Contact lenses, or simply contacts, are thin clear plastic discs that are placed on the surface of the eye (over the coloured portion of the eye – the iris) for correction of vision or other therapeutic and cosmetic purposes. The contact lenses placed on the surface of the eye float on the tear film covering the cornea (the outermost layer of the eyeball along with the sclera).  There are different types of contact lenses that serve different purposes, are made of different materials and have varying intended duration of use. The most widely used contact lenses are those used as alternatives to spectacles to correct refractive errors.

When viewing an image, the light rays from the object travel through the layers of the eyeball and get bent, due to the inherent differences in refractive index, to converge at the retina. The retinal layer has sensory cells, rods and cones, that pick up and transmit the sensory input through the optic nerve to the visual cortex in the brain where the image is processed and vision is perceived. The eyeball has the property to elongate or shorten its shape and, thereby, its focal length in order to accommodate objects that are near or far. However, the power of accommodation of the eye is limited and the focal length cannot be altered beyond a certain point. Due to differences in eyeball shape or corneal surface irregularities, refractive errors arise. The most common refractive errors are:

  • Myopia: Also known as nearsightedness, this makes it hard to focus on distant objects due to a longer effective focal length of the eyeball.
  • Hypermetropia: Also called farsightedness, it occurs due to the overall shorter length of the eyeball. It is difficult to focus on closer objects and reading glasses may be needed.
  • Astigmatism: Corneal surface irregularities result in distorted vision, which needs refractive error correction in a specific meridian.
  • Presbyopia: With advancing age, the power of accommodation of the eye diminishes and problems arise with focusing on objects both near and far.
  1. Types of contact lenses
  2. Indications for contact lenses
  3. How to use contact lenses correctly
  4. Complications of using contact lenses
  5. Contraindications for contact lenses

Following are some types of contact lenses:

  • Soft contact lenses: The most popular kind of contact lenses used for refractive error are soft contact lenses. These are made of soft and flexible materials and have a higher water content in them, allowing greater gaseous diffusion of oxygen and the cornea to “breathe”. Daily disposable soft contact lenses are available and so are lenses that can be kept for longer durations (usually upto a maximum of one month). Soft contact lenses that are reusable must be stored correctly in an appropriate case suspended in contact lens solution to prevent drying out or bacterial growth. While soft contact lenses are the most comfortable to use, they do not always award the best vision.
  • Hard (rigid) contact lenses: The first type of contact lenses to be used were hard contact lenses. Rigid contact lenses do not allow oxygen exchange and “starve” the cornea within hours of use. However, they provide excellent vision. Today, hard contact lenses are not used routinely for refractive error correction and are reserved for therapeutic use such as those used to treat keratoconus (a condition of the cornea that makes it abnormally cone-shaped, thereby distorting vision). Hard contact lenses are easier to manipulate and fit on the corneal surface and last for a longer time compared to soft contact lenses.
  • Gas permeable hard contact lenses: Addressing the shortcoming of hard contact lenses, gas-permeable hard contact lenses were created. By combining the pros of soft contact lenses (gas permeability allowing oxygen exchange) and hard contact lenses (easier to fit and long lasting), these lenses are doubly beneficial. These lenses are designed to be worn overnight by myopic (shortsighted) people in an attempt to mould the cornea and correct the refractive error by changing the corneal curvature.
  • Scleral contact lenses: Scleral contact lenses are special, large and rigid lenses that are placed such that they cover the whites of the eye as well as the iris and do not come in contact with the cornea. Such lenses are designed to treat eye conditions affecting the cornea, like keratoconus.
  • Treatment contact lenses: Some contact lenses are designed specifically for therapeutic purposes and not for regular daily wear. The main aim of therapeutic contact lenses is to treat corneal and ocular surface diseases (OSDs) and they are used in pain relief, enhancing corneal healing, corneal sealing, corneal protection and drug delivery. Some examples of treatment contact lenses include, but are not limited to: 
    • Soft bandage contact lenses: These contact lenses are designed to protect injured or diseased corneas from the mechanical rubbing of blinking eyelids to allow healing.
    • Collagen corneal shield contact lenses: A type of soft bandage contact lens, which can be medicated, or soaked in a drug to be delivered, and applied to the eye to deliver medication to the cornea. Also aids in corneal healing after surgery or trauma.
  • Coloured contact lenses: Coloured contact lenses can have refractive power correction or be plain without refractive error correction properties. Such contact lenses are used to address the cosmetic appearance of unevenly coloured irises (for example, heterochromia iridium where the irises are of different colours), pale irises (as seen in albinism, a rare genetic disorder of pigment cells affecting the skin, hair and eyes), or incomplete irises (occurring with coloboma – a developmental anomaly in which the ring of the iris does not fuse in the womb, resulting in a hole or gap). Coloured contact lenses can also be used for purely aesthetic reasons to alter appearance as per the wearer’s discretion.

