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CL 1 > Soft Contacts Lens: Fitting and Management > Flashcards

Soft Contacts Lens: Fitting and Management Flashcards

1
Q

Material properties

A

safe

inert

nontoxic

biocompatible

chemically and physically stable

good wettability

deposit resistance

durable

easy to formulate and manufacture

good optical clarity

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2
Q

Materials

A

polymerization of different monomer combinations, creates a balance of:

  • water content
  • refractive index
  • hardness
  • mechnical strength
  • oxygen permeability

silicone:

  • a high Dk value (oxygen permeability)
  • good comfort
  • good wettability
  • optical clarity
  • deposit resistance

HEMA - first hydrogel lens to allow oxygen

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3
Q

DK value

A

how much oxygen allowed through contact lens

needs to be at least 84

silicone hydrogel allows higher oxygen permeability with proper hardness and mechanical strength

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4
Q

Final Evaluation

A

transparency

hardness and stiffness

tensile strength

modulus of elasticity

refractive index

wettability

ionic charge

hydration (water content)

oxygen permeability/oxygen transmission

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5
Q

Modulus of elasticity

A

silicon hydrogel > hydrogel material

pros: stiffer, resists deformation, holds shape, easier to handle, better VA maybe
cons: edge lift, flutting, superior epithelial arcuate lesions, mucin balls, GPC

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6
Q

Oxygen permeability

A

DK value

property of lens material itself

not affected by power

hydrogel - Dk value increases as water content increaes

silicone hydrogel - Dk value decreases as water content increases

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7
Q

oxygen transmission

A

Dk/t

Dk divided by average thickness of lens

considers how much oxygen for a given lens can reach the cornea

lens power indirectly affects Dk/t

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8
Q

holden and mertz

A

measured corneal swelling following lens wear and compared to measurements from without wearing lenses

Dk/t = 24 for daily wear to avoid corneal swelling

Dk/t = 87 for extended wear

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9
Q

water content and ionic charge for classification of lens groups

A

water content and ionic charge affect:

strength

refractive index

deposit resistance

Dk

interaction with contact lens solution

as water content increases:

  • lens strength, deposit resistance, and refractive index decreases
  • oxygen permeability increases
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10
Q

classification of lens group

A

low water content is defined as <50% water, high water content is defined at >50%

  1. group 1: low water content, nonionic polymers:
    includes HEMA and hydrophobic monors, attracts less deposits, less oxygen permeability, stays clean longer
  2. group 2: high water content, nonionic polymers: lower protein interaction due to nonionic polymer matrix, avoid sorbic acid and potassium sorbate
  3. group 3: low water content, ionic polymers - greater attraction towards tear proteins and lipids, therefore exhibit more deposits than nonionic group
  4. group 4: high water content, ionic polymers: strongest proteins attraction, avoid heat disinfection
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11
Q

silicone hydrogel

A

latest and greatest technology in soft cl

  • very low water content
  • high oxygen transmissibility
  • beware of silicone allergy
  • the higher the amt of silicone, the lower the water content = the more oxygen transmitte to cornea
  • silicone material has higher modulus of elasticity (high resistance to deformation or stress), stiffer material compared to hydrogel

remember: hydrogel material has higher water content so it’s more fragile, therefore the modulus of elasticity is lower -> flimsier material

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12
Q

manufacturing methods

A

lathe cutting: PMMA, RGP, many soft CL

spin-cast: manufacture soft lens, hydrogel materials into a cast, spinning action determines final power

cast-molded: cost effective, reproducible, less labor intensive process for high-volume manufacturing

combination

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13
Q

lathe cutting

A

process begins with long, plastic cyl of material cut into lens buttons followed by:

  1. lathing: the hard, dry button is ground on a lath which cuts lenses into different front curves, base curves, and secondary curves when necessary
  2. polishing: removes any lathing marks, improves the optics, and smooths the edges
  3. hydration: for soft lenses - the brittle dry lenses are immersed in saline and become soft, flexible lens
  4. extraction: all unpolymerized chemicals or materials are removed
  5. tinting: if there is a handling tint
  6. finishing: full quality inspection
  7. sterilization: lenses are placed in autoclave for 20 minutes
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14
Q

spin casting

A

liquid lens polymer injected into spinning mold, followed by lens material being treated with heat and UV light (curing) -> causing liquid to solidify

front surface of lens determined by curvature of the mold

back surface is determined by combination of temp, gravity, centrifugal force, surface tension, amt of liquid in mold, rate of spin

high reproducible and thin, comfortable edges

small problem: often decenter on eye -> temporally or superior temporal

tends to be flat -> moves a lot (good an easy though)

