SCL Fitting 2

Question 1

Generally speaking how do we pick soft contact lenses initially?

Answer 1

By availability of the prescription - you can check this using the ACLM book

Question 2

How do you view the lens border?

Answer 2

White diffuse light and you swing the illumination system from side to side so you can diffrentiate between shadows and the lens border

Question 3

What is the correct VLM we are looking for when fitting soft contact lenses?

Answer 3

0.25 – 0.5mm

Hello, Aleena. What’s that forehead saying?

[If less than it is too tight (<0.20) , if more than it is too loose (>1.00)]

Question 4

What is conjunctival drag and when might it occur?

Answer 4

Conjunctival drag - this is when the conjunctiva moves with the lens as the lens is too tight.

[It is important to note that the lens movement seperate from the conjunctival movement is next to none]

Question 5

Why may we see an impression ring after the fit of soft contact lenses?

Answer 5

Impression ring occurs when the lens is too tight (or edges are too sharp - but normally due to tight lens)

Question 6

If our soft contact lens is too flat what may we see?

Answer 6

Edge lift

Question 7

How do we check for lens lag?

Answer 7

So basically we put a beam of the correct width (should be ideally 1mm) between the edge of the limbus and the edge of the lens so that it occupies all space in between.

Then we get the px to look in a direction (we test all four directions- upwards is the most significant). When the px is looking for example to the right we then do the same thing and put our beam between the limbus and the edge of the lens. We assess whether that gap has gotten bigger or smaller or stayed the same.- This is lens lag

Question 8

What is an ideal lens lag?

What lens lag indicates a fit that is too tight?

What lens lag indicates a fit that is too loose?

Answer 8

Ideally: up to 1.0mm

Possibly tight <0.2mm

Loose: >1.0mm

Question 9

What is the risk of having too much sag?

Answer 9

It causes the lens to drop

Question 10

What does a lag of 0mm mean?

Answer 10

The width of the limbus to the edge of the contact lens stays the same when a px looks in a particular direction

Question 11

True or False- SCL make use of tear lens power

Answer 11

False - soft contact lenses do not make use of tears to correct refractive error thus BVP should make use of full ocular rx for SCL

Question 12

What is the push up test?

Answer 12

It is a measure of tightness

Question 13

How do you conduct the push up test and what do results of the test indicate?

Answer 13

Px looks slightly up (so that lower lens border is free from lid)

• Use finger to put pressure on lower lid
• Move lens vertically
• Allow lens to re-centre
• Judge movement (related to distance between lens border and limbus - based on recovery)

Correct: slow to move; steady recovery; 40-60%

Tight: Difficult to move with slow to no recovery, 65-100%

Loose: Easy movement and fast recovery, 35-0%

Question 14

What is a clinically significant result of the Push Up Test that requires changing the lens?

Answer 14

You must change the lens if PUT >75% or <25%

Question 15

Why do we look out for a -0.50D change in rx (by look out double check the fit of the lens and health of the eye?

Answer 15

To ensure a myopic creep is not being caused by CL induced hypoxia seen in continuous extended wear

Question 16

In regards to a pxs VA when blinking what is an ideal outcome?

Answer 16

That it remains stable on blinking

Question 17

What can we assume/infer (in conjuncion with other observations) about the fit of the SCL if vision improves after blinking?

Answer 17

The fit of the SCL is steep

Question 18

What can we assume/infer (in conjuncion with other observations) about the fit of the SCL if vision declines after blinking?

Answer 18

Fit is too flat

Question 19

When fitting a px with SCL for the first time what is recommended?

Answer 19

We choose two different materials in each eye and see which one the px gets on best with

Question 20

What will steepening the BOZR do to the fit of the SCL?

Answer 20

It will tighten the fit - [perhaps leading to better centration]

Question 21

What will flattening the BOZR lead to?

Answer 21

A looser fit

Question 22

Does a larger TD increase or decrease lens movement- and so what does this mean for centration?

Answer 22

Larger TD will decrease lens movement (so becomes steeper) which may help centration.

[Essentially the more your lens moves the less likely it is to always be in the centred (i.e. centered)]

Question 23

What patient and lens factors have shown to cause discomfort?

Answer 23

Patient factors:

• An irregular or thin tear film
• Increased conjunctival staining and Palpebral Staining

Lens factors:

Lens factors are simply due to poorer centration, and a loose fit – Sometimes material choice or lens edge