# Contact Lens Exam 2 Study Guide _Alana_

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```					CORNEA + CONTACT LENS MT2

 DIAGNOSTIC CL SELECTION

-   BASE CURVE
o Important K-values: (1) K (2) Kmean
o Base curve: 0.75D flatter than Kmean
o Fudge FLAT  always fudge toward flatter BC
 Flatter BC will yield apical touch fluorescein pattern  AT easier to quantify
 If your choices are btwn a lens 0.125D steeper or 1-2D flatter, choose the slightly steeper lens
 Example: Kmean = 43.12  BC = 42.37 (AA)
   42.37 is not in your trial set  42.00 v. 42.75: choose the flatter BC (42.00)
-   CONTACT LENS POWER
o Add 0.75 to the SRv EDS power to achieve a tear lens of -0.75
 Example: SRv = -2.75 -0.75 x180  EDS = -3.12  CLP = -2.37
o Fudge PLUS  always fudge toward more (+) CLP
 More plus CLP allows for a minus OR
 More plus CLP yields 20/40ish VA  pt will accept the challenge w/ (-) bc VA will
increase  prevents overminus
 More plus CLP with a minus OR will control pt’s accommodation
 More minus CLP yields 20/15 VA  pt won’t accept the challenge w/ (+) during OR  pt
overminused
 Example: CLP = -2.37  FIT -1.50  minus OR (patient will desire 0.87 addn’l minus)

 FP ANALYSIS

OBSERVE AND RECORD

-   Apical relationship: AT, AA, AC
-   Toricity in tear lens: WTR, ATR, OBLIQUE, SPH
-   Peripheral clearance: MAX, MIN, AVE (clock hours)
-   Lens positioning: C, HI, LO, N, T
-   EX: AT by 0.25D/DS/MAX/C

APICAL RELATIONSHIP: relationship + amount (if appl)

-   Apical relationship = how closely the base curve of the lens approximates the curves of the cornea
o Does the lens fit flat, steep, or just right?
o CL must be centered on the cornea to determine apical relationship
-   Apical alignment (AA)
o Fit: ideal (TL = -0.75)
o Bearing: area of maximum, even bearing throughout OZ
-   Apical touch (AT)
o Fit: flat (TL > -0.75)
o Bearing: dark area of bearing seen in center of OZ; surrounded by green
 Lens too flat for cornea  only touches cornea in center
 Lens too flat  compresses tear layer  tear layer appears black if too thin
o Quantifiable
 Flatter lens = more AT = less area of bearing = smaller dark area
 Steeper lens = less AT = more area of bearing = larger dark area (closer to AA)
-   Apical clearance (AC)
o Fit: steep (TL < -0.75)
o Bearing: dark ring of bearing seen in mid-periphery btwn OZ & SC; green seen in center of OZ
 Lens too steep for cornea  vaults over apex and touches cornea in mid-periphery
o Unquantifiable
 Steeper lens = more AC = bright green in OZ + bubbles (lots of space btwn CL + cornea)
TORICITY IN TEAR LENS: type + amount

-   Toricity = shape of the bearing (spherical or oval)
o More toric lens = smaller, narrower, more oval area of touch
o Less toric lens = larger, wider, more spherical area of touch
-   SPH: no toricity
o AT: area of bearing is circular in OZ
o AC: area of bearing is complete ring in mid-periphery
-   WTR: 180 is flatter meridian and 90 is steeper meridian w/ more power
o AT: area of bearing looks like a horizontal cigar in center of OZ
 Narrower cigar = more WTR toricity
o AC: area of bearing looks like ears in periphery
 Smaller ears = more WTR toricity
-   ATR: 90 is flatter and 180 is steeper
o AT: area of bearing looks like vertical cigar in OZ
o AC: area of bearing looks like hair + chin in periphery
-   Closer the area of bearing to the OZ = closer the lens is to alignment

PERIPHERAL CLEARANCE: amount + clock position

-   Peripheral clearance = amount of edge lift seen w/ lens in place; how much clearance under 3rd/2nd curve
o Impact on tear pump efficiency and 3-9 staining
-   Not necessarily uniform around the lens
o Spherical cornea: PC fairly uniform around the edge
o Toric cornea: more PC in some areas and less in others
-   Options
o Average
o Minimum: less edge lift = less green seen around edges
o Maximum: more edge lift = more green seen around edges (often seen with AT)

LENS POSITIONING

-   Len position = where the lens settles on the cornea
o Centered: seen w/ spherical cornea
o High: seen w/ WTR cornea + flat lenses (riding underneath upper lid)
o Low: seen w/ WTR cornea (shoots high during blink + settles low)
o Nasal: rarely seen but associated w/ ATR cornea
o Temporal: seen w/ ATR cornea
-   Lens movement = how much the lens moves

WETTABILITY

-   Wettability = how the tears react with the lens (tears aren’t uniform)
-   Poor wettabillity
o Caused by
 Poor front surface quality (scratches/wax)
 New lens may still have wax coating on  tears bead up on lens
 Poor tear quality/quantity
o Uncomfortable
 Lids drape over dry surface part of time
 Can affect vision
-   Improving wettability: polish lens; treat w/ menicon progent; clean lens; artificial tears
HOW TO

