Assessment of Myopia

Thread view:

Enable EMail Alerts

Start New Thread

Thread rating:

Robert Kopp - 25 Apr 2005 02:59 GMT

Spectacle lenses for myopia are stronger than contact lenses for the same
patient. If one is merely asked to state the degree of myopia for a given
individual, is the preferred figure the one using spectacle correction or
contact-lens correction? Or should you always specify what correction was
used?

Signature

Robert T. Kopp
http://analytic.tripod.com/

Reply to this Message

Mike Tyner - 25 Apr 2005 03:30 GMT

> Spectacle lenses for myopia are stronger than contact lenses for the same
> patient. If one is merely asked to state the degree of myopia for a given
> individual, is the preferred figure the one using spectacle correction or
> contact-lens correction? Or should you always specify what correction was
> used?

Spectacle Rx is the convention. Not everyone wears contacts.

Between +400 and -400 they're usually the same.

-MT

Reply to this Message

Jan - 25 Apr 2005 12:10 GMT

Theoriticaly the "Anterior principal point of the overall system" is the
point where the ametropia is measured exact (see Gullstrand's eye at
http://www.zeiss.de/C12567A100537AB9/allBySubject/9F6B8DBA78C734D3C1256D0100435EDF)

This point is +/_ 1,5 mm lying behind the top of the cornea.

For reasons off simplicity the amount of ametropia is written down with the
according distance between the used trialglasses and the top of the cornea
when done correct.
For the higher amounts in ametropia it really matters.

In fact, when fitting contactlenses you always have to calculate back to
this point (top cornea)
Real opticians also are familiar with this important issue when selling
spectacles to people with a higher amount of ametropia.
One of the reasons professional optometrist's ALWAYS are prescribing with
the according ''vertex distance'' on a RX.

Signature

Jan (normally Dutch spoken)

Reply to this Message