The following posts wer submitted to the ROP list in response to a discussion concerning questions about the strength of prescription lenses. The ROP list was moderated by Dr. Scott Richards until 2002. It is now hosted at YahooGroups.
Date: April 20, 1999
From: Sarah J. Blake
The way I understand it is glasses only correct refractive error, which involves how light patterns enter the eye. Glasses cannot correct retina problems, which is why not all people wearing glasses correct to 20/20. Some of my friends are wearing -12 and only correct to 20/40. This is because they have additional problems hindering their vision. I know that the shape of the eye and the condition of the lens has something to do with refractive error. I have no lens in my functional eye. I don’t know if this affects near-sightedness or not. Hmmmm… Maybe time to call and pick my last optometrist’s brain. He still discusses stuff from my history of treatment with him and is a huge source of information for me.
Date: April 29, 1999
From: Sarah J. Blake
I got off and called the optometrist about the prescription thing. I’ve just gotten incredibly curious about this one. I talked to the assistant, and what she’s told me is that the lens contains 32 diopters of refractive power. If you’re near-sighted, your eye has too much, but if your lens is removed that’s 32 diopters gone. So my +16 is what it takes to equalize things. If I still had my lens, I suppose my prescription would be around -16.
Date: April 30, 1999
As I’m recalling low vision seminars that I previously attended, your information jogged my memory. I do recall learning that nearsightedness is the result of not having enough diopters and farsightedness results from The position of having too many diopters, so to speak. This works in conjunction to where the focal point of light rays are positioned in relation to the retina. If focusing short of the retina, the person is nearsighted and requires a minus prescription to push the rays back onto the retina for a clearer focus in the distance. On the other hand, if the light rays focus behind the retina, the person is short of diopters and requires a plus prescription to enable the rays to focus on the retina. Thus increased diopters enable the person to see more clearly.
I never realized that the human contains 32 diopters. Also, it makes sens that removing the lens would detract that amount of diopters, so a person would need a lens to replace them in order to restore clarity. This wold make sense that the person would have a very high plus power in a contact or lens in glasses to compensate for the loss of diopters. Also, it would also concur with circumstances that the Director of the agency where I was employed did not require a lens implant but a very low power minus lense since he was severely nearsighted before the onset of his cataract and did wear a -27 lens up until his surgery. On the other hand for those of us who require a plus prescription due to being farsighted, or for persons who have a low power minus lens being nearsighted, removal of the lens would necessitate some replacement of diopters or prescription adjustments to enable the eye to focus as clearly as possible.
Sarah, thanks for your input. Valuable points worth noting and helpful in understanding the nature of prescriptions a bit mor eclearly.
Date: April 30, 1999
From: Scott Richards
Those are some good explanations (and some good deductions) about plus and minus lenses. Pam’s description was entirely accurate concerning minus lenses. Plus lenses are used for far-sightedness (a.k.a. hyperopia). In hyperopia, the eye is too short (or the light is focused behind the retina, depending upon one’s point of view!). The plus lens bends the light rays inward so they focus on the retina. A minus lens bends the light rays outward so they focus on the retina instead of in front of it.
+27 is a rather high lens power. This could be explained by an extremely small eye or an eye that has lost its lens (presumably due to lensectomy at the time of a vitrectomy).. The lens in the eye usually provides about +20 diopters of power, and this would have to be compensated for if it were removed.
Intraocular lenses are always artificial, never from donors. They are made of a number of different materials, usually plexiglass (PMMA) or silicone.
Contact lenses or intraocular lenses cause less image magnification or minification than glasses, and are visually superior for most people. They do have the downsides of requiring surgery or daily insertion, so it becomes an individual choice as to the pros and cons. For adults, the image size disparity between the eyes can make fusion or binocular vision impossible. For infants (those wonderfully plastic and adaptable creatures!), the image disparity doesn’t seem to cause so much trouble. Check with your ophthalmologist as to which is best for you.
Examination under anesthesia may be needed to measure for glasses, depending upon how cooperative the child is in the office, the degree of media opacity, etc. It seems a shame, but it’s often the only way to do it.
Date: May 1, 1999
From: Kathy Burkleo
In regards to your question about a lens implant, I have what is called an “intraocular lens implant”. In very simplistic terms this is how I got an artificial lens: When I had a cataract removed out of my right eye that has vision, the doctor zpped the cataract, including my own lens, with laser, then made a little slit above the iris, in the white part, and then stuck a little vacuum cleaner type thingy in through the slit, sucked out the zapped cataract and lens, and then he inserted a teeny little artificial, plastic lens with a little “tail” on each side for stability, in through the slit, positioned it, and stiched the slit. Before the surgery he took all of thee measurements and stuff and had a special lens made. So when the bandage was removed the next day…WOW! I could see better than I ever had! Since an artificial lens doesn’t adjust like a real lens (which is similar to an automatic focus on a camera, the doctor fine-tuned my vision with glasses. It was really neat because I had always had these thick glasses. Now with the artificial lens and thin glasses, I see much better.
Date: June 19, 1999
From: Bethany Stark
I have twin sons with ROP. Last week we went to their retina specialist and a new optometrist. My son HAD a prescription of -4.00, which was measured about 7 months ago (he’s now 2.5). The new optometrist, who has an excellent reputation and told me that she got a fantastic refraction because he sat very still, measured his refraction at -19.00!!! The retina specialist said that his eye was the shape of someone who is very nearsighted, so he backed the optometrist up. Neither of them seemed shocked and said that it goes along with being preemie, and could get worse. I do trust these people and intellectually believe that they are right, but….
Here’s my difficulty. At the EI center he goes to, they were in shock and said, but it seems like he can see pretty well, he puts pegs in a board and he was climbing up steps without looking down. Where I go to get his eye glasses filled, they were in shock. “Oh, that is sooo strong, and changed so fast…” When I tell him to pick up something off a patterned carpet, he reaches right down and gets it. I don’t really know the function of someone with -19.00, how much or how clear, and how much he might be going on visual memory in some situations.
We are still waiting for the prescription to be filled, probably a week or so before we get the glasses. He hates wearing his current ones, which, according to the two doctors, are much too weak. My DH says that we’ll know if the new prescription is really off, or if it seems to help by Yale’s interest to wear them.
I’m interested in people’s experience in this area. Has anyone had a prescription change that fast? The doctors were not at all amazed; weren’t interested in retesting etc. Could the prescription be off, or are these other opinions, lay people who haven’t had experience in this area? I’m sure a -19.00 doesn’t walk into an average eye glass store very often. Any thoughts?
Date: June 19, 1999
From: Sarah J. Blake
The average person may not realize what a difference the correct glasses prescription can make until that prescription is found. That’s just my humble opinion, of course, but there are some things which may be hard but not impossible for a child who is near-sighted. Those things might be tons easier with the right pair of glasses.