Monofocal vs. EDOF vs. Trifocal IOLs: Modulation Transfer Function & Light Splitting

A Diffractive Trifocal IOL does not physically move or focus dynamically; its anterior or posterior surface is engineered with concentric diffractive echelette steps measuring sub-micron heights:

$$d = \frac{\lambda}{2(n_{\text{IOL}} - n_{\text{aqueous}})} \quad [\text{Constructive Phase-Shift Diffraction}]$$

By splitting the incoming wavefront via constructive and destructive interference:

• 50% of Light Energy: Directed to the 0th diffraction order for Distance vision ($\infty$).
• 25% of Light Energy: Directed to the 1st order for Intermediate vision ($60\ \text{cm}$, computer/dashboard).
• 25% of Light Energy: Directed to the 2nd order for Near reading ($40\ \text{cm}$, phone/books).
• Light Loss / Scatter: Approximately 12% to 15% of total light is lost to unwanted higher diffraction orders, permanently reducing retinal contrast sensitivity in low-light environments.

To eliminate night glare halos, next-generation EDOF Lenses (such as Alcon Vivity) utilize non-diffractive wavefront-shaping elements (X-WAVE technology):

1. A central $2.2\ \text{mm}$ elevated plateau stretches the focal wavefront into a continuous elongated beam of light.
2. Delivers seamless 6/6 distance and crisp 6/7.5 intermediate computer vision.
3. Generates a night-glare and halo profile identical to a standard monofocal lens! (Near smartphone reading still requires a mild $+1.25\ \text{D}$ reader).

On an optical bench (ISO 11979-2), a standard Aspheric Monofocal IOL achieves an outstanding MTF score of $> 0.65$ at 50 line-pairs/mm, delivering pitch-black contrast and crisp night driving. A trifocal IOL drops to an MTF of $0.28\text{--}0.35$.

For patients who chose monofocal lenses or who experience residual night starbursts from trifocals, ELLASUV DriveSafe Night HMC Spectacles eliminate parasitic reflections and optimize night-driving visual acuity.