Soft contact lenses

Question 1

What are the ideal scl material/properties?

Answer 1

1. High Dk/t (oxygen permeability) – however does not matter too much with SiH lenses.
2. SiH – 5x more breathable than hydrogel.
3. Low modulus (soft) – with higher modulus, comfort may be reduced however these lenses are easier
   to handle and to tell if they are everted.
4. UV protection

Question 2

Name some properties of Hydrogel ?

Answer 2

-Comfortable + contain water- so transports oxygen
-Has lower oxygen transmissibility and poor wetting.
- becomes dehydrated with increased WT- so tightens on eye- worse for minus rx than plus

Question 3

Name some properties of SIhy?

Answer 3

-let 5x more oxygen reach the cornea than regular hydrogel
lenses.
–> Better for ew
-Higher modulus so good for handling as it keeps its shape which is good for new
wearers. (However, it can cause some rubbing underneath the eyelid so there is an upgraded
version which is the silicone+ hydrogel lenses.)

Question 4

explain how water content effects lenses ?

Answer 4

The higher the water content, the higher the Dk/t so there is more oxygen transmissibility to
the cornea.
-With hydrogel, the WC is how much o2 they will recieve.
Vs
- SiHy lenses depends on the amount of silicone used, not the water content. Bc O2 cna get through the silicone parts of lens not just water
o However, high water content leads to lens instability, more deposits and low refractive index.
o This is solved by SiH.(bc lower water content but higher 02 permeability)

Question 5

Water content and dry eye?

Answer 5

High w.c = lens initially feels comfortable
lens is designed to hold water- but will naturally evap during day / acts like sponge and reabsorb more fluid in the tears.

Question 6

What are water gradient lenses? + give example

Answer 6

gradient= lower w.content at core of lens than at the surface.
-allows more o2 to flow through lens
-More comfortable due to minimal friction: as 100% water on front + back surface of lens
Example is : Dailies Total 1 lenses. (spec brand aswell) - w.c transitions from 33% to 88% on surface

Question 7

What is the effect of modulus?

Answer 7

*resistance to deformation
– High modulus (stiffer lens): discomfort from edge interaction with lid. Results in contact
lens associated papillary conjunctivitis (CLAPC).
- Low modulus (softer lens): more forgiving to fit as the squeeze pressure is lower and
tends to move better.

Question 8

Name 2 DD lenses, 2-Weekly, 2 Monthly lenses (brand name too)

Answer 8

daily sph:
-Easyvision Vitrea (Dailies Aqua Comfort Plus)
*hyrdogel
-Dailies Total 1 *Sihy
Monthly:
-E.vision Uvicia plus
(Avaira vitality)
E.V opteyes (Biofinity)

2-weekly
-Acuvue oasis