Contact lenses

Contact lenses

Nowadays on the market, there are numerous types of contact lenses with different uses. Here is a short description of them all.

The basic division is on soft and gas permeable contact lenses. Depending on their characteristics and individual needs, they all have good and bad sides.

SOFT LENSES

Soft contact lenses were designed about 45 years ago. They are bigger than the GPs, pliable and conform to the front surface of the eye. They fully cover the cornea, as well as a smaller part of the sclera. Soft lenses are immediately comfortable to wear. Since the exchange of tears is harder, their material must be oxygen permeable. Soft contacts can be individual (lathe-cut soft lenses) and standardized.

1. Individual contact lenses are “the custom suit” for your eyes. The manufacturer we collaborate with produces lenses according to the medical report we issue after detailed examination and measures in our clinic. There are innumerable combinations regarding this type of lenses.
2. Standardized lenses are a matter of choice. They are changed more often, which gives the patient safety in maintenance and wearing. If worn more rarely and only on special occasions, daily lenses are an ideal solution. Every morning you put a new fresh lens and dispose of it in the evening.

During the examination, we can determine which type of lenses are the best for you of all the possibilities and which suit your habits and your way of life the most.

GAS PERMEABLE CONTACT LENSES

GP lenses are the forerunner of all the lenses we have nowadays. Sometimes they are called semi-rigid or rigid gas permeable lenses. They have a smaller diameter than the soft lenses and are produced individually, according to the measurements of your eye. They “swim” in the tear film, so there is an exchange of tears, and the cornea metabolism is uninterrupted. They are also suitable for refractive errors where other types of correction have been proved unsuccessful – high amounts of astigmatism or irregular cornea.

Through the thin, perfectly polished optics, GP contact lenses provide perfect visual acuity and have a longer expiration date. It is recommendable to change them every year but it is even better to change them according to the medical report and eye scan during a medical checkup. You will get all detailed advice in our clinic regarding the maintenance and handling of these contact lenses. The duration time to wear the lenses can be extended. When you start to wear GP lenses, adaptation is necessary. You cannot wear them every waking hour on the first day. Instead, we have to agree on the adaptation plan.

SCLERAL LENSES

Scleral lenses belong to a special type of gas permeable lenses. They don’t touch the corneal surface, but vault over the cornea – they sit on the sclera (the white of the eye), which makes them comfortable to wear. They also vault over the limbal zone which is important for uninterrupted corneal metabolism. In the limbal zone, there are stem cells responsible for the cell regeneration of the corneal epithelium. Most often this type of correction accomplishes a stable and better visual acuity compared to other techniques. With the right choice of lenses, every contact with the cornea is avoided. The lens is filled with tears and acts as a wet chamber for the eye. This way it is an ideal indication for patients with the disorder of the front surface of the eye as a consequence of Sjogren’s syndrome, Facial paralysis, Filamentary keratitis, and Stevens-Johnson syndrome. Scleral lenses can also be used with eyelid disorders, Lagophthalmos, or severe cases of trichiasis.

CONTACT LENSES AFTER INJURIES, SURGERIES, AND DUE TO CORNEAL DISORDERS

After perforations or corneal surgeries, there is usually a scar. On the cornea, one can see wrinkles and irregular surface, which influences the optics of the eye. Depending on the condition, sometimes it is possible to correct the visual acuity with glasses. Still, most often the only solution is the correction with special contact lenses. Between the lens and the cornea, there is a tear film, so irregularities are fixed, and the front surface of the lens presents the ideal optics.

Keratoplasty is a transplantation of a donor’s cornea. It is performed with serious deformities where a surgeon can replace only a part of or the whole cornea. When determining the lens, one must take care that the lens does not compromise the corneal metabolism. The contact lens presents an optimal possibility of correction after keratoplasty in the following cases:

• After surgery, there are major irregularities of the front part of the cornea
• With a high degree of regular astigmatism
• When there are major differences between the diopters of the right and the left eyes.

