Topic by Bovril

  • Bovril
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Topic

l am short sighted and have in recent years had a -8 (R) and -8.5 (L) prescription for contact lenses and -10 (R) and -10.5 (L) for specs. A recent highstreet eye test reduced my Left eye to -10.25 for spectacles but upped it to -9 for contact lenses. Is it possible for one eye to need opposite powers for contacts and spectacles?...P.S apparently my astigmatism had changed, is that a possible explanation.Thanks for any help..

  Reply by Cat

  • Cat
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For budding ophthalmologists

A - 10.25 in glasses would normally be a - 9.00 in contacts. Your old Rx in contacts at -8.50 was too weak.

At - 10.00, 1 whole diopter is taken off to compensate for the difference in the distance the lens is from your eye.

Over - 6.00, contacts go in 0.50 steps, so they went to - 9.00 instead of -9.25.

What they gave you is what it should be.

  Reply by Dragon

  • Dragon
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For budding ophthalmologists

because of contact lenses being placed on the eye, the power they require is different to spectacles. with being shortsighted this means the prescription would be slightly weaker for ur contact lenses.

there is a general rule to calculate which power u require for ur contact lenses & then the optometrist will check this by holding a few lenses over the top. this time u may have preferred slightly more in ur contact lenses.

the astigmatism will have an affect on ur contact lenses. generally half the astigmatic part (cyl) is added to the sphere part, so if this is increased this could be why ur contact lens prescription has increased.