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15
Q

Cast molding

A

make mold

liquid polymer poured into concave half of mold and convex portion of applied and clamped into place

material is cure with UV light and hydrated

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16
Q

contraindications

A

inflammation, disease of ant. seg., systemic disease that can be complicated by CL wear, poor hygiene, poor compliance, lack of motivation

irregular cornea (keratoconus, ocular trauma), autoimmune disease, immunocompromised patients, chronic allergies, chronic antihistamine use, GPC

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17
Q

indications

A

good tear quality and quantity

spherical RE

low astig.

low lenticular astig.

atheltes

unable to adapt to GP lenses

occasional/flexible wearer

desires tint to enhance or change eye color

previous GP adherence

previous 3 and 9 oclock staining with GP lenses

high motivation

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18
Q

soft lens advantages

A

excellent initial comfort

min. adaptation time

part-time wearing schedule possible

risk of corneal distortion min.

min. spectacle blur

dislocation uncommon

foreign-body sensation rare

ability to fit and dispence from inventory

low incidence of flare

low incidence of discomfort from excessive lens lag

ability to change or enhance eye color

simplicity of fit

rarely causes excessive tearing

disposable/frequence replacement possible

therapeutic use possible

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19
Q

soft lens disadvantages

A

reduced VA in uncorrected astig.

limited durability

oxygen transmission w/ hydrogels

deposit formation/ GPC possible

greater chance of bacterial contamination/infection

greater risks with noncompliance

more difficult to verify

limitation of corrections

quality of vision may be reduced

GPC

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20
Q

patient factors affecting material selection

A

RE

handling issues

deposit-prone patients

marginal dry eye

therapeutic use

ocular disease

age

aphakia

occupation

part-time wearers

refitting GP wearers

compliance

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21
Q

Refractive error selection

A

best candidates: spherical RE, low asitg, low lenticular astig

22
Q

handling issue

A

first time wears will benefit from thicker lens or increased stiffness/modulus of elasticity

ex. sihy material better for first time wearers

handling tint

23
Q

deposit-prone patient

A

soft lens are more prone to deposits than GP wearers

recommend frequent replacement - especially daily disposable

recommend hydrogen peroxide sol.

24
Q

marginal dry eye

A

50% of CL wearers report dry eye

ocular factors affecting dry eye: wettability, dehydration, cl sol., poor tear film quality, environmental temp, time of day, humidity, wind, blink rate

25
Q

therapeutic use

A

used for

corneal erosions, chronic epithelial defect, bullous keratopathy, mechanical trauma, dry eyes, filamentary keratitis

26
Q

ocular disease

A
  • diabetics benefit from daily disposables due to dec. wound healing
  • daily wear also recommended in epithelial stained corneas, decreased tear film, chronic allergies
27
Q

age

A

children may have diff. inserting large dia. lenses
-smaller dia. avail.

presbyopes may have difficulty viewing lens when cleaning or handling

  • add visibility tint
  • recommend thicker higher modulus lens
28
Q

aphakia

A

higher oxygen transmission critical due to thick lens center, usually silicone based

limited parameters

lenses can be very expensive

29
Q

refits

A

refit GP wearers to soft lenses

  • inability to adapt to GP lenses
  • chronic staining
  • chronic adherence that doesn’t improve

reduce wear time until cornea re-stabilize

use disaposable trials until cornea stabilizes

30
Q

compliance

A

patient are noncompliant with lens care and disinfection of lenses - daily disposables

patient sleep in their lenses - extended wear

patient eduction and information regarding adverse events

patients refuse to follow proper wear, care and handling steps should not be fitting into cl

31
Q

lens design parameters

A

base curve

diameter

power

center thickness

tint

replacement schedule

32
Q

base curve parameter

A

curvature of back surface of lens

optimize fitting relationship of lens to central and midperipheral cornea

flatter corneas -> flatter bc

steeper cornea -> steeper bc

flat k > 45 D; fit steeper bc

flat k is 41-45: fit medium bc

flat k < 41D: fit flatter bc

for k< 45D; fit flatter bc (8.7)
for k>45D: fit steeper bc (8.3)

bc in radians

33
Q

BC radian dioptric conversion formula

A
  1. 5/ radius = diopter
  2. 5/diopter = radius

diopters: steepen a lens -inc. the value
flattening a lens - dec. the value

radius of curvature: steepen a lens - lowering the value
flattening a lens - inc. the value

