(3b) Minus Cylinder Method

Question 1

Procedures for astigmatic ametropia MCM

Answer 1

• aim is to obtain -ve cylinder lens
• use cylinder lens (has dividing line corresponding to axis)
• locate sphere meridian (more plus/more hyperopic) and neutralise with sph lens
• then neutralise cylinder meridian with -ve cyl lens of its estimated power AT THE AXIS FOUND
• drive beam along trial cyl axis
• neutral reflex will be seen at all directions once both meridian neutralised

Question 2

what is the sphere meridian if both reflexes either against, or with respectively

Answer 2

faster brighter, duller slower respectively

Question 3

How to double check cyl axis with Lindner’s method

Answer 3

• checking brightness/speed
• scope beam 45o both directions away from axis
• if one is “with” and the other “against”, rotate trial axis towards “with” until equal
• if one brighter/faster, rotate trial axis to duller one until equal

Question 4

Causes of inaccurate ret findings

Answer 4

• incorrect wd
• scoping OFF patients visual axis
• patient not fixating distant target
• did not obtain a reversal/neutrality
• did not locate PM
• did not recognise split (scissors) motion

Question 5

final rx with and without wdl

Answer 5

with: added ds/added dc x axis
without: added ds minus wdl/added dc x axis