-   NaFl
o Wet orange end w/ multipurpose soft CL solution (NOT GP wetting solution)  shake off excess
o Instruct patient to tilt head back and look down towards their nose
o Hold upper lid and dab strip onto superior bulbar conjunctiva  have patient blink a few times
o FP = viewing the tear lens
o Use burton lamp or SL w/ cobalt filter (10-16x)
o Look for areas of bearing more than areas of green in OZ + SC jxn
o Evaluate the lens while it is centered on the cornea
o Remove, clean, & reapply a lens if there are signs of non-wetting or dry out

 INITIAL CL EVALUATION

INDICATIONS FOR CL WEAR

-   Refractive error
o Desire freedom from spectacles + reject refractive surgery
o GPs correct M, H, A, P
o High myopes, hyperopes, or astigmats benefit from reduced visual distortion & enhanced peripheral
vision when wearing CLs vs. specs
o Anisometropia: CL reduce spectacle magnification
-   Cosmesis
o Enhance or change the appearance of the eye
o Freedom from spectacles
o Prosthetic lenses can mask disfigured corneas or irides
-   Presbyopia
o Many multifocal correction options
 Distance CL + PT reading specs
 Near/intermediate CL + overcorrection specs for distance
 Monovision correction (most common option)
 Multifocal GPs (imultaneous or alternating vision)
 Modified monovision: one eye wears SV or MF optimizing distance + other eye wears SV or MF
optimizing near
-   Irregular astigmatism
o Irregular astigmatism induced by keratoconus, postrefractive surgery, corneal scarring, post-RK
o Spherical, aspheric, bitoric, & reverse geometry GP designs optimize vision for irregular corneas
 Front surface of GP creates smooth refracting surface
 Tear lens minimizes optical distortion caused by surface irregularity
-   Corneal dystrophies
o Eyelid interaction w/ fragile corneal epithelium & mechanical effects of CL application/removal disrupt
the epithelium
o SCL used as a bandage lens + worn on extended wear basis
 Best treatment for chronic & recurring corneal erosions
-   Amblyopia
o Opaque or high-plus contact lens used as an occluder/patch
-   Nystagmus
o Eyelids interact w/ lens edge to provide biofeedback to the patient on the mvmt of the lens
o Sensation enables patient to reduce amplitude/frequency of nystagmus
-   Prism correction
o CL can correct/reduce vertical hyperphoria
o Only BD corrections up to 4 can be achieved w/ CL due to gravity + lid interaction w/ prism profile
o Problems: no 1:1 effect
 GP: lens centration
 SCL: corneal edema (prism in carrier portion)
PROCEED W/ CAUTION

-   Pinguecula/pterygium
o Monitor changes in corneal topography + k’metry distortion in pts w pterygium
o Increased success rate if conjunctival injection, corneal staining adjacent to pterygium’s leading edge,
& peripheral corneal desiccation are minimized
-   Dexterity
o Patients w/ decreased manual dexterity need to make compensations or CL wear should be limited
 Issues most prevalent in geriatric/pediatric population
o Options include continuous wear lenses, application/removal assistant, limitation of use
-   Hygiene
o CL wear ill-advised when patients present w/ poor hygiene or report history of noncompliance
-   Environmental
o Jobs that have dusty/dirty workplaces may contaminate lenses or decrease comfort
o Noxious fumes can cause ocular irritation
-   Severe allergies
o Irritation, itching, redness, & mucus discharge can limit successful lens wear
o Alterations to palpebral conjunctiva can diminish CL comfort and cause excessive lens mvmt
-   Dermatologic problems
o Acne rosacea, psoriasis, + eczema can cause staph lid disease & exotoxins that can deteriorate
integrity of cornea  CL wear contraind
-   Glaucoma
o SCL can absorb medication + prolong the contact time of the medication to the AC
o SLC can hinder delivery of medication to the eye
o Removal of SCL prior to medication is safest recommendation
-   Dry eye
o CL wear contraind in dry eye pts that exhibit corneal staining & disrupted epithelium
 Breaks in natural defense of epithelium may lead to secondary infection
o Treatment options: changing lens material, care system, ATs, rewetting drops, punctal plugs
-   Thyroid dysfxn
o HyperT: exophthalmia  incomplete closure upon blinding leads to dryness of eye
o HypoT: dry eye symptoms
-   Diabetes
o Corneal basement membrane disorders can increase erosions
o Corneal sensitivity diminished + corneal healing slower
o Caution + regular F/U care advised
-   Immunocompromised
o Immunocompromised have increased risk for ocular infections secondary to CL wear
o Drugs that diminish immunity include topical/systemic steroids, cancer drugs, RA drugs

