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Medical Forum / General / Vision / April 2008Need to know specific name of computerized phoropter
I just had cataract surgery in my left eye last week, and an intraocular lens was placed by the ophthalmologist. I'm having the right eye done in a few days. My vision in my left eye, with the implanted lens, is excellent. I haven't had it checked yet but I'm guessing it's 20/15. Prior to the surgery, it was about 20/200. My question: I believe that the prescription the Doc took for the intraocular lenses was done, not by a traditional phoropter (that device with the two hundred lenses where you are asked, "which is better 1 or 2) but instead was done with a computer controlled device that you look into and measurements are taken by the computer. I'm guessing that the measurements involve the curvature of the cornea. I'm convinced that whatever this device is called, it's accuracy is far superior to the conventional phoropter because my vision has never been sharper (and I've worn glasses my whole life). Does anyone know the name of this device? Thanks for info. In article <cb457b83-3034-4b75-a357-4d3d09b92c0e@m1g2000pre.googlegroups.com>, I'm not a doctor, but have had cataract surgery in both eyes. > I just had cataract surgery in my left eye last week, and an > intraocular lens was placed by the ophthalmologist. I'm having the > right eye done in a few days. My vision in my left eye, with the > implanted lens, is excellent. I haven't had it checked yet but I'm > guessing it's 20/15. Prior to the surgery, it was about 20/200. It may be too soon to tell, but I hope this isn't bad news. The eye continues to heal over the first few weeks, and most people experience a change in vision as the eye changes shape due to healing. > My question: I believe that the prescription the Doc took for the > intraocular lenses was done, not by a traditional phoropter (that > device with the two hundred lenses where you are asked, "which is > better 1 or 2) but instead was done with a computer controlled device > that you look into and measurements are taken by the computer. I'm > guessing that the measurements involve the curvature of the cornea. Cataract surgery involves eliminating the refraction caused by the lens inside your eye. There is no way to measure how much this refraction is, but it is generally so large that ignoring it causes big problems in vision, thus the IOL. The best that can be done is to measure the curvature of the cornea and the distance between the cornea and the retina. Your doctor takes these numbers and plugs them into a formula, adding a fudge factor based on experience, and any changes due to doctor decisions or patient requests. This is how the doctor determines the strength of the IOL to implant. I was lucky, both eyes ended up perfect. My reading indicates that a reasonable goal is plus or minus .5D. An optometrist can do much better with a phoropter. However, a phoropter is useless in determining the strength for the IOL. > I'm convinced that whatever this device is called, it's accuracy is > far superior to the conventional phoropter because my vision has never > been sharper (and I've worn glasses my whole life). My suspicion is that your vision is so fine, because the cataract was removed. Based on my experience, this is a major, and welcome, improvement. > Does anyone know the name of this device? Thanks for info. I don't know the name, but it uses sound waves to measure the distance. I would suggest that at your next appointment, ask the staff to tell you what your vision is in the left eye. Also, ask the doctor to verify what I posted, since things change and not every doctor does the surgery the same.  SignatureDan Abel Petaluma, California USA dabel@sonic.net You may have had your refraction measured with an "autorefractor" which uses infrared light to measure refraction all the way back to the retina. Autorefractors are a cheap/easy way to estimate the refraction, but they aren't yet _more_ accurate than subjective refraction. As Dan said, if you really _needed_ cataract surgery then by far the biggest improvement would have been from replacing the cloudy lens. Nobody would brag about prescribing glasses from an autorefractor. It may be some time before subjective refraction is surpassed by an instrument like the autorefractor. technique. The thing is, the doctor isn't actually doing that test... _you_ are. And no instrument is better at distinguishing what's sharp for _you_ than _you_. -MT >I just had cataract surgery in my left eye last week, and an > intraocular lens was placed by the ophthalmologist. I'm having the [quoted text clipped - 14 lines] > > Does anyone know the name of this device? Thanks for info. > You may have had your refraction measured with an "autorefractor" which uses > infrared light to measure refraction all the way back to the retina. [quoted text clipped - 9 lines] > actually doing that test... _you_ are. And no instrument is better at > distinguishing what's sharp for _you_ than _you_. If you have had lens implants to treat cataracts, why not give control of phoropter settings (with some professional guidance) to the patient in order to fit glasses? I have seen the argument presented here that doing so with accommodation present leads to the patient selecting too negative a lens. Thus the "is one better than two process" gets used. With lens implants, that argument becomes fallacious. Bill > If you have had lens implants to treat cataracts, why not give control > of phoropter settings (with some professional guidance) to the patient > in order to fit glasses? I have seen the argument presented here that > doing so with accommodation present leads to the patient selecting too > negative a lens. Thus the "is one better than two process" gets used. > With lens implants, that argument becomes fallacious. Sure, I do this all the time, especially with cyl axis. There are difficulties with cyl and sphere because one has to be traded off against the other and it's my experience that people tend to over-select cylinder. I do it myself, choosing ~half a diopter more than the conventional JCC test indicates. And overprescribed cylinder easily causes headaches. -MT > Bill > > If you have had lens implants to treat cataracts, why not give control > > of phoropter settings (with some professional guidance) to the patient [quoted text clipped - 10 lines] > conventional JCC test indicates. And overprescribed cylinder easily causes > headaches. This trade-off arises because cylinder and sphere are not independent functions. Zernike functions are orthogonal and complete. That means that any wavefront distortion can be be matched in a unique way using Zernike functions. It does not tell you how many are needed for a specified accuracy. Thus, sphere (one function) will not be affected by astigmatism (two functions) and vice versa. Although I am not familiar with how these wavefront distortions are measured for eyes, the popularity of lasik and similar procedures is making matching with Zernike functions more familiar to ophthalmologists and optometrists. I do not know of a neat optical way to replace cylinders in a phoropter with the more complex aspherics corresponding to the Zernike functions for astigmatism. Bill >I just had cataract surgery in my left eye last week, and an >intraocular lens was placed by the ophthalmologist. I'm having the [quoted text clipped - 14 lines] > >Does anyone know the name of this device? Thanks for info. I sure hope it wasn't a Marco 3D-Wave. Did it look like this? <http://tinyurl.com/4dyelb> |
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