Week 5 - SCL fitting 1

Question 1

What are the 5 steps of selecting the first contact lens?

Answer 1

1. Decision on modality of wear from H&S and slit lamp examination
   2.Oxygen and water content considerations
   3.Decision on material
   4.Choose a lens as a starting point
   • BOZR/TD
   • Also have to consider range of Rx available
   • And cost
   5.Refer to manufacturer’s guidelines for fitting guidance

Question 2

What are the decisions of modality of wear for football, full time at work and overnight shift? (doctor)

Answer 2

1. Lenses for occasional football, max of 3 hours wear, twice a week
   - daily disposable
2. Lenses for full time wear at work, 9 hours a day, 6 days a week
   - monthly replacement
3. Lenses for overnight shift work (doctor), up to 16 hours wear
   - extended wear

Question 3

What decision on modailty would signs of hypoxia pose?

Answer 3

• Consider if extended wear is appropriate
- Think about a lens that will supply the cornea with more oxygen, look at the dk values (oxygen permeability) in the ACLM or dk/t (oxygen transmissibility) on the manufacturer’s website

Question 4

What decision on modailty would signs of previous pathology pose?

Answer 4

• E.g Scar from ulcer
- Consider if contact lens wear is appropriate
- Think about daily disposable lenses to simplify care regime if
Px was previously on replacement lenses

Question 5

Why are Water content and Oxygen considerations important for contact lenses?

Answer 5

• Water content
If the patient reports current/old lenses are drying up then think about water content - higher water content draws out more water the tear film
• Oxygen
The longer the wear time, the higher the oxygen transmissibility will ideally be
- i.e. higher for extended wear than daily wear.
- It is a balancing act depending on the Px requirements. This is not quite so true for silicone hydrogel which all have high dk/T.

Question 6

What will help you decide on which material is best?

Answer 6

• Modality, water content and oxygen requirements
• Options are HYDROGEL and SILICONE HYDROGEL
• What is available for your patient?
• Cost, does your patient have a budget? (Never compromise ocular health for cost)

Question 7

What is the BOZR? (Back optic zone radius) and how is it fitted?

Answer 7

• 1 (because it will fit most patients) or 2 base curves
• Fit slightly flatter than the flat K as you want some lens movement
• Standard soft lenses on the market are designed to fit most patients (8.3-9.0mm).
• Specialist companies offer a range from 6-12mm

Question 8

How is BOZR calculated?

Answer 8

• Flat K x 1.1
• Flat K plus approximately 0.7
Example: K’s of 7.7 and 7.8mm
So flat K x 1.1 = 7.8 x 1.1 = 8.6mm
Or Flat K + 0.7 = 7.8 + 0.7 = 8.5 mm

Question 9

What is TD (Total diameter)?

Answer 9

• Set by the manufacturer for all standard lenses between 13.8 and 14.5mm
• Aim for about 1mm extra all around the cornea (total of 2mm greater than HVID) so the standard lenses will work for a normal corneal diameter of 11-12mm
• Specialist lenses range from 10-17mm for different sized corneas

Question 10

What are 5 types of manufacturers?

Answer 10

• Coopervision
• J&J
• Alcon
• Bausch & Lomb
• Menicon

Question 11

Whats the Dailies total 1?

Answer 11

• New technology
• Bit different from standard materials
• Not a silicone hydrogel but still combines low water with high oxygen
• “Water gradient” design

Question 12

What are acuvue Oasys with transitions?

Answer 12

• Balances both indoors and outdoor light, filters blue light and blocks harmful UV
• Offers superior optical precision with exceptional colour contrast enhancement
• Helps Px vision recover from bright light 5s faster

Question 13

Why do we need to adjust Rx for BVD?

Answer 13

• Obviously a CL is closer to the eye than glasses.
• We need to adiust for this as the Rx increases and treat each meridian separately if there is a cyl.
K= F/(1-dF), where F = spec Rx in Dioptres, & d = BVD, in metres.

Question 14

When do we use a toric lens?

Answer 14

• If the cyl is <1.00D then you can try a spherical equivalent i.e. sphere plus half the cyl
- For example: -2.00/-1.00 × 90 = -2.50
• Remember what the patient is wanting the lens for at this point, if it is for occasional use when playing football then this may work well. If it is for all day use in the office then perhaps not.

Question 15

How do we record the lens specification?

Answer 15

• Once we have chosen a lens we need to record the lens specification. This takes the following form: BOZR / TD / RX
- Lens name
E.g. 8.4/14.0/-3.00
Acuvue Oasys

Question 16

Before inserting a contact lens, what must be done?

Answer 16

• Hands must be washed and dried, nails must be short
• Remove contact lens from sterile packaging with index or middle finger (check packaging for damage)
• Check it is the correct way round
• Look for any obvious damage to the lens