Contact lenses are used for a myriad of reasons that range from refractive error correction, therapy and cosmetic purposes. Some of the indications for contact lens use include:

  • Refractive error correction: As a substitute to traditional spectacles or glasses, contact lenses designed with the correct power are used for everyday wear by individuals suffering from myopia, hypermetropia, astigmatism and presbyopia.
  • Keratoconus: A deformity of the cornea in which it becomes conical and results in blurry vision. Scleral contact lenses are used to reshape the corneal surface for vision correction.
  • Pain relief: By compression and medication delivery, treatment contact lenses help reduce pain, especially following operative procedures. 
  • Enhancing corneal healing: Many treatment contact lenses are used for this purpose after surgical procedures.
  • Corneal sealing: After surgical procedures, collagen corneal shield contact lenses can help.
  • Corneal protection: Soft bandage contact lenses are effective in preventing blinking-related friction eye injuries.
  • Drug delivery: Medicated treatment contact lenses are used to deliver drugs to the cornea.
  • Iris defects or abnormalities: Cosmetic contacts can be worn to cover up iris defects in: 
    • Aniridia (missing iris)
    • Albinism (pale iris)
    • Coloboma (incomplete gaping iris)
    • Heterochromia iridium (differing colours of the two irises)

Correctly inserting and removing contact lenses is essential to prevent any undue injury or contamination.

  • Inserting contact lenses:
    • Wash and dry hands thoroughly.
    • Open the contact lens case and take the first lens on the index finger of the non-dominant hand and rinse it with contact lens solution. Water should never be used.
    • Transfer the lens on to the index finger of the dominant hand and ensure that the right side is facing up (concave side to the ceiling). If not, then flip it. Ensure the lens is undamaged; if damaged, then discard it.
    • Hold open the upper and lower eyelids with the free hand and while looking forward into a mirror (or up at the ceiling), gently place the lens onto the eye surface.
    • Close the eye and blink or roll the eye around to get the lens to sit comfortably on the eye. If uncomfortable, remove the contact lens, rinse with the solution and attempt again.
    • Repeat with the second lens.
  • Removing contact lenses: 
    • Wash and dry hands well. 
    • Hold the lower eyelid down with the middle finger of the dominant hand.
    • With the index finger of the same hand, gently slide the lens downwards to the white part of the eye.
    • Pinch the lens between index finger and thumb and remove.
    • Place the lens on the palm, wet with contact lens solution and rub for 30 seconds to remove dirt and grease. Rinse again with the solution.
    • Place in the contact lens case and cover entirely with lens solution.
    • Repeat with the second lens.
  • Following practices are essential to prevent contact-lens-related complications:
    • Ensure hand hygiene before inserting or removing contact lenses.
    • Do not use damaged lenses.
    • Do not wear contact lenses to sleep and ensure to soak them overnight in disinfectant solution.
    • Throw out the contact lens solution in the contact lens case after putting the lenses in and rinse it with saline.
    • Do not use water or saline for cleaning contact lenses.
    • Replace contact lens cases every three months.
    • Do not use contact lenses for longer than the stipulated duration.
    • There is no evidence to suggest an increased risk of contracting COVID-19 through contact lens wear compared to spectacle lens wear if all hygiene practices are followed.