CASE HISTORY

-   Chief complaint
o CC = primary reason for patient’s visit
 May be more than one reason
 Might not be elicited during initial case hx
 Address the CC at the end of exam  describe findings + recommendations to patient
o Questions
 Close-ended Qs: used in self-administered pre-exam patient history forms (Y or N)
 Open-ended Qs: used in examination during case history
 Focused Qs: used in examination during case history for follow-up, secondary info
o Wording
 Minimize use of professional terms + eye jargon (focus vs. accommodate)
 Phrase questions concisely
 One question at a time
 Don’t use accusatory questions
-   Personal medical hx
o General health
 CL recommendations are modified based on systemic conditions/medications
 Diabetes
 Symptoms relevant to CL wear
o Reduced corneal sensitivity
o Poor corneal healing  corneal ulceration more likely w/ CL wear
o Refractive error fluctuations
 Prescribing considerations
o Extra patient education needed to discuss potential side effects
o CL wear contraind for moderate/severe diabetes
 Pregnancy
 Largest group of CL pts are F btwn 15 – 45yo
 Symptoms relevant to CL wear
o Less stable tear film  CL intolerance
o Corneal curvature may steepen  alter fit
 Common complaints
o Decreased wearing time
o Change in comfort
o Medications
 Many systemic medications have ocular side effects
 Dry eye symptoms
 Complaints: decreased CL wear time + decreased comfort
 Meds: decongestants, antihistamines, anti-HTN, oral contraceptives, anti-acne
 Refractive changes (esp myopia)
 Complaints: fluctuating vision w/ CL wear
 Meds: oral contraceptives
 Ocular irritation
 Complaints: decreased comfort
 Meds: salicylates, drugs taken at high therapeutic doses (excreted in tears)
 Mydriasis
 Complaints: flare + glare w/ CL wear (pupil size exceeds workable OZ)
 Meds: stimulants, antihistamines
 Miosis
 Meds: codeine
o Allergies
 Patients w/ mild/seasonal allergies succeed w/ CL wear
 Prescribing considerations
 Reducing hours of lens wear during symptomatic times
 Antihistamines can cause dry eye
 Patients may be allergic to preservatives in drops + care solutions
o Thimerosal (Hg based): immediate + delayed sensitivity rxns
o Use preservative-free drops or daily disposable CL
o Life-style
 Dietary supplements + hydration: impact CL comfort/success
 Alcohol consumption: contribute to dry eye
 Smoking: increases risk of microbial keratitis w/ CL wear
-   Personal ocular hx
o Previous eye care + eye wear
o Eye conditions: cataracts, glaucoma, dystrophies/degenerations, dry eye
o Eye injuries/trauma
o Eye surgeries: refractive, pterygium (many pts will forget to tell you)
o Eye medications (prescribed/OTC)
 Absorbed by SCL  increase contact time in eye + alter desired effect
 Preservatives (benzalkonium chloride)  hypersensitivity reaction
 Ointments coat lenses  blurred vision or contaminate the lens
-   Family hx
o Heredity does not play significant role in CL success
 Systemic + ocular conditions w hereditary basis should be investigated
o Parents w/ high myopia concerned about child’s RE
 GP lens wear + orthoK often used to stabilize/reduce progression of myopia
-   Contact lens hx
o Reason patient wants CL
o Expectations regarding CL wear
 Desired types of correction may not be appropriate for patient
 Help patients re-set unrealistic expectations
 Patient education on front end can increase success of CL wear
o Motivation + maturity: crucial to CL success
o Previous experience: how long ago, type of CL, wear schedule, care system, compliance, reason lens
was not successful (high cost, inconvenience, poor vision, poor comfort?)
 Details of previous experience can remediate + ensure future CL success
o More successful experience
 More frequent lens replacement
 New lens materials
 Improved care systems (less preservatives)
-   Vocation/avocation
o Cannot adequately address pt’s needs w/o knowing how pt uses their vision & specific visual demands
o CL wear in sports + hobbies
 GOOD:  FOV, no risk of specs being dislodged/broken
 BAD: no ocular protection  safety eyewear recommended over CL
 Recommend: safety eyewear over CL, daily disposables
o Water-related
 GOOD: daily disposables
 BAD: acanthamoeba contamination, do not recommend swimming in RGPs
 Recommend: daily disposables, prescription diving masks, watertight goggles
o Environmental conditions
 GOOD: CL do not become fogged with changes in temperature
 BAD: CL wear can become uncomfortable or contaminated in dry, humid, or dusty environmt
o Daily disposables minimize care system + contamination
 Travelers/campers
 Water-related sports
-   Goals + expectations
o Offer patient ALL options
o Which lens you try first depends on pt’s goals/expectations
 RGP v. SCL
 Sphere v. toric
 Cosmesis/tint
 Daily disposables v. replacement schedule
 FTW v. PTW v. EW
 Care system + compliance
 Cost (pt will let you know if they can’t afford it)
o Spectacle users: PT wear desired due to vocational, hobby, sports, social reasons
o CL users: need backup pair of specs + sun protection
-   Follow-up care
o Vision: can you see?
o Comfort: how do they feel?
o Wear time: affect on vision/comfort?
o Care system: can they use it correctly (compliance)
o Happy: is patient happy? Anything else patient needs?
TESTING PROCEDURES

