Full range of vision lens type combines wide variety of lenses, such as multifocal bifocal, multifocal trifocal and hybrid models combining true EDOF technology with basic multifocal technology. These lenses may have different working distances for near vision and different visual acuity at intermediate range. Full range of vision type IOLs provide good far and good near distance vision (in a range of 33-40cm depending on model) and good intermediate vision in range of (60-80cm), however bifocal lenses do not provide good intermediate vision by design and for demanding intermediate tasks you may need additional glasses. Actual vision quality with that lens type depends on lens model and residual refraction and astigmatism.
key Full Range of Vision IOL features
Quality of vision with Full Range of Vision lenses depends mainly on optical principle and optics specifications in terms of working distances and planned visual acuity. 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 create full range of vision i.e. near fo far.
Full range of vision IOL may use the following technologies:
1. Diffractive bifocal lens with good far and good near vision, while having poor intermediate zone.
2. Segmented bifocal lens with good far and good near vision, while having poor intermediate zone.
3. Diffractive trifocal lens with good far, intermediate and near distance visual acuity, but different lens models may have different behaviour and visible changes in visual acuity between focal points as well as different optimal vision distances at intermediate and near depending on model and specification.
4. Diffractive hybrid lens with good far and smooth and continuous visual acuity across near and intermediate zone.
Differences in lens optics technologies affects visual acuity at particular distances, contrast sensitivity and image clarity in dim light conditions and positive dysphotopsia profile of the lens. Differences may vary, but generally multifocal lenses tend to have lower contrast sensitivity comparing to monofocal or extended range lenses, and therefore this lens type might be not suitable for patients having certain eye conditions such as glaucoma, retinal issues or corneal abnormalities.
Also, patient's brain has to adapt to specific of image formation of that lens type, and this process, called neuroadoptation may vary between peoples. Neuroadoptation may be seeing as low quality far vision or inability to read at the early post operative stage. However it improves over time as patient's brain adapts to new image formation. Positive dysphotopsias (halo effect) might be observed more often with full range of vision lens than with any other lens type. But general patient satisfaction by full range of vision lenses are high, as these lenses provides the best independence from glasses among all IOL type available.
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.