While an effective, easy and cosmetically-pleasing means to address refractive errors, the daily use of contact lenses, when done incorrectly, increases the risk of many eye problems. Some of the problems arising with contact lenses include, but may not be limited to:

  • Problems in the conjunctiva: The conjunctiva is the pinkish-red soft tissue that lines the inside of the upper and lower eyelids and covers the sclera (peripheral portion of the outermost layer of the eyeball). Inflammation of the conjunctiva is called conjunctivitis.
    • Allergic conjunctivitis: Sometimes, due to the preservatives used in the contact lens care solution, an allergic reaction may develop in the eyes after a period of regular use. Redness, burning and itching are the common signs and symptoms that reduce over time.
    • Giant papillary conjunctivitis: A common occurrence in contact lens users, an allergic reaction to the material of the lens prompts the development of papillae (small finger-like projections on the inner surface of the eyelids), which causes redness and irritation. Upon development of giant papillary conjunctivitis, it is advised to pause the use of contact lenses for a few months and then try a different type of lens.
    • Toxic conjunctivitis: A problem seen with soft contact lens use, lens cleaning solution or other chemicals get absorbed into the lens and irritate the eye. Conjunctivitis occurs in reaction to these chemicals sequestered by the lens.
  • Problems in the cornea: The cornea, along with the sclera, form the outermost layer of the eyeball. The contact lens is placed on the tear film present on this layer of the eye. Corneal inflammation is referred to as keratitis.
    • Superficial punctate keratitis: The most common problem occurring with contact lens wear is corneal inflammation due to superficial punctate keratitis. As a result of reduced blinking, dry eyes develop, which is aggravated further by dust, dirt, smoke, or certain medications resulting in an irritated, sore and red eye.
    • Corneal injury: Scrapes and scratches to the cornea can occur with the use of a damaged contact lens, while inserting or removing the lens or due to grit trapped underneath the lens.
    • Contact lens induced red eyed or infiltrative keratitis: A deeper inflammation (as compared to superficial punctate keratitis) can occur with prolonged use of extended wear contact lenses, resulting in an extremely sore and very red eye. Management warrants discontinuation of extended contact lens wear, giving a rest to the eyes and, later, substitution with shorter duration lenses.
  • Corneal infections: Microbial keratitis is a severe complication of leaving in soft contact lenses for longer than recommended. The eyes are painful and red with a sensation of something being in them, giving way to more serious complications like vision loss. While bacterial infections are more common, infection by acanthamoeba can be much more damaging.
    • Bacterial keratitis: While bacteria do not readily invade the cornea, wearing improperly cleaned contact lenses can easily introduce it into the eye, prompting infection.
    • Viral keratitis: Cold sore causing virus (herpes simplex) and shingles causing pox virus (varicella zoster) are commonly implicated. Ulcers can form in the cornea.
    • Acanthamoeba keratitis: A rare but dangerous complication of contact lens wear, it results in a long lasting extremely painful infection of the cornea (pain is disproportionate to the appearance of the eye), with reduced vision and corneal ulceration. Some cases recover completely but others may need surgery with corneal graft replacement.

Certain factors warrant due consideration before initiating contact lens wear or make it impossible altogether. Contraindications include:

  • Unwillingness or inability to handle and/or care for contact lenses
  • Acute or active inflammation anywhere in the eyes: Uveitis, keratitis, conjunctivitis, etc. 
  • Chronic inflammation of the eye
  • Bacterial infection anywhere in the eye
  • Preexisting eye disease prompts evaluation
  • Monocularity: Possessing only one functioning eye
  • Abnormal eyelid function
  • Severe dry eye: Due to facial paralysis (as with bell’s palsy) or systemic diseases like Sjögren’s syndrome
  • Corneal neovascularization: Cornea does not normally have any blood vessels in it (avascular) but certain diseases can cause blood vessels to emerge which deprive the cornea of oxygen
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