Astigmatism Flashcards
Definition
It is a type of refractive anomaly in which the eye doesn’t have the same refractive power in all meridians
Breakdown of Astigmatism term
A: No
Stigma: Point
Tism: condition
What is the physiological astigmatism?
It is astigmatism with the rule that is found in almost emmetropic eyes.
The vertical meridian is more curved than the horizontal by 0.25D
Why vertical meridian is more curved than horizontal?
Because the lids press on the anterior surface of making the vertical meridian more steeper
Regular astigmatism
- The two principle meridians (highest & lowest power) of the astigmatic system (cornea) are at right angle.
- The change in the power is gradual.
Types of regular astigmatism according to the steepness of the vertical meridian (the rule of egg)
With the rule (most common) : vertical meridian steeper than horizontal and corrected with (-) cyl. X 180°
Against the rule: the opposite and corrected with (-). X 90°
Oblique astigmatism
What is oblique astigmatism?
It is a type of regular astigmatism where the two meridians ar at right angles to each other, but instead of being at 180° and 90°, they are at 45° and 135°.
Types of regular astigmatism according to position of image in relation to the retina
Simple myopic or simple hypermetropic : one of the foci falls on retina and the other fall in front or behind it.
Compound myopic or compounf hypermetropic : The two are myopic or the two are hypermetropia
Mixed: one myopic and the other hypermetropic
Etiology of astigmatism in general:
Cornea is the most common:
Physiological (0.25)
Congenital (inherited)
Acquired (keratectasia, dt ulcer or refractive surgery or corneal facet (conea pana), trauma, inflammation and scar, large chalazion or tumor pressing on the cornea
Lenticular causes of astigmatism
Congenital (tilting of the lens, lenticonus)
Subluxation
Acquired: traumatic subluxation
Irregular astigmatism
It is astigmatism in which two principle meridians (highest & lowest power) of the astigmatic system are not at right angle
The change in power is not gradual
Causes of irregular astigmatism
Keratoconus
Conreal opacity
Pterygium
Immature cataract
Causes of regular astigmatism
Lenticular is rare
Corneal : congenital, postoperative( after cataract extraction), or keratoplasty.
Symptoms of Astigmatism
Running letters : الحروف يطيحن مني
Tilted point : ظل لكل حاجة
He can distinguish some letters, and some don’t at the same level. In E symbol chat.
Blurring of vision : distorted object
Uniocular diplopia (in high degree)
Accomodative asthenopia
Symptoms of eye strain:
Headache
Photophobia
Nausea and fatigue
Investigations and Signs of astigmatism
Head tilt or side looking
Oval tilted disc
Different power in different meridian
Red reflex: oval or band
Scissor shape relfex (irregular astigmatism) or spinning relfex (keratoconus)
Astimatic fan : placido’s disc
Astigmometer (keratomerter)
Corneal typography
