Contact lenses and diving -Questions Welcome - by Idocsteve

[craracer]

First and foremost, thank you for offering up your knowledge to us. We truly appreciate it.

I have a few relatively simple questions for you:

1.) I use Acuvue Oasis for Astigmatism lenses. What I've noticed is that I am not able to focus on small detailed items when they are at close range. Having said that, I am able to do so with my glasses. Why is this?

2.) My practitioner highly suggests using a product called "Clear Care" for lens cleaning. The bubbles are fun to look at, but is this method more effective than simply using a no rub formula?

3.) Provided the lenses are cared for on a daily basis, and no eye or physical health issues are present, and in a perfect world, what is the expected lifespan of the contact lenses I have mentioned above? My method for determining this time frame is most likely poor at best. I wear them until I notice a vision change, which can't be corrected by cleaning.

Again, I truly appreciate what you are doing.

 

[idocsteve]

1) I'll bet you're in your early to mid 40s. As you get further into presbyopia, you will notice your near vision acuity dropping off...and this happens with contact lenses before it happens with eyeglasses in myopic (nearsighted) patients due to complex optics known as "principle planes". In hyperopes the near vision drops off first with eyeglasses, and then contact lenses. Eventually you'll notice it with your glasses as well and you'll require bifocals or progressives. The Oasys lens is available in a bifocal and it works quite well.

2) Clear Care is Hydrogen Peroxide based, it's expensive, and in my opinion overkill for disposable lenses unless you've got a sensitivity or allergy to all of the commonly available disinfecting solutions. It is no more effective as a cleaner than no rub solutions however it may have an edge as far as disinfection goes.

3) The Oasys toric contact lens is designed and I believe, FDA approved, for 2 week replacement but is sometimes Rx'd up to a month. Always follow your eye care practitioners recommendations regarding replacement. Wear it longer than that and risk everything from an eye infection, to contact lens intolerance, to vision loss, to blindness. Just don't do it.

 

[craracer]

Thanks for the quick reply, and yes, I'm in my early 40's.:depressed:

Looks like I my habit of lens disposal Q3-4 months needs an immediate change. I'll toss the current pair out tonight

 

[JKPAO]

Thanks Idoc.
See you topside! John

 

[idocsteve]

I grabbed this post off of another thread. Edited for length only.

I have a prescription mask I ordered through a local dive shop here, but after I picked out a mask, the dive shop owner just shipped it off with my prescription. No one ever marked where my pupils would be and I guess when the company got the mask and prescription they just put the "readers" where they wanted to. I can use it (sort of) by closing one eye and looking sideways but all in all, it was a big mistake so I either wear an uncorrected mask or that.

The distance between the centers of your eyes is called "Pupillary Distance" often abbreviated "pd" and this is sometimes written on the Rx along with the eyeglass prescription. It can vary from as little as, say 45mm in a child, to 80mm in a person with a large head and widely spaced eyes...the average being somewhere around 56-62mm. When reading, the eyes converge, and the pd decreases by about 3mm.

When eyeglasses are fabricated, the lenses are ground in such a way that the optical centers of the lenses align with the optical centers of the eyes. If this is not done, then the person wearing the glasses is looking through "induced prism" which can cause anything from eyestrain to diplopia (double vision).

If pd is not considered when fabricating bifocals, then the bifocal segments will not be in the proper position for reading and may be off horizontally, and/or vertically (known as "seg height").

Obviously this is exactly what happened to you.

In my every day life, I wear no-line bifocal glasses, I guess they're called progressives and I ALWAYS take them off to read. I can't see distance at all, but my close up vision is pretty good.

Progressives are often referred to as "no line bifocals" but not all "no line bifocals" are progressives. Many nearsighted patients wear bifocals for convenience only, so they don't need to remove their eyeglasses whenever they want to read, however when reading for long periods of time they do remove the eyeglasses because their natural nearsightedness is better than what is provided by the progressives, and a much wide field of view is available when not wearing the progressives for reading.

My previous dive mask was an off the rack prescription mask that corrected my distance but ruined the close up. What would be a good choice for me

Consider contact lenses at least for diving. The various types of contact lenses including bifocal contact lenses and monovision are discussed in this thread. You might be a good candidate for monovision and you could possibly get by with wearing only one contact lens, for distance, in your dominant eye.

 

[JonKranhouse]

Bifocal flat two-window masks ALL have poor stereoscopic bifocal near vision - it's "normal" to have to look through either one lens or the other. That doesn't make it OK, good or right... just "tradition." Why? The structure of the nose-pocket, combined with underwater magnification, gets in the way when your eyes converge to see close objects. This is especially aggravated for people with a narrower than average PD. Some folks with wider-spaced eyes see 3D up close, sort-of. A single contact for close focus is great, as IDocSteve suggest.