-   Prefitting data should be precise  baseline to monitor changes over time
-   VA
o Entrance VA through HbRx needed before any msmts/testing performed (medical-legal purposes)
o BVA needed monocularly/binocular @ distance/near
-   Entrance tests: CT, EOMs, NPC, confrontations, amplitudes, stereo, pupils, PD
-   Preliminary msmts
o Horizontal visible iris diameter
 Helpful in determining SCL BC
o Pupil size in moderate-to-low illumination
 Useful in determining GP OZD (OZD = PS + 1.5mm)
 Important to evaluate in MF CL
o Palpebral fissure
 Useful in determining GP OAD (nomograms)
 Wider PF = larger OAD
 Helpful in determining SCL toric rotational stability
 Smaller SF = increased visual performance w/ toric SCL
o Eyelid position
 Useful in determining OAD + fitting philosophy
 Lid-attachment: upper eyelid covers superior limbus in straight ahead gaze
 Interpalpebral: upper eyelid does not cover a portion of superior cornea
 Useful in determining centration/rotation for MF GPs + application/removal
 Translating design successful if lower lid tangent to or slightly above inferior limbus
 Translating design unsuccessful if lower lid >1mm higher/lower than inferior limbus
o Eyelid tension
 Assessed during lid eversion
 Useful in determining centration/rotation for MF GP fitting + removal
 Lax tension/flaccid upper lid
o Lens may slip under lower eyelid upon downgaze
o Difficulty removing lens
 Excessively taut
o Difficult to achieve lens position that does not tuck under upper lid
 Assess frequency + completeness
 Concern for exposure keratitis (dryness) in inferior 1/3 of cornea
 Fit w SCL or large-OAD/lid-attachment GPs to optimize stability of tear film
 Rx routine re-wetting drops
 Lower 1/3 corneal staining
 SCL removal (pinching SCL directly off cornea will remove some epithelium)
 Lagophthalmos (nocturnal exposure)
 Blepharitis
 Hair spray
o Iris color
 Useful in determining cosmetic/therapeutic tints
 Cosmesis
 Tinted SCL allow enchancement/changes to natural color
 Tinted GPL not used for cosmesis  smaller diameter than cornea
 Therapeutic
 Opaque tinted CL useful in patients w/ corneal scarring or iris colobomas
-   Keratometry
o K’metry performed prior to applying DxCL
 Quantity: corneal toricity
 Quality: mire distortion
o Important in prescribing GP BCs
 BC flatter for larger OAD
 BC = flat K-value (fitting on K)
 BC = flat K-value + adjustment for corneal toricity
 BC = 0.75 flatter than ave K-value (SCCO)
o Amt of corneal toricity assists in lens design
 Spherical/aspheric BC = corneal toricity < 1.50D
 Toric/bitoric BC = corneal toricity > 2.5D
 Flatter than 42.00D = 9.6mm OAD
 42.00 – 44.00D = 9.2mm OAD
 Steeper than 44.00D = 8.8mm OAD
o Mire quality
 Poor mire quality results from tear film insufficiency, irregular cornea, corneal distortion
o Irregular corneas
 Flatter than 36D  attach -1.00 trial lens & subtract 6D from drum reading
 Steeper than 52D  attach +1.25 trial lens & add 8D to drum reading
-   Slit lamp eval
o Baseline SLE must be completed prior to fitting patient w/ CL
   Mag: 10-16X
   Illum: medium
   Lighthouse: angle not fixed
   Light: parallelpiped to find, optic section to determine depth
o   Filters
 Cobalt blue: excites NaFl to observe TBUT, corneal staining, or FP
 Red-free (green): enhances view of blood vessels
 Yellow: enhance view of corneal staining + FP
 Helpful with FP evaluation of GP materials containing UV-inhibitor
o   Lids/lashes
 Evert to look for CLPC
    EW (protein deposits)
    Torn/chipped CL (mechanical)
 Indicate infection/hygiene
o   Bulbar conjunctiva
 Indicate injection, pterygium, pinguecula
o   Palpebral conjunctiva
 Indicate bumps, concretions
o   Tear film
 Observe break-up time (not always related to sx)
o   Cornea
 Observe clarity
 Indicate SPK, ulcer, staining, neovascularization, FB
 EX: Peripheral corneal desiccation (3-9 staining)
    Result of disruption to epithelium (no O2 or fresh tears reaching cornea)
    Caused by suctioned lens, lids not flush against cornea
   EX: FB tracts
    Fresh: ice-skating imprint
    Old: scabbed imprint
-   Tear film evaluation
o TBUT & NITBUT
 Measure tear film quality
 Normal: >10sec || Abnormal: <10sec (dry eye)
 Notes: instilling NaFl will disrupt normal quality of tear film & can skew results
o  Schirmer tear testing
 Measures tear film production
 Normal: 15mm of wetting in 5 min || Abnormal: <15mm wetting (dry eye)
 Notes: presence of strip causes irritation + increased reflex tearing
 Measures tear film production
 Normal: 10-20mm wetting in 15sec
 Notes: less irriation bc thread is small  less reflex tearing
o Tear meniscus height
 Measures overall tear volume + regularity of volume across lower lid
 Normal: 0.22mm
-   Objective + subjective refraction (r’scopy > AR) (vertex powers >+4.00)
-   Add determination (add  0.25D every 4 years) (high add relative to age = overminused distance)
-   DxCl application
-   OR (vertexed)
-   FP evaluation of fit (apical relationship/toricity/PC/position)

VITAL DYES/STAINING

-   Sodium fluorescein
o Stains: intercellular spaces + damaged epithelial cells (no penetration of intact epithelial cells)
o Uses: evaluate corneal epithelium integrity; evaluate GP fit
o Filter: cobalt blue
o Advantages: water-soluble, low toxicity to ocular tissues
-   Rose Bengal
o Uses: evaluate anterior segment tissue integrity
o Filter: none (red/brown stain)
-   Lissamine green
o Stains: dead/devitalized cells & mucus
o Uses: alternative to RB
o Filter: none (blue stain)

