Decoding the 'Defocus Curve' to analyse visual performance of Presbyopia correcting IOLs

The presbyopia correcting IOLs offer in addition to good visual acuity for distance, a range of vision. Hence just checking distance and near vision in these patients will not reveal the whole picture. One needs to understand how to assess the range of vision offered by these lenses. To do this the simplest way is to draw up a 'Defocus Curve'. This lecture series presentation will help you to understand what makes the defocus curve tick.

[@Sipu79]

One important factor that is not often discussed is that any extended range is always traded for image quality and contrast. So choosing a monofocal will give you the best possible dynamic range and image quality, because the number of photons going to the lens is a constant and more you spread the light, the more compromised your vision over that range will be.

[@PhacoPoint]

I agree that the light energy distribution curve will be nearly 100% for monodical IOLs with proper spectacle correction for intermediate and near. This is certainly a trade off for those desiring spectacle independence after cataract surgery. In patients with significant cataracts the contrast and brightness is already significantly compromised and hence they actually end up being very happy with the results

[@Sipu79]

@@PhacoPoint yes, any iol is better than not being able to see. But often this comes as a surprise for patients as they are not informed or they haven't done enough reading on the issue. Since they will be getting permanent implants it's important to understand this. Another surprise people often don't realize is how multifocals actually show your brain 3 pictures at once with different focal lengths, which is the source of the dysphotopsias. People don't understand it's not the same as accommodating natural eyes. In any case, it's a great presentation of defocus curves. Thanks for posting it.

[@rajatnona]

Excellent presentation 👏

[@saladademusicacia3926]

Ola. Qual LIO tem a menor perda de contraste? Tecnys synergy ou zeiss at lisa?

[@PhacoPoint]

Hello. In my opinion the technis synergy has less contrast loss

[@PhacoPoint]

the technis material has a higher Abbe number that causes lesser chromatic aberrations and the negative aspheric optic reduces spherical aberration which leads to a better contrast

[@kruthi4136]

Hello sir... Kindly explain diff (if any) n mechanism involved in using plus n minus lenses in examination to frame defocus curve..

[@PhacoPoint]

Hello Kruthi. There is a difference. Minus lenses stimulate accommodation and since the amplitude of accommodation can be converted to distance we can thereby effectively check resultant va at different distance. If plus lenses are used it would blur the vision as the focal point moves in front of retina