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Stage 1 Visit 2 > Competency 5.1.1 > Flashcards

Competency 5.1.1 Flashcards

1
Q

Factors Affecting Comfort of a Contact Lens Material

A

o Higher modulus materials are less comfortable (e.g. early SiHy)
o Higher water content lenses can dry out and cause discomfort
o Poor wettability is related to reduced comfort

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2
Q

What is Oxygen Permeability?

A

o This the amount of oxygen that gets through the lens onto the cornea
o Is a combination of the oxygen transmittibility of the material and the thickness of the lens

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3
Q

Oxygen Permeability of Hydrogel Lenses

A
  • water content of these lenses is what determines the oxygen permeability of the lens
  • to obtain high Dk/t we need a high water content and therefore we risk drying the eye out.
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4
Q

Example of Hydrogel Contact Lens Material

A

Poly-HEMA

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5
Q

Oxygen Permeability of Hydrogel Lenses

A
  • the oxygen permeability of the lens is dependent on the amount of silicone used in the lens
  • allows for high Dk/t values to be obtained without drying the eyes out towards the end of the day
  • . Silicone hydrogels can produce approx 5x higher Dk/t values when compared to a hydrogel
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6
Q

Advantages of Hydrogel Contact Lenses

A
  • Highly flexible material
  • Good initial comfort
  • Thinner lenses
  • Affordable
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7
Q

Disadvantages of Hydrogel Contact Lenses

A
  • Low oxygen permeability
  • Potentially higher risk for eye infections and other hypoxia-related issues
  • Not ideal for overnight wear
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8
Q

Advantages of silicone hydrogel Contact Lenses

A
  • High oxygen permeability
  • Easier to handle (particularly for new contact lens wearers)
  • Better durability
  • Extended wear and overnight wear options available (longer wear time)
  • Available in a variety of modalities
  • Available in different designs
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9
Q

Disadvantages of silicone hydrogel Contact Lenses

A
  • Early silicone hydrogel lenses sometimes had wettability challenges although newer SiHy materials have similar or better wettability than hydrogel lenses
  • Early silicone hydrogel lenses used stiffer materials, however, newer SiHy materials have improved flexibility similar to that of hydrogels9
  • Potentially higher risk for giant papillary conjunctivitis (GPC), an allergic reaction in the inner part of the eyelid with early SiHy materials, however, this is not a concern with newer, low modulus monthly and 1 day SiHy lenses.
  • Slightly higher price, although newer lenses like clariti® 1 day are close to price parity with 1 day hydrogel lenses.
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10
Q

Spherical Soft Contact Lens Designs

A
  • Suit patients with little to no astigmatism (upto 0.75DC)
  • Go up in 0.25DS steps but this may change to 0.50DS at higher powers
  • Use spherical equivalent if there is astigmatism present
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11
Q

Toric Soft Contact Lens Designs

A
  • Corrects astigmatic refractive errors
  • Must sit in a specific orientation to provide the correction
  • Toric lenses feature markings to allow for identification of where and how the lens is sitting
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12
Q

Methods of Stabilising Toric SCLs

A

o Prism-ballast designs are thinner at the top and thinner at the bottom of the lens and the weight helps keep the lens orientated correctly
o Peri-ballast (similar to prism-ballast) the thicker area is closer to lens periphery.
o Thin zones at the top and bottom of lens allow the actions of the lids to maintain orientation
o Posterior torics feature a toric back surface which conforms to the cornea, allowing stability

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13
Q

Types of Multifocal Soft Contact Lens Design

A
  • Concentric
  • Aspheric
  • Segmented
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14
Q

Concentric Soft Multifocal Contact Lens Design

A

o Alternating rings of distance and near prescriptions
o Can be centre-distance or centre-near

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15
Q

Aspheric Soft Multifocal Contact Lens Design

A

o Features a gradual change in power from distance to near Rx
o Can be centre-distance or centre-near

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16
Q

Segmented Soft Multifocal Contact Lens Design

A

o Acts more like a traditional bifocal
o Distance prescription is always located in the upper section of the lens
o Lids help move the lower near prescription up into pupil view when patient looks down to read

