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