Astigmatism and Presbyopia Flashcards
When parallel rays of light enter the eye with accommodation relaxed and do not come to a single point focus on or near the retina.
Astigmatism
When the cornea has unequal curvature on the anterior surface
Corneal astigmatism
When the crystaline lens has unequal curvature on the surface or in its layers
Lenticular astigmatism
Sum of corneal astigmatism and residual astigmatism
Total astigmatism
Constitutes majority of astigmatism
Corneal astigmatism
Two principal meridians are perpendicular to each other
Regular astigmatism
Type of astigmatism in which in minus cylinder axis is found around horizontal meridian
With-the-rule astigmatism
Type of astigmatism in which in plus cylinder axis is found around horizontal meridian
Against-the-rule astigmatism
The sum of two axes of the two eyes equals approximately 180°
Symmetrical astigmatism
Infants are born with what type of astigmatism?
Against-the-rule astigmatism
The first accurate description of astigmatism was credited to?
Thomas Young
What charts are used for astigmatism?
Clock dials and fan dials
A type of symmetric astigmatism in which both eyes have with-the-rule astigmatism
Homologous astigmatism
With accommodation relaxed, both principal meridians focus in front of the retina
Compound myopic astigmatism
With accommodatoon relaxed, one meridian tends to focus behind the retina, while the other focuses in front of fhe retina
Mixed astigmatism
It is the loss of accommodation inside the eye
Presbyopia
Optometric management for presbyopia
Reading glasses, multifocal lenses containing near add, bifocal, trifocal, and progressive add lenses
A theory that states that presbyopia is caused by the biomechanical changes in the lens capsule and lens
HHG Theory
A theory that states that presbyopia is caused by the weakening of the ciliary muscles
DDF Theory
Causes of sclerosis
Nutritional changes, UV rays, infrared radiation
A type of presbyopia which is known as the earliest stage; borderline, beginning, early, or pre-presbyopia
Incipient presbyopia
A result of the continuous gradual decline in accommodation; a condition in which virtually no accommodation ability remains
Absolute presbyopia
A condition which can still be overcome by a hard or forced ciliary effort
Facultative presbyopia
Adult patients eventually report visual difficulties when faced with gradually declining accommodatjve amplitude and near task demands
Functional presbyopia
A condition in which near vision difficulties result from an apparent decrease in the VA in dim light
Nocturnal presbyopia
TRUE or FALSE: Signs of presbyopia include vertical wrinkles on the forehead
TRUE
It is the maximum increase in optical power that an eye can achieve in adjusting its focus from as far as possible to the nearest possible
Amplitude of accommodation
A small scale Snellen’s chart
Near chart VA
Plus lenses are what type of lenses?
Convex lenses
The DDNN rule is used for?
Monovision
