How to prescribe Presbyopic power in Myopia.

Correction Options in Myopia with Presbyopia
Correction Options in Myopia with Presbyopia

Understanding Myopia with Presbyopia:

Myopia with Presbyopia Ray Diagram
Myopia with Presbyopia Ray Diagram
  • Myopia is condition where total power of our eyes increase and lead to rays focus in front of the retina.
  • The parallel rays coming from infinity focus in front of the retina when accommodation is at rest.
  • If a patient is myopic as well as presbyopic then he/she will see clearer at near without correction as compared to emmetropic patient with presbyopia.
  • Because in Myopia, rays focus in front while see at distance but rays focus on the retina or close to retina while see at near.
  • If Myopic power is equal or close to presbyopic power, then without presbyopic correction two possibilities are there:

1. Without myopic correction patient will see near clear but will see blur at distance.

2. With myopic correction patient will see distance clear but near blur.

  • Ideally, we should correct for both near and distance for clear visual acuity at near and distance.

But the question is “Should we give full correction or under-correction in myopic patient with presbyopia”

  • Few things need to be considered:
    • Patients demand.
    • Amount of Power.
    • Comfort Level with Previous Glass.

Patients demand:

  • If a patient main concern is for distance work, then we have to give full correction for myopia and required presbyopic power.

Amount Power:

  • If patient is having high degree of myopia, then we can go under-correction of myopia and minimum or no correction for presbyopia.

Comfort Level with Previous Glass:

  • If patient is not comfortable with previous Bifocal and progressive, then we can follow under-correction for myopia and minimum correction for presbyopia (for bifocal or progressive) or no correction for near (Single Vision).

Now another question arises:

How under-correction in myopia will lead to minimum or no correction for presbyopia?

  • Let’s take an example.
  • A patient with OU -5.0DS for distance and OU +1.50DS for near. He was advised a bifocal, but he was not comfortable with that bifocal spectacle.
  • Now if we separate near and distance power then:
    • At Near patient will need: -5.0 + 1.50 or -3.50DS
    • At Distance he will need: -5.0DS.
  • This problem can be solved in two ways:

Technique-1: Distance correction -3.50 or -4.0DS with no Add

Technique-2: For Distance -4.50 or -4.25DS with near add +1.00 or +0.75DS.

Technique-1: Distance correction -3.50 or -4.0DS with no Add

Technique 1 to prescribe Presbyopic Power in Myopia
Technique 1 to prescribe Presbyopic Power in Myopia
  • With a -3.50 or -4.0DS instead of -5.0DS, he will see little blur at distance but will see clear at near.
  • Because with a -3.50DS lens, rays will focus in front of the retina but for near it will focus on the retina.
  • Thus, he will see little blur at distance but will see clear at near.

Technique-2: For Distance -4.50 or -4.25DS with near add +1.00 or +0.75DS.

Technique 2 to prescribe Presbyopic Power in Myopia
Technique 2 to prescribe Presbyopic Power in Myopia
  • In 2nd technique, if we give -4.50 or -4.25DS instead of -5.0D, then he will see almost 6/6 with both eyes but for near he will need 0.50 to 0.75D less addition power.
  • Because a -4.50D lens will lead to focus the rays in front but very close to the retina.
  • And for near, he will need a +1.0D lens instead of +1.50D as 0.50D is under-corrected for distance.
  • Thus, an addition power of +0.75D or +1.0D instead of +1.50D may easily be accepted by him in a bifocal spectacle.

Conclusion:

  • If patient’s profession requires fine distance visual acuity, then we have to give full correction.
  • If patient’s profession requires fine near visual acuity, then we can go for no distance correction for very mild myopia (-0.25 to -1.0) or under correction for distance.
  • If patient is having facing problem with previous spectacles (Bifocal or Progressive), under correction of myopia along with less addition power may be helpful.

1 Comment

  • Sarwar Ali

    Your seasons are very useful for me….thank you so much

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