Introduction:
Contact lenses are one of the most regularly used medical devices. These are worn directly over the cornea. These are used to correct refractive errors and moderate-to-severe eye problems. Also, cosmetic contact lenses are becoming popular because of their aesthetic value. Several people using contact lenses are developing eye problems. Recent scientific studies have pointed out that regular contact lenses may cause pathologic changes in the human eyes, which can be very harmful.
What Are Contact Lenses?
Contact lenses are plastic-like devices that are fitted over the cornea. These lenses are classified into four types according to their use and rigidity, and they are:
A. Soft Contact Lenses: These are made up of soft, flexible plastic materials. These lenses help in the passage of oxygen. Silicone hydrogel is used to fabricate these lenses. Due to their flexibility, these lenses are very comfortable.
B. Rigid Gas Permeable (RGP) Contact Lenses: These lenses are durable, easy to use, and less prone to fracture. These lenses are also permeable.
C. Extended Wear Contact Lenses: These types of lenses can be used for a much longer duration of time. These are also made up of flexible materials.
D. Disposable (Replacement Schedule) Contact Lenses: These types of contact lenses are used for single-use purposes.
Different materials are used to fabricate contact lenses. These are:
1. Polymethyl Methacrylate (PMMA): Lenses made up of these materials are rigid and have no oxygen permeability.
2. Hydroxyethyl Methacrylate (HEMA) Hydrogel: These materials are biocompatible and expensive. Their oxygen permeability is less, and protein deposition on the lens surface is one of their main drawbacks.
3. Rigid Gas Permeable: These are silicon-containing materials. These materials are hydrophobic, durable, and have high oxygen permeability.
4. Silicone Hydrogel: Silicone hydrogel materials are durable and have high oxygen permeability. As silicon is a hydrophobic (repels water) material, hydrophilic (mixes with water) materials are added to it to make them hydrophilic.
5. Polyvinyl Alcohol (PVA): These materials are inexpensive and easy to fabricate. These have poor oxygen permeability.
What Is the Use?
Various contact lenses can be used for various purposes. These are:
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Soft contact lenses are used to correct myopia (a vision problem where near objects are visible but not far objects), hyperopia ( a vision problem where far objects are visible but near objects appear blurred), astigmatism (blurred vision), presbyopia ( gradual loss of ability to focus on nearby objects).
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Multifocal contact lenses have bifocal design. Here two types of lenses are used, one for distant vision and another for near vision.
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Tinted contact lenses are used to treat color blindness.
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Orthokeratology or ortho-k lenses are used to reshape the cornea to improve vision.
What Is the Cause of Complications?
Contact lens-related complications are characterized by persistent or episodic ocular discomfort related to using contact lenses. The risk factors are:
1) Contact Lens-Related Factors:
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Inappropriate material.
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Faulty design of the lens.
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Improper fit of the lens.
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Improper care system.
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Faulty use.
2) Environmental Factors:
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Ocular surface condition.
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External environmental factors like heat and humidity.
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Occupational factors.
What Are the Complications?
Several complications are associated with the use of these lenses. These are:
1) Hypoxia-Induced Changes: The avascular cornea gets oxygen and nutrients from the tear film. Excessive wear of polymethyl methacrylate and rigid contact lenses are responsible for such hypoxic changes because of the disruption of contact with the tear film. Corneal changes observed due to the hypoxic conditions are:
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Corneal epithelial thinning.
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Stromal edema.
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Ocular and limbal erythema.
2) Superior Epithelial Arcuate Lesion (SEAL): This lesion occurs in the superior cornea, within about 2 mm (millimeter) of the superior limbus (border between cornea and sclera), between the limbus and the contact lens rim. Improper lens fit and lens design are responsible for this. This is characterized by the following:
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White or opalescent epithelial lesion.
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Burning sensation in the eye and a scratchy feeling.
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Watery eyes.
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Eyelid retraction or drooping
3) Allergic and Toxic Reactions: Allergic reactions due to contact lens wear are serious complications. Several factors cause this. Irritation or allergic reaction caused by surfactants, lubricants, and buffer solution present on the lens solution. These chemicals cause solution-induced corneal staining (SICS), less commonly known as preservative-associated transient hyperfluorescence (PATH). An annular staining pattern in the peripheral corneal region characterizes this. Silicone hydrogel materials absorb the chemicals in the lens solution and release these materials into the ocular surface. Severe cases are manifested with features of:
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Corneal irritations.
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Conjunctival hyperemia (dilation of blood vessels of the eye).
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Limbal epithelial changes (breakdown of epithelium in the cornea, corneal scarring).
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Delayed hypersensitivity caused by these chemicals may cause limbal stem cell deficiency (breakdown of the epithelial cells on the limbus).
4) Contact Lens-Induced Papillary Conjunctivitis: Conjunctival inflammation is caused by silicone hydrogel lenses. The inflammation can be of two types; local and generalized. While local inflammation is asymptomatic, the generalized reaction is caused by an immunologic reaction caused by the denaturation of tear film coating on the lens surface. The hydrophobic nature of these lenses is responsible for depositing lipid substances on the lens surface. This is manifested by:
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Conjunctival erythema (dilatation of blood vessels).
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Pruritus (itching of the eyes).
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Mucoid discharge.
.5) Microbial Keratitis: This corneal infection is caused by bacteria and fungi. Hypoxic conditions and microtrauma induced by the lens lead to the accumulation of microorganisms. Gram-negative bacteria, such as Pseudomonas aeruginosa, Haemophilus influenzae, and gram-positive species, such as Streptococcus pneumoniae, are responsible for bacterial-induced keratitis. Contact lens-induced acute red eye response is a common condition associated with it. This is manifested by:
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Severe unilateral conjunctival injection.
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Pain and redness in the eye.
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Photophobia (a problem associated with exposure to light).
Contact lens-associated peripheral ulcer (CLPU) is associated with sterile circular epithelial lesions at the periphery, and anterior stromal infiltrates. A grayish-white infiltration characterizes fungal keratitis with feathery borders with satellite lesions.
How to Treat It?
The treatment includes:
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Use appropriate lenses to suit the requirements.
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To change lenses on a regular schedule.
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Use of lubrication along with lenses.
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Change lens solution on a regular interval.
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Use lenses with high oxygen permeability.
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Infectious conditions can be treated using topical antibiotics (Ciprofloxacin, Levofloxacin), and corticosteroids can also be applied. Topical application of Natamycin (5 percent), Amphotericin B (0.15 to 0.30 percent), topical Voriconazole (1 percent), and Miconazole (1 percent) is indicated in fungal infections.
Conclusion:
Contact lenses are one of the most regularly used ophthalmic devices. Several eye problems can be treated with contact lenses. Selection of proper lenses and maintaining lens hygiene are very important to reduce complications caused by contact lenses. Moreover, proper diagnosis is required to treat lens-related complications.
