Eyeglass prescription adjustment for mask lenses?

[Luango]

Does anyone really know what adjustments need to be made to a Rx for lenses in a mask? I got conflicting information from everyone I asked even some docs that specialize in scuba lenses.

My eyeglass prescription is -4.25 both eyes with -.25 astigmatism in the left. I want the get the standard replacement lenses that come in half diopters for Oceanic's 4site mask.

Someone told me that if I go up to -4.5 my eyes would get stuck that way permanently. I don't think that is possible , is it?

What my research tells me, am I wrong?
Myopia (nearsighted like me) is caused by an egg shaped eyeball and the lens tries to compensate, so an artificial lens in front of the eye does not permanently change anything.

There are two issues in Rx for scuba lenses: water make things look bigger and the lenses a father from eyes the in eyeglasses.

They're farther away right? even in a low volume mask? I think eyeglass prescriptions assume a 12mm vertex distance, contacts 0mm, but scuba mask >12mm maybe. Compensation is need for vertex distance in prescriptions +-4.0 or greater because prescriptions are written in .25 incriminates and 4.0 is the point where vertex distance makes significant enough difference. Prescriptions are increased in strength for greater vertex distance and vice versa.

Just my theory that the refraction of water making things look bigger can or should be ignored, similarly to how a magnifying glass can produce a in focus enlarged image that can be view from up close or far a way and remain the same. If true no change in Rx would be need for the water.

For astigmatism divide it in half and add it to the spherical diopter, keeping correct +- signs. For me, -.25/2 = -.125 then -4.25 +(-.125) = -4.375. Just for that I think I should round up to -4.5 at least in the left eye anyway.

All that and I still cannot find anyone who knows what they are talking about.

 

[JT2]

Try this site for some good info.
www.allaboutvision.com/sports/diving.htm

 

[JT2]

I meant for this to be a reply to the post about prescription lenses for scuba masks.....Could someone please work their magic and move it there???

 

[TexasMike]

** ZAP **

That'll be one bottle of cold Shiner Bock, please

 

[Dee]

Yo...Mike! We were ***ZAPPING*** at the same time!

JT...you might want to go into that first post and change the subject line to something about eyeglass prescriptions. Mike and I sort of reversed each others efforts!

 

[Dectek]

When trying to get the same type of information....I was told to get ½ of what your eyeglass script was for. The distance that the lenses are away from your eye when wearing a mask will make up that other ½.
I feel for you , but I no longer have that problem.
I look forward to my first dive with 20/20 eyes.
Actually the right eye is 20/20 and left 20/25. LASIK!!!:holycow:

 

[Rebel-ron]

As a register optician and diver that needs an optical correction under water. There is a rx compensation that can be made to fit your individual prescription.
The reason things look bigger underwater is due to there being an airspace between your eye and the water on the outside of your dive mask. The Rx compensation does little to correct this due to the air is still there. If you get in a pool and open your eyes the image will be of normal size. The other reason things appear larger is the face plate on the mask is flat . I am a -2.50 myopic, ( near sighted ) I wear contacts they work fine, but the water magnification is still there , just ignore it. There is a mask on the market that has a curved face plate and it has no correction in it but due to the curve corrects your vision from a -200 to -450. However it only works under water, when you come up you can not see the boat clearly. Also the egg shaped eye causes astigmatism not Myopia .