PATIENT CONSIDERATIONS

-   Wearing schedules
o One hour break before & after CL wear
-   Cosmetics
o Apply CL before make-up
o Remove CL before make-up removal
-   Lid hygiene
o Warm soaks for meibomian glands
o Cool soaks for itch
o Eyelid scrubs for crusty lids
-   Part time wearers
o GP: build-up wear time over few days
o SCL: redisinfect the evening before wear; consider daily disposables
-   Accommodation/convergence
o Myopes
 Focus + converge more through CL
 Earlier development of presbyopia than spec wearers
o Hyperopes
 CL may delay onset of presbyopia
-   Compliance: wearing schedules, lens care, lens replacement, follow-up care
o Emphasize patient education = increased compliance = decreased CL complications
 LENTICULAR CL

-   WHAT: all SCL & mostly plus lenses (minus lenses too)
o Lens is one piece  not fused
-   WHY: decrease mass/bulk of plus lenses (thinner lenses)
o Improves comfort
o Improves centration
o Increases O2 transmission (Dk/L)
-   WHEN: CLP ≥ +4.00
-   HOW: specify optic cap size, junction thickness, flange radius
o Optic cap size
 Optic cap: OZ of front surface
 Size: 7.8mm (optic cap > F2 OZ)
 OC = OZ + 0.2
 Purpose: increased FOV; enhances centration
o Junction thickness
 Junction: thinnest/weakest area of lens btwn (+) lens OZ and carrier portion
 Size: higher Dk = thicker jxn thickness
 PMMA: 0.12mm | Low Dk: 0.13mm | Mid Dk: 0.14mm | High Dk: 0.15mm
 Purpose: used to specify center thickness
 CT = [(0.017)(CLP)] + [jxn thickness]
 Flange radius: peripheral curve on front surface; F1 radius of curvature
 Size: 0.5mm flatter than SCr
 Purpose: maintains usable edge; provides slight minus carrier effect
-   EFFECT: ~25% thinner
o Non-lenticular ct = (0.023)(CLP) + 0.19
o Lenticular ct = (0.017)(CLP) + jxn thickness
o EX: +4.00D  0.28mm to 0.21mm center thickness
o EX: +10.00D  0.42mm to 0.31mm center thickness
-   LENTICULAR SHAPES
o Plano carrier: used w/ any (+) lens
 Front & back surface of lens is parallel from edge of OZ to edge of lens
 Minimizes CT
o Minus carrier: used w/ high (+) lenses
 Allows lid to pick up lens and hold on
 Used with lid-attachment fittings
o Plus carrier: used w/ high (-) lenses
 Thins out extra edge thickness
 Indicate “plus lenticular”  no need to specify/calculate flange radius
o CN bevel: used w/ thick (-) lenses
 Diamond cone tool shaves off extra edge plastic (plus-ing the edge)
 Rarely used bc automated lays cut take care of it
-   LENTICULAR GPs
o High plus: specify (-) lenticular
o High minus: specify (+) lenticular
o Lid attachment: specify (-) lenticular
o ALL SCL (including toric)
-   EXAMPLE: 44.50(7.58)/+7.37/9.2/7.6/8.28/12.00/0.2/0.36/(+)/#1tint/FP60 (mid Dk)
o Optic cap: OZ + 0.2 = 7.6 + 0.2 = 7.8mm
o Flange radius: SCr +0.5 = 8.28 + 0.5 = 8.78mm
o CT: (0.017)(CLP) + jxn thickness = [(0.017)(7.37)] + [0.14] = 0.26mm
 LENS SWITCH

RGP LENS SWITCH AVOIDANCE

-   Always apply & remove right lens first
-   Place a dot on right lens
-   Right lens = gReen; left lens = bLue

IF SWITCHED

-   Fit altered
o In office: radiuscope analysis; FP analysis
o SAME BC  swap makes no difference (OR still plo in each eye)
o DIFFERENT BC  blur in overplussed eye (negative OR)
 Original
   OD: 44.00/-2.00 (AA, OR plo)
   OS: 43.50/-2.00 (AA, OR plo)
   Swap
   OD: 43.50/-2.00  AT by 0.50 (too flat)  FAP  OR +0.50
   OS: 44.00/-2.00  AC by 0.50 (too steep)  SAM  OR -0.50
   BLUR IN OS  overplussed by 0.50D
-   Vision altered
o In office: lensometery
o SAME POWER  swap makes no difference (OR still plo in each eye)
o DIFFERENT POWER  blur in overplussed eye (negative OR)
 Original
   OD: 8.6/-2.00 (AA, OR plo)
   OS: 8.6/-3.00 (AA, OR plo)
   Swap
   OD: 8.6/-3.00  OR +1.00 (too much minus for OD)
   OS: 8.6/-2.00  OR -1.00 (too much plus for OS)
   BLUR IN OS  overplussed by 1.00D
o    DIFFERENT BC/DIFFERENT POWER  BC OR + PWR OR
 Original
   OD: 42.00/+4.00 (AA, OR plo)
   OS: 43.00/+3.50 (AA, OR plo)
   Swap
   OD: 43.00/+3.50
o BC: AC by 1.00 (too steep)  SAM  OR -1.00
o PWR: Too much minus for OD  OR +0.50
o Final OR = -0.50
   OS: 42.00/+4.00
o BC: AT by 1.00 (too flat)  FAP  OR +1.00
o PWR: Too much plus for OS  OR -0.50
o Final OR = +0.50
   BLUR IN OD  overplussed by 0.50D

