Contact Lens Fitting

Contact lens fitting is a necessary procedure that adds safety to the use of contact lenses. Incorrect use of contact lenses can lead to infection and permanent impairment of vision. In addition, a non-fitting lens does not achieve the desired visual acuity, so the wearer’s refractive error cannot be adequately corrected.

Indications (areas of application)

Contact lens fitting is always indicated for first-time or new use of contact lenses to ensure optimal use. Indications for contact lens use are as follows:

  • Cosmetic indication – replacement of glasses with contact lenses, desire to change the color of the iris.
  • Medical/optical indications – High anisometropia (unilateral refractive errors); high ametropia (refractive errors: Myopia (nearsightedness) and hyperopia over 8 dpt (diopters); irregular astigmatism, i.e., the two optical planes of the eye are not perpendicular to each other due to an irregular curvature of the cornea).
  • Therapeutic indication – e.g., use as so-called bandage lenses: e.g., for perforating cuts of the cornea.
  • Drug carrier – Soft contact lenses can store eye drops and the active ingredients contained therein and continuously deliver to the eye.
  • Other indications – eg sports; professions or activities where fogged glasses are a hindrance.

Contraindications

Contraindications to the use of contact lenses are:

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 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

First, a detailed medical history should be taken. This usually includes a general part, an environmental history, an allergy history and a medication history. An ophthalmologic history is also part of the introductory conversation during contact lens fitting. The visual acuity and refraction of the patient’s eyes are then determined. The visual acuity can be determined, for example, with the help of the so-called Landolt rings (standard vision mark that consists of a black ring interrupted at one point and offered to the observer in different sizes). The power of the contact lens is expressed in diopters (dptr). In the case of isolated farsightedness or nearsightedness, the lens is referred to as a spherical lens. If astigmatism is also present, a toric lens is used. Furthermore, ophthalmometry is used to determine the surface curvature of the cornea in order to detect and measure corneal astigmatism. The determination of the pupil and corneal diameter as well as the corneal sensitivity also play an important role in the ophthalmological examination during contact lens fitting. The so-called tear film break-up time (BUT, measure of the severity of a dry eye) should also be determined; a shortened BUT significantly limits the use of contact lenses. Another technical method for measuring the corneal surface is videotopography. Here, the surface of the patient’s cornea is measured optically and then displayed in a color-coded format. With this system, an optimal contact lens back surface can be calculated from a data set. However, based on this procedure, no individual contact lens is manufactured, but only approximately the optimal lens for the patient is selected.In the end, the visual acuity and the wearing test as well as the close observation of the mobility and the fit are decisive for the evaluation of the fit of a contact lens.

Hard contact lenses

Proper fit of a hard contact lens is determined using a fluorescein (fluorescent dye) image. If the contact lens fits properly, you will find an even distribution of color with smooth transitions from the center to the outside. The tear film circulation is also checked. In the so-called steep fit, the colorant collects centrally under the contact lens, while the contact lens rests only with the outer edge on the cornea. If the lens fits too steeply, tear circulation can be disrupted. The flat fit is the opposite: here, a strong, peripheral fluorescein ring is found. In this case, the contact lens sits centrally on the cornea while rising peripherally. The lens should cover the pupil well, but not the corneal edge. In addition, it should not permanently touch the edge of the eyelid; this can cause irritation. It should be easily movable (1-2 mm) during the blink and should not cause a distinct foreign body sensation when worn.

Soft contact lenses

Fluorescein is not used when evaluating the fit of a soft contact lens, as the lenses may store the dye. The mobility and centration characteristics of the contact lens are important. If the eyelids are spread, the lens must be mobile, otherwise it will fit too tightly, similar to a suction cup on the cornea, and may damage it by reducing oxygen supply. Steep fitting leads to unstable visual acuity, a foreign body sensation, and decentration of the contact lens. In addition, mobility is reduced and the lens may leave an imprint on the cornea. With a flat fit, unstable visual acuity, decentration, and decreased mobility are also found; in addition, air bubbles underneath the lens may cause visual disturbances.

Possible complications

Complications include those that occur when contact lenses are not used properly and may 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 abscessation (formation of an abscess), which occurs mainly in contact lens wearers (especially permanent contact lens wearers) and is caused by so-called acanthamoeba, a protozoan species.
  • Conjunctival and / or corneal injuries – eg corneal ulcer (corneal ulcer).
  • Burning
  • Epiphora – leakage of tear fluid over the lid margin.
  • Endothelial changes
  • Sensitivity to the insertion solutions
  • “Ghost images” – due to dirty lens.
  • Itching
  • Upward displaced lens
  • Fog vision
  • Overwear syndrome – overuse of contact lenses can cause central corneal edema (corneal swelling) and superficial epithelial defects.
  • Fungal keratitis (corneal infections caused by fungi); causative agents of the infections are various molds of the genus Fusarium (very rare).
  • Photophobia – glare sensitivity
  • Reduced visual acuity, fluctuating visual acuity.
  • 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, esp. 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 and conjunctival irritation.
  • Toxic keratopathy – damage to the cornea by toxic-acting substances, such as the cleaning solution of contact lenses.