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17
Q

Soft Contact Lens Parameters

A
  • BOZR
  • TD
  • Water Content
  • BVP
  • Lens thickness
18
Q

Back Optic Zone Radius (BOZR) of a Soft Contact Lens

A
  • This is the curvature of the back optical zone of the lens
  • Helps to ensure good fitting of the lens over the cornea
  • Obtained by taking the flattest K and multiplying by 1.1
19
Q

Total Diameter of a Soft Contact Lens

A
  • Most common diameter is 14.2 but diameters fall into range of 13.8-14.3mm
  • There is a change of diameter of 0.1 to 0.8mm due to reduction of ocular surface temperature compared to ambient room temperature
  • TD is obtained by taking HVID and adding 2mm
  • If lens is too large
    • poor movement
    • less tear exchange
  • If lens is too small
    • Excessive movement
    • Poor centration
    • Poorer comfort
20
Q

Water Content of a Soft Contact Lens

A
  • This is the amount of water contained within a CL
  • Especially in Hydrogels this is a compromise between oxygen transmissibility and amount of evaporation
  • If there is a high % water content:
    o Increased comfort
    o Less stability
21
Q

BVP of a Soft Contact Lens

A
  • Differs from that of the spectacle prescription
  • Is lower in CLs for a myopic Rx
  • Is higher in CLs for a hypermetropic Rx
22
Q

Lens Thickness of a Soft Contact Lens

A
  • A thin lens:
    o Increases oxygen transmissibility
    o Reduces ease of handling
    o Has a shorter life
    o Creates a thinner post-lens tear film (corneal dessication)
23
Q

What Should be in a CL H&S

A
  • Motivation
  • Occupation
  • Lifestyle
  • Ocular History
  • General Health
24
Q

Lens Choice Based on How Often They Would Like to Wear Them

A
  • A patient who is only wishing to wear the lenses for occasion social or sporting use could benefit from daily disposable lenses
  • A patient who is looking to wear the lenses FT most days of the week could benefit from monthly replacement lenses
  • A patient who is looking to wear the lenses almost all waking hours could benefit from a lens which is suitable for EW
25
Q

Lens Choice Based on Previous CL experience

A
  • If prev non-compliance then consider daily disposables even when wear modality would be better suited to a monthly lens
26
Q

Lens Choice Based on Occupational Demands

A
  • VDU Use
    o What type of VDU
    o Working distance considerations in a presbyope
    o How much time on VDU as this is known to reduce blink rate
    o If lots of VDU usage then lenses with good wettability are advisable
  • Driving
    o Reduces blink rate
    o Factors such as air conditioning can affect lenses
    o Regular gaze changes can affect toric wearers
  • Enviroment
    o Dusty enviroments and those with toxic fumes present a contraindication
    o Pilots are only allowed to wear distance only contact lenses
27
Q

Lens Choice Based on Lifestyle/Hobbies

A
  • Sport
    o SCLs are more advisable for sports due to safety reasons
    o Advise eye protection for sports such as squash
  • Swimming
    o Discuss the increased risk of infection
    o If insistent on swimming then advise daily disposables with tight fitting goggles over the top
  • Outdoor Activity
    o UV protection
    o Still need to encourage sunglasses wear
28
Q

Lens Choice Based on General Health

A
  • Diabetes
    o Cornea is adversely affected in 70% of diabetics
    o DM can result in slow and incomplete corneal healing
    o Daily disposable CLs to minimise infection risk may be advisable
  • Arthritis
    o May suffer from inflammatory dry eye
    o Affects manual dexterity
    o Could benefit from a lens with a higher modulus
  • Skin Conditions (Eczema)
    o May be more vunerable to excessive deposits, lid irritation, punctate keratitis and blepharitis
  • Thyroid Dysfunction
    o Concern around exposure keratopathy related to TED
    o TED can cause incomplete blinking and meibomian gland dropout
  • Allergies
    o More likely to have pre-existing papillae
    o Can be more vunerable to CLAPC
    o Can be more prone to reactions to SCL solutions
  • Smoking
    o Not commonly asked
    o Associated with 3.7x increase in bacterial keratitis risk
29
Q

