Guide to Extended Depth of Focus (EDOF) IOL optics
- Subhabrata Bhattacharya
- Nov 12, 2023
- 14 min read
Updated: Mar 6
Learning Objective: At the end of the reading, you will get an understanding of the design of the Extended Depth of Focus (EDOF) IOLs in the market, and how they differ from one another.
Depth of focus & Image quality-
The world of Intra Ocular Lens (IOLs) has gone a sea change in the last twenty years. A plethora of lens options is now available starting with the presbyopia correcting bifocal and trifocal IOLs, to more recent introduction of EDOF IOLs. The depth of focus and image quality are the two most important aspects of post operative visual rehabilitation. Unfortunately, the two are antagonistic. There will be a drop in depth of focus if image quality is to be enhanced, an example being the aspheric lenses. On the other hand, if depth of focus needs to be increased, this may come at the cost of image quality. So there is no free lunch in optics. The bifocal and later trifocal presbyopia correcting IOLs were introduced to increase the depth of focus of patients, but this came often at a cost of photic phenomenon and a resultant drop in image quality.
What is depth of focus (DOF)?
Depth of field can be defined as the nearest and furthest image in a picture that are acceptably clear. In the below picture some objects are sharp and clear while others not. The ones that can be clearly seen falls within depth of field of the camera. Depth of focus is often loosely interchanged with the word depth of field. Depth of focus however is on the image side of the retina, while the depth of field on the object side. Both are intertwined. Visually you will have no depth of field if the lens does not offer depth of focus on the retinal side.
