TK Estimation of Target IOP in Primary Open Angle Glaucoma

Dr Muhammad Tariq Khan, Vitreoretinal Consultant

LRBT Hospital, Lahore Pakistan

Two variables are used in developing a formula for setting a target IOP
1 highest recorded IOP
2 CD ratio estimated clinically with 90D lens

FORMULA Deduct numerical % of highest recorded IOP from highest recorded IOP and from the resultant substract the 10th multiple of CD ratio.

EXAMPLES

A WHEN IOP IS CONSTANT
Example IOP 38mm Hg CD ratio 0.8

Numerical % of 38 is 38/100 x 38= 3.8x3.8=14.44
38-14.5= 23.5
10th multiple of 0.8=10x0.8=8
23.5 – 8 = 15.5 mm Hg

Example IOP 38 same as in previous CD ratio0.5
Same formula target IOP is 18.5mm Hg
Less damage less IOP drop is required vice versa

B WHEN CD RATIO IS SAME

Example IOP 30mm Hg CD ratio 0.6
Same formula calculates target IOP as 15mm Hg

Example IOP 40mm Hg CD ratio 0.6
Same formula calculates target IOP as 18mm Hg

Higher the presenting IOP higher drop is required. Vice versa
The average drop is 50% to 55%