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Real Eyecare |
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Why Bifocal Studies Failed? |
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Bifocal studies failed for several reasons:
1. The top segment for distance correction is too strong
2. The bottom segment for near correction is not weak enough, i.e., the "add" is not enough
3. The top segment is used for reading
4. The reading distance is too close |
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Home |
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The Cause of Myopia |
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The "typical" bifocal uses an OVER-PRESCRIBED or FULL-PRESCRIBED minus lens for distance correction with an "add" of +0.50 to +1.50 Diopter for near correction. |
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For example, if a myope is at 3D myopic, his bifocal will be -3.00D or more for distance correction with an "add" of ,say, +1.00 Diopter which will add up to -2.00D for near correction. |
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| First reason |
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Now, normally speaking, how many hours does a child spend looking at objects 20 feet or further away? Half an hour? One hour? Nowadays, most children spend their time indoor. Even if they spend their time outdoor, they are not looking at objects 20 feet or further away the whole time they spend outdoor. So, on average, we could say the children spend about 10% of their waking hours (don't be picky here, this is just an example, hope you get the idea) looking at objects 20 feet or further away. This means their eyes are completely relax for only 10% of their waking hours. (Figure 17A) |
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Now, when we (or the children) spend our time indoor, how many hours do we spend looking at objects 20 feet or further away? How big is our house? How big is the living room, the dining room, the bedroom, the bathroom? How big is our office, or cubicle? How big is the classroom? etc. Again, when we (or the children) are staying indoor, how many hours do we spend looking at objects 20 feet or further away? I believe it is very close to zero. When we (or the children) are staying indoor, we don't spend the whole time looking at the clock on the wall in the living room from another end of the living room. Even if we do, the eyes are still under a constant state of stress (due to accommodation) since the living room is not 20 feet long. |
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What do we (or the children) do when we are staying indoor? We eat, we chat, we (the children) play with toys, we take a shower or a bath, etc. (you get the idea). When we eat, how far away is the dinner plate from our eyes? When we chat, how far away are the people we are chatting with away from our eyes? When the children play with their toys, how far away are their toys away from their eyes? When we take a shower, how far away do we look? |
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In summary, the eyes are under a constant state of stress (due to accommodation) if fully-prescribed minus lens are used, especially when staying indoor. (Figure 17B) |
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This is one of the reasons bifocal studies failed. |
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The bifocal studies might not have failed if the top segment for distance correction was lowered by one diopter or so. (Figure 17C) We will discuss this more later. |
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| Second reason |
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The second reason bifocal studies failed is that the "add" is not enough. Doing close work with regular glasses without the "add", the eye is under a lot of stress as shown in Figure 19A. |
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With an "add" of +1.00 Diopter, assuming a reading distance of 13 inches (1.1 feet), the eye is still under a lot of stress as shown in Figure 19B. |
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The bifocal studies might not have failed if the "add" was increased to +3.00 Diopter or so, assuming a reading distance of 13 inches, which would have eliminated accommodation completely. (Figure 19C) |
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| Third reason |
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The third reason bifocal studies failed is that the top segment (distance correction) is incorrectly used for reading since most children do not know or were not taught how to use bifocal glasses correctly. So, even if the "add" were increased to +3.00 Diopter or so, and assuming a reading distance of 13 inches, the studies would still have failed since reading with the top segment puts the eyes under a tremendous amount of stress as shown in Figure 19A. |
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| Fourth reason |
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| Fourth reason |
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The fourth reason bifocal studies failed is that the reading distance is too close.
Do children normally read at 13 inches or more? Normally speaking, most children don't. So, even if the "add" were increased to +3.00 Diopter or so, the studies would still have failed since most children read at a very close distance which puts the eyes under a tremendous amount of stress as shown in Figure 19D. |
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In summary, bifocal studies failed for these reasons:
1. The top segment for distance correction is too strong
2. The bottom segment for near correction is not weak enough, i.e., the "add" is not enough
3. The top segment is used for reading
4. The reading distance is too close |
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realeyecare@yahoo.com |
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