Contact Lenses
A contact lens is a thin, curved, transparent or tinted optical device that is placed directly on the cornea of the eye to correct refractive errors, provide therapeutic benefits, or for cosmetic purposes.
Types of Contact Lenses
1. Based on Material
Soft Contact Lenses (Hydrophilic lenses)
- Made of hydrogel or silicone hydrogel
- Highly comfortable, allows oxygen to pass
- Used for daily wear, extended wear, or disposable use
Rigid Gas Permeable (RGP) Lenses
- Made of fluorosilicone acrylate
- Allows oxygen permeability, provides sharp vision
- Used for high astigmatism, keratoconus, and post-surgical cases
Hybrid Lenses
- Rigid center with soft skirt
- Combines benefits of soft and RGP lenses
Scleral Lenses
- Large-diameter lenses that cover the sclera
- Used for irregular corneas, severe dry eyes, and keratoconus
PMMA (Polymethyl Methacrylate) Lenses
- Hard lenses, rarely used now
- Does not allow oxygen permeability
2. Based on Wear Schedule
- Daily Disposable Lenses – Worn for one day and discarded
- Biweekly/Monthly Lenses – Worn for a specific period and cleaned daily
- Extended Wear Lenses – Can be worn continuously for several days
- Conventional (Annual) Lenses – Lasts for a year with proper maintenance
Uses of Contact Lenses
Refractive Error Correction
- Myopia (Near-sightedness)
- Hyperopia (Far-sightedness)
- Astigmatism (Irregular corneal shape)
- Presbyopia (Age-related near vision loss)
Therapeutic Uses
- Bandage Lenses – Protects cornea in cases of corneal ulcers, abrasions, post-surgical healing
- Drug-Delivery Lenses – Can deliver medications
Cosmetic Uses
- Colored lenses for eye color change
- Prosthetic lenses for damaged or missing iris
Orthokeratology (Ortho-K)
- Special rigid lenses worn overnight to reshape the cornea temporarily for myopia control
Materials Used in Contact Lenses
- Soft Lenses → Hydrogel, Silicone Hydrogel
- Rigid Lenses → Fluorosilicone Acrylate
- Scleral Lenses → Highly oxygen-permeable materials
Standards for Contact Lenses
- Oxygen Permeability (Dk Value) – Higher Dk allows better oxygen flow
- Base Curve (BC) – Determines lens fit on cornea
- Diameter (DIA) – Affects coverage and movement
- Power (Diopters, D) – Corrects refractive error
- Water Content – Affects comfort and oxygen transmission
- FDA Classification – Based on material and wear schedule
Packaging and Storage Solution
- Contact lenses are packaged in sterile saline or multipurpose solution inside a blister pack
- RGP and scleral lenses may come in a storage case with conditioning solution
Application (How to Insert Contact Lenses?)
- Wash Hands – Use soap and dry hands with lint-free tissue
- Inspect Lens – Ensure it is clean and not inside out
- Hold Upper and Lower Lids – Prevent blinking
- Place Lens on Cornea – Use index finger
- Blink Gently – Lens should settle naturally
Removal of Contact Lenses
- Wash Hands – Maintain hygiene
- Soft Lenses – Pinch gently and remove
- RGP Lenses – Blink technique or lens removal plunger
- Scleral Lenses – Use suction device if needed
Hygiene and Maintenance
- Cleaning Solutions: Multipurpose solution, hydrogen peroxide-based cleaner
- Avoid Tap Water: Can cause infections (e.g., Acanthamoeba keratitis)
- Lens Case Cleaning: Rinse and air-dry daily, replace every 3 months
- No Sleeping with Lenses (unless approved by eye doctor)
Indications for Contact Lens Use
- Refractive errors (Myopia, Hyperopia, Astigmatism, Presbyopia)
- Keratoconus
- Post-corneal surgery (LASIK, PKP)
- Aphakia (absence of the natural lens)
- Severe dry eyes (Scleral lenses)
- Cosmetic enhancement
Contraindications for Contact Lenses
- Active eye infections (e.g., Conjunctivitis, Keratitis)
- Severe dry eyes (unless using scleral lenses)
- Poor hygiene compliance
- Uncontrolled diabetes (higher infection risk)
- Allergy to lens materials or solutions
- Occupational hazards (e.g., dusty environments)
Complications of Contact Lens Wear
- Infections (Bacterial, Fungal, Acanthamoeba Keratitis)
- Hypoxia (Low oxygen supply to cornea)
- Corneal Neovascularization
- Giant Papillary Conjunctivitis (GPC)
- Dry Eye Symptoms
- Contact Lens-Induced Acute Red Eye (CLARE)
Special Topics
1. Contact Lens-Induced Corneal Hypoxia
- Due to insufficient oxygen permeability, leading to corneal swelling
- Prevented by using high-Dk lenses
2. Myopia Control with Contact Lenses
- Ortho-K lenses reshape cornea overnight
- Multifocal contact lenses slow myopia progression
3. Pediatric Contact Lenses
- Used in congenital cataracts, anisometropia, high myopia
4. Contact Lenses and Digital Eye Strain
- Blue-light blocking lenses available for digital screen users
Conclusion
Contact lenses are an essential part of optometry and ophthalmology, offering a versatile solution for vision correction, therapeutic use, and cosmetic enhancement. Proper hygiene, compliance, and understanding contraindications are crucial for safe and effective use.
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Optometry