Contact Lenses Explained

Contact lenses serve as a substitute for eyeglasses and are formally small adhesive shells, usually made of plastic. They are worn on the corneal surface and float in the tear fluid. Contact lenses are used to compensate for refraction (equalize the refractive power of the eye) in cases of defective vision. They are often used as a substitute for eyeglasses and offer several advantages in addition to an improved cosmetic result: In hyperopia (farsightedness) and aphakia (absence of the lens), contact lenses can widen the field of vision. A myopic (nearsighted) patient benefits from retinal image enlargement and thus improved visual acuity. When looking sideways, the lens follows the direction of the eye, avoiding visual errors caused by glasses. The field of vision is not narrowed by the frame of the glasses. Other advantages of contact lenses are that they cannot fog up, pressure points of any spectacle frame are avoided and the natural appearance of the person is not changed. Clear disadvantages of contact lenses compared to glasses are an increased risk of infection or injury, allergies, greater hygiene effort and expense, and fluctuating visual acuity depending on the tear film. Elderly patients with shaky hands in particular may have problems handling contact lenses.

Indications (areas of application)

Indications for the use of contact lenses can be divided into sub-areas. Cosmetic indication

  • For cosmetic reasons, the patient wants to replace his glasses with contact lenses.
  • In addition, there may be a desire to change the color of the iris.

Medical / optical indications

  • High anisometropia (unilateral refractive errors), for example, unilateral aphakia, absence of the lens) – This can lead to the compensatory failure of binocular vision (vision with both eyes, which is a prerequisite for three-dimensional vision).
  • High ametropias (refractive errors) – (myopia (nearsightedness) and hyperopia (farsightedness) over 8 dpt (diopters)).
  • Irregular astigmatism – The two optical planes of the eye are not perpendicular to each other due to an irregular curvature of the cornea. This is the case, for example, in the so-called keratoconus (progressive, conical deformation of the cornea of the eye), scar astigmatism (scarring changes in the cornea after injury), condition after keratoplasty (surgical replacement of diseased cornea with suitable donor material) or after refractive corneal surgery (eye laser).

Therapeutic indication: e.g. use as so-called bandage lenses.

  • Perforating corneal incisions – For small incarcerations (entrapment of tissue) or incisions, the contact lens can possibly replace a corneal suture.
  • Keratitis filiformis (filiform keratitis) – A common cause of this corneal inflammation is keratoconjunctivitis sicca (dry eye syndrome). This disease takes its name from the visible fine characteristic epithelial filaments.
  • Recurrent corneal erosions – Recurrent or poorly healing superficial corneal lesions due to trauma, for example.
  • Drug carriers – Soft contact lenses can store and continuously deliver eye drops and the active ingredients they contain to the eye.

Other indications

  • Sports (sports where there is a risk of injury from the lenses, such as martial arts).
  • Professions or activities where fogged glasses are a hindrance (eg, police, firefighters, cooks).

Contraindications

Absolute contraindications

  • Inflammation – e.g. inflammation of the conjunctiva or cornea due to herpes simplex.
  • Monocularity – With the exception of the situation of significant visual improvement (improvement in visual acuity) by the contact lens.
  • Lack of ability to safely use contact lenses – reliability, motivation, hygiene, intelligence.
  • Sicca syndrome (Sjögren’s syndrome; of which the severe form) – autoimmune disease with possible keratoconjunctivitis sicca (disease of the conjunctiva and cornea); drying up of the tear fluid with the symptom of dry eye.
  • Reduced corneal sensitivity

Relative contraindications

  • Allergies
  • Eyelid diseases
  • Eyelid position problems
  • Keratitis sicca (dry eye)
  • Medications that have effects on the cornea (e.g., antidepressants or beta blockers).
  • Environmental factors that have an impact on the cornea (eg, dust or fumes).

The procedure

For the first use, it is important to learn the correct application to avoid injury. The insertion of the contact lens is done after moistening it with buffered NaCl solution (saline) as sterile as possible. The contact lens is taken on the fingertip, the eyelid is spread. During the approach, the lens is fixed and then inserted. After that, first the upper eyelid and then the lower eyelid is released. Soft contact lenses should be carefully removed from the eye between the index finger and thumb. When removing hard contact lenses, the eye is opened wide. The eyelid skin is pulled firmly to the lateral canthus (corner of the eye) so that the contact lens falls out. A contact lens fitting is necessary to determine the appropriate contact lens or to determine the suitability of an already selected contact lens. Driving is allowed, but a spare pair of glasses must be carried. The following types of contact lenses are available:

