Dr. med. Andreas Zarth
Contact lens Types
Today with contact lenses and with spectacles any form of refractive error (short-, wide-, presbyopia, and strabismus) can be corrected. Contact lenses are superior for correcting corneal changes. The fact that the contact lens is located directly on the corneal surface, the tear film under the lens can correct irregularities of the corneal surface and in this way form a uniform optic which is not possible using spectacles.
Contact lenses are a high quality medical product. Basically, they are made of optically active polymers. They are available in different shapes and designs. The choice of lens depends on the specific characteristics of the eyes (visual acuity reduction, corneal geometry, tear film, tear production, etc.), and the demands on vision system.
Below are descriptions of the main types of contact lenses:
Rigid or hard contact lenses have a high gas and oxygen permeability, which makes them particularly comfortable. They are easy to use and especially are an ideal companion for corneal changes. Irrespective of the type of lens regular optical and ophthalmological checks are important. Because pathological changes in the eye or abnormalities in the tear film may for example be caused by hormonal irregularities which may show no obvious symptoms initially, but which may often lead to later lens intolerance. For hard lenses a checkup is recommended every six months.
Soft or hydrophilic contact lenses are flexible and slightly larger than hard lenses. They adapt to the corneal surface exactly which makes them less suitable for compensating corneal changes. They sit firmly and thereby reduce the risk of loss, especially when in water. Soft lenses are generally perceived from the outset as pleasant to wear whereas hard contact lenses need some time to adapt to. For soft lenses regular checkups are recommended every four to six months.
In the past presbyopia could only be compensated for with reading glasses or lenses. Progressive lenses, which are also known as multi-focal lenses, provide sharp, clear vision at all distances, comparable to progressive lenses in spectacles. Regardless of viewing direction, head or body posture multifocal lenses ensure smooth transitions from afar to close up and vice versa. They are available as both hard and soft lens versions.
Specialty or therapeutic lenses usually find application in diseases or damage to the cornea, for example keratoconus (protrusion of the cornea). Refractive errors in vision, which are caused by corneal changes in many cases, can only be corrected with contact lenses.
Basically normal contact lenses can also be worn during sports, provided they meet the following criteria: high oxygen permeability, guaranteed ability to dissipate heat and a level of UV light protection. Only when these requirements are met will the cornea be adequately supplied with oxygen and the eye produces enough tears. Corneal damage from oxygen deprivation can go for a long time unnoticed.
Color or cosmetic lenses are soft lenses that let the natural eye color appear to change. They are a lens usually used on a monthly or daily basis often in the context of special events.