If your dead set on on an Rx mask solution...use bonded-on bifocal lenses on a 1 or 3 window mask without a nose pocket - one that has below-lens pinch-pockets like this:

This type of mask minimizes nasal-side structures that block close-focus work; it's especially nice when setting functions on an underwater camera. BUT - if you need to pinch your nose to equalize, your regulator may get in the way! Some people need to use both hands to reach over / around the regulator.

Per independent research via the UHMS, the HydroOptix mask has superior close-focus 3D vision which achieves superior manual dexterity, and the Double-Dome optics create a "magic" bifocal effect (shameless plug over).

 

[idocsteve]

Bifocal flat two-window masks ALL have poor stereoscopic bifocal near vision - it's "normal" to have to look through either one lens or the other. That doesn't make it OK, good or right... just "tradition." Why? The structure of the nose-pocket, combined with underwater magnification, gets in the way when your eyes converge to see close objects.

That makes sense. Which makes an argument for only one bifocal seg more practical.

Since you can't possibly use both segs at the same time unless you've got an unusually wide pd, then why bother with two segs in the first place?

In general it would make sense to place the seg in front of the non-dominant eye but there are exceptions.

There's a way to determine which eye is dominant one...it's posted earlier in this thread.

 

[Diver0001]

idocsteve,

I have a +2 or so above water and in teh parking lot before the dive I can read the SPG fairly well.

Under water, however, I have more trouble with it. I have to concentrate on the SPG to read it accurately and if you want me to follow a compass course you can pretty much forget it unless that course is N, S, E or W.

My question is this: I know I need a mask with perscription lenses. If I'm a +2 above water, what do you think I'll need *under* water?

R..

 

[idocsteve]

if you want me to follow a compass course you can pretty much forget it unless that course is N, S, E or W.

My question is this: I know I need a mask with perscription lenses. If I'm a +2 above water, what do you think I'll need *under* water?

R..

I wouldn't even wear a prescription, just let someone else do the navigating.

On a more serious note...I'm going to be quite honest and tell you that I don't know much if anything about Rx masks nor whether or not there is a conversion factor because you're going from water to air to the eye as compared to an "air only" medium.

I would think that the difference in the Rx would be negligible but that's about as much as I can give you on this one.

 

[JonKranhouse]

I have a +2 or so above water and in teh parking lot before the dive I can read the SPG fairly well.

If you can read your gauges in full daylight above-water, that DOES NOT mean you’re OK when diving, when illumination intensity is radically reduced.

Sadly, dive instructors are not taught that 30-feet underwater the light intensity can easily be just 1/100th of what’s above water (sun 48-degrees below perfectly straight-up / AKA the “critical angle,” combined with low-visibility water). When your pupils dilate in dark conditions, many people discover they can no longer focus, just as a camera’s wide-open iris causes poor “depth of field.” Depending upon your Rx, dim light could impact your far vision, or make reading your gauges impossible, or both. All this is entirely predictable and easily preventable, based upon your vision Rx.

I suggest you confirm your "reader" diopter need in VERY dim light. It may be closer to +2.5.

Diopters are a metric unit of measure. Put a +1 on a camera lens that's focused at infinity and 1-meter is what's actually in focus; +2 w/lens @ infinity = 1/2 meter in focus; +3 = 1/3 of a meter in focus, etc.

Submerged, objects appear BOTH 33% bigger and 25% closer – both are true simultaneously (PADI's Encyclopedia of Diving gets the facts wrong - it's not "either," it's both at the same time). This magnification is why true angle-of-view gets so narrower underwater. Both magnification and lateral chromatic aberration is not uniform but gets worse as you look off-axis (i.e. away from where your nose is pointing):

(more details)

To precisely compensate for underwater magnification, bifocal diopter is adjusted for that 25% reduction in distance (e.g. +2 in air = 500 mm in focus; reduce that distance by 25% = 375 mm, requiring 2.66 diopter; but ophthalmic lenses only come in .25 increments). Also, the "vertex" distance (cornea-to-inner-surface of lens) of a dive mask lens is further than a spectacle lens, which requires a reduction in a positive lens (like holding a magnifying glass further from your eye). Bifocal strength is HIGHLY subjective: the stronger the bifocal, the narrower the view, and arm extension can easily position objects for a best compromise position.

That's a very detailed technoidal way of saying:
1. Confirm what you need in VERY VERY VERY dim light above water
2. Add 0.25 diopter, unless...
3. If you're a photographer needing to confirm critical focus on an LCD screen, use +0.50 extra on one eye (each eye does not need to be the same strength because you don't see through them both at the same time anyway, per post #126).

Now, all that said, the "magic bifocal" phenomenon of dome optics is why hundreds of divers wear contact lenses to use some of the 9,000 double-dome masks we've shipped around the world since 2003. You get great close focus AND distance vision in the entire field-of-view (i.e. your eyes behave as they did when you were in your 20's).

(details on HydroOptix website)