Considering Px needs - fitting Contact lenses Flashcards
True or False - A contact lens specification must be given out to patients.
True
What must a contact lens soecification include?
- Name and address of individual
- If under 16 then name of person signing for child, and their address.
- name of practice where fitting took place
- sufficient details of lens so it may be ordered - not just the rebranded name
What may a px doing lots of outdoor activities make you consider in regards to their lenses?
UV block
What are advantages of hydrogels?
Better wetability thus less lens deposits - (where a lens drys out, deposits are formed).
Decreased risk of allergies (to the lens deposits).
Initially more comfortable because of their water content generally being higher on average.
What are the disadvantages of hydrogel lenses?
Less comfortable at the end of the day especially on px with dry eye
lower oxygen permeability thus less suitable for extended wear
Why do hydrogels tend to have higher water content than silicone hydrogels?
Because hydrogels can only absorb oxygen through water
whereas silicone hydrogels can also absorb oxygen through their silicone component.
Why may a px with dry eye intially like a high water content lenses but find them uncomfortable toward the end of the day?
At first they are quite thin and wet and feel nice on the cornea, however, they are designed to have a high water content at all times - naturally water from the lens will evaporate causing it to dehydrate- the lens material won’t like this and so will compensate by taking water from whatever is the nearest available sourcve which happens to be the tears - causing an even drier sensation for the wearer.
What is the disadvanatge of a low water content for hydrogel lenses?
Lower water content means higher modulus - so lens is a bit stiffer - as a result it may be more noticeable to the wearer making it less comfy.
Lower water content means less oxygentransmissibility but this might be okay for short wearing times.
Why is oxygen availability not something to fret over generally?
Generally speaking you require a dt/k of 37 to have 0% corneal swelling throughout the day.
Max dk/t of hydrogels is 40 and avg is 22-28. This isn’t alarming as relaistically our cornea can cope with small levels of corneal swelling - infact we experience on average 4% corneal swelling overnight.
When would we be concerned with Dk/t in hydrogel wearers?
Extended hours of use so like over ten hours a day just to err on the side of caution
Pxs with high rx as their lenses will be significantly thicker.
What are the limitations of the Dk/t values given in the ACLM book?
Generally quoted for a prescription of -3.00DS
ACLM quotes DK of the material - not the shape of the lens
If a px with dry eye really wanted silicone hydrogel lenses under what conditions would we allow it?
Roughly speaking:
Lesser wear times in one day - so like less than 10 hours.
If she finds Low water content lenses comfortable at the start of the day - because then lens is less likely to dry out the eyes by the end of the day
What is the water content of RGPs?
0%
What are the advanatages of silicone hydrogels?
High oxygen permeability
Suitable for pxs that are likely to/ or in the past have suffered with hypoxia related symptoms.
And so alows for extended wear within one day e.g. 12 or so hours.
What are the disadvantages of silicone hydrogels?
Collects more lens deposits than hydrogel lenses
Not suitable for siliocne intolerant people
