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Hello Sir,

Based on what I have learnt, this is the thought process I have:

Since I can read 20/20 on Snellen chart most of the times with my current prescription, so I will take that as starting point. My current prescription is –

RIGHT SPH: 1.75

RIGHT CYL: 0.75, AXIS: 20

LEFT SPH: 2.25

LEFT CYL 1.50, AXIS: 140

Then I can think of two approaches to derive at differentials.

APPROACH 1:

-Subtract 1.50 from spherical number for both left & right eye

-Since I have cylindrical power in both eyes I will drop 0.75 cylindrical from left & add 0.50 spherical. In right I have 1.50 cylindrical so I will drop 1.00 cylindrical and add 0.50 spherical. So in left 0.50 cylinder is still unaddressed so I will keep 0.50 cylindrical in left. Based on this reduced power will be:

RIGHT SPH: 0.75 (1.75 – 1.50 + 0.50)

RIGHT CYL: Take no cylindrical power

LEFT SPH: 1.25 (2.25 – 1.50 + 0.50)

LEFT CYL 0.50 Axis: 140

APPROACH 2:

-Subtract 1.50 from spherical number for both left & right eye

-Keep the cylinder power as is in both eyes don’t reduce it.

Based on this reduced power will be:

RIGHT SPH: 0.25 (1.75 – 1.50) [Here I have doubt that 0.25 is too less number so I am not sure if this would be correct]

RIGHT CYL: 0.75, AXIS: 20 (Keep the cylinder as is)

LEFT SPH: 0.75 (2.25 – 1.50)

LEFT CYL 1.50, AXIS: 140 (Keep as is)

I am not sure which approach would be correct. So need your guidance on this.

Thankyou for your guidance, this is a really tricky one.

Jyoti