34
Q

diameter

A

diameter is measurement of full length of lens

overall diameter of lens should cover cornea 360 degrees and scleral - 0.5 mm in all direction

estimated dia: add 2 mm to HVID

increasing diameter, steepens/tightens the overall fit

35
Q

power

A

predicted power determined by patient’s spectacle
-vertexed back to corneal plane if rx > 4 D

if pt has low amt. of astig, do spherocylindrical calc.

underminus if power na

36
Q

4-6-8 rule

A
  1. 25 less if -4.00 to -5.75
  2. 50 less if -6.00 to -7.75
  3. 75 less if -8.00 to -9.75

vertex both meridians

37
Q

residual astig.

A

CRA: calculated residual astig.

  • amt of astig. comes through after cl placed on eye
  • residual astig. for spherical soft lenses = refractive astig.

CRA = refractive astigmatism (TRA) - keratometric astig (K)
-in soft lenses: CRA = TRA

38
Q

center thickness

A

minus power lenses range from 0.04 - 0.18 mm in center thicness

plus lens range from 0.2 to 0.7 mm in center thickness

thinner lens drape cornea more and move less with blink

thicker lens used for patients need assistance with lens handling

39
Q

tint

A

enhancing

opaque tints

handling tints

40
Q

replacement schedule

A

daily dispoables

weekly replacement

2 week replacement

monthly replacement

quarterly replacement

41
Q

sagitta

A

sag is measure of lens curvature

base curve as size

sagitta is relationship diameter and base curve = how it fits overall

steeper curves = grater sag

larger dia. = greater sag = tighter fit

dec. sag will loosen a lens on the eye
- flattening a base curve
- reducing diameter

inc. sag will tighten a lens on eye
- steepening a base
- inc. dia

42
Q

correcting sagitta

A

lens too tight:
-decrease sag: flatter BC, smaller dia

lens too loose:
-inc. sag: steeper bc, larger dia.

43
Q

5 essential evaluation elements

A

CLAMO or CHAMP

Comfort
Health
Acuity
Movement
Position
CLAMO
Coverage
location
acuity
movement
over-refraction
44
Q

position eval

A

complete covage and extends 0.5 mm onto scleral

good centration

45
Q

movement eval

A

ideal movement: 0.5 mm to 1.mm

push-up test: nudge lower lid to see if lens is moving

primary gaze: observe at 5 or 7 o clock pos.

superior gaze: lens should move with blink, more mvmt than primary gaze

lateral gaze: lens follow the movement

no movement and excessive movement can cause adverse affects - discomfort, awareness, and hypoxia

46
Q

acuity eval

A

should be 20/25 or better

clear, sharp, constant, and acceptable per patient

over-refraction required

flexing phenomenon

47
Q

health eval

A

lens condition must be assessed

lens is clear, cornea is clear, tears clear

48
Q

comfort eval

A

overall these are believed most comfortable cl on market - rgp, hybrid, scleral

uncomfortable: debri under lens, excessive mvmt, edge stand off, surface or edge rip, material allergy, gpc, dehydration

49
Q

chararcteristic of loose lens

A

position - superior or sup. temporal

mvmt - excessive

vision - inconsistent

healthy - mucus build up

comfort - lens awareness

50
Q

characteristic of tight lens

A

position - inferior

mvmt - little to no mvmt

vision - flexing phenomenon

healthy - hypoxia

comfort - initially great

no tears to oxygen

51
Q

other aux tests to check eval

A

over keratometry: quality of mires represent lens fitting

  • loose len: distorted mires immediately after blink
  • tight len: clear mires, then distorted

retinoscopic reflex

slide back test: slide lens off cornea either finger lower lid

  • observe how much effort it took
  • observe how fast lens returns to central pos.
  • loose lens: slide easily return quickly cornea
  • tight lens: slide off with more effort, will not return quickly cornea

tear smears

fluorescent dyes - fluorosoft

push up test

CL 1 (5 decks)

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