Selection of contact lenses according to the base curve radius2015-07-02 00:00:00
Some time after the beginning of wearing of contact lenses patients come again to their refractionist and complain about vision deterioration, the feeling of "floating" lens in the eye. Most of these complaints are related with the improper selection of contact lenses, that is with the mismatch between the base curve radius and the convexity of the cornea.
The degree of wearing comfort of contact lenses is defined by their fitting quality. It can be compared with the selection of shoes. If you purchase larger size shoes they will probably fly off the feets while walking. And if the size is smaller, you will not go without corns. The same situation is observed when wearing contact lenses: mismatched diameter and base curve radius can cause serious discomfort.
What types of lens fitting are there?
Depending on the match of contact lens parameters to corneal membrane of the eye, there are following types of improper fitting.
- Flat. It is observed when the corneal radius is less than the base curve radius of the lens. It leads to the increased mobility of contact lenses and their decentration, that is perceived by user as the instability of visual function;
- Steep. In this case the contact lens fitting is practically motionless. It can cause corneal edema that, in it's turn, results in significant vision deterioration. The consequences of the steep fitting are such serious complications as keratitis and hypoxic damages of eye cornea.
Only professional ophthalmologist can determine the correctness of lens fitting in the process of personal examination of the patient (as well as the examination with the help of the slit lamp). In this way, it is becoming apparent that the selection of contact lenses can not be carried out without the medical supervision of qualified specialist.
In some cases properly selected eye lenses can lose their fitting. That is why it is recommended to consult with the professional ophthalmologist in 2 weeks after the beginning of wearing of contact lenses.
How the selection of contact lenses is carried out?
First of all, the doctor measures the parameters of eye cornea with the help of refractometer. It allows to determine the base curve radius and the diameter of contact lenses more precisely.
If it is necessary, the selection is carried out with the help of the trial pair of contact lenses and the slit lamp. The doctor determines the mobility and the correctness of fitting of medical lenses on the eyes.
Also the correct fitting can be determined by the instillation of fluorescein into the eyes. This substance is well-known for it's ability to glow under the influence of the rays of ultraviolet spectrum.
The correct selection of contact lenses implies not only the determination of the most suitable lens shape, but also the matching of lens material. For example, silicone-hydrogel and hydrogel lenses have different degrees of mobility and despite of the same base curve radius they differ between each other by fitting options.
Due to the high degree of oxygen permeability steep fitting of silicone-hydrogel lenses is not so dangerous to eye cornea as of hydrogel lenses.
The correct selection of contact lenses can be carried out at Online-Shop Ecolens.ch. In order to help people to select contact lenses more precisely, manufacturers usually produce each lens series with two or more parameters of base curve radius. As an example, let's take a closer look at the following lenses:
- Johnson & Johnson company: 1-Day Acuvue TruEye (9,0 и 8,5), Acuvue Advance (8,7 и 8,3), Acuvue 2 (8,7 и 8,3).
- Bausch + Lomb company: coloured lenses SofLens Natural Colors (8,7 и 8,4), PureVision (8,6 и 8,3), Optima FW (9,0, 8,7 и 8,4).
- CIBA Vision company: Air Optix Night & Day Aqua (8,4 и 8,6).
If you want to save your eye health while wearing contact lenses, it is extremely important to use special moisturizing eye drops and disinfectant solutions, do not forget about scheduled replacement of eye lenses and lens cases. However, it should always be remembered that the most important thing is correct selection of contact lenses, carried out under the medical supervision of professional ophthalmologist with the help of the modern and qualitative equipment!