Astigmatism

[skytry]

hi All,
just having a full eye test after having a eye lens
replacement approx. 18 months ago,
the optometrist went through both eyes thoroughly, I was impressed,

having spoken too many here re viewing problems of astigmatism through my 102mm Refractor scope,
and not so bad in my 6in S/Watcher refractor, still had a little astigmatism there,

both eyes tested to astigmatism, CYL -0.75, now too rectify this problem with Tele-Vue Dioptrx lenses, so 2 of these lenses I shall purchase so the bino's can be used again,

then it shall be back too viewing without any false colour, hopefully
and having purchased a selection of Tele-Vue eyepieces, all good,
I am slowly getting above average gear together, it's taken a while,

having met with Brian N, here in Palmerston NT, I have learn so much
from him, I am very thankful, and we had a good nights viewing last Saturday, it was a good night, another this Saturday, clouds permitting,

so with 2 Dioptrx lenses, I'm back too good viewing again,

regards,
Peter.

[blink138]

hi peter
can you tell me what your RX was before the intra ocular lens and your final RX after the device was inserted?
i am interested in the level of performance post surgery with the intra ocular device in place and settled........ and if the new lens causes any flaring for astronomical observations
regards
pat

[skytry]

hi Pat,
my RX before & RX after, I cannot comment, ie, not known,
all that was stated, very bad cataract,

after the lens replacement, I had post surgery complications in the operated left eye,
it is a complicated story, after many revisits, my left eye is getting
alot better, yet I still cannot use it through the eyepiece yet,
my eye, time is healing, it is nearly 20/20 vision now,
the Dioptrx will help emmensely, my Dioptrx correctors shall be 0,75 both eyes

if you are contemplating a lens replacement, have confidence, do it,
9 out of 10 have no after surgery problems,

hope this answers your query, feel free to ask any more questions,

regards,
Peter.

[blink138]

hi peter i was just wondering what your final correction was as my business is an opticians in perth
no the reason i was interested in your story was that i was enquiring to an opthamologist here about astigmatic intra ocular implants
pat

[GraemeT]

Peter, If your refraction is -0.75 Cyl, this means that you need a cylindrical or astigmatic lens at a certain axis which should be also specified on your prescription. Any correcting lens of this type will (should) have one or two engraved lines on the periphery which indicate the orientation of the lenses in the mount. Astigmatic (or toric) lenses are orientation sensitive.
I suspect that 0.75 Dioptrix lenses will be +spherical form, which can be easily duplicated by racking the eyepiece in a millimetre or so, and won't correct for astigmatism. Check with your supplier of the Dioptrix before laying out the cash.
If you have any doubts, take the lenses to your prescriber for verification.

OOPs, See below.

[GraemeT]

Peter, On further research on the Dioptrix lenses, they ARE cylindrical lenses, so all is good.
Pat, I have one eye with an intraocular lens post cataract, no flaring with the telescope. This is a single vision implant, but people with bifocal/progressive implants suffer from constant annoying flare in low light levels and big pupils. Many disappointed patients have I seen who have believed the advertising hype from the IOL manufacturers.
Cheers
Graeme - retired optometrist

[blink138]

ah, now that is information I was wondering about Graeme! perhaps the flaring problem only manifests itself in multifocal IOL's
interesting...... I would like to find out about possible flaring in the single vision toric IOL's for a friend and fellow member here as I think he has 1.5 dioptres of astigmatism which would be nice to correct with an IOL
pat

[skytry]

hi Graeme,
the CYL reading for both eyes is -0.75,
this is a single vision implant,
the eye with the new lens, and the original eye not touched,

regards,
Peter.

[GraemeT]

The Rx needs a cylinder axis, and usually a spherical component, even if it's zero, something like: R plano -0.75 x 175°. This allows the lens to be oriented at the correct angle relative to the horizontal line through the centres of both pupils, in this case 175°. You don't have to worry about that, it's your optometrist's job to put it in the right place!

