Axis indicator plate for trial frame

Catalogue Number: 3279
Axis indicator plate for trial frame
Category: Equipment
Sub-Category: Equipment, other clinical
Time Period: 1900 to 1939
Description Of Item: Black annular plate with handle 38 mm in diameter with axis pointers and engraved in white with numerals from 0 to 17, twice through 360 degrees. Pointers are coincident with 90 degree mark. Reverse side is engraved with numerals from 0 to 9, both clocwise and anti-clockwise from one of the pointers which is coincident with the 0 mark.
Historical Significance: Plate appears to be designed to be inserted into a trial frame which lacks axis markings to determine cylinder axis during retinoscopy or of the axis of a cylindrical trial lens placed in a trial frame. The notation on one side is the reverse of the now conventional anticlockwise notoation for each eye. The notation on the other side is for a system specifying axis to the left (anticlockwise) and right (clockwise) from the vertical, zero, position.
How Acquired: Donated by Alan Isaacs, honorary life member of the College
Date Acquired: 1999
Condition: Good
Location: Archive office. East wall shelves unit 3. Drawer 2

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