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Contact Lenses 3 > Unit 2 > Flashcards

Unit 2 Flashcards

1
Q

GP options for astigmatism

A
  1. Spherical GP lenses
  2. Front surface toric
  3. back surface toric
  4. Bitoric
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2
Q

Spherical GP for astig

A

These lenses are called for when there is no astigmatism and when the degree of astigmatism is corneal
-The lacrimal lens neutralizes the astigmatism

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3
Q

Rule of thumb when considering spherical GP

A

The astigmatism if the pxs spectacle rx should be less than 2.50
-If the spectacle cyl is greater than 2.50 we might need a toric lens

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4
Q

Mathematically, how do we know if the astigmatism is corneal?

A

Recall total astigmatism = corneal astig + lenticular astig
-calculate the RA

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5
Q

Design of front surface toric

A

-Spherical posterior curve
-Toric anterior
ex. BC 7.50mm
Anterior curves 8.00mm/7.40mm

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6
Q

When is front surface toric used?

A

When there is over 1.25D of rx cylinder correction w/ a spherical or near spherical cornea
-1.5BD prism is used to help stabilize the lens

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7
Q

Design of a back surface toric

A

-Toric posterior curvature
-Spherical anterior curvature

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8
Q

When is back surface toric used?

A

Used when corneal astigmatism is approx 2/3 of the refractive astigmatism
Mathematically- Corneal astig power / spectacle rx power

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9
Q

design of a bitoric

A

Toric curvatures on both the anterior and posterior surfaces.

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10
Q

When is bitoric used>

A

When there is high corneal astigmasim
-High means more than 2,50
-Can improve lens positioning in high corneal astigmatism

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11
Q

SPE bitoric design (spherical power effect)

A

Has both front and back surface toric surfaces but the optics of a sphere when combined with a tear lens
-Can rotate on the eye without impacting vision

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12
Q

what does SPE correct ?

A

ONLY for the induced cylinder

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13
Q

how does SPE bitoric lens work

A

plus cylinder ground on the front surface which cancels out the induced cylinder power created by the lacrimal lens and posterior curve

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14
Q

example of a SPE bitoric lens

A

43.00/46.00
-2.00/-5.00
-SPE have the same difference in base curve meridians as power curve meridians

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15
Q

Design of CPE bitoric lens

A

Used when a SPE bitoric results in significant cylindrical over rerefraction
-Front surface corrects both the induced astig and the residual astig
-CPE lenses must be rotationally stable to avoid inducing further astig

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16
Q

how does CPE bitoric lenses work

A

perform a sphero-cylindrical OR and add the OR to the diagnostic lens power per meridian

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17
Q

Bitoric fitting philiosphy - SADDLE FIT

A

-fit on k in each meridian
-allows for better alignment with the overall toric corneal shape
-tighter fit, more centered
-not used often

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18
Q

bitoric fitting philosophy - LOW TORIC SIMULATION

A

-fit flat meridian on k and steep meridian 0.75D flatter than steep k
-More common fitting philosophy
-provides stability

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19
Q

benefits of GP multifocals over soft cl multifocals?

A

-better optical correction
-corrects corneal astigmatism
-resist deposits better than soft
-more stable w. blink
-often more comfortable for dry eye pxs

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20
Q

Who is a good candidate for GP multifocals

A

-someone w astigmatism or higher rx
-someone who has worn GP lenses in the past
-someone who wants the best possible vision

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21
Q

who is NOT a good candidate for GP multifocals

A

-someone who is looking for occasional use
-someone who has only worse soft CLs and is not interested in GP lenses due to perceived comfort issues

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22
Q

Modalitites of GP multifocals

A
  1. Corneal GP lenses
  2. Hybrid lenses
  3. Scleral lenses
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23
Q

types of multifocal RGP lenses

A
  1. Simultaneous
    -aspheric
    -concentric
  2. Translating / alternating
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24
Q

Simultaneous designs ; features

A

-blend the rx for distance and near
-place 2 images on the retina at the same time
~ relies on the visual system ot select clearer image when needed
-same design used in multifocal soft CLs

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25
Q

aspheric lens

A

-gradual change in power from distance to near
-allows distance , intermediate and near correction
-pupil dependent
-more balanced all around

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26
Q

concentric lens

A

-discrete rings of distance and near power
-central portion of the lens is typically distance
-less pupil dependent
-can cause ghosting and flare

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27
Q

customization options for aspheric lenses

A

-you can adjust distance zone on many of the lenses
-you can customize the add powers with add zone sizes

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28
Q

features of translating and alternating design

A

-AKA segmented multifocal design (upper and lower segment)
-Similar to bifocal or trifocal eyeglass lenses
-relies on the physical movement of a lens on the eye for gaze-specific positioning
-lower lid holds the lens in palce so when the px looks down the pupil looks down into the segment

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29
Q

types of translating/alternating deisgn

A

-crescent design
-inverted cerescent
-straight top

30
Q

fitting translating/alternating design GPs

A

-obtain proper lens movement
-move segment height up or down dependent on px needs
-add prism if needed to help move the lens down more quickly and improve rotation

31
Q

which CL is better with some degree of lid control? Concentrics and aspheric or translating design?

A

Concentrics and aspherics

32
Q

which CL is better when it is resting on or above the lower lid? Concentric and asphric or translating desig?

A

Translating designs

33
Q

which one often has a longer adaptation period ? Simultaneous or translating ?

