toric formula

[JJ]

ooops been a while and using charts to figure things out really stunts your brain.

can anyone provide me an explanation or formula for:

Spectacle Rx -3.75 -1.25 x 75

ok chart tells you to order toric contact lens -3.50 -1.25

but spec rx -3.50 -1.25 would stay the same in cls

thanks :hammer:

[chip anderson]

Unless the lens has "enough stiffness" to pick up a little minus from the tear beneath the lens (and some do) the formula is wrong. At powers over four diopters you have to start compensating for vertex (distance from lens refracted with to cornea) but not at less than four diopters.

Chip

[JJ]

thats what i thought and have done for years once 4 D i vertex comp.

but all the charts and a new computer program i found if you put in -3.75 -1.25 = tell you to order -3.50 -1.25 thats why im stumpt

[chip anderson]

Of course on the cylinder axis the actual power is -5.00 so the cylinder could probably stand .25 to .50 reduction, but would probably be O.K. without change.


Now some of the toric models from Cooper have different methods of calculation than other of their toric's. I have trouble remembering which so possibly I save their lenses to use when my back's against the wall.

Chip

[vitalogy44]

JJ said:
ooops been a while and using charts to figure things out really stunts your brain.

can anyone provide me an explanation or formula for:

Spectacle Rx -3.75 -1.25 x 75

ok chart tells you to order toric contact lens -3.50 -1.25

but spec rx -3.50 -1.25 would stay the same in cls

thanks :hammer:

The reason for this is because you are at that "exact" power. If you order that in -3.75 in contacts, it is probably going to be more like a -4.00. So, when you get that close to -4.00, you can typically cut it back a little. That -5.00 cyl meridian will compensate somewhat for that. I will some times base it on the patient's age.........

[Stopper]

Typically you would not adjust the power until over -4.00 but with some of the stiffer or thicker lenses you can get a little bit of a tear lens, as someone has already posted. Some of the Sunsoft and Hydrosoft torics are lenses known for this effect. An old optima toric also comes to mind. But with most of the newer torics this effect is rare. if you vetex the cyl power you could use a .75 or 1.25 cyl in the contact lens. I would probably start with the .75 cyl but that is just my preference. One has to make that judgement based on the interation with the patient.