CLM - Introduction to Advanced Contact Lenses - PAP Week 1 Flashcards
List 10 consideraions when determining whether a patient is a good candidate for contact lenses.
Motivation level
Medications
Prior ocular history
Activities
Occupation
Working environment
Visual tasks
Hygiene
Manual dexterity
Intended wearing schedule
List four general clinical indications for contact lenses.
High refractive error
Anisometropia
Presbyopia
Elective paediatric
Should pupil diameter be taken when doing a baseline exam for contact lenses?
Yes, high and low illumination
Define BOZR. What else is it known as?
Back optic zone radius - also base curve
It is the radius of curvature of the back surface of the lens
Define TD.
Total diameter
Full/total contact lens diameter
Define BVP.
Back vertex power
Power of a lens
Define WC.
Water conent
Percentage of water
Define Dk.
Oxygen permeability
Amount of oxygen passing through a contact lens material over a set period of time and pressure difference
Define Dk/t.
Oxygen transmissibility
Amount of oxygen passing through a contact lens of specified thickness over a set amount of time and pressure difference
Give the general format for SCL parameters.
BOZR/TD/BVP
How many BOZRs do soft contact lenses tend to have? In what four modalities may it be different (and what number of BOZR)?
Many only have one BOZR
Some have two:
-extended wear
-monthly
-fortnightly
-daily disposables
What is an average K reading (both mm and D)? What soft contact lens BOZR is expected to fit this reading?
43.00D or 7.8mm
Expect that most 8.6/7.7mm lenses will fit most eyes
What is considered a steep K reading (both mm and D)?
> 45.00D or <7.5mm
What BOZR should be chosent to trial first and why (for SiHy lenses)?
To minimise mechanical issues, choose the steepest BOZR
What total diameter is generally expected?
Usually >2.00mm of HVID
What effect can an excessively large total diameter lens have (2)?
Reduces lens movement
Inadequate tear exchange
What effect can a small total diameter lens have (3)?
Excessive movement
Poor centration
Less comfort
Are disposables generally available in a large number of total diameters?
No, usually only one available (for a given brand)
In what two ways is back vertex power calculated?
From spectacle refraction (taking into account vertex distance)
From over-refraction with a trial contact lens
When using a spherical lens, what power is used to account for cyl and how is it calculated?
Using spherical equivalent power using Sphere (D) + 0.5 x Cyl (D)
How should BVP be calculated in toric lenses?
It must be calculated separately in each meridian
At what dioptre levels would vertex distance need to be taken into account for soft contact lenses?
≥ ±4.00D
What is the clinical pearl on whether contact lenses or spectacles provide better VA for myopes and hyperopes?
Myopes
CLs < Glasses
Hyperopes
CLs > Glasses
Define the 2C MAP acronym.
Centration
Coverage
Movement
Acuity
Push-up
List the three degrees of decentration for a contact lens and list the cutoffs for each.
Mild <0.5mm
Acceptable 0.5mm - 0.8mm
Excessive >0.8mm
Make sure direction of decentration is noted
Define lens lag.
The amount that the lens trails the movement of the eye when gaze is directed.
List the three degrees of lens lag for a contact lens and list the cutoffs for each.
Insufficient <0.2mm
Acceptable 0.3mm - 0.7mm
Excessive >0.7mm
What can excessive lag result in (2)?
Poor centration
Bad optics in gazes
What can zero lag result in?
Lens adherence
What should be evaluated when checking lens coverage?
Whether or not the lens always completely covers the cornea (including gazes)
List the three degrees of lens coverage for a contact lens and list the cutoffs for each.
Ideal ≥1mm (all gazes)
Acceptable ≥0.5mm (all gazes)
Unacceptable <0.5mm (any gaze)
What does lens movement promote?
Post-lens tear film exchange and mixing
How is lens movement quantified?
Vertical change in lens position before and after a normal blink
List the three degrees of lens movement for a contact lens and list the cutoffs for each.
Inadequate <0.2mm
Well-fitting 0.25mm - 0.5mm
Excessive >1.0mm
What is checked during a push-up test?
How easily the lens moves a push-up
How does a well-fitting lens move with a push-up test?
Moves easily and rapidly and reliably returns to a central location
List the two degrees of lens rotation for a toric contact lens and list the cutoffs for each.
<10 degrees acceptable
≥10 degrees requires compensation
Describe the LARS acronym for lens rotation compensation.
Left Add Right Subtract
What is meant by lens stability for toric soft contact lenses?
Degree of rotation is constant between blinks
List three reasons why lens stability may be inadequate.
Stabilisation methods arent working
BOZR is too flat
Diameter is too small
Ideally, how long should a clinician wait after applying a contact lens to an eye?
Wait 2-3 minutes for the contact lens to settle