 GP MATERIALS

o Superior vision  better on low contrast letters
o Higher Dk (excluding silicone hydrogel)  not much of an issue anymore
o Better tear exchange
o Unlimited parameters + superior specialty designs
o Verifiable
o Modifiable + durable
o Better for dry eyes (esp scleral lenses)
o Less patient dependent + increased patient loyalty
o Poor initial comfort
o Longer adaptation  build up wear time over time; not good for occasional wear
o Increased FBs
o Dislodge in sports
o Tints not useful  GP small + moves upon blinking
o Spectacle blur/corneal warpage due to localized bearing or low Dk materials

Dk = PERMEABILITY

-   Terminology
o Permeability (Dk): material’s ability to be permeable to O2
 Specified by manufacturer as permeability thru center of -3.00D lens
 Used to compare materials
 Inaccurate w/ different powers + different companies
 Cornea only receives HALF the O2 w/ +3.00 SCL
 Different companies = different data collection = different results
o Transmissibility (Dk/L): material’s ability to transmit O2 at given thickness
 Varies based on power of lens
 High (+): less transmissibility through center
 High (–): less transmissibility through edges or mid-periphery
o EOP (equivalent O2 %): how thirsty the eye is for O2 after material is removed
 Looks at effect on the eye instead of directly measuring through surface
-   Dk dependent on:
o Polymer
o Temperature:  temp =  Dk
o Partial pressure of O2:  ppO2 =  Dk
o Boundary layer effects: controversy
 Companies would cheat & use different data markers/tests to make their product look better
 Different companies using different processes still came up w/ similar rank order of Dk
materials
-   Purpose of Dk
o Comparison shopping: predict lens performance + corneal physiology
 Higher Dk used for: thicker lenses, extended wearers, corneal irregularities
 Higher Dk drawbacks: harder to modify, scratch easy, less bend, less durable
o Product development
 Does new product with higher Dk have attributes of a lower Dk material?
-   Dk categories
o Low Dk = ≤50
o Mid Dk = 50 – 100
o High Dk ≥ 100
o Hyper Dk ≥ 150
-   What happens with increased Dk
Increased                                          Decreased
O2 transmissability (no longer 1:1 relationship w/ Wettability (lens w/ Fl has better wettability)
excessively high Dk)
Corneal physiology                          Machinability/modifiability (too much heat will warp lens)
Deposits (easily rubbed/rinsed off GP)      Durability (lens material softer)
Flexure/warp
Scratchability (lens material softer)
WETTABILITY

-   Wettability = ability of a hydrophobic lens material to become hydrophilic
-   Importance
o Increases comfort
o Better optics
-   Measurement
o Sessile drop: wet material = low wetting angle = water droplet spreads out on material
o Captive bubble
-   Variability
o Method used
o Material: flat v. lens form
o Solution used: wetting v. saline solution
o Pre-conditioned lens: lens wets better if soaked beforehand
o Testing environment: temperature, PPO2, etc
-   Maximizing lens wettability before dispensing
o Order lens pre-soaked from lab
o Clean + soak the lens after analyzing
-   If lens not wetting well, splotchy black spots appear during FP analysis
o Polish the surface to remove was from lab
o Progent treatment (bleach)

LENS MATERIALS

-   Silicone hydrogel
o EXCELLENT: O2 permeability (high Dk)
o POOR: less wettability; deposit resistance
o FAIR: mechanical/optical stability
-   Methacrylic acid (HEMA)
o EXCELLENT: wettability
o POOR: mechanical/optical stability
o FAIR: O2 permeability; deposit resistance
-   Polymethylmethacrylate (PMMA)
o EXCELLENT: mechanical/optical stability; deposit resistance
o POOR: O2 permeability (Dk = 0  impermeable)
o FAIR: wettability
-   Fluorine
o EXCELLENT: deposit resistence
o GOOD: wettability, O2 perm
o FAIR: mechanical/optical stability

HISTORY

-   PMMA: first lens
o Dk 0 – 0.2
o Terrible wetting angle but wet well on eye
o Very durable, easy to modify
o Edema generator  localized edema leading to corneal distortion
o Spectacle blur
o “BP flex”: crosslinked PMMA for better wettability
-   CAB: cellulose acetate butyrate
o Brand names: Rx56, Cab-curve, MESO, GPII
o Dk 4-12 (first effort for O2 transmissability)
o Not functional  poor wettability, warped easily, deposited easily
-    Silicon acrylates (PMMA copolymers)
o Dk 12 – 70
o “Polycon I” (1979)
 Dk 5
 Design: thin & user-friendly
 Clinical differences seen
o “Polycon II”  what changed the field
 Dk 10-12
 Design: lenticular, thin, lid attached
o “Paraperm O2”: Dk 15
o “Paraperm EW”: Dk 56; marketed to be slept in
-    Butyl styrene “Airlens”
o Dk 25
o Design: not made for human fitting  off the market
-    FSA: fluoro-siloxane acrylates
o Dk 30-151 (increase in Dk)
o Design: less surface charge than SA = fewer deposits
o Today’s GP lenses
 “Fluoroperm 60” (Dk 60): routine fits + keratoconus; easily modifiable
 “Boston XO” (Dk 100): routine fits + irregular corneas
 “Boston XO2” (DK 141): overnight ortho-K
-    Menicon: Dk 250
-    Plasma surface-treated GPs
o Procedure: low temperature ionized gases remove organic contaminants from lens surface
o Benefits: surface more hydrophilic, wetting angle decreases, removal of residue
o Drawback: loses affect in ~6mo (sooner if polished or abrasive cleaners used)
-    Special features: UV inhibitors, tints, EW, MF, aspherics, keratoconus

