Medical uses of implant lenses
An implant lens (intraocular lens) is used to replace a natural lens when it no longer is functional, for example, during cataract removal when the natural lens becomes blurry, or during refractive lens exchange, when an intraocular lens helps correct severe myopia, farsightedness and astigmatism. An intraocular lens implanted in the eye has the same functions as the natural lens and is practically the same as to its optical characteristics.
How implant lenses work
Most implant lenses comprise two components, i.e. an optical component and a support component. The optical component of an implant lens is made of a transparent material biologically compatible with eye tissues. There is a difraction area on the surface of the optical component to get a clear vision. The purpose of the support component is to secure the implant lens to the natural eye lens capsule. The service life of IOL implants is unlimited; they require no replacement and retain their optical characteristics for many years.
Main characteristics of the lens
Transparency. Human crystalline lens helps refract light to be focused on the retina. Crystallins are lens proteins responsible for transparency.
Flexibility. The eye uses the so-called accommodation mechanism to focus on object at different distances from it – the eye lens uses its ciliary muscles to change its curvature and focus on objects. The elasticity of the lens and surrounding muscles lowers with the age, and, as a result, natural accommodation weakens.
The lens lacks vessels or nerve endings, so it receives all its nourishment from the aqueous humor. The diameter of a lens of an adult is about 9 to 10 mm, while its thickness is 3,6 to 5 mm (depending on the strain of accommodation). The lens is located within a thin, elastic, transparent capsule.
Loss of lens functions results in
- Age-related farsightedness, which is the loss of lens ability to change its curvature and focus on objects at a near distance.
- Age-related cataract, which is blurriness of the lens due to the aging process.
- Congenital cataract, which is blurriness of the lens due to congenital defects.
- Lens astigmatism, which is disorder of the lens shape and incorrect focusing of the light.
A rare condition is aphakia, or absence of the lens from the eye due to injury or surgery.
What are indications for IOL implantation?
Intraocular lens (implant lens) is implanted if a patient has one of the following conditions:
- cataract, when the blurry natural lens is exchanged for an implant;
- severe myopia, farsightedness или astigmatism (refractive lens exchange), when natural lens refraction is insufficient.
Characteristics of modern intraocular lenses
- Optical parameters
Each lens implant has a relevant set of optical parameters to ensure good vision. Optical power is customized for each patient depending on his or her vision apparatus and purpose of the surgical intervention.
- Biocompatible material.
The materials that are used for manufacture of modern intraocular lenses are biologically compatible with eye tissues, non-allergic and cause no rejection. Among most frequently used materials are acrylic, hydrogel, silicone and collamer.
Modern intraocular lenses for temporary installations are made of a flexible material, so it can be folded and placed inside the eye using an injector through a microscopic slot of 1,8 mm in size. The lens then unfolds on its own and secured inside the lens capsule.
These lenses have their optical and support component combined into a single lens structure and manufactured from the same biocompatible material.
Generally, most modern intraocular lenses have blue-light filter. The natural human lens has in-built protection from the adverse effect of ultraviolet radiation of a particular range. Blue-light filter is similar to the natural lens filter to ensure the same level of protection for the retina, which is especially important for elderly people.
- Spherical aberration correction.
Intraocular aspheric lenses are specifically designed to correct spherical aberration and get a better image at nighttime. Such lenses help eliminate haloing, glares or strobing.
Spherical optics forms an imperfect image as optical power is unevenly distributed.
Aspherical lens has the same optical power at all points to produce a better image.
- Astigmatism correction.
Sometimes people have astigmatism concurrent with other eye disorders (myopia or cataract), so it is not enough to implant regular intraocular lenses. In these cases, toric lenses are implanted to address astigmatism.
- Age-related farsightedness correction.
Every person above 40 starts losing his or her accommodation strength, i.e. the ability of the lens to change focus quickly for a clearer image of objects at different distances from the eye. As people age, their lens gradually loses its flexibility (even if they had excellent vision before) and ability to change its curvature quickly, so one may now require glasses to work with objects located at a nearer distance. Modern lens varieties, such as multifocal (pseudoaccommodating) or trifocal, have a special design of the optical component for good vision at different distances, functioning like the natural lens and eliminating the need to wear glasses.
Modern intraocular lenses combine several properties at once. The combination is selected according to the treatment tactics and wishes of the patient. For example, all lens models implanted by Excimer clinic are flexible, made of biocompatible material, and most of them are one-piece. Some of the properties, such as aberration correction, are especially valuable for professional drivers who need to have good vision under any lighting conditions.
Types of intraocular lenses (IOL) used by Excimer:
How do we select intraocular lenses at Excimer?
At Excimer, we select intraocular lenses depending on the comprehensive diagnostic data for each patient. Before surgeries (cataract removal or refractive lens exchange), we use a cutting-edge IOL Master optical coherent biometer (Zeiss, Germany) to calculate optical parameters. The calculation is especially important for implantation of high-tech complex optics (multifocal or toric lenses) to obtain maximum vision. When selecting a lens, we also take into account many other parameters such as the patient’s age, lifestyle, occupation, profession, individual wishes, etc, to give our patients a new quality of vision.