Mono-Focal set for Near Vision

[NeLso]

I have had distance glasses since childhood, but never experienced reading glasses.
Those who are nearsighted know that glasses allow them to see a wide range of distances.

My understanding is that reading glasses (for normal presbyopes) allows the user to focus at only a SPECIFIC distance.  Is this true?

I am losing my ability to accomodate.  With my "distance glasses", it is difficult to focus on near objects and I am forced to remove my glasses to see close.

My question:
If I opt for a Mono-Focal IOL, and set it at a focus of 10 inches, what will I have to do to see at 11, 12, and 13 inches?
In addition, at what point will a standard nearsighted pair of glasses allow me to focus to infinity.   (ie. at what distance does optical infinity start?)

Currently with my natural lens, everything beyond about 12 inches is blurry.  I can accomodate to about 10 inches.

Thank you in advance!

[John C Hagan III, MD, FACS, FAAO]

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[NeLso]

Thank you so much for the informative reponse.

A big question-mark in my head had to do with "near vision verses distance".  

I deliberately wear glasses that don't focus well at distance... perhaps one or two lines higher than 20/20 on the chart is where I can see.  I am comfortable with it.  I do have glasses that correct distance to 20/20, but I rarely use it.  (only for driving)

What I have noticed is that with my stronger 20/20 glasses I can only focus as close as arms length, 20 inches.  With my weaker glasses, I can focus to 14".  Removing my glasses altogether and I can see as close as 7".  

I don't know how reading glasses work... and that was my biggest dilemma!

So, I bought a pair of +1.5 reading glases to experiment with.   Doing a number of experiments (holding the lens in front of my glasses,etc), I found that reading glasses brings the near focal point closer.  Therefore, I am able to "simulate" distance verse near, (and the changes that I will need to adjust to), but unfortunately, I can't figure out how I might simulate a complete loss of accomodation.

I understand optical infinity is 17 feet.  Therefore with mono-focals set for distance, I can relate to what I should be able to expect beyond 17 feet.... hopefully near perfection!  For near vision, I understand I will have to wear reading glasses and hold everything at a fixed distance.  (and I'll be able to adjust that distance somewhat by swapping in/out different powered reading glasses?)

It's the distance between 16 inches and 17 feet that is my big question mark.  How do I simulate (or understand/relate to) what to expect?   As you so graticiously explained, -1.50 would equal 2 feet.  But how do I simulate the amount of blur I would expect to see for distance vision?

I am headed down the aspherical mono-focal (with blue filter) path because it appears all anomolies are correctable with glasses.

I have a cataract in one eye only.  I am in my early 40's

Again, thank you so much!!.

[John C Hagan III, MD, FACS, FAAO]

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[peakhope]

Just to fill in what Dr. Hagan said: A correction of -1.50 would correspond to a focal distance of: 1.5 -> 3/2 -> 2/3 meters, or about 2 feet. And -1.25 -> 5/4 -> 4/5 meter, or about 32 inches. And the "distance" eye he mentions would be -0.25 -> 1/4 -> 4 meters, or about 13 feet.

Generally, 20 feet is considered close enough to stand in for optical infinity, which is why it is used for standard eye tests.

I was nearsighted with heavy astigmatism my whole life, so I could see fairly well very close (until I lost the ability to accommodate), but wore glasses all the time. I chose Crystalens HD's, hoping to just need reading glasses in the worst case. I was fortunate to have a great outcome and am very happy with my choice. Crystalens is not perfect, and is not the right choice for everyone.

[John C Hagan III, MD, FACS, FAAO]

If you do not have cataract surgery you will continue to lose your ability to focus and your bifocals will have to be made stronger and stronger.

If you have cataract surgery with monofocal IOLs your eye cannot focus afterwards however there is some pseudo-(false) accommodations due to pupil constriction and perhaps some residual astigmatism.

We have emphasized this before that picking and IOL to put in the eye is NOT an exact science and carries a risk of at least +/- 0.50 diopters and in long, short eyes and eyes with previous RK or lasik its larger.

Near vision in not set that close (10 inches).  In good light a residual refractive error of     -1.50 often works well for not only reading but shopping, computer shaving/putting on make up.   Mini monofocal with distance bias puts distance eye at -0.25 and near/mid at -1.50   the depth of focus is probably on the order of 3-4 inches either side.  Minimonofocal with near bias would put the mid at about -1.25 and the near eye at -2.50.

Use the search feature there is tons of information. Discuss with your surgeon. Plan on wearing no line bifocals some of the times for some things.

JCH MD