 FLEXURE/WARP

WARP

-    Warp = what happens to a lens; inherent in a contact lens (common)
-    Warp caused by: heat (hot car; cleaning too much) & GP material (higher Dk)
-    Measured outside eye via: radiuscope, lensometer
-    Bitoric v. warp
o Bitoric: typically >1.00D of difference btwn BC findings; 2 different lensometry readings
o Warped: <1.00D of difference btwn BC findings; no change in power (still spherical on lensometer)
-    Characteristics of warp
o Warp keeps same average BC
   Original: 44.00D
   Warped by 0.25: 44.12 x 43.87
o   Amount of toricity in TL reduced by amount of warp
   Power still reads as spherical
   OR is generated from toricity in TL but OREDS still plo
o   OR cylinder changes by amount of the warp
   Original: OR plo
   Warped by 0.50D: OR +0.25 -0.50
o   Fit/apical relationship does not change
   Equivalent sphere of the TL stays the same bc mean BC stays the same
   Warped lens will still line up flat meridian to flat meridian and steep meridian to steep
FLEXURE

-   Flexure = additional amount the lens changes on the eye from when it was warped; in situ
-   Flexure caused by: eyelid pressing on the CL over the cornea
-   Measured via: over-K, OR cylinder change, FP toricity change
o    Over-k’metry is difficult to do on small lens bc it moves around a lot
-   Characteristics of flexure
o OR cylinder changes by amount of flexure
o FP toricity change
o Apical relationship does not change

WARP + FLEXURE SUMMARY

-   FIT
o    Does not alter apical relationship
o    Reduces toricity of TL by W/F
-   OR
o    Does not alter EDS of OR
o    Changes OR cylinder by amt of W/F

FLEXURE DEPENDENT ON:

-   Center thickness:  thickless =  flexure/bend
-   Overall thickness: high plus/high minus lenses have less flexure
-   Corneal toricity (fulcrum): less toricity = less flexure (nothing to bend over); could still have warp
-   Fit/lens position: centered lens has more flexure bc bending over corneal apex; decentered lens
superior/inferior has less flexure bc peripheral cornea is flatter
-   Material: softer materials w/ higher Dk have more flexure than lower Dk materials

STUDIES

Authors                                 Findings
Harris + Chu                                - No flexure w/ spherical cornea for PMMA
- PMMA will flex if ct < 0.13mm
o   Other variables: tear film, loose lids
-    Lens flexes 1/3 corneal toricity if ct = 0.08mm
o   Anticipate warpage of 0.50 with 1.50D corneal toricity
Harris + Applequist                          -    High minus lenses flex less than low minus lenses for PMMA
o   Higher minus has greater center/overall thickness wrt low minus
Karatzas, Miyazaki, Dr. E                    -    Silicone acrylates will flex if ct ≤ 0.16mm
o   Increase center thickness to minimize/avoid flexure
Lopez, Stem-Francian, Dr. E                  -    High minus lenses flex less than low minus lenses for silicone acrylates
Prescher, Bywater, Dr. E                     -    Fluoropolymers will flex if ct < 0.18mm
o   Higher Dk is more apt to bend at larger center thickness (flexes more readily)
Harris et al                                 -    RGP lenses flex more than PMMA
Miller + Andrasko                            -    Flexure increase as Dk increases
Prescher, Bywater, Dr. E                     -    Flexure increase as Dk increases for newer fluoropolymers
Herman                                       -    Flexure is BC dependent
o   Flatter BC have less flexure (lens rides high and has no fulcrum to bend over)
o   Steeper BC have more flexure (rides more centerally on the cornea)
o   Lenses fitted steeper than K flex more than lenses fitted flatter than K
ENHANCE/AVOID FLEXURE

-   ENHANCE
o Rx lenses as THIN as possible (overall): decrease Ct while maintaining edge thickness of 0.10mm
 Eliminate third curve (bicurve lens)
   Reduces ct by 0.05mm
   Reduces ct by 0.01mm
   Steepen SCr by 0.2mm
   Reduce ct by 0.01mm
o    Rx lenses w/ high Dk
o    Fit to enhance centration
-   AVOID
o    Rx lenses thicker
o    Rx lid-attached lenses
o    Rx bitoric lenses (no fulcrum)

FLEXURE RULES  change toricity in TL = change fit and OR

Corneal toricity       OR cylinder       Change in OR cylinder
WTR                    ATR               OR cylinder reduced by amt of warp (warpage makes vision better)
WTR                    WTR               OR cylinder increased by amt of warp (warpage makes vision worse)
ATR                    ATR
ATR                    WTR               Does not exist

