Intraocular Lens Power vs. Contact Lens Rx

[jhcoleman1953]

Can someone explain, in “Optics for Dummies” terms, how intraocular lens power relates to contact lens prescription power?  I’ve had monovision correction with contacts for several years; -9.0 D for distance, -5.75 D for close-up.  During cataract surgery, my doctor implanted a 12.0 D intraocular lens for distance and a 14.0 D lens for close-up.  Intuitively, I would think the more “powerful” lens (14.0 D) would be for distance while the smaller number (12.0 D) would be for close-up.  And I have no idea how a -9.0 D corrective lens prescription equates to a 12.0 D intraocular.  I work in the scientific research field, and I’m usually pretty good at tracking down such info, but I can’t wrap my head around this.  Thanks for any help.

[JohnHaganMD]

HERE IS A LINK TO AN EXPLANATION:  https://cataract-community.zeiss.com/iol-calculation-formulas-explained

[JohnHaganMD]

If you have an optics background you can search the internet for intraocular lens formula for determining IOL powers. The variables are axial length of eye, anterior chamber depth, radius of curviature of the cornea and two constants one specific to the IOL type and the second an empiric modification based on analysis of the surgeons previous experience.   Your thinking on the IOP power is 180 degree wrong.   As things get nearing they require more bending by the IOL thus the larger IOL is for near.

[jhcoleman1953]

OK, thanks.  That makes sense for the IOL.  But how does the IOL power relate to contact lens Rx, which, in my case was measured in negative numbers?  Or am I trying to compare apples and oranges here?

[JohnHaganMD]

No not at all.   minus numbers indicate myopia, the lens diverge the incident light rays. IOL power almost always positive.  converge the light rays.