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Extended Depth of Focus IOL ( EDOF)

Extended Depth of Focus IOL ( EDOF)

The increase in life expectancy and lifestyle changes have resulted in an increasing number of patients requesting spectacles for independent near and intermediate vision for their daily activities, aside from excellent distance vision.

Some of our valued suppliers have come up with EDOF (Extended Depth of Focus) IOLs in Hydrophobic Platform. The optic of these IOLs has been uniquely designed to provide excellent visual acuity for far and intermediate vision, and reasonably good near vision.

Understanding EDOF concept

Presbyopia-correcting IOLs can be divided into three broad categories: MF IOLs, extended depth-of-focus (EDOF) IOLs and accommodative IOLs. EDOF IOLs, or extended range-of-vision IOLs, are a relatively new technology in the treatment of presbyopia.

The basic optical principle is to create a single-elongated focal point to enhance the depth of focus, on the contrary to monofocal IOLs (in which light is focused on one single point) or MF IOLs (which has two or three discrete points).

However, the term EDOF should be limited to those IOLs in which a manipulation has been made in their aberrometry profile to enlarge the depth of field. Those IOLs which have a MF design and, on top of it, also offer a manipulated aberrometry optical profile, should be called ‘hybrid EDOF IOLs’.

EDOF IOLs are classified in to two types: Pure EDOF IOLs and hybrid MF-EDOF IOLs. Pure EDOF IOLs are based on the spherical aberration-based optics or the pinhole effect, but have no multifocality. Hybrid MF-EDOF IOLs include diffractive-EDOF IOLs, refractive-EDOF IOLs and diffractive-refractive-EDOF IOLs.

Spherical Aberration based EDOF IOL

It was shown that aspheric IOLs which effectively reduce spherical aberration improve the optical quality over spherical IOLs. On the other hand, higher positive SA in eyes having received an aberration-free IOL results in a better distance-corrected near visual acuity than that following implantation of negative-SA IOLs (that have reduced corneal SA).Similarly, intentional induction of SA within the IOL design can increase the depth of focus.

EDOF IOLs utilising the pinhole effect

The pinhole effect is another concept which allows a greater depth-of-focus to be obtained. In general, it could be stated that the smaller the pupil size, the greater the depth of field (and depth of focus).9 Following this principle, the use of an opaque pinhole mask in a monofocal IOL enhances the depth of focus

Hybrid MF – EDOF IOLs

Chromatic aberrations (CAs) are associated with focal length difference between the visible spectrum of different colours of light. The human cornea produces a CA, in which blue light is diffracted more than red light.

The optical design also has an impact: a refractive optic maintains the same CA of the cornea, so with this lens the final ocular CA will increase, as will the dispersion of the wavelengths. On the contrary, diffractive IOLs can reverse CA: red blends more than blue.

So, diffractive IOLs can minimise the CA in every eye. Achromatisation does not bring an extended depth-of-field improvement but rather an improvement in the contrast sensitivity function. Thus, diffractive could lead to an improvement of the contrast sensitivity and the quality of vision.

This elongated focus is introduced to eliminate the overlapping of near and far images caused by traditional multifocal IOLs and the halo effect; ideally EDOF IOLs should enhance intermediate and near visual performance, while minimally affecting distance vision. In this way, EDOF IOLs differ from multifocal IOLs, in which the secondary out-of-focus images correspond to the additional foci and might induce halos.

There is a wide range of IOLs available on the market. A careful and thorough patient examination, taking into account IOL selection based on lifestyle and visual needs, is essential to avoid patient misunderstandings about the expected outcomes.