As a rule, the lens creates good visual acuity and improves the quality of life.
With many corneal diseases, a special type of contact lenses changes the quality of life. By this, we mean degenerative corneal diseases – degeneration of corneal epithelium, keratoconus, keratoglobus, pellucid marginal degeneration of the cornea (PMD), Terrien’s marginal degeneration, cornea after pterygium surgery, conditions after traumatic injury, as well as Sjogren’s syndrome with decreased production of tears.

LENSES AFTER REFRACTIVE EYE SURGERY

Refractive eye surgery is used to improve the refractive state of the eye. Current procedures and ways to correct the diopter with the Excimer laser cause complications very rarely. However, throughout life eyes can sometimes change. The most often conditions are the progression of myopia (short-sightedness) or the change of cornea after radial keratotomy, the procedure which used to be popular in the past. Contact lenses are also a choice with the problem of double images or halo images.

COSMETIC LENSES

In case of loss of the iris as a result of an injury or an inborn defect, extreme photophobia or light sensitivity occurs. In such cases, the lack of the iris is corrected with a specially designed lens in the same color as the other eye, based on the image of the iris. The lens is cut and colored manually. In case there is a complete loss of vision, the scar on the cornea can be covered with a prosthetic lens that fully covers the cornea.

COLOURED CONTACT LENSES

Colored soft contacts can be a fashion statement. They are used when filming movies and on other occasions.

ORTHO-K LENSES

Orthokeratology is by definition a reduction, modification, or elimination of the refractive error with a programmed application of the contact lens.

Since the introduction of the contact lenses, corneal modeling was considered as an unwanted and uncontrolled reaction to wearing hard contact lenses. With the introduction of computer technology and corneal topography, ortho-K lenses were created. They are worn overnight and removed in the morning, so the patient can see clearly during the day. After one night of wearing them, the diopter is corrected by about 70%, whereas the rest of the refraction is corrected within 10-30 days.

New studies suggest that ortho-K lenses comprise the corneal tissue by using the design of reversible geometry. A thin layer of tears between the back surface of the ortho-K lens and the central cortex has a hydraulic function, and it compresses and probably redistributes the epithelial cells on the surface from the center toward the periphery. That explains how patients with properly fitting ortho-K lenses can wear them without central corneal staining or irritation.

Ortho-K lenses reduce the sagittal depth and change corneal curvature. This shape od cornea refocuses the rays of light towards macula, which reduces or eliminates the need for myopia correction. Ortho-K lens is suitable for:

• Younger or older short-sighted people
• Recreational or sports activities for which wearing the optical correction is disabled
• People in professions where a good uncorrected visual acuity is necessary – police officers, pilots, professionals in deep diving.

In the last few decades, there has been an increase in myopia, i.e. short-sightedness all over the world, especially in the category of high myopia. High myopia complications are glaucoma, cataract, ruptures, and retinal ablation.

Children develop emmetropia, “zero” diopter around the age of 8. A six-year-old child with average myopia with -1.0 diopter will get -0.5 diopter per year; by the teenage period, he will have about -5.0 to -6.0 diopter. Reducing the level of progression by 1/3, the possibility of high myopia is reduced by 70%. There are other ways to slow down myopia progression but the advantage of orthokeratology is that lenses are worn only by night. Parents put and take off the child’s lenses and he doesn’t wear them throughout the day or at school.

EXAMINATION

If the contact lens is indicated, we analyze the form of your eyes with corneal topography and tomography. When determining special contact lenses, we also do optical coherence tomography to measure the sagittal depth of the eye (epithelial map).

Finally, we can choose and place a trial lens into your eye. On the OCT instrument, we can measure the eye zones, estimate the position of the lense, and depending on the results, adjust it further.

It is of vital importance to learn how to place the lenses correctly, as well as how to remove and maintain them adequately to prevent potential complications.