I've made an update to EyeDock's [oblique crossed cylinder calculator](http://www.eyedock.com/index.php?option=com_jumi&fileid=3&Itemid=84). It still uses your trial toric lenses power, rotation, and over refraction to determine which toric lens to try next.
However, I realized that this was still leaving some unnecessary work for the practitioner using this calculator. For one, it's nice to know that the *best* lens is one that corrects -4.25 diopters of cylinder with an 86 degree axis. However, I know that most lenses I regularly work with do not come in those exact powers. Traditionally I have looked up what powers the lens *does* come in and tried to find the closest match. This required rounding to the closest axis, reducing the cyl to the closest power the lens comes in. To make matters worse, I usually also need to adjust the sphere power to maintain the spherical equivalent to make up for my cyl power adjustments.
Once I've made all these changes I start to wonder how big of an impact my compromises will make on the final result. How much will my axis rounding and cyl power reducing affect my patient's visual acuity?
This is what I attempted to address with these calculator updates. I've added a feature that lets you enter which brand of trial contact lens you have on your patients eye.
With this information the calculator can look up the available lens parameters on EyeDock and find the best match to the *ideal* lens. It will intelligently round to the best axis, adapt the cyl power to the closest option, and make adjustments to the sphere power as needed.
It also gives you a sense of how close you are to the ideal lens by calculation the uncorrected Rx. From here it makes a prediction about what the potential visual acuity will be with this lens, which will enable you to make a decision about the lens's worthiness. Of course, the calculator may throw in its own 2 cents: If the potential vision seems poor it will suggest you try another lens brand. (1)
Here's a little walkthrough of the calculator:
I hope this allows my fellow clinicians to save a little time in their busy practices. As always, let me know if you have any thoughts or comments!
Todd M Zarwell OD FAAO
(1) If another brand was suggested, I was really, really tempted to have the calculator suggest some alternatives. However, I decided this was beyond the scope of this tool. For one, the calculator does not even know the patient's true refraction. For two, the oblique cross cyl calculator is making decisions based on how this particular brand rotates on the eye, but we can't necessarily expect another brand to behave the same way. Do to these information limitations I decided it would be presumptuous to try to make a suggestion about alternative lens brands and powers. My advice would be to type in the patient's original refraction into the search bar and start from scratch.