Extended range of vision lens type combines wide variety of lenses, which are now called EDOF or Extended Depth of Focus. These lenses may have different focus extension technologies*, and different working distances. Extended range type provides good far vision and good intermediate distance vision starting at 60-80cm as a standard, and some models of that type extends that range, starting functional vision at 45cm. For demanding near tasks, in many cases reading glasses will be needed, however it depends on visual task, lens model and residual refraction.
key Extended Range of Vision IOL features
Quality of vision with Extended Vision Range lenses depends mainly on optical principle, optics specifications in terms of working distances and planned visual acuity - basically focus extension technologies. However optics asphericity type and visible light filter may play some role as well. Long term stability of any lens depends on material type and quality, however that type of lenses considered premium, and majority of lenses of that type have good materials.
An important characteristic of that type of IOL is a technology, used to extend focus.
Focus extension IOL technologies might be:
1. Diffractive rings to elongate depth of far focal point or true EDOF type of optics
2. Diffractive rings to create 2 focal points or standard multifocal technology, but different to multifocal lenses, these focal points tuned to provide more vision at intermediate range, while standard multifocal lenses tuned for near distance vision.
3. Aberration profile shaping lenses, which elongates focus by inducing spherical aberration and higher order aberrations of the optics
4. Basic refractive optics, which might be considered as subtype of multifocal lenses, but with same focus on intermediate without near distance.
Differences in focus extension technologies affects visual acuity at particular distances, contrast sensitivity and image clarity in dim light conditions and positive dysphotopsia profile (halo effect) of the lens. Differences may vary, but generally lenses using aberration profile tend to have lower contrast sensitivity and less positive dysphotopsia profile, while diffractive rings type optics may give wider range of vision and higher contrast sensitivity, especially of true EDOF type. Refractive optics behave like multifocal, while might have less positive dysphotopsias than diffractive multifocal optic. See your IOL model specifications.
Lens materials: might be either hydrophilic or hydrophobic. Both materials are good, but has basic differences.
Hydrophilic lenses might be injected via smaller incision, but have more tendency for secondary cataract.
Hyprophobic materials have less secondary cataract probability, but generally need slightly larger incision.
However, both lenses types are injected via small and safe incision of less than 2.4mm.
Material quality: normally is described in terms of chromatic aberration and represented via so called ABBE number. The higher ABBE number is, the smaller amount of chromatic aberration lens produces and thus creates better image quality.
Optics type: lens type might have positive spherical aberrations, zero shperical aberrations and negative spherical aberration.
Extended Range of Vision lenses normally have zero or negative spherical aberrations.
Zero spherical aberration of the lens provides good image quality.
Negative spherical aberration of the lens provides maximum image quality.
Zero and Negative type of lenses are called "aspherical", however particular asphericity type may influence image quality in different way, based on patient cornea aberrations or anatomical eye specific.
Light filters: any intraocular lens has UV (ultra violet) light filter built in.
Some IOLs have visible light filters. Different light filters has different intensity and color, but generally they are yellow and that type of lenses might be not suitable for peoples, who need maximum amount of light available during night-time or precise color reproduction.