Soft CL Fitting (Spheres) Flashcards
What are the advantages of SCL?
- Comfort/ easy to adapt
- less lid adaptation than GP (large & hydrophilic) - Lower incidence of:
- overwear syndrome
- spectacle blur
- corneal staining
- flare
- foreign particles
- loss - reduced corneal sensitivity only a bit
- Economic & Disposable (limiting deposition)
- Can change iris colour with tints & opaques if people want
- Good for sport
What are the disadvantages of traditional soft lenses?
- Poorer subjective vision & more variable vision
- increased breakage and tearing (fragile lenses)
- Lens deteriorate with age (deposits & discolouration –> limited life span)
- Need to disinfect –> can become very expensive
- Inability to modify/ verify
- Contamination (with pharmaceuticals/ fluorescein) –> must be sterile!
- Complications (due to limited Dk/t & post-lens tear exchange)
- vascularisation
- papillae/ GPC
- conjunctival injection
- stromal and endothelial disturbances
- increase redness
What Hx taking do you need to take for CL visit?
Ask patients:
- Reason(s) for visit
- reason for wear/ motivation
- realistic expectations
- indications for CL wear - Demographics, GP, last eye test + previous lens wear
- was it successful or nah?
- what type?
- how long did you wear it for?
- what is the comfortable wearing time?
- modality
- care solutions that px uses + hygiene (how they clean it) - Personal ocular hx
- eg. previous infections, surgery, dry eyes etc - General health/ Medication that px is taking
- any allergies
- any diabetes, hyperthyroid, arthritis? - Fam ocular hx
- Social hx
- occupation
- hobbies
- environment
- driving
What are some baseline measurements?
- HVID (horizontal visible iris diameter)
- VPA (vertical palpebral aperture)
- Pupil size
- in maximum dim illum
- average room illum - Corneal topography - central keratometry
What does it mean if CL is moving too much and not moving?
Moving too much –> too loose –> need steeper curve
Not moving much –> too tight –> need flatter curve
What are the BOZR?
Usually between 0.6-1.0mm FLATTER than average Ks
- most brands only have 1 or 2 BOZRs
- BOZR = BC
What are TD?
Usually ~2mm more than HVID
(usually between 13.8 to 14.5mm)
- TD drop 0.1 to 0.8mm @ eye temperature
- small VPA can make larger TD harder to insert and remove
How to calculate BVP(CL)?
BVP (CL) = F (spec)/ 1-(VD in metres) x F(spec)
- if BVP spec is acceptable VA
Using the information given, calculate the BOZR rage, TD and which TD are acceptable, and BVP
Keratometry:
7.60@30 7.55@120
HVID:
11.5mm
SPec Rx:
-6.00D sphere BVD 12mm
Flattest K = 7.6 + (flatter) 0.6 to 1.0mm
–> BOZR: range between 8.2mm to 8.6mm
TD: 11.5mm (HVID) +2mm = TD ideally ~ 13.5mm
But, can accept: 13.80, 14.00, 14.20mm
BVP: -6.00D @ 12mm
-5.75D @ 0mm (corneal plane)
- Larger radius of curvature = the flatter
- Smaller radius of curvature = the steeper
- myopes wear steeper BC
- hyperopes wear flatter BC
What are the lens parameter choices?
HVID —- Description —– TD
<10.50 —- Small —– 13.80mm
10.50 to 12.00 —- Average —- 14.00 to 14.20mm
>12.00 —-Large —- 14.50mm
Average Ks —- Description —- SCL BOZR
<7.6mm (>44D) —- Steep —- 8.3
7.6 to 8.00 (44-42D) —- average —- 8.6
>8.0mm (<42D) —- flat —- 8.9
How do we assess SCL spherical lens fit?
Centration, Coverage & Movement!
Static and dynamic (open eye, blink, push up)
- primary gaze (x,y mm or draw/ describe centration)
- movement on blink (primary/ upgaze in mm)
- Lag on horizontal gaze (mm)
- Recovery from push-up (tightness) (speed or 0% = loose, 100% = tight)
What happens when you have optical decentration?
Reduces vision especially for more complex designs like - aspherics and MF
What do you ALWAYS have to remember for limbal area, too much movement, and too little movement?
Limbal area: cannot be compromised by the lens edge
Too much movement: decreases comfort
Too little movements: poor physiology
Are there bubbles in correct, steep, and flat fitted CL?
