Difference between revisions of Correction

BO is Base out, BI is Base in, BU is Base up and BD is Base down.

You will note that most prescriptions will round to the nearest quarter diopter.  This is the level of precision available in standard pre-ground lenses, which make glasses cheaper and faster to make than custom ground lenses.  You may have a more precise prescription if it is written for specific lens grinding systems, or a less precise prescription it is written for contacts.

Your prescription is specifically written for either contacts or glasses.  [[Vertex Distance]] plays a role in effective lens strength, so the contacts which sit closer to your eye may be written as a weaker prescription than glasses.  Vertex Distance is hard to measure, and contacts may act differently as the eye adapts to them, so if you have a strong lens your optometrist may need to do additional refraction tests with the contacts in and adjust your prescription slightly.

* [[Normalized]]

* [[Differentials]]