contact lenses lec1

1. Contact Lens Theory 1 – Course 1
Augmented reality in a contact lens
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2. Contact Lens Theory 1 – Course 1
TOPTOPIC
1. Contact lens history and evolution
2. Contact lens definition, design, classification and
terminology
3. Converting radius to dioptres
4. Contact lens vertex distance compensation
Reading material
N. Efron – Contact Lens Practice
Chapter 1 – Pages 3-9
Contact lens design & specifications – Pages 444-445
Vertex distance corrections – Pages 446-447
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3. Contact Lens Theory 1 – Course 1
1. Contact lens history and evolution
1508
LEONARDO DA VINCI
Italian artist, scientist
- Sketched and designed several ideas for contact lenseskketchedand designed
several ideas for contact lens
- Described a method of neutralizing the corneal refractive power when eye is in the
water
“Study without desire spoils the memory, and it
retains nothing that it takes in.”
― Leonardo da Vinci
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4. Contact Lens Theory 1 – Course 1
1632
Rene Descartes
French philosopher and mathematician
-modified da Vinci’s ideas
and envisioned the corneal
contact lens
- presented a paper to the
French Royal Academy
stating that the living eye
can be neutralized or
corrected
“Divide each difficulty into as many parts as feasible and
necessary to resolve it”
- Renee Descartes
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5. Contact Lens Theory 1 – Course 1
• - used Descartes' principle to neutralize cornea
• - studied astigmatism, refraction and accommodation
• - experimented with light and glass
• - corrected his own vision using a ¼-inch long water-
filled glass tube which contained a microscopic lens
1801
Thomas Young
Medical education
• - discovered that vision could be corrected by
placing a lens directly on the cornea
• - designed lenses that fit directly to the eye by
grinding a contact lens to conform to the eye's
surface
1823-1827
Sir John Herschel
English astronomer
• - created an actual glass lens that could be worn
(and tolerated) by the eye
• - the glass lens covered the entire eye, was "scleral"
in nature and prevented the eye from drying out.
1887
F.E. Mueller
German glassblower
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6. Contact Lens Theory 1 – Course 1
• - both used contact lenses to correct optical
defects and produced the first contact lenses with
correction
• - Adolf Eugen Fick (1829-1901) first fitted
animals with the contact lenses and later made
them for people. Lenses were 18-21mm in
diameter made from crown glass
1888
A. Eugen Fick
Swiss physician
Edouard Kalt
French optician
• - perfected a method of making molds of living
eyes and used them to form lenses which fit
exactly to the shape of the eye
1929
Joseph Dallos
Hungarian physician
• Contact lenses are designed and perfected
in plastic (United States).
1936-1939
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7. Contact Lens Theory 1 – Course 1
• - created the first scleral lens made of
synthetic plastic which could be tolerated for
about 4 hours (the lenses had to be removed
after 4 hours of wear to replace the saline
solution that filled the space between the eye
and the lens)
• - introduced the lenses to the manufacturing
process
1939
William
Fienbloom
American
optometrist
Haptic lens from the 1940s – Photo courtesy of
Physick.com
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8. Contact Lens Theory 1 – Course 1
• - Contact lenses were made an official part of the
practice of optometry in USA1945
1948
Kevin Toughy
optician
designed
plastic contact
lenses to
cover only the
eye's cornea
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- designed plastic contact lenses to cover only
the eye's cornea
Sclar contact lenses

9. Contact Lens Theory 1 – Course 1
• - designed a contact lens with concave surface
following the eye's shape which rested on the
cornea and was smaller than the size of the iris
• - no solution as used with scleral lenses was
required
•- lenses could be worn all day
1950
George
Butterfield
American
optometrist
• - patented the silicon elastomer contact lens
1956
Walter
Becker2020-09-30 Tatiana Mighiu 9

10. Contact Lens Theory 1 – Course 1
• - developed