Eye Care I - Contact Lenses Lecture Notes

A comprehensive set of practice questions and answers covering contact lens types, materials, benefits, contraindications, and maintenance procedures based on the lecture notes.

What are three primary reasons individuals choose to wear contact lenses over eyeglasses?

Cosmetic reasons, eyeglasses not providing satisfactory vision, and eyeglasses being a hindrance during sports or other activities.

What are the specific benefits of contact lenses regarding peripheral vision and temperature changes?

They provide greater clarity in peripheral vision with no obstruction from frames and do not fog up due to sudden temperature changes.

Which medical conditions are contraindications for contact lens usage?

Chronic conjunctivitis, blepharitis, recurrent infections, poor blink rate, insufficient tear production, diabetes (for extended-wear), chronic colds, pregnancy, and the use of oral contraceptives.

What are the broad classifications of contact lenses based on chemical make-up and physical properties?

Rigid gas-permeable (RGP) Lenses and Soft Lenses (Hard lenses are no longer used).

How do RGP and Soft Lenses differ in terms of water absorption?

RGP lenses absorb less than $10\%$ water, while Soft Lenses absorb more than $10\%$ water.

Why is oxygen permeability important in contact lenses, and what can hypoxia cause?

It allows the eye to breathe; hypoxia can cause red eyes, blurred vision, eye discomfort, and may increase the risk of eye infections.

Compare the size and coverage of RGP and Soft Lenses.

RGP lenses are smaller in size, whereas Soft Lenses are larger, covering the whole iris and part of the cornea.

What is the difference between Hydrogel and Silicone hydrogel materials in soft lenses?

Hydrogel has lower oxygen permeability, while Silicone hydrogel (e.g., Acuvue Oasys) has higher oxygen permeability comparable to RGP lenses.

What are the advantages of Soft Contact Lenses over rigid lenses?

They are easier to remove, more comfortable, unlikely to cause photophobia or spectacle blur, and less likely to trap foreign particles or become dislodged.

What are the disadvantages of Soft Contact Lenses?

Not all wearers achieve excellent visual acuity, they can tear easily, have shorter average life ($12-18$ months), and can adsorb chemical compounds from eye products.

Why is it important to routinely clean contact lenses to remove tear residue (protein and oils)?

Residues can harden into tenacious deposits that irritate the eyelids and corneal epithelium, act as a growth medium for bacteria, and cause infection or decreased visual acuity.

What is the function of non-ionic or amphoteric surfactants in cleaning solutions?

They emulsify oils and aid in solubilizing other debris.

Why should a dehydrated lens not be placed directly into the eye?

It causes discomfort, and if lenses are allowed to dry out during storage, accumulated deposits become more difficult to remove.

What is the purpose of enzymatic cleaners, and how do they work?

They are used weekly to remove protein deposits by hydrolyzing polypeptide bonds.

What are Multipurpose solutions (MPS), and what are their components?

An all-in-one system for cleaning, rinsing, disinfecting, and storing; they contain surfactants, disinfectants (e.g., biguanide, polyquad), and lubricants.

Can saline solutions be used for soft contact lens disinfection?

No, saline is never to be used for disinfection; it is only for rinsing, storage, or thermal disinfection.

What is the distinction between cleaning and disinfection of contact lenses?

Cleaning is the removal of deposits and debris from the surface; disinfection is the inactivating/killing of microorganisms.

How is hydrogen peroxide neutralized in peroxide disinfection systems?

It must be neutralized into oxygen and water using a catalase tablet or a catalytic disc.

What should a patient do if they mistakenly insert a lens directly from a peroxide solution without neutralization?

Immediately remove the lens, flush the eye with sterile saline solution, and consult a doctor if pain persists.

What are the five functions of conditioning solutions for RGP lenses?

1. Enhances wettability; 2. Aids formation of a cushioning tear layer; 3. Increases comfort; 4. Disinfects the lens; 5. Stabilizes the lens on the fingertip for easier insertion.

What is the recommended replacement schedule for contact lens storage cases?

They should be cleaned thoroughly on a routine basis and replaced at least every $3$ months.

What are three important 'Do Not' counseling tips for contact lens users?

Do not wash/rinse lenses with water or saliva, do not swim with lenses, and do not sleep with lenses (unless specified).