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Monofocal lens set for near vision

Posted , 11 users are following.

Dapperdan7
Dapperdan7

hi guys. im curious as to why i never hear of people getting a monofocal vision set for near instead of for far. for myopes, the pleasure of not needing glasses to drive etc would perhaps be outweighed by having less of an adjustment to just put glasses on to see for intermediate and far, as we all have been doing that for as long as we had myopia. is there a down side to getting a close monofocal lens? thoughts?

also, for those who have gotten monofocal implants set for far distance, at about what distance from your eyes does your vision begin to get blurry as you get nearer something?

thanx much. trying to amass info for the future

dan

1 like, 86 replies

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  • Lynda111
    Lynda111 Dapperdan7

    Posted

    Well Ron, however my cataract surgery worked out, whether it was by design. ( choosing. the Tecnis I monofocal and. aiming for intermediate) or I just got lucky, I am pleased with the vision I have and rarely having to use readers.

    • RonAKA
      RonAKA Lynda111

      Posted

      It is good that it works for you, but it is not really a recipe that many others could follow unless they have a moderate amount of astigmatism that is left uncorrected. Astigmatism is a vision defect that changes with the angular position around the eye. It in effect is working like a multifocal lens. It is not going to be the best for sharpness and clarity, but it does seem to extend the range of vision. I kind of have a similar thing going on but to a lesser degree. My near eye in monovision has 0.75 D of astigmatism. It potentially could be significantly reduced with Lasik but it would hurt my reading vision. In my case though the astigmatism causes a drop shadow on letters, and I don't particularly like it. I wish now I had gotten a toric lens, but that ship has sailed....

  • Spring1951
    Spring1951 Dapperdan7

    Posted

    My limited understanding of this is that if you select intermediate or distance you don't get anything in the near range as iols are not flexible and your vision will be worse given your natural lens had some flexibility and rendered good close up vision?

    I was told you only get one target area and for the other areas they cannot guarantee how good your eyesight will be. Someone told me 2.5 for near vision which is worse than wha ti now have.

    • RonAKA
      RonAKA Spring1951

      Posted

      That is not quite true. The defocus curve for each lens shows what the range of vision will be. There are no drop off the cliff points. The vision just reduces as you get further from the optimum point. For example my close eye in monovision is about -1.4 D. The theoretical peak vision point would be 1 meter divided by 1.4 or about 70 cm or 2 feet. In actual fact I can see quite well from about 10" out to 6-8 feet. Distance is not so good though and I am probably about 20/40 to 20/50 at distance in that eye.

    • Spring1951
      Spring1951 RonAKA

      Posted

      Thanks. Can you recommend a good book on this subject? E-book would be preferable.

    • RonAKA
      RonAKA Spring1951

      Edited

      I am afraid I am unaware of a book. I have gained my knowledge of defocus curves by looking at the various curves for different lenses. If you google IOL defocus curve and look under images, you should get many hits for the various defocus curves. Most of them are for EDOF or MF IOL and are a sales pitch as to why they are "better" than a monofocal. Most do however compare the lens to a monofocal and you will find lots of examples to look at. The key points to understand in viewing these graphs are:

      .

      1. The vertical axis is visual acuity, usually in LogMAR units
      2. A LogMAR of 0.2 is about 20/32 for vision and considered to be the cutoff of good vision
      3. The horizontal axis is usually in diopters with negative (closer distances) to the right. And although sometimes they are reversed, the readings to the right side of 0.0 D is for distances shorter than infinity.
      4. You can convert diopters to distance by dividing 1 meter by the absolute value of the diopter. -1.0 D = 1 meter, -2.0 D = 1/2 meter, and so on.
      5. Almost always the curve is shown with the peak vison at the 0.0 D position or full distance as that is the standard way an IOL is set - to give peak vision at distance.
      6. If the IOL is set to peak at say for example -2.0 D, then the whole visual acuity curve shifts to the right. Then you can read the impact this shift has on visual acuity at other distances. In this example visual acuity will increase at close distances and decrease at the far distances.
      7. EDOF lenses will have a lower slope to the right as they maintain vision better as you get closer.
      8. MF lenses will have humps of improved vision as you get closer. This is where the bifocal and trifocal effects of their design kick in.

        .

        That is about it.

  • Spring1951
    Spring1951 Dapperdan7

    Posted

    Thank you so much for your detailed reply. I will jot that down for later. Unfortunately currently I am not able to really process this as it is brand new and I don't have the experience or training to comprehend it....but maybe later as I gain new knowledge. Again thanks!

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