A

Translating design but it has exceptional VA

34
Q

considerations on what to chose between simultaneous vs translating

A

-practitioner preference
-px eyelid anatomy (lid position, lid laxity)
-other px considerations (adaptation)

35
Q

what is corneal warpage

A

altered or distorted shape of the cornea

36
Q

causes of corneal warpage

A

Poor fitting GP lens
-exessive movement
-eccentric location
-localized heavy bearing
Long term PMMA wearer

37
Q

Signs of corneal warpage

A

-distorted mires on keratometry
-irregular astigmatism on topography

38
Q

Symptoms of corneal warpage

A

Blurry vision - even with glasses
-once the CL are removed the px experiences significant blurred vision

39
Q

treatment for corneal warpage

A

-refit
-discontinue lens wear until cornea returns to normal shape

40
Q

what is GP lens warpage

A

-GP lens gets twisted or bent out of shape
-creates permanently induced toricity within the lens
aquired over time and permanent

41
Q

causes of GP lens warpage

A

-heat generated from routine lens handling
-storing a lens in a hot enviroment
-agressive rubbing while cleaning lens

42
Q

GP lens warpage

A

-GP lens warpage can be hard to see with the “naked eye”
-verify the presence of warpage using a radiuscope (a spherical GP lens will have 2 different radii of curvature in the radiuscope)
Alternative - perform over keratometry (will measure toricity over the spherical GP lens)

43
Q

other sides of GP lens warpage incudle..

A

-no precise end point on over refraction
-unusual fluroscein pattern
-altered lens fit

44
Q

symptoms of GP lens warpage

A

blurry vision

45
Q

treatment for GP lens warpage

A

-lens replacement if warpage is >0.50D

46
Q

what is lens flexure

A

bending of a GP lens while the lens is on the eye

47
Q

physiology of lens flexure

A

-all GP lenses show some flexibility
-a combination of lid pressure, blinking, and capillary attraction combine to bring the GP lens in closer contact with the cornea

48
Q

causes of lens flexure

A

-corneal astigmatism (>1.50D)
-steep lens
-centre of lens is to thin

49
Q

signs of lens flexure

A

-cylinder OR
-over-keratometry : will measure toricity (assuming a spherical GP lens)

50
Q

Symptoms of lens flexure

A

-blurry vision
-fluctuating vision
-CL discomfort

51
Q

treatment for lens flexure

A

-flatten the lens
-increase thickness
-fit a back surface toric or bitoric

52
Q

the cylindrical over-refraction changes by the amount of warpage or flexure ..

A

-if the cornea is WTR and the OR is WTR, the amount of WTR cylinder in the OR increases by the amount of warp/flexure
-if the cornea is WTR and the OR is ATR, the amount of cylinder in the OR decreases by the amount of warpage/flexure

53
Q

GP complications defined

A

-Negatively impact the health of the eyes (discomfort)
-reduce the CL corrected VA (blurred vision)
-result in undesirable lens fit and lens conditions (CL dropout)

54
Q

Px causes of GP complications

A

-Not following proper cleaning and sterilization instructions
-purchasing CLs from unautharized CL sources
-sharing their CLs with others
-sleeping in their CLs if they are not approved for extended wear

55
Q

GP lens complications: role of the optician

A

-identify abnormal situations that represents a GP lens complication
-take action to over-come the complication, if possible
-educate the px to prevent complications from happening in the future

56
Q

Common GP complications well cover

A

-corneal staining (3 and 9 oclock)
-dellen
-foreign body tracking
-lens adherence
-crazing
-dimple veiling
-poor surface wetability

57
Q

what is 3 and 9 oclock staining

A

horizontal dying of the cornea and/or adjacent conjunctiva

58
Q

causes of 3 and 9 staining

A

GP related: thick edge, decentered lens
eye related: poor tear film, incomplete blink

59
Q

symptoms of 3 and 9 staining

A

irritation, tearing

60
Q

treatment for 3 and 9 staining

A

-refit GP; thinner lens edge, improve centration
-ocular lubricants

61
Q

Dellen

A

-localized areas of peripheral corneal thinning
-often appear as oval shaped excavations running parallel to the limbus
-fluroscein pools in the DELLEN

62
Q

symptoms of dellen

A

-ranges from none to mild irritation
-no impact on VA b/c only the peripheral cornea is involved

63
Q

treatment for dellen

A

-stop wearing CL temporarily so the cornea can return to its normal thickness
-improve GP fit

64
Q

Foreign body tracking

A

when a FB is trapped underneath the lens, it causes epithelial damage and corneal staining
-often a track like appearance in a random pattern
-often unilateral

65
Q

symptoms of foreign body tracking

A

-range from none to severe discomfort

66
Q

treatment for foreign body trackign

A

-clean the lens
-preservative free AT
-may require anti-biotic drop

67
Q

lens adherence

A

-results when a GP lens “Sticks” to the eye (no movement with blinking)
-GP lens can adhere in any position (MOSTLY NASSALLY)
-most common with extended/overnight wear but also in daily

68
Q

symtpoms of lens adhernce

A

-difficulty removing lenses
-intermittent cloudy vision (from trapped mucous underneath)

69
Q

signs of lens adherence

A

-corneal indentation
-patch of corneal staining

70
Q

causes of lens adherence

A

-dryness or deposits on back surface
-lens decentration
-peripheral sealoff

71
Q

treatment for lens adherence

A

px education
-use lubricants
-NO overnight wear
Refit lens

Contact Lenses 3 (5 decks)

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