Refraction

1. Presbyopia:
Is anormal condition associated with age in which
accommadation tall short of the demand for the
usual reading range .
Causes of decline of accommadition:
1) inelastic lens (rigid)
2) Weakness of the ciliary muscle.

2. Aphakia:
Absence of the crystalline lens from pupillary
area.
Aetiology:
1) Cangenital
2) Trumatic
3) An intra –ocular surgury.
Pseudophakia :-
An eye with an intra ocular lens

3.  Accommodation :-
 Is ability of the eye to increase its refractivity by a
change in crystalline lens .
 The acco is concentration with veiwing of object
closer than optical infinity (reading manily).
Mechanism:
Contracture of ciliary muscle & relaxation of the
Suspensory ligment the lens become more convex
increase in thickness and decrease in diameter.

4. Amplitude of accommodation :
Is total plus power which could added to eye
optical system (up 14D-0.5D) variation of
accommodation through our life (with advancing
age).
 Far point :(relax acco)(punctum)(remotum)
 Near point:(fully excreted)(proximum).

5.  Hypermetropia
 Hypermetropia: (aetiology_causes)
1. Axial hypermetropia(short axial length)
2. Curvature
3. Index
4. Dislocation of the crystalline lens posteriorly.
 The hypermetropia eye is aweak eye (lacks
plus power corected with plus lenses ).

6.  SIGN:
1. Small eye
2. Small (constricted)pupil
3. Shallow anterior champer.
there synrkientic action:
Accmmodition
Convergence
pupilary

7. Symptoms:
 Difficality of during near task
 Headech
 Eye train
 Discomfort
 Tendency to develop diplopia
 Tendency to develop squint