Astigmatism and Presbyopia Flashcards
Inability of the human eye to on objects up close that results with aging.
Presbyopia
The cornea has an unequal curvature on its anterior surface.
Corneal Astigmatism
A condition in which near vision difficulties result from an apparent decrease in the AA in dim light.
Nocturnal Presbyopia
When the two principal meridians are not perpendicular to each other.
Irregular Astigmatism
Condition which can still be overcome by a hard or forced ciliary effort.
Facultative Presbyopia
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
Attributes all of the loss in accommodation to bio-mechanical changes in the lens capsule & lens and none to the ciliary muscle; lens based.
H-H-G Theory
The sum of corneal astigmatism and residual astigmatism
Total Astigmatism
Is the maximum increase in optical power that an eye can achieve in adjusting its focus from as far as possible (beyond infinity for a longsighted eye) to the nearest possible.
Amplitude of accommodation
Three types of regular astigmatism
WTR, ATR, OBL
The amount of ciliary muscle contraction needed to produce a unit change in accommodation progressively increases with age; muscle based.
D-D-F Theory
When the two principal meridians are perpendicular to each other.
Regular Astigmatism
Weakening of the ciliary muscles Hardening of the nucleus of the lens Sclerosis of the lens fibers and capsules Less elasticity of the capsule Range of accommodation is diminished
Etiology for Presbyopia
When the crystalline lens has an unequal curvature on the surface or in its layers.
Lenticular Astigmatism
Accommodative ability becomes insufficient for the patient’s usual near vision tasks at an earlier age than expected.
Pre-mature Presbyopia
When one of the principal meridians is focused on the retina and the other is not focused on the retina (with accommodation relaxed).
Simple Astigmatism
The earliest stage at which symptoms or clinical findings document the near vision effects of the condition.
Incipient Prebyopia
When both principal meridians are focused either in front or behind the retina (with accommodation relaxed)
Compound Astigmatism
Assumed that excess plus power with accordance to Px’s correction for far represents the amount of assistance required by the accommodation for the distance of testing. This will require the use of astigmatic chart.
Cross Cylinder Technique
The sum of the two axes of the two eyes equals approximately 180.
Symmetrical Astigmatism
Optometric management for Presbyopia
Convex Lenses
Multifocal CL
The sum of the two axes of the two eyes does not equal approximately 180
Asymmetrical Astigmatism
Adult patients eventually report visual difficulties when faced with gradually declining accommodative amplitude and near task demands.
Functional Presbyopia
Diagnosis for Astigmatism
Visual Acuity
Keratometer
Refraction
A small scale Snellen’s chart. The patient should hold the chart at approximately 40 cm (16 inches). This will determine the Px’s near grade.
Near chart VA
With accommodation relaxed, one meridian tends to focus behind the retina, while the other focuses in front of the retina.
Mixed Astigmatism
Nutritional changes
Action of UV rays
Exposure to intense infrared radiation
Causes of Sclerosis
Optometric management for Astigmatism
Cylindrical Lenses and Toric CL
_________, even if corrected, usually exhibit refractive difficulty first.
Hyperopes
Asthenopia or ocular fatigue usually occurs in this eye condition.
Astigmatism
