

corrected by cylindrical lens with axis perpendicular to meridian

Question 43

Treatment of compound astigmatism :

Answer 43

change to simple astigmatism by giving spherical lens , then the error corrected by cylindrical lens

Question 44

Treatment of regular/irregular :

Answer 44

by hard gas permeable CL , intracorneal ring , crosslinking & keratoplasty