  • Form stable contact lenses – This includes the hard and gas permeable contact lenses.
  • Hard contact lenses – These are made of PMMA (polymethyl methacrylate, Plexiglas), they are unbreakable, have a high form stability and are well wettable. The hard contact lenses are impermeable to O2 and CO2. They are used mainly for corneal astigmatism.
  • Gas permeable contact lenses – These can be made of CAB (cellulose acetobutyrate), fluorosilicone acrylates, fluorocarbons or silicone acrylates. Gas permeable contact lenses are much better tolerated, unlike hard contact lenses.
  • Soft (flexible) contact lenses – These contact lenses are made of so-called hydrogels or copolymers, which have a water content of 30-80%. Soft contact lenses are better to fit than rigid contact lenses and are better tolerated. However, they have a higher wear rate than these and are not equally hygienic due to a high tendency to deposit.
  • Replacement or disposable contact lenses – Intended for replacement after 14 days to three months or daily (improving hygiene).

Contact lens shapes: The shape of a contact lens (similar to the cut of eyeglass lenses) determines its physical or optical properties and thus its field of application.

  • Bifocal – These contact lenses have a range of curvature for near correction as well as distance correction.
  • Multifocal – These contact lenses feature a variety of concentric ring zones of varying curvature.
  • Spherical – The contact lens has an identical curvature in all meridians. They are suitable for the correction of myopia and hyperopia.
  • Toric – These are contact lenses, each of which has different curvatures on its front and back. They correct an astigmatism caused by corneal curvature.

Possible complications

Complications include those that occur when contact lenses are not used properly and can be a sign of a damaged or dirty contact lens and corneal irritation.

  • Allergies – allergic reactions to the contact lens material or care product.
  • Acanthamoeba keratitis – Acanthamoeba keratitis is a severe form of keratitis (corneal inflammation) with abscess formation (formation of an abscess/pus accumulation in a non-preformed body cavity), which occurs mainly in contact lens wearers (esp. permanent contact lens wearers) and is caused by so-called acanthamoeba, a protozooen species.
  • Injury to the conjunctiva (conjunctiva) and / or cornea (cornea) injuries – eg Ulcus corneae (corneal ulcer).
  • Burning
  • Epiphora – leakage of tear fluid over the edge of the eyelid.
  • Endothelial changes
  • Sensitivity to the insertion solutions
  • “Ghost images” – due to dirty lens.
  • Keratitis (corneal inflammation) – esp. in:
    • Use of old contact lenses
    • Sleeping with contact lenses (6-8 times the risk of eye infection).
  • Upward displaced lens
  • Fog vision
  • Overwear syndrome – too frequent use of contact lenses can cause central corneal edema (corneal swelling) and superficial epithelial defects.
  • Photophobia (sensitivity to light).
  • Fungal keratitis (corneal infections caused by fungi); causative agents of the infections are various molds of the genus Fusarium (very rare).
  • Reduced visual acuity, fluctuating visual acuity.
  • Pruritus (itching)
  • Giant papillary conjunctivitis (synonym: gigantopapillary conjunctivitis) – inflammatory disease of the conjunctiva of the eye (conjunctivitis), which occurs mainly in wearers of soft contact lenses.
  • Redness – so-called injection, ie sprouting of fine blood vessels.
  • Pain, especially after removal of the contact lens.
  • Tight lens syndrome – the contact lens is too tight and immobile on the cornea, this leads to acute symptoms such as a painful red eye, corneal edema (water retention in the cornea) and conjunctival irritation.
  • Toxic keratopathy – damage to the cornea by toxic-acting substances, such as the cleaning solution of contact lenses.

Durability of contact lenses

  • Daily disposable lenses should be disposed of after wearing once
  • Monthly lenses should be disposed of after about four weeks.
  • Hard contact lenses can be worn for up to two years.

Hygiene rules for contact lens wearers

Five tips to keep your lens and eye clean:

  • Wash hands: To prevent dirt and germs from getting into the eye.
  • Cleaning: Put contact lens on the cleaned palm and gently rub a few drops of detergent on the lens with your fingertip. Then rinse with saline solution. Never clean or store with tap water, otherwise germs can form on the lens.
  • Disinfect: Store contact lenses overnight in suitable solution to kill bacteria, fungi or viruses and remove protein residues.
  • Clean storage case: Disinfect and replace every three to six months.
  • Follow manufacturer’s care instructions: Only use storage solutions that are suitable for the respective lens type.