Maskless and disappointed.. for now

[JonKranhouse]

Oreocookie:

As I said before RE a strong + diopter Rx:

I believe it is unethical to make an Rx mask for a high POSITIVE diopter Rx using the "conventional" approach, because such a plano-convex lens greatly reduces your field-of-view [much worse than a non-Rx mask] while simultaneously causing fuzzy vision for off-axis views. Instead, we recommend a lens "carrier" to preserve more field-of-view.​

If indeed your left eye (your "good" one) has a combined Rx of +4 diopter on one axis (+2.0 SPH & +2.0 CYL), and your right eye has a combined +5.0 diopter, then high index material would slightly reduce the geometry problem I mention. But you'll still have significant loss in field-of-view and off-center blurring. Please confirm your Rx has ALL "+" values (not "-" values).

You could DIY your own "carrier" by cutting off the temple pieces of some robust plastic-frame eyeglasses. The trick is finding a design that fits inside the mask well, without cramming into your nose. Yes, this is an inelegant solution, and you'll have to judiciously treat three surfaces with anti-fog gel. But the acuity and field-of-view advantage with the "carrier" is far superior to custom-made bonded-on or solid-block lenses. And $100 less expensive (for mask + carrier + Rx lenses) vs. high-index plano-convex lenses that are single-vision (i.e. not bifocal) installed in a mask.

All that said, your field-of-view and acuity will be best with contact-lenses. BUT - you must be careful to follow all hygiene protocols. The least expensive torics, daily-disposable "Ciba Focus Dailies Toric," are less than $1.00 per lens.

Contact lens divers on vacation often get lazy and keep their contacts in many many hours after diving. Some people sleep in extended wear contacts, as they do at home. No!!! Not on a dive vacation!!! That's when itchy / dry eyes become a problem, even with the new materials -- REMOVE SHORTLY AFTER DIVING!!

Since you're new to diving, if you opt for contact-lenses, make sure you take the time to get used to wearing contacts before going on vacation. The task loading of learning to wear contacts + learning to dive is not safe. If you choose to go with contacts, because you're farsighted, BE SURE to carry a small magnifying mirror (otherwise you'll never be able to focus to insert the lenses). Also, start to desensitize your blink-reflex, so you'll be popping in contacts like a pro, by getting comfortable with putting in eye drops without wincing.

BTW -- how old are you? Does your Rx have an "add" number (for bifocals)? I hope I'm not insulting you -- just wanting to give you a fully-informed recommendation.

 

[oreocookie]

Jon,
I checked the Rx and realised that while the numbers I originally stated were slightly off, for all intents and purposes, they're close enough, and yes, all numbers are in fact +. No "add" number either. I'm 20 (and been wearing glasses for 19 years).

I'm not sure I understand exactly how your lens carrier would be better for field of vision than lenses bonded onto the inside of the mask, though I'll admit I'm a bit fuzzy on how the bonding process would affect field of vision either and how the two methods differ (I'm sort of picturing almost a pince-nez type thing for the lens carrier) other than there being, as I understand it, some air space between the Rx lenses and the mask that isn't there with the bonded lenses.

 

[JonKranhouse]

Hi oreocookie,

The "perfect" way to look through a lens is perpendicular to the lens (90-degrees). Imagine looking through a thick plate-glass window, but at a 45-degree angle - you see distortions. When evaluating Rx mask geometry, it's not just the thickness of the lens, but what happens when it's immersed.

When looking through your eyeglasses in air, they're concave toward your eye. This geometry allows slightly off-center gazes (i.e. views away from where your nose points) to have good acuity. Now, take your glasses off, flip them upside down, and look through the front (wrong) side, so the lenses are bulging toward you. When you look through the convex side, you can barrel distortions are exaggerated. And when you look off-axis, images get fuzzy vs. the normal way of using your eyeglasses. (Depending upon your CYL axis, astigmatism correction will be OK, or be pretty far off.)

The schematic images shown on the PDF from our website might help. The carrier keeps the lenses slightly further away from your face than normal eyeglasses, and the natural elasticity of the face-skirt keeps the carrier from falling out.

 

[peterbj7]

I also have strong axis effect in one eye, and have found through expensive experience that that eye is intolerant of an error in axis on a correcting lens of more than 1/4 degree. Unfortunately the normal tolerance in manufacturer is 1/2 degree (in Britain at any rate, but I imagine it's universal). So it's hit and miss whether a lens will work for me, and that's with the close relationship at an optician's. I would have no confidence buying a correcting lens mail-order.

 

[JonKranhouse]

Hi Peter,

To notice the variation of a CYL axis of just 1/4 of one degree is, frankly, surprising. As your eyeglasses rest on your face, you’ll have multi-degree variations from optimal. Possibly, your eyeglasses made earlier, that were not acceptable, had far greater problems. Only examination through a lensometer gives accurate info.

peterbj7
"I would have no confidence buying a correcting lens mail-order."

