RIGID CONTACT LENS PRESBYOPIC
CORRECTION
Objectives of this lecture:
1. To be able to understand RGP bifocal applications as well as monovision and reading glasses
2. To understand RGP bifocal lens designs, fitting and problem-solving
INTRODUCTION
•Most Rapidly Growing Segment: 200 million presbyopes by the year 2000
(every 10 seconds a new presbyope)
•Only 7% Wearing Contact Lenses due to:
Practitioner Confidence
Spectacle Market
•The demand will increase with the introduction of Acuvue Bifocal:
GET READY
RIGID LENS ALTERNATIVES
A. Single Vision/Reading Glasses
B. Monovision
C. Aspheric/Simultaneous Vision Multifocals
D. Segmented & Concentric/Translating or Alternating Vision Bifocals
Simplest
Requires Least Time
Most Consistent Vision
Cosmesis???
Frequent Removal
a. Each eye has uninterrupted vision
b. Simultaneous vision bifocals create blur
("3-D" Effect, Retinal Illuminance)
c. Fear and perceived difficulties with translating design
Candidates
Good contact lens candidate
Early presbyopia
Varied (non-critical vision needs)
Anisometropia
Material/Fitting Considerations
Lens
Material
Good Wettability and adequate oxygen transmission
Examples:
A. RGP
Medium-High DK F-S/A
B. Hydrogel
Disposable/Planned Replacement
Fitting/Patient Education
Demonstrate
add power
Prescribe full amount
Allow up to 4 – 6 weeks for adaptation
Binocular
function testing
Selecting the proper eye for near
Non-dominant
Reduced BVA
Higher
myopia
Driving?
Special Considerations
1. Two
distance lenses, 1 near lens (double dot second distance lens)
2. Handling
tint
Driving Rx – minus power over near eye (good centration to minimize prismatic effect)
Advantages/Problems
Advantages
No special lens design
Inexpensive
Only one lens changes for present wearers
More physiologically acceptable
Problems
Suppression
Depth Perception
Contrast Sensitivity
Night Driving
Liability
Legal Implications (Harris, Classe)
Practitioners are legally and clinically responsible
All corrective alternatives should be presented and discussed
Explain all compromises
Informed consent recommended
Bottom Line
Monovision is an effective option
Proper patient selection and education is essential
Always consider bifocal contact lenses for every presbyopic patient
RGP BIFOCALS
•The demand is HERE!
•RGP Bifocal Sales Up
•Give Patients a Choice
"There’s No Such Thing"
"They
Don;’t Work"
"Certainly (then fit MV")
•Results of a Study
•Berkeley Patient
Patient Consultation
RULE of 3 (or 4):
Number of Fits
Patient Consultation
Patient Selection
Fitting
Problem-Solving
•Provide options to patient
including:
Distance CLs + readers
Monovision
Bifocal CLs
•Assess Motivation
Advise PT about compromises with
CL Correction
Is motivation simply not to wear
spectacles?
Do they desire to be 25 years old
again?
Patient Consultation
•Explain the dynamics of bifocal CLs
If
properly fit, they provide acceptable vision at distance and near
They move up
and down during the blink cycle, unlike spectacles that remain stationary
They may
experience transient blur with certain directions of gaze
Can the
patient accept mild compromise in vision?
•4 – 8 weeks to adapt
Lens changes are the rule!
No Monday morning surprises
Bottom Line: 80% success
•Pre-fitting Evaluation
Pupil Size
Lower Lid Position
Lid Tonicity
Vertical Fissure Size
Tear Quality
Simultaneous Vision – both distance and near images received by the retina; one image is suppressed. Bivision will exist and images will be formed on the retina at the same time. The patient will selectively repress the image that isn’t going to be used. For true simultaneous vision, the segment must remain within the pupillary boundary in all positions of gaze and in order to give equally bright images, the distance and near areas of the lens should cover equal areas of the pupil.
