Chapter 14: Principles and Problems of Contact Lenses Flashcards
Basic Principles
1) Determine refractive error (Refraction)
2) Determine flat and steep corneal meridians, and axis
3) Choice of lens type based on medical and ocular history, and specific needs of the patient
Characteristics of Contact Lenses
Prescription information:
1) Spherical equivalent, cylinder and axis
2) Diameter of lens
3) Base curve
4) Lens thickness
5) Material, polymer, or brand name
6) Edge blends or peripheral curves
7) Lens tint or lens color
8) Wearing instruction
9) Care regimen
10) Schedule of follow up
Advantages: they do not distort peripheral vision, do not fog, better for certain kinds o refractive errors (high power, keratoconus, nystagmus, irregular astigmatism)
Disadvantages: high maintenance, increased risk of infection, not recommended for certain environments (dust), higher cost, easier to lose
Soft Lenses
Flexible contact lenses that permit oxygen and carbon dioxide diffusion through the lens material itself, with minimal tear buildup
Most commonly used lens type today
Advantages: More comfortable, rarely cause spectacle blur, less risk of overwear, less expensive
Disadvantages: variable vision due to dehydration of the lens, less durable
Rigid-Gas Permeable Lenses
Contact lenses that permit oxygen and carbon dioxide diffusion through both the lens material and the tear pump
Advantages: More comfortable than PMMA, better suited for problems like keratoconus and irregular astigmatism
Disadvantages: more fragile and prone to protein deposit buildup, more expensive
Spectacle Blur
Temporary blurred vision upon switching from contacts to eyeglasses
Polymethyl Methacrylate Lenses
Contact lenses that provide oxygen by means of a tear pump only, there is no diffusion through the lens materials
Oxygen-Permeable
The ability of a contact lens to transmit oxygen through it material
Extended-Wear Contact Lenses
Soft contact lenses that are approved for overnight wear for up to 7 days
Associated with adverse corneal effects and corneal ulcers
Daily-Wear Contact Lenses
Rigid and soft contact lenses intended to be worn for fewer than 24 hours consecutively while awake
Associated with oxygen depravation to the cornea if not used as directed
Disposable Contact Lenses
Soft contact lenses designed for both daily and extended wear, and then to be discarded after 1-4 weeks
Planned-Replacement Contact Lenses
Contact lenses that are designed to be replaced on a regular schedule determined by the ophthalmologist according to patient wearing characteristics and other factors (typically between 1,2,3,or 6 months)
Toric Contact Lenses
A contact lens that is specified to correct astigmatism
Bifocal Contact Lenses
A contact lens that is multifocal, consisting of a portion that corrects for distance and another portion that corrects for near vision
Monovision
An artificially produced system creating visual clarity for near in one eye, and for distance in the other eye. This can be done with either contact lenses or surgically (LASIK or cataract surgery)
There is decreased stereopsis with monovision
Keratoconus
A rare degenerative corneal disease in which the center of the cornea thins and assumes the shape of a cone, seriously affecting vision
Will typically have RPG contact lenses prescribed
Corneal Bullous Edema
Swelling of the corneal tissue severe enough to cause blisters on the surface of the cornea and decreased vision
Care of Contact Lenses
1) Cleaning and disinfecting the contacts in order to prevent infection and remove deposits
2) Lubricating the lenses
3) Using the lenses as instructed by the physician
4) Cleaning and Disinfecting
5) Lubrication
Enzyme Cleaners
A specially designed detergent removing protein deposits from contact lenses
Proteolytic Enzymes
Enzyme cleaners that are capable of dissolving proteins
Triphasic Enzymes
A specialized cleaning agent that dissolved adhered substances on contact lenses
Surfactant Cleaners
A specialized contact lens cleaning solution and wetting agent
Insertion of Contacts
1) Wash hands
2) Remove lens from case
3) Rinse lens with saline
4) Place lens on tip of index finger
5) Pull down lower eyelid, look up, and place lens on lower portion of globe
6) Close your eyes and massage eyelid to center the lens
Removal of Contacts
1) Wash hands
2) Look up, pull down lower eyelid and place index finger on lower edge of lens
3) Move lens down the globe
4) Compress lens between finger tips
5) Remove lens
6) Clean lens and place in storage case
Problems with Contact Lenses
1) Allergies to lens solutions
2) Solution-Contact lens interaction
3) Overwearing syndrome
4) Improper contact lens fitting
5) Giant Papillary Conjunctivitis
6) Irritation and Tearing
7) Corneal edema, vascularization, infiltrates, corneal ulcer, infections, abrasions
8) Inability to remove lenses
9) Losing lens in eye
