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APCO > Soft CL Fitting (Spheres) > Flashcards

Soft CL Fitting (Spheres) Flashcards

1
Q

What are the advantages of SCL?

A
  1. Comfort/ easy to adapt
    - less lid adaptation than GP (large & hydrophilic)
  2. Lower incidence of:
    - overwear syndrome
    - spectacle blur
    - corneal staining
    - flare
    - foreign particles
    - loss
  3. reduced corneal sensitivity only a bit
  4. Economic & Disposable (limiting deposition)
  5. Can change iris colour with tints & opaques if people want
  6. Good for sport
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2
Q

What are the disadvantages of traditional soft lenses?

A
  1. Poorer subjective vision & more variable vision
  2. increased breakage and tearing (fragile lenses)
  3. Lens deteriorate with age (deposits & discolouration –> limited life span)
  4. Need to disinfect –> can become very expensive
  5. Inability to modify/ verify
  6. Contamination (with pharmaceuticals/ fluorescein) –> must be sterile!
  7. Complications (due to limited Dk/t & post-lens tear exchange)
    - vascularisation
    - papillae/ GPC
    - conjunctival injection
    - stromal and endothelial disturbances
    - increase redness
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3
Q

What Hx taking do you need to take for CL visit?

A

Ask patients:

  1. Reason(s) for visit
    - reason for wear/ motivation
    - realistic expectations
    - indications for CL wear
  2. 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)
  3. Personal ocular hx
    - eg. previous infections, surgery, dry eyes etc
  4. General health/ Medication that px is taking
    - any allergies
    - any diabetes, hyperthyroid, arthritis?
  5. Fam ocular hx
  6. Social hx
    - occupation
    - hobbies
    - environment
    - driving
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4
Q

What are some baseline measurements?

A
  1. HVID (horizontal visible iris diameter)
  2. VPA (vertical palpebral aperture)
  3. Pupil size
    - in maximum dim illum
    - average room illum
  4. Corneal topography - central keratometry
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5
Q

What does it mean if CL is moving too much and not moving?

A

Moving too much –> too loose –> need steeper curve

Not moving much –> too tight –> need flatter curve

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6
Q

What are the BOZR?

A

Usually between 0.6-1.0mm FLATTER than average Ks

  • most brands only have 1 or 2 BOZRs
    • BOZR = BC
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7
Q

What are TD?

A

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

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8
Q

How to calculate BVP(CL)?

A

BVP (CL) = F (spec)/ 1-(VD in metres) x F(spec)

  • if BVP spec is acceptable VA
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9
Q

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

A

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
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10
Q

What are the lens parameter choices?

A

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

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11
Q

How do we assess SCL spherical lens fit?

A

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)
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12
Q

What happens when you have optical decentration?

A

Reduces vision especially for more complex designs like - aspherics and MF

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13
Q

What do you ALWAYS have to remember for limbal area, too much movement, and too little movement?

A

Limbal area: cannot be compromised by the lens edge

Too much movement: decreases comfort

Too little movements: poor physiology

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14
Q

Are there bubbles in correct, steep, and flat fitted CL?

A

Correct: no bubbles
Steep: Under periphery
Flat: Buckling at the edge

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15
Q

Can you use Fl in CL?

A

Not used in normal hydrogel soft lenses

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16
Q

What do you need to make sure for Over-refraction?

A
  1. Max plus power while maintaining optimum VA, with normal refraction for each eye in turn
  2. check if BV is comfortable (can perform binocular balance if needed)
  3. 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

17
Q

What is the impact of CL fit on VA?

A

correct: good, consistent
steep: poor & variable, improves with a blink
flat: variable, worse after a blink

18
Q

What are some fitting tips for BOZR and TD?

A

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
19
Q

What if rational changes to BOZR and/ or TD doesn’t improve the fit?

A

change to a different CL make/ design

20
Q

What makes up a CL prescription?

A
  1. Parameters: BOZR/ TD/ Sphere/ Cyl/ Axis/ Add
  2. Type: Brand/ series (material, water %)/ Tint
  3. Lens replacement: DD/ 2wk/ 1month/ FR/ Annual
  4. Lens wear mode: DW/ EW/ CW
  5. Lens care regime: MPS/ H2O2/ none/ drops
  6. Instructions: Hours per day/ days per week/ precautions
21
Q

What are the 5 CL wear modalities?

A
  1. Daily wear (DW) - worn during waking hours and removed before sleep
  2. Flexi-wear (FW) - mostly worn during waking hours, with occasional napping/ overnight wear
  3. Extended wear (EW) - wear lens all day with up to 6/7 nights, or 13/14 nights sleeping in lenses, then 1 night off
  4. Continuous wear (CW) - wear lenses all day up to 30 days sleeping in CL, then 1 night off
  5. Overnight wear (ON) - sleeping in lenses and removing during day (Ortho K)
22
Q

What are the 5 CL replacement schedules?

A
  1. Conventional/ annual - 12 month replacement interval recommended
  2. Frequent replacement - 3 or 6 month replacement interval recommended
  3. Monthly - 1 month replacement interval recommended
  4. Two weekly - 14 day replacement interval recommended
  5. Daily disposable - single use CL
23
Q

What are other tint lens features?

A
  1. Handling tints
    - no effect on hue discrimination
    - don’t reduce glare
    - permanent, not affected by Lens Care Products (LCP)
  2. Cosmetic tints
    - transparent, highlights iris colour
    - opaque, changes iris colour
  3. UV blocker
    - but… they don’t block UV completely
24
Q

What must you ask in a CL hx?

A
  • 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?
25
Q

What are the key additional measurements required for CL fitting?

A
  • HVID
  • VPA (vertical Palpebral Aperture)
  • pupil size (max dim illum and average room illum)
  • corneal topography (central keratometry)
26
Q

Define BOZR, BOZD, BVP, TD, BC, SAG

A
  • 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
27
Q

What are 4 rules of thumb for calculating the best initial trial lens parameters?

A

HVID, TD, average Ks, BOZR

if cyl less than 4D ??

28
Q

What is a typical flat, average and steep BC for a SCL?

A

a. Flat: 8.9
b. Average: 8.6
c. Steep: 8.3

29
Q

How do we assess and record SCL fit?

A

Centration, movement, coverage

  • Static and dynamic (Open eye, blink, push up)
  • Movement on blink
  • Lag on hori gaze
  • Recovery from push up
30
Q

What is variable VA which improves immediately after blink indicative of?

A

Steep: poor and variable, improves after a blink

31
Q

What kind of O/R do we do with spherical SCLs?

A

It’s normal to do over Rx with spherical CL unless you’re planning to fir a toric CL

APCO (13 decks)

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