EXAMPLES

-   WTR cornea + ATR OR
o Km 43.75/42.25 @ 180 | OR +0.25 -0.50 x90 (OREDS = plo) | FP AA/-1.50 x 180/average/hi
o If lens warps by 0.50 it will reduce OR cylinder by 0.50ATR but maintain same EDS
 New OR: plo DS (OR cylinder decreases and OR sphere decreases to maintain EDS)
 New FP: FP AA/-1.00 x180 ( toricity in TL by 0.50)
o Happy patient
-   WTR cornea + WTR OR
o Km 43.75/42.25 @ 180 | OR +0.25 -0.50 x180 (OREDS = plo) | FP AA/-1.50 x 180/average/hi
o If lens warps by 0.50 it will increase OR cylinder by 0.50WTR but maintain same EDS
 New OR: +0.50 -1.00 x180 (OR cylinder increases and OR sphere increases to maintain EDS)
 New FP: AA/-1.00 x180 ( toricity in TL by 0.50)
-   ATR cornea and ATR OR
o Km 43.75/42.25 @ 90 | OR +0.25 -0.50 x90 (OREDS = plo) | FP AA/-1.50 x 180/average/hi
o If lens warps by 0.50 it will increase OR cylinder by 0.50ATR but maintain same EDS
 New OR: +0.50 -1.00 x090 (OR cylinder increases and OR sphere increases to maintain EDS)
 New FP: AA/-1.00 x180 ( toricity in TL by 0.50)

 FITTING PHILOSOPHIES

DETERMINING BC

-   SCCO: BC = 0.75D flatter than ave-K (verify fit via FP)
-   On-K: BC = flat K-value (most prevalent way to pick BC)
-   Nomogram systems: BC depends on OAD/OZD + corneal toricity
-   Indiana university: BC = (flat K-value) + (1/3)(K)
-   Lid-attachment: popular in 80s/90s  may not be best way to fit
-   Topography based: BC uses simulated K
-   Examples
o K-values: 44.00/42.50 @180 (K = 1.50)(Kave = 43.25)
 On-K: 42.50
 SCCO: 42.50
 IU: 43.00
o K-values: 43.75/43.00 @180 (K = 0.75)(Kave = 43.37)
 On-K: 43.00
 SCCO: 42.62
 IU: 43.25

DETERMINING CLP

-   SCCO
o DxCLP = 0.75D more plus than SRv(EDS)
o CLP = DxCLP + OR
-   OR: yields best data
-   On-K: CLP = spherical component of subjective refraction (power in flattest/on-K meridian)
o EX- K-values: 43.50/42.50 @180 | SRx: -1.75 -0.50 x180
 On-K: 42.50
 CLP = 1.75D

-   Best way: apply the fitting lens and look at the OAD on the eye
-   Nomograms: OAD depends on HVID + PF (smaller PF = smaller OAD)
-   Area of cornea covered: OAD should cover 60% of cornea (PMMA lenses)
-   Size of pupil: OAD = pupil size + 4mm

OZD

-   Nomogram: OZD depends on pupil diameter (smaller pupil diameter = smaller OZD)
-   Base-curve: OZD = BCr in mm (steeper curvature = smaller diameter for k’conus)

PERIPHERAL CURVES

-   Blended
o SCCO doesn’t blend (too hard to see curves)
o Common before we had automated lays
-   Tetra-curve (4)
o More curves = more difficult to modify/change fit
o Scleral lenses use more than 2 curves
-   Aspheric
o Aspheric curves = cant modify the lens
o Aspheric periphery made by many blends + narrow curves
-   Up to lab (most common)
o 1 – 1.5mm flatter than BCr

CENTER THICKNESS

-   ATAP: as thin as possible  cannot be thinner than 0.12mm
-   SCCO: ct = 0.023(CLP) + 0.19
o Minus lenses made much thinner this way
-   Plano = 0.19mm
o Subtract 0.01mm for every 1D minus (minus lenses still end up thick)
o Add 0.02mm for every 1D plus
o Add 0.02mm for every 1D K toricity
LID ATTACHMENT

-   Donald Korb started philosophy
o Observe CL mvmt & interaction w/ lid on a blink
o Upper eyelid should catch lens + keep it under upper eyelid
-   BCr: 0.25mm (1.50D) flatter than K  range of 0.15 to 0.70mm FLAT
-   Edge contour is critical
o Apex of edge biased twd anterior 1/3
o Lenticular minus edge
-   Diameter: 9.5mm (BIG)
-   Lens position: high rider; mimics upper eyelid (verify pupil covered by OZ)
-   Good candidates
o WTR cornea (lens rides high w/ WTR)
o Tight eyelids covering superior limbus
-   Not the best fitting philosophy
o K topography changes from localized bearing
 Increase in WTR
 Keratoconus-like appearance
 Flattening of superior cornea due to lens riding high
 Steepening of central/inferior cornea
o 3-9 staining occurs
o Must discontinue lens wear for longer period of time prior to LASIK  corneal exhaustion

ASPHERICS

-   Concept: create an aspheric, elliptical CL that better contours the elliptical cornea
o Aspheric: steeper curve in middle w/ gradual flattening in periphery (- to more +)
o If contour cornea exactly, then lens will never come off
-   Characteristics
o Aspheric F1 or F2 surface
 Aspheric F2: low add; better fit