10 - scl fitting and eval (10a + 10b)

what is the general diameter range of SCL?

12-16 mm

what is the general power (BVP) range of SCL?

±30 D

what is the CT (-/+) range of SCL?

(-) → 0.03 - 0.18 mm

(+) → 0.20 - 0.70 mm

what is the base curve of a SCL also known as?

sagittal depth or vault

what is the base curve of a SCL much flatter than? why?

much flatter than Ks d/t large diameter

What are the ranges of BC for a spherical SCL?

8.00-9.20mm

What are the types of posterior curve for a spherical SCL?

most are monocurve or bicurve

less commonly aspheric

What is true regarding the anterior curve of all spherical SCL?

all are lenticulated

How does the CT of a spherical SCL compare to a GP?

thinner than GPs

What is the minimum CT for a spherical SCL?

0.03mm

How does the minimum CT change for higher water content spherical SCL?

need thicker CT for those lenses → affects transmissibility

What is the benefit of having a larger overall diameter of a soft CL?

improves comfort and stability of lens

What is the downside to having a large OAD with SCL?

BCR need to be flatter d/t increased sag → which means there is reduced tear exchange

How much post-lens tear exchange is there with a blink in a SCL?

only 2%

What is the goal of the ideal SCL fit?

1. produce good and stable vision

2. comfortable

3. wearable for practical periods of time

4. provide minimal physiological response

5. centered, adequate movement, good coverage in all positions of gaze

what is the fitting procedure?

1. prefitting exam

2. select wear/disposable schedule and modality

3. select brand/BCR based on sag depth

4. select power

5. assess fitting characteristics → coverage, centration, movement

What is the advantage of a daily disposable/more frequent disposal schedule for a SCL?

1. lowest rate of overall complications

2. lowest level deposition

3. fewest unscheduled visits

4. great vision, sometimes improved comfort

what are some factors to consider when choosing a SCL?

1. wearing schedule (and replacement schedule)

2. oxygen needs

what are the disadvantages of extended wear/less frequent wear schedule?

highest rate of overall complications → rates are ~the same with conventional (non-disposable) EW

The first available soft contact lenses had how many BCR options?

6

How do you choose what BCR to use for a spherical SCL that offers two types?

if patient's K's flatter than average (43.50) → fit with flatter BCR

if patient's K's are ~43.50 → flat to middle range

if patient's K's steeper than average (43.50) → fit with steeper BCR

what do you change if movement is excessive or comfort is poor?

move to a slightly steeper lens

when do you perform sph/cyl over-refraction for a SCL?

for troubleshooting/moving to a toric

when do you perform spherical over-refraction for a SCL?

standard for spherical lenses

for a neophyte, who applies the len to eye?

YOU (the dr)

what is the settling period for a SCL?

at least 10 mins → look to check if grossly too small or too tight

further assessment may be necessary after 3-4 hrs or 1-2 weeks of wear

what is an indicator that the SCL dehydrated on the eye?

if poor tear volume → fit will tighten over time

How is coverage for a spherical SCL assessed? What do you want?

in primary gaze

want it to go past limbus and onto sclera 360º

How is centration for a spherical SCL assessed? What do you want?

assessed if over cornea in primary gaze → check inf, sup, temp, nasal

How is movement for a spherical SCL assessed?

what happens during blink in primary gaze and lateral or upgaze

How much movement in a spherical SCL do you want in primary gaze (post-blink)?

0.30-1.00mm of movement

How much movement in a spherical SCL do you want in up or lateral gaze?

up to 1.5mm acceptable

How will a SCL move if it is steep? How will the centration be?

little movement → well centered

How will a SCL move if it is flat? How will the centration be?

too much movement → decentered

how is movement described?

1. adequate

2. minimal

3. excessive

what is the push-up movement?

use lower lid to see how easily lens can be pushed up displaced → may be best indicator to determine flat lens

How do you steepen a spherical SCL?

decrease in BCR in mm (increase in diopters)

or

increase the OAD

How do you flatten a spherical SCL?

increased the BCR in mm (decrease in diopters)

or

decrease the OAD

To change the sag depth of a spherical SCL you can change the BCR or the ______?

OAD

To change the sag depth of a GP you can change the BCR or the ______?

OZD

what do you change to increase sagittal depth to decrease movement?

↑ OAD and hold BCR constant

steepen BCR and hold OAD constant

increase OAD and steepen BCR

what do you change to decrease sagittal depth to increase movement?

↓ OAD and hold BCR constant

flatten BCR and hold OAD constant

decrease OAD and flatten BCR

What is the cut off for prescribing spherical SCL?

cyl above 0.75D (≥-1.00D)

what are the types of tints for SCL?

1. handling tint

2. enhancing tint

3. opaque tint

4. prosthetic masking tint

what are the uses of prosthetic tints?

1. iris defects

2. corneal opacities

3. color vision deficiency

4. blind eye

5. patch for diplopia

what causes iris defects?

1. ocular albinism

2. traumatic iris injury

3. congenital iris pathologies