Correct: no bubbles
Steep: Under periphery
Flat: Buckling at the edge
Can you use Fl in CL?
Not used in normal hydrogel soft lenses
What do you need to make sure for Over-refraction?
- Max plus power while maintaining optimum VA, with normal refraction for each eye in turn
- check if BV is comfortable (can perform binocular balance if needed)
- Can check px’s visual stability by subjective px report & examine effects of blink on ret reflex or regularity of topography mires
** always start O/R with sphere first
What is the impact of CL fit on VA?
correct: good, consistent
steep: poor & variable, improves with a blink
flat: variable, worse after a blink
What are some fitting tips for BOZR and TD?
BOZR:
- Steeper (smaller) BOZRs –> will tighten the fit
- Flatter (larger) BOZRs –> loosen the fit
- Tightening the fit may –> better centration
TD:
- more effective at changing lens fit than BOZR changes
- changes to TD impacts the centration & movement
- Larger TDs –> slower movement but may help with centration
- Smaller TDs –> give more movement but may cause decentration
What if rational changes to BOZR and/ or TD doesn’t improve the fit?
change to a different CL make/ design
What makes up a CL prescription?
- Parameters: BOZR/ TD/ Sphere/ Cyl/ Axis/ Add
- Type: Brand/ series (material, water %)/ Tint
- Lens replacement: DD/ 2wk/ 1month/ FR/ Annual
- Lens wear mode: DW/ EW/ CW
- Lens care regime: MPS/ H2O2/ none/ drops
- Instructions: Hours per day/ days per week/ precautions
What are the 5 CL wear modalities?
- Daily wear (DW) - worn during waking hours and removed before sleep
- Flexi-wear (FW) - mostly worn during waking hours, with occasional napping/ overnight wear
- Extended wear (EW) - wear lens all day with up to 6/7 nights, or 13/14 nights sleeping in lenses, then 1 night off
- Continuous wear (CW) - wear lenses all day up to 30 days sleeping in CL, then 1 night off
- Overnight wear (ON) - sleeping in lenses and removing during day (Ortho K)
What are the 5 CL replacement schedules?
- Conventional/ annual - 12 month replacement interval recommended
- Frequent replacement - 3 or 6 month replacement interval recommended
- Monthly - 1 month replacement interval recommended
- Two weekly - 14 day replacement interval recommended
- Daily disposable - single use CL
What are other tint lens features?
- Handling tints
- no effect on hue discrimination
- don’t reduce glare
- permanent, not affected by Lens Care Products (LCP) - Cosmetic tints
- transparent, highlights iris colour
- opaque, changes iris colour - UV blocker
- but… they don’t block UV completely
What must you ask in a CL hx?
- Reasons for visit
- Demographics, GP, last test and previous lens wear
- Personal ocular hx (POH)
- General health
- fam ocular Hx
- Social Hx - hobbies/ occupation
- Suggest CL wear to px?
What are the key additional measurements required for CL fitting?
- HVID
- VPA (vertical Palpebral Aperture)
- pupil size (max dim illum and average room illum)
- corneal topography (central keratometry)
Define BOZR, BOZD, BVP, TD, BC, SAG
- BOZR: back optic zone radius (btwn 0.6-1mm flatter than average Ks)
- BOZD: back optic zone diameter
- BVP: back vertex power (of a CL can use formula Fspec/ 1-(VD xFspec))
- BVP specs HVID)
- BC: base curve (curvature of the CL)
- SAG: sagittal height/ depth - amount of space between lens and cornea
- Constant BOZR + vary TD = Vary SAG
- Constant TD + Vary BOZR = Vary SAG
- Vary BOZR & TD + constant SAG
What are 4 rules of thumb for calculating the best initial trial lens parameters?
HVID, TD, average Ks, BOZR
if cyl less than 4D ??
What is a typical flat, average and steep BC for a SCL?
a. Flat: 8.9
b. Average: 8.6
c. Steep: 8.3
How do we assess and record SCL fit?
Centration, movement, coverage
- Static and dynamic (Open eye, blink, push up)
- Movement on blink
- Lag on hori gaze
- Recovery from push up
What is variable VA which improves immediately after blink indicative of?
Steep: poor and variable, improves after a blink
What kind of O/R do we do with spherical SCLs?
It’s normal to do over Rx with spherical CL unless you’re planning to fir a toric CL