Eccentricity: Deviation from a
circle or rate of flattening
0 = circle
0 – 1 = ellipse
>1 = hyperbola
0.45 - 0.70 = single vision
0.70 - 0.90 = presbyopic
Posterior surface – in principle, the aspheric back surface increases in plus power as the light falls more and more peripherally
Representative Examples:
Traditional (High Eccentricity)
Designs
VFL 3 (Corforma)
•BCR : 6.9 – 7.6mm
•Fit 3D Steep; apical clearance; mid-peripheral alignment
Contemporary Lower Eccentricity
Designs
•Fit 1.00 – 2.00D steeper than "K"
•Representative Examples:
Lifestyle GP
Boston Multivision
Tangent Streak No-Line
Essentials
Best Candidates:
Loose Lids
Large palpebral aperture
Lower lid margin well above or below limbus
Pupil about 3 – 4mm
Steep corneas
Advantages/Disadvantages:
Advantages:
No prism
No segment
No image jump/segment flare
Conventional center thickness
Good intermediate vision
Disadvantages:
Problems with high adds (typically
provide up to 1.25D Add; most newer designs have added +power to front surface
to increase add; still limited to up to 1.75D and optical quality is
compromised.
Must Center!
Steep BCR
Flare
Do They Translate?
Troubleshooting
If excessive movement, inferior decentration or apical bearing, select steeper
BCR
If lens continues to decenter and/or move excessively, go to translating design
Available in many types:
•D-shape (Fluoroperm ST)
•Executive (Tangent Streak, Solitaire)
•Crescent (Solutions)
•Decentered Target
One Piece Vs. Fused
Tangent Streak (Fused Kontacts): Representative Example
A. Executive Bifocal
Prism (2-3 PD), Truncated
Fit 0.25 – 0.50D Flat
Fine line for segment
No jump due to distance/near zones at a tangent
Fitting:
Lens should position low in primary position
Sufficient translation should be present on down gaze
Truncation provides positive stop at lower lid margin
Dx Set: 9.4/9.0mm OAD; +2.00/+2.00D Add & -2.00D/+2.00D Add; 2PD
BCR Selection:
Corneal Toricity BCR
0.00D
1.0D Flat
0.50D
0.50D Flat
Over 1.0D Not Steeper than 1/4
toricity
Fitting Nuggets:
Have 2-3 diagnostic sets (aspheric and translating)
Use trial lens over-refraction
Check VA in various illuminations
Translating Fitting Nuggets:
Evaluate position of lower lid to limbus
Evaluate position of seg line to pupil in straightahead gaze (no laughling!)
Evaluate translation in downward gaze
Troubleshooting:
Excessive Rotation
•Flatten BCR 0.50D
•Increase Prism .5PD
Lens is too high
•Increase prism .5PD
•Flatten BCR 0.50D
No translation
•Intermittent or Constant?
•Flatten BCR 0.50D and order with flatter PCR
•Consider increasing prism/truncation
Blur at Distance
•Lens too high (treat as before)
•Lens too low (incr. OAD)
•Seg height too high
•Excessive movement (same as too high)
Blur at Near
•Seg height too low
•No translation
•Patient drops head, not eyes
•Excessive rotation
Best Candidates –
segmented/translating design
Lower lid within 1mm of lower limbus
Moderate to tight lower lid tension
High add requirement
Distance acuity requirement
Segment Design
Advantages/Disadvantages
Advantages:
Variable segment height
High adds possible
Large near zone
Translation
Disadvantages
Jump with One-Piece
Prism necessary
Expense
Time-Consuming
LENS SELECTION
Occupation
Early vs. High Add computer users
High versus low critical vision
demands
Add power requirement
Pupil size and dynamics
Lower lid position
CASES
SUMMARY
Provide all options; not just
monovision
Explain differences in bifocal
contact lenses vs. spectacles
Have several diagnostic sets
Choose simultaneous or translating
vision
Remember troubleshooting rules
Bifocal CL’s provide good value
Bifocal Cl’s provide vision that is
acceptable to most PTs
Fitting bifocal CL’s is WORTH YOUR EFFORT