Potential Ocular Health barriers to CL wear

A
  • any acute or sub-acute inflammation of the anterior segment
  • acute or chronic eye infection
  • corneal dystrophies
  • pterygium or pinguecula
  • dry eye or blepharitis
  • previous or current microbial keratitis
  • Ocular conditions requiring frequent drop use such as glaucoma or allergy
30
Q

Water Content Considerations for Lens Choice

A
  • To maintain stability a high water content lenses absorb water from the ocular surface
  • can lead to ocular dryness
  • if patient has dry eyes then a lower water lens should be considered
31
Q

Oxygen Considerations for Lens Choice

A
  • The more time the patient would like to have the lens in their eye, the higher the oxygen transmissibility will have to be.
32
Q

Back Optical Zone Radius Impact on Lens Choice

A
  • calculated by flattest K multiplied by 1.1
  • Most lenses will have only one BOZR option
  • The idea is to fit slightly flatter than the corneal curvature to allow for tear exchange and tear movement
33
Q

Steps of Soft Contact Lens Fitting Routine

A
  • Lens insertion
  • VA check
  • Over-refraction
  • Fit check
    • Centration and Coverage
    • Comfort
    • Movement on Blink
    • Lag
    • Push up test
34
Q

Over-RefractionCentration and Coverage

A
  • Conduct a simple spherical over-refraction
  • Remember not to give initial +0.25DS due to 3m room.
35
Q

Centration and Coverage in SCL Fit

A
  • The lens should cover the cornea, overlapping onto the bulbar conjunctiva in all positions of gaze
  • of particular importance in multifocal lenses as decentration can affect the lenses aberrations.
  • Use fitting cross to note centration and note that no limbal touch
36
Q

Comfort Assessment in SCL Fit

A
  • very subjective measure which holds little clinical value but is worth asking regardless
  • ask the patient to gauge the comfort of the contact lens from 0 to 10
  • Be wary of reduced corneal sensitivity in diabetics which may report a poor fitting lens as comfortable.
  • worth noting that a tight fitting lens will also not be reported as uncomfortable.
37
Q

Movement on Blink in SCL Fit

A
  • Movement on blink with the eye elevated has been shown to be more diagnostic of overall lens movement than with the eye in primary gaze
  • Normal movement is of around 1/3mm
  • Use amount of lens overlap (around 1mm) to gauge movement
38
Q

Lag in SCL Fit

A
  • is the resistance of the lens to movement away from primary gaze
  • If the lens is nice and mobile then it will tend to lag behind the movement due to interactions with anatomy e.g lids
  • Lag has been shown to be more clinically useful than sag which is actually a measure of distortion of lens shape rather than lens mobility
  • results can be interpreted in percentage increases in overlap:
    • Ideal fit is 50-100% increase
    • Loose fit is over 100% increase
    • Tight fit is less than 50% increase
39
Q

Push Up Test in SCL Fit

A
  • very useful diagnostic test for lens fit.
  • The speed of recovery is the more useful aspect of assessment compared to how easy the lens is to dislodge
  • The ideal lens neither drops instantly back down nor sluggishly moves back to its position, it performs somewhere inbetween.
  • clinical experience is required to make this judgement
40
Q

Reasons not to have Limbal Touch in SCLs

A
  • Ocular stem cells are at the limbus so if the lens was to touch this area there would be a decrease in stem cell viability
  • The area of the limbus is the end of the corneal vascular area, if a lens was to touch this then neovascularisation of the cornea could occur
41
Q

Contact Lens Specification Example

A

BOZR/TD/Rx
Lens name

8.4/14.0/-3.00
Acuvue Oasys

42
Q

College Guidance for Contact Lens Specification

A
  • Optom details
  • sufficient details of any contact lens fitted to enable the lens to be replicated. This would normally include some or all of the following information:
    o power
    o base and peripheral curves of the lens
    o total diameter
    o material
    o design (including details of the generic brand) of the contact lens(es)
  • the date the specification expires
  • any clinical information that should be taken into account by a supplier.

Stage 1 Visit 2 (16 decks)

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