Soft CL Fitting

Question 1

What are the 5 steps in selecting a 1st lens?

Answer 1

1. Decision on modality of wear from H&S & SL examination -> what’s safe for px and what px wants the CLs for
2. Oxygen & water content considerations -> based on what px told you & what see on SL
3. Decision on material -> hydrogel? SiHy? Or not SCL all together
4. 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
5. 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

Question 2

What are the decisions on modality of wear from H&S?

Answer 2

1. Lenses for occasional football, max 3 hrs wear, 2x week
   o Daily disposable  if available in their Rx
2. Lenses for full time wear at work, 9hrs day, 6days/week
   o Monthly replacement  ocular health permitting
3. 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
4. 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
5. Lenses for FT wear, 16-17 hrs/day, 6 days/week
   o Fortnightly or monthly replacement  think about oxygen  requires more oxygen to eye

Question 3

What are the decisions on modlity from H&S and SL examination?

Answer 3

• 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

Question 4

What are the oxygen and water content considerations for soft CLs?

Answer 4

• 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

Question 5

What are the decision on material for soft CLs?

Answer 5

• 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

Question 6

How to calculate Back Optic Zone Radius?

Answer 6

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

Question 7

How do you calculate total diameter?

Answer 7

• 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

Question 8

What is the important thing to remember when fitting people with CLs?

Answer 8

• 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

Question 9

How do you adjust an Rx for BVD?

Answer 9

• 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

Question 10

When should you use toric lenses rather than spherical lenses?

Answer 10

• 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

Question 11

What is lens specification?

Answer 11

• 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

Question 12

How does BVD change plus lenses?

Answer 12

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

Question 13

How does BVD change minus lenses?

Answer 13

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

Question 14

Describe coloured soft lenses?

Answer 14

• 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)

Question 15

Describe theatrical soft lenses?

Answer 15

• 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

Question 16

Describe specialist companies’ range of CLs - Mark Enoovy, Menicon, Cantor & NIssel?

Answer 16

• Mark Ennovy:
  o Daily, monthly and 3-monthly replacement lenses
  o Tinted lenses
  o Extended Rx ranges (± 30 dioptres and up to 8 dioptres of astigmatism)
  o TD of 11.50-16mm and base curve of 6.50-9.80mm available with different lenses
  o Myopia management lenses
• David Thomas (Menicon):
  o Daily, monthly and longer-term replacement lenses
  o Soft lenses for keratoconus
  o Extended range available such as +45.00 to -30.00 sphere and up to 10 diopters of cyl
  o TD from 12 – 20mm
• Cantor & Nissel:
  o Wide selection of soft and rigid lenses
  o Extended Rx ranges (± 30 dioptres and up to 6 dioptres of astigmatism)
  o Base curves of 6.60 to 10.40mm and TD of 11 to 20mm
  o Lenses for keratoconus
  o Wide range of prosthetic (e.g. px has uneven pupil sizes etc) and theatrical lenses

Question 17

Describe the reasons as to why a CL needs to fit well?

Answer 17

• Comfort:
  o Px satisfaction
• Constant corneal coverage:
  o Helps w/ comfort
  o Helps avoid peripheral corneal staining – due to exposure
• Good centration:
  o Gives good corneal coverage
  o Gives stable peripheral vision
• Movement on blink or version:
  o Adequate post-lens lubrication with each blink
  o Exchange of metabolic waste – from lens moving & tears circulating
  o Avoidance of conjunctival staining
• Optimum tightness on push-up:
  o Avoidance of discomfort through excessive movement or excessive mechanical squeeze force
  o Avoidance of adherence with dehydration
  o Avoidance of conj indentation
• Good peripheral fit (i.e. alignment):
  o Avoidance of conj indentation from tight lens
  o Avoidance of edge stand-off if lens too flat
  o Comfort
• Good & stable vision:
  o Px satisfaction

Question 18

What are the minimum requirements for soft lens fitting?

Answer 18

The minimum requirements of an acceptable-fitting soft lens are as follows:
* full corneal coverage at all times
* some movement on blink and / or version
* absence of excessive movement
* no conjunctival indentation or edge stand-off – need somewhere in between

Question 19

Describe over-refraction of soft CLs?

Answer 19

• Normal subjective refraction but should be quick as have fitted a lens based on correct spec Rx
• For spherical lenses carry out BVS & if VA is adequate then stop there – try +0.25DS & -0.25DS (only give minus if improves VA)
  o Think about VA w/ specs & what lenses are required for
• If VA is reduced, then assess cyl as well  px may need toric lens
• If VA is fluctuating, then fit of lens may be the issue – look at it again on SL – blink having large impact on VA

Question 20

Give common examples of soft daily disposable spherical CLs?

Answer 20

Coopervison MyDay (SiHy)
Coopervision Clariti 1 Day (SiHy)
J&J Acuvue Oasys 1-day (SiHy)
J&J 1 Day Acuvue Moist (Hydrogel)
Bausch & Lomb BioTrue Oneday (Hydrogel)
Alcon Dailies Total 1 & Precision 1 (Water Gradient lens)

Question 21

Give common examples of soft monthly replacement spherical CLs?

Answer 21

Coopervision Biofinity XR (SiHy, licenced for sleeping)
Coopervision Proclear (Hydrogel)
J&J Acuvue Vita (SiHy)
Bausch & Lomb Purevision 2 (SiHy, licensed for sleeping)
Alcon Air Optix Night & Day Aqua (SiHy, licensed for sleeping)
Alcon Total 30 (water gradient lens)

Question 22

Give common examples of soft weekly/fortnightly replacement spherical CLs?

Answer 22

J&J Acuvue Oasys (SiHy, fortnighlty replacement lens when worn for daily wear & a weekly replacement lens when worn as an EW lens (6 nights of wear)
Menicon Premi0 (SiHy)