[GraemeT]

Pat,
The flaring only occurs when there is a non spherical or non toric surface on the IOL, eg. bifocal or annular progressive surfaces or fresnel type surfaces. These are designed to provide two focal points through the same pupil and can be tolerated by a few people who are able to suppress the second (blurred) image as they change from distance vision to near vision. In my experience, a significant number of people find extreme difficulty in adapting. Astronomers would find these IOLs intolerable. On the other hand, a plain toric IOL is ideal. I have referred to several surgeons who only do cataract surgery, and who can achieve a perfect uncorrected plano result. I'm an example, not only is my left eye plano, colours are brighter, and there are no annoying diffraction fringes arising from the cataract spikes that used to be there.
The main selling point for the multifocal implants is the freedom from needing reading specs, but this is usually not an issue for someone who has needed readers for some years. The disadvantages are greater cost and the fact that once you have one, you're stuck with it.
Cheers,
Graeme

[DavidU]

Great info Graeme :thumbsup:

[skytry]

hi Graeme,
your report,
The Rx needs a cylinder axis, and usually a spherical component, even if it's zero, something like: R plano -0.75 x 175°. This allows the lens to be oriented at the correct angle relative to the horizontal line through the centres of both pupils, in this case 175°. You don't have to worry about that, it's your optometrist's job to put it in the right place!,

my question is,
is it better for the optometrist to make the corrector lens, with all the 175° required & -0.75,
than purchase the Tele-Vue off the shelf corrector lens,
or is the Tele-Vue off the shelf corrector sufficient for general viewing,

regards,
Peter

[blink138]

great info thanks graeme
pat

[blink138]

yeah peter that is why i was interested in the first place........ why not give you the full correction for your astigmatism then we would not have to be worried about a parracor and give you a low spherical, or, as lucky graemes result plano!
i had an elderly patient yesterday at my practice who informed me he had his right eye cataract removed and showed me his final rx......... the doctor had kindly given him -5.5 dioptres of astigmatism to deal with
unbelievable!
pat
great result by the way graeme!

[skytry]

hi Graeme,
ok, I do read what you are saying, and understand,
if a -0.75 corrector surfaces at a good price, I shall purchase,
just too see,

otherwise I shall wait till I get home and have a corrector made up
by the Optometrist, to the exact prescription,

could the corrector be made to fit in a filter lens frame,
eyepiece filter screw in type that is supplied,
or does it have too be on the top of the eyepiece,

regards,
Peter

[GraemeT]

Peter,
The advantage of the Dioptrix is that it is made in a thin, flat, multicoated form in a mount designed to fit the TeleVue eyepieces and probably others. Should it not fit what you have, it's probably able to be removed from the mount and put in a standard filter mount.
A lens from an optical outlet would require a custom ground lens which would then require fitting to an appropriate mounting. This could prove quite expensive compared with a readymade product. As I read the advert for Dioptrix, it is up to you to make the alignment yourself. With a -0.75, this should not be a big deal, as you merely rotate the corrector to get the clearest image. Once you have determined the best orientation, you note the position of the mount relative to your head angle for repeatability, remembering that if you change your head angle as you do with a dob when you alter the altitude, you need to realign the corrector.
Sounds complicated but you'll soon get the knack.

[GraemeT]

Pat,
There's no point in incorporating the sphere as the normal action of the focusser will do that.

I wouldn't be referring to or recommending that bloke again! Any surgeon worth his salt should be able to do better with eyes closed.

[blink138]

sorry guys I obviously meant a dioptrix not a parracor....... doh!
pat

[blink138]

yes I know Graeme but I have not seen any cataract operation with a plano result.... that is why I said even if the surgeon accomplishes a low spherical residual and rids him of his astigmatism you would have to be very happy with that
pat

[GraemeT]

Pat,
the two fellows that had most of my referrals would get within half a dioptre of plano in 90% of the time. Their main difference was that they ceased all other surgery and became cataract specialists. When you do nothing else, you get very good at it.

[blink138]

totally agree graeme
pat

[skytry]

hi Graeme,
thank you for your help,
and information, I have learnt alot,

the RX question, I shall still answer if required,
yet again, I may find out for my own interest also,

regards,
Peter.