Refractive vs. Diffractive IOLs: Key Optical Differences
Both refractive and diffractive IOLs are types of multifocal intraocular lenses that divide incoming light into two or more focal points, but they use fundamentally different optical principles to achieve multifocality. 1
Optical Mechanism
Refractive multifocal IOLs use different zones or surfaces with varying refractive powers to create multiple focal points, similar to how traditional bifocal glasses work with distinct optical zones. 1
Diffractive multifocal IOLs utilize microscopic concentric rings etched onto the lens surface that diffract light into multiple focal points through wave interference patterns. 1
Clinical Performance Differences
Distance Vision
- Refractive IOLs provide superior uncorrected distance visual acuity compared to diffractive designs (weighted mean difference of -0.04 logMAR, p < 0.01). 2
- This advantage makes refractive lenses preferable when distance vision is the primary priority. 2
Near Vision
- Diffractive IOLs deliver significantly better uncorrected near visual acuity than refractive designs (weighted mean difference of 0.13 logMAR, p < 0.01). 2
- Reading acuity and reading speed are superior with diffractive IOLs (p < 0.01 for both). 2
- Diffractive designs allow patients to read smaller print sizes (weighted mean difference of 0.56, p < 0.01). 2
Intermediate Vision
- Refractive IOLs, particularly rotationally asymmetric designs, provide better intermediate vision at defocus levels of +1.00 to +1.50 diopters. 3
- No significant difference exists in uncorrected intermediate visual acuity overall between the two designs (p = 0.05). 2
Optical Quality and Side Effects
Contrast Sensitivity
- Refractive multifocal IOLs demonstrate significantly better photopic contrast sensitivity than diffractive designs (p = 0.04). 3
- At middle spatial frequencies (3,6,11.4 cpd), diffractive IOLs show 6-10% lower contrast sensitivity. 4
- Under glare conditions, diffractive IOLs perform 8-16% worse at middle and high spatial frequencies. 4
Photic Phenomena
- Diffractive IOLs produce significantly more halos and glare than refractive designs. 2
- The risk ratio for halos with diffractive IOLs is 3.14 (95% CI: 1.63-6.08, p < 0.01). 2
- The risk ratio for glare is 1.36 (95% CI: 1.15-1.61). 2
- Recent comparative studies show nearly all participants prefer refractive designs due to less halo/glare. 5
Higher-Order Aberrations
- Refractive IOLs, particularly rotationally asymmetric designs, induce higher wavefront aberrations including total higher-order aberrations, tilt, and primary coma (p = 0.02). 3
- However, diffractive IOLs from the ZMB00 family show higher internal aberrations including trefoil, coma, tetrafoil, and spherical aberration compared to some refractive designs. 6
Spectacle Independence
Diffractive IOLs provide superior spectacle independence with a relative risk of 0.27 (95% CI: 0.20-0.38, p < 0.01) compared to monofocal lenses, and this advantage extends when compared to refractive multifocal designs. 2
Clinical Decision Framework
For patients prioritizing:
- Distance vision and contrast sensitivity: Choose refractive multifocal IOLs 2, 3
- Near vision and reading ability: Choose diffractive multifocal IOLs 2
- Minimal photic phenomena: Choose refractive designs 2, 4, 5
- Maximum spectacle independence for near tasks: Choose diffractive designs 2
Important Caveats
Both IOL types result in reduced contrast sensitivity and increased incidence of halos compared to monofocal IOLs, though the magnitude differs between designs. 1 The American Academy of Ophthalmology emphasizes that selection depends on patient visual needs, expectations, motivation for spectacle independence, and willingness to accept potential compromises. 1
Newer diffractive lenses demonstrate better outcomes than older diffractive or refractive designs, particularly for near vision, quality of vision, and reduced halo risk. 7