Single-vision lenses are used to correct farsightedness, nearsightedness, or astigmatism. They are most often used as an aid by children and young people aged 12 to 40. They are also used by the elderly population when correcting age-related farsightedness (“short arms”). These lenses are designed to correct either nearsightedness or farsightedness, but not both at the same time. They can only be used for a focused distance. Anything beyond that distance is not perfectly clear and affects the progressive growth of diopters and eye strain.
Progressive lenses (multifocal) are commonly used by people over the age of 45, with more dynamic jobs and visual demands that require instantaneous change of focus or those who cannot see clearly near or far. There is a wide range of progressive lenses and the type can be determined individually depending on the job and everyday life and needs of each person. For people who spend a lot of time in front of a computer there are progressive work lenses. They are more affordable and can be used by people as young as 35 years of age. Sometimes progressive lenses must be prescribed for children as well, especially if a child underwent cataract surgery.
There are also lenses that focus vision at 40 cm and at a distance. Such lenses are called bifocal. They are ideal for the elderly. Most often, given the great limitations they carry with them, they are chosen by people who have already had experience with this type of correction lenses.
Glasses for children are most often frames with single-vision lenses and present a transient therapy for most patients. For children’s glasses, the size of the frame is very important, it needs to be individualized – neither too big, nor too small. Children have a low nasal root, and it is important that a child cannot look over the frames. The correction must be constant if so prescribed, with a fixed distance from the eye. It is very important that the child likes the frame so that h/she is motivated to wear glasses and correct the vision error.
Strabismus glasses correct eye errors in which the visual axis of one eye is not parallel to the visual axis of the other eye when looking into the distance. We call this condition squinting or strabismus. There are problems that occur when looking at something near when the angle of one eye is not equal to the angle of the other eye. This causes headaches for anyone who works in front of a computer, reads, or sews for a long time. It is important to emphasize that there is no age limit for strabismus, and the condition gets more complicated as a person gets older. It is important to choose as small glasses as possible so part of the thickness of the prismatic lens can be “lost” by installing it in a small frame. Getting used to such glasses can take up to two weeks.
Sunglasses protect our vision from the harmful UV effects of sunlight. Previously, sunglasses were a luxury item, and they could only be worn by people who see well or those who wear contact lenses to first correct their refractive error. Nowadays, sunglasses can be worn by everyone. Large companies (Essilor, Zeiss, Rodenstock, Hoya, etc.) have produced prescription lenses with a scalable protection option: UV filter, the percentage of obscuration that depends on operating conditions, anti-reflective layer, polarized layer, reflex (mirror) layer, etc. Very rounded lenses can also be made, but they still require expertise and experience in production. The performance and the price depend on the materials used for producing such lenses and, of course, on the diopter.
Soft contact lenses nowadays offer a wide range of applications. From single-vision, photosensitive, toric (for astigmatism) to multifocal and therapeutic. The age limit has dropped significantly due to better materials, and it is possible to offer contact lenses to children from 6 years of age. They are used as a useful tool in slowing the progression of myopia. Except in everyday conditions, they are worn by athletes, even those in water sports. They are ideal for beach, swimming, and sports. It is not recommended to wear them for work in front of a computer if the work is more than 4 consecutive hours a day and they are not recommended for extremely large cylinders (above 3.25 DCYL). It is important to emphasize the cleanliness in maintaining the contact lenses. Regular corneal check-ups by an ophthalmologist are necessary at least once a year.
Rigid and semi-rigid contact lenses (Hetych®) cover almost all corneal problems resulting in refractive error. Today’s materials and processing standards are at a high level. They are the most effective aid in correcting any eye defects caused by an irregular cornea or diopter strength of the eye. The difference between rigid and semi-rigid lenses is in the material. In rigid lenses, the material is optical glass. PMMA (Perspex / Plexiglas) is a semi-rigid lens that has poor oxygen permeability and has been replaced by more modern RGP (Rigid Gas Permeable) materials. Oxygen permeability through such lens is very large and it is safer to wear all day.
- The Rose K2 lens is a semi-rigid contact lens that corrects vision in people with keratoconus, pellucid marginal degeneration, and after corneal transplantation and post-laser surgery. It is available very quickly because the authorized production of these lenses is in Zagreb.
- The scleral lens is the largest semi-rigid contact lens that also corrects all types of eye defects, and interestingly, some types are also used in the military as a replacement for glasses because they protect the integrity of the cornea if pebbles get to the eye or after detonations.
- Orto K lens or “night lens” is scleral semi-rigid lens used to correct diopters during sleep. It has the highest gas permeability (125 Dk). The process of correcting the collagen structures of the cornea and diopters happens during the night, so we see perfectly during the day. The problem is that the cornea slowly returns to its natural state of refractive error during the day and that is why it is important to wear the lenses always in the evening when sleeping. Initially, the clarity period is about 3–4 hours. After complete adjustment in some users, the diopter is corrected up to 18 hours. We do not recommend correcting more than 4 diopters with an Orto K lens.
Hybrid lenses are intended for keratoconus correction and post-laser surgery. They are made of a soft part (skirt) and a hard central part (made of RGP material). If conventional semi-rigid lens in people with keratoconus or any type of irregular astigmatism is uncomfortable, it is replaced with hybrid lens.