RE “mail order.”
In the USA, well over 20,000 eye doctor practices that “dispense” prescription eyewear, and lots of eyeglass shops, do NOT have a “lab” on site. They get lenses made “mail-order,” under business-to-business contracts.

When a dive shop sends out a mask to a prescription mask provider, the dive shop is also working “mail order.” When that mask arrives back from the Rx lens fabricator, the dive shop sure doesn't have a lensometer to validate what they’re selling their customer. Heck, most dive shops don’t even have proper carbon monoxide monitoring. (And kudos to you for the good practices you follow to ensure safe air quality, as I’ve read about here on SB.)

The MOST important factor: having accurate Rx info from your eye care professional. Few eye doctors will be so generous with their "chair time" as to cogitate over 1/4-degree adjustments to see what's subjectively preferred by a patient, when most people cannot perceive a difference of less than 2-degrees for a "middle of the road" Rx. So for folks having a challenging Rx, take an active, participatory role when getting refracted behind a phoropter (measure twice, cut once)...

 

[tfsails]

I didn't read the whole string, and maybe this has been suggested before, but here goes: Get a second opinion from an ophthamologist, not an optometrist.

I've worn contacts for 27 years now, had lots of infections and bouts of conjunctivitis while I was learning how to stick 'em in and remove 'em. Once I learned how to do that, maybe I've had one episode of conjunctivitis, probaby when I was drunk one night and tried to remove the contacts for the second time that night (duh.........) or something stupid like that. The point is, if you tolerate contacts well they can work wonders for people with all sorts of eye anomolies, and infections are rare.

Of course, if you never get out of bed you don't have to worry about getting hit by a car either. That's my two cents' worth; that and a quarter will get you a cuppa coffee....

 

[peterbj7]

Hi Peter,

To notice the variation of a CYL axis of just 1/4 of one degree is, frankly, surprising. As your eyeglasses rest on your face, you’ll have multi-degree variations from optimal. Possibly, your eyeglasses made earlier, that were not acceptable, had far greater problems. Only examination through a lensometer gives accurate info.

Jon

I agree, it is surprising. It is nonetheless true, as has been found on two or three occasions when lenses have been supplied that were well within tolerances, the initial prescription was correct, and the only thing wrong with the lens was the axis. A problem is that I use bifocals and quite rectangular frames, so the opportunity to rotate the lenses once manufactured is slight. On one occasion it turned out to be possible and those glasses were fine; on the other occasions they had to be remade. I generally used Zeiss punctals because of the clarity of the glass and their superb aspheric performance, but in terms of axis they were no better than any other.

Actually, my eye examinations are annual and so far as I can manage are with someone I have used before and whom I know does a good job. The examination still takes around 1 1/4 hours. Is that long?

Peter

 

[oreocookie]

Jon,
I understand how orientation of the lens effects vision (turning glasses in different direction and looking at the distortion can be entertaining if you're bored enough), but is this to suggest that bonded lenses might be flat against the mask and convex toward the eye (there was a diagram of that in the link you mentioned)? Otherwise if the lenses are the same shape (concave toward the eye), I can't see how your method would be any better than theirs.
btw- I think it might be beneficial to have a photo of the lens carrier in an actual mask on the site, instead of just a side-view diagram.

Are you able to put the lens carrier into other masks, or would I have to buy one of yours? If I went to my lds and tried on a ton of masks and bought whatever fit best, would you be able to do anything for me at that point in terms of correction or would I need to look elsewhere?

 

[JonKranhouse]

The examination still takes around 1 1/4 hours. Is that long?

Waayyy long for a "middle of the road" Rx - but not unusual for a challenging Rx

...is this to suggest that bonded lenses might be flat against the mask and convex toward the eye

For a positive Rx, required for farsighted divers, in a conventional mask (flat on the ocean-side), the lens MUST be convex towards your eye. Conversely, to make a negative lens, for nearsighted divers, the side facing one's eye is ALWAYS concave.

Animation on our website makes understanding basic optics / refraction really easy (a moving picture's worth 10,000 words).

The only way to make a positive lens that's concave toward your eye, to preserve field-of-view, is to make a "meniscus" shaped lens --which is curved on the front. That's how your eyeglasses are made. But you can't submerge a curved-front lens without the shape of the air inside the mask creating a negative lens (That's what our MEGA 4.5DD is - a negative lens for nearsighted divers.)

Here are some photos I just grabbed. Notice on the inside of our Rx1 mask, the "dimple" downward between the lenses. This "dimple" provides room for the bridge of the lens carrier frame.

Top-view of carrier frame:

I imagine the lens carrier could fit into other masks -- but we've never investigated because so many people get a good fit with our Rx-1. Just look for a mask with a similar indent at the bridge of the nose, to ensure room for the lens-carrier.

 

[shotthebreeze]

If your LDS can't figure out how to order/change lenses in a scuba mask, how are they going to handle the OW class?