"Sturm's Conoid" for undergraduate MBBS Students. Covers the basics of Sturm's Conoid, including the ray diagram and explanation of Sturm's interval and circle of least confusion. it's application in Astigmatism has been covered. Also encompasses salient points for PGMEE

1. STURM’S CONOID
Dr. Abhishek Onkar

2. Fortunately for most people who wear glasses, it is not essential that
the examining practitioner understand all of the optical details involved
before writing.

4. Sturm’s conoid

5. • The light rays which hit the lens horizontally form a vertical focal line, so,
a point image appears as a vertical line. The light rays which hit vertically
form a horizontal focal line, so, here a point image appears as a horizontal
line.
• The focal interval of sturm: The distance between these two focal lines is
called the focal interval of sturm (sturm’s conoid interval).The images
formed here are blurred circles of different sizes.
• Circle of least confusion/diffusion: The smallest cross-section of a blur
circle between the two focal lines formed by the astigmatic lens. Also
defined as “At the dioptric midpoint of focal lines the cross-section of
sturm’s Conoid appears as a circular patch of light rays with best overall
focus.

6. Application
• This concept of Conoid of Sturm happens when there
is astigmatism present in the eye.
• It is corrected with a sphero cylinder lens in such a way that the circle
of least confusion is placed on the retina making the image clearer.