Retinoscopy for Astigmatism

Question 1

What is Astigmatism?

Answer 1

A visual defect in which the unequal or non uniform curvature of one or more refractive surfaces of the eye (usually the cornea), prevents light rays from focusing clearly at one point on the retina

• instead theres 2 focal points each formed by one of the two different curvatures of the cornea and/or lens of the eye
• these 2 diff curvatures are almost always perpendicular to each other

Question 2

What is spherical ametropia?

Answer 2

• one power in all meridians
• power 1 = power 2
• need only spherical lenses

Question 3

What is astigmatic ametropia?

Answer 3

• diff power in the 2 principal meridians

- use spherical and cylindrical lenses

Question 4

What are cylindrical lenses?

Answer 4

• cyl lenses can be thought of in the same ways as spherical lenses, except that their power occurs in only one of the two main meridia of the lens
• in the perpendicular meridian there is no power at all
• so when we are correcting astigmatic ameteropia, we use a spherical and cyl lens
• we then have the power of sph in one meridian only
• and the power of the sph and cyl in the perp meridian