Topic 1 CL TYPES AND APPLICATIONS

Question 1

1) narrate simple history of CL

Answer 1

1st cl was created to improve vision of keratoconous px and afocal scleral lens on rabbit in 1888. Lens was made using glass

1948 PMMA corneal lens (not o2 permeable)

1970 RGP (o2 permeable)
soft hydrogel by bausch and lomb 

1990 disposable SCL

Question 2

2) list with examples, the 4 main applications of CL

Answer 2

1. vision
   - spherical, toric and multifocal
2. therapeutic
   - keratoconus, drug delivery (soft cl), bandage (soft CL), myopia control (ortho k)
3. cosmetic or prosthetic
   limbal ring and iris colour changing, prosthetic for corneal scar

4.enhancement performance
enhance colour perception (chroma gen), reduce photophobia, block UV and can be made photochromic

Question 3

3) understand the FDA groupings for SCL materials

Answer 3

group 1: non-ionic polymer, low water
group 2: non-ionic polymer, high water

group 3: ionic polymer low water
group 4: ionic polymer high water

*all of the above are hydrogel!
*low water = 50%
high water >50%

group 5: Silicone hydrogel (SiHy)

Question 4

4) compare and contrast 4 aspects of Hydrogel and Silicone hydrogel

Answer 4

1. Dk: hydrogel lower Dk than SiHy
2. water content: hydrogel 30-78%, SiHy 33-56 %

3. modulus: hydrogel lower (harder to handle, more comfy) 
SiHy higher (easier to handle, less comfy)

4.wettability: hydrogel more wettable, more hydrophilic, attract more protein
SiHy less wettable, attract more lipid

Question 5

what are the 4 types of contact lens?

Answer 5

1. Conventional (non-disposable) SCL. Patient typically replace the lens every 6 months to a year.

Disposable lenses. Sold in pack of 6 pieces (monthly disposable) or 30 pieces (daily disposable). Only Johnson & Johnson produces biweekly disposable SCL.

Gas Permeable Corneal Lens. (widely known as RGP until recently) It is typically smaller than the cornea ~ 9-10 mm

Scleral lens. It is biggest of all CLs ~ 15-16 mm. Can be prescribed when SCL and rigid corneal lens could not correct the vision adequately. It is also made of rigid gas permeable materials.