Soft CL Fitting Flashcards
What are the 5 steps in selecting a 1st lens?
- Decision on modality of wear from H&S & SL examination -> what’s safe for px and what px wants the CLs for
- Oxygen & water content considerations -> based on what px told you & what see on SL
- Decision on material -> hydrogel? SiHy? Or not SCL all together
- Choose a lens as a starting point -> doesn’t mean one & only lens that can try (unless it is due to Rx issues etc) -> may be other options
a. Back Optic Zone Radius (BOZR – curvature of lens) / Total Diameter (TD)
b. Consider range of Rx available
c. Cost good fitting in correct Rx that’s safe for px is more important - Refer to manufacturer’s guidelines for fitting guidance
a. E.g. how much movement they anticipate with their lens
b. Which base curve to pick based on K readings
NEED PX TO BE SPECIFIC ABOUT HOURS THEY WANT TO WEAR LENSES FOR
What are the decisions on modality of wear from H&S?
- Lenses for occasional football, max 3 hrs wear, 2x week
o Daily disposable if available in their Rx - Lenses for full time wear at work, 9hrs day, 6days/week
o Monthly replacement ocular health permitting - Lenses for overnight shift work (doctor/paramedic/nurse/oil-rig worker (hygiene can’t always be guaranteed)), up to 16hrs wear (may be sleeping at points during wear)
o Extended wear - Lenses for FT wear at work, 9hrs/day, 6days/week, admits previous non-compliance w/ solutions
o Daily disposable if understand compliance of daily no sleeping w/ them in, not wearing them more than once shorter 1st recall to check - Lenses for FT wear, 16-17 hrs/day, 6 days/week
o Fortnightly or monthly replacement think about oxygen requires more oxygen to eye
What are the decisions on modlity from H&S and SL examination?
- Signs of hypoxia on SL -> neovascularisation, oedema, swelling
- Consider if EW is appropriate
o Think about lens that will supply cornea with more O2, look at Dk values in ACLM or Dk/t (O2 transmissibility) on manufacturer’s website - Signs of previous pathology previous scarring e.g. scar from ulcer – indicates corneal insult in past
o Consider if CL wear is appropriate
o Think about daily disposable lenses to simplify care regime if Px prev on replacement lenses not everyone with small scar is a no – just hint to be more cautious
What are the oxygen and water content considerations for soft CLs?
- O2:
o Longer wear time, higher O2 transmissibility will ideally be i.e. higher for EW than daily wear
o Balancing act depending on Px requirements
o SiHy all have high Dk/t - Water:
o If px reports current/old lenses drying up think about water content
o Higher water content draws out more water from tear film – SiHy have good O2 with lower water content
What are the decision on material for soft CLs?
- Now know modality, water content & O2 requirements
- Main options: HYDROGEL and SILICONE HYDROGEL
- Think about Rx range – what is available for Px?
- Think about cost – does Px have budget? NEVER compromise ocular health for cost
How to calculate Back Optic Zone Radius?
To calculate:
BOZR = Flat K x 1.1
OR BOZR = Flat K + 0.7 (ONLY if px has normal K values & they are not particularly extreme)
e.g K’s of 7.7 and 7.8mm:
BOZR = flat K x 1.1 = 7.8 x 1.1 = 8.6mm
BOZR = flat K + 0.7 = 7.8 + 0.7 = 8.5mm
* Why K’s are measured – to find best BOZR for px
* Decides which curve is wanted
* Most lenses come in 1 (as will fit most pxs) or 2 base curves
* Fit slight flatter than flat K as want some lens movement - & need tears to be exchanged under lenses
* “Process of trial and error” – Nathan Efron
* Standard soft lenses on market are designed to fit most Px’s (8.3 – 9.0mm (base curve of lenses not K’s))
* Specialist companies offer range from 6-12mm – speak to CL company about ordering specialist lenses & check their specific guidelines
How do you calculate total diameter?
- Set by manufacturer for all standard lenses
- Approx 13.8 – 14.5mm
- Aiming for overlap onto conjunctiva ~1mm extra all around the cornea (total of 2mm greater than HVID) so standard lenses will work for a normal corneal diameter of 11-12mm
- Specialist lenses range from 10-17mm for different sized corneas
What is the important thing to remember when fitting people with CLs?
- Not always only one lens for every px
- May be several lenses that will be suitable
- Make informed decision based on info you have and then assess fit
- Trial & error element to SCL fitting
- Often first lens px tries will not be final lens they are prescribed
How do you adjust an Rx for BVD?
- CL closer to eye than glasses
- Adjust this as Rx increases and treat each meridian separately if there is a cyl
- K = F/(1-dF)
o F = spec Rx (D), d = BVD (metres) - Look at number at end, when going from glasses to ocular Rx:
o Myopic Rx should reduce
o Hyperopic Rx should increase
When should you use toric lenses rather than spherical lenses?
- If cyl is <1.00D then can try spherical equivalent i.e. sphere plus half the cyl
- E.g -2.00/-1.00x90 = -2.50D
- Remember what px is wanting lens for:
o This may work well for occasional use when playing football
o May not work if CL is for all day use in office
What is lens specification?
- Once chosen lens, need to record lens specification
- BOZR/TD/Rx
Lens name - e.g 8.4/14.0/-3.00
Acuvue Oasys
o NB – just be careful as this specification would be for the 2-weekly not daily or transition
How does BVD change plus lenses?
For plus lenses:
-↑BVD -> effective power ↑
-↓BVD -> effective power ↓
-e.g. if put +8.00 onto eye for CL then it won’t be enough for px to be see
-Therefore, for CL fitting: more plus is needed than what spec Rx states
How does BVD change minus lenses?
For minus lenses:
-↑BVD -> effective power ↓
-↓BVD -> effective power ↑
-Minus lens is too powerful when placed on eye (make it more plus, closer to 0)
-Therefore, for CL fitting: less minus is needed than what spec Rx states
Describe coloured soft lenses?
- Commercially available for people wanting to change or enhance their eyes
- Not specifically designed for px for specific reason
- 2 daily options:
o Alcon FreshLook Illuminate Rx Plano to -8D
o Alcon FreshLook One-Day Rx Plano to -6D
Both have low Dk (26) – fine for social occasion but not for long-term/full-time wear
o No hyperopic Rx in dailies - 4 monthly options:
o Alcon Freshlook Colourblends/Colours/Dimensions
o Alcon Air Optix Colours SiHy Dk of 110 so better if px wants to wear them lots
o Coopervision Expressions Colours
o Bausch & Lomb SoftLens Natural Colours Dk 6 (full-time wear not recommended)
o These lenses come in range of prescriptions - +6.00 to -8.00 (not every lens) - Annual:
o Cantor & Nissel Cosmetic Lenses
Specialist lens company lots of Rx options (high cyls & high spheres)
Describe theatrical soft lenses?
- In UK it is illegal to sell lenses without fitting & ongoing care
- Clearcolour Phantom lenses – Dk of 10 & water content of 38% - available from Mid-Optic
o Only available in plano - Cantor & Nissel – wide range of Rx’s available specialist & custom lenses made for specific reason
