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level: Module 5

Questions and Answers List

level questions: Module 5

Question	Answer
A refractive condition where the optical system is incapable to form single focus.	Astigmatism
Who is the father of astigmatism	Thomas Young
It is the strongest greatest power meridian (steeper)	Power Meridian
Least power, lowest power meridian (flattest)	Axis Meridian
(=) means?	Combine
"x" means?	Axis
It is the interval or gap between the two focuses/foci	Interval of Sturm
It is the midpoint of first and second focus	Circle of Least Confusion
Power meridian and axis meridian are 90 degrees apart. Example: PM=150 AM=60	Regular Astigmatism
Power meridian and axis meridian are not 90 degrees apart Example: PM=85 AM:30	Irregular Astigmatism
Greatest power meridian is at the vertical meridian and the least power meridian is at horizontal meridian. PM: 60-120 AM: 0-30, 150-180	With the rule/direct astigmatism
If the two principal meridians (AM/PM) are 30 degrees away from 90 and 180. PM or AM: 30-60, 120-150	Oblique Astigmatism
Greatest power meridian is at the horizontal meridian and the least power meridian is at vertical meridian. PM: 0-30, 150-180 AM: 60-120	Against the rule/indirect astigmatism
Cornea contributes the greatest dioptric power	Anterior Cornea
Astigmatism may be produced by the tilting of the crystalline lens, approximately -0.25DC of ATR is produced	Lenticular Astigmatism
What is the physiological amount of astigmatism?	-0.50DC x 90
A classification of astigmatism where in one foci is on the retina and the other is in front of the retina	Simple Myopic Astigmatism
A classification of astigmatism where in both focuses are in front of the retina	Compound Myopic Astigmatism
A classification of astigmatism where one focus is in front of the retina, and the other is behind the retina	Mixed Astigmatism
A classification of astigmatism where in both focuses are behind the retina.	Compound Hyperopic Astigmatism
A classification of astigmatism where in one foci is on the retina and the other is behind the retina.	Simple Hyperopic Astigmatism
Lower amount of +SPH = higher amount of -CYL	MA
Same amount of +SPH = -CYL	SHA
Higher amount of +SPH = lower amount of -CYL	CHA
Plano = -CYL	SMA
Any amount of -SPH = any amount of -CYL	CMA
+3.50DS = -2.75DC x 45	CHA
-1.75DS = -1.75DC x 85	CMA
+1.50DS = -3.25DC x 90	MA
+1.00DS = -1.00DC x 140	SHA
Plano = -4.50DC x 70	SMA
By orientation: -3.75DS = -4.50DC x 145	OA
By orientation: -1.75DS = -1.25DC x 54	OA
By orientation: +4.00DS = -2.50DC x 25	WTR
By orientation: -2.25DS = -1.50DC x 160	WTR
By orientation: +1.25DS = -5.25DC x 90	ATR
By orientation: -7.50DS = -3.25DC x 110	ATR
Astigmatism that is from the cornea which can be measured from keratometer.	Cornea Astigmatism
Relatively small in amount and is almost always against the rule. Main cause is tonicity of the back surface of the cornea and tilting of the crystalline lens.	Internal Astigmatism
What is the average amount of internal astigmatism?	-0.50DC x 90
Astigmatism of the eye as determined by objective or by subjective refraction. Includes both corneal and internal astigmatism	Refractive Astigmatism
What kind of ophthalmic lenses are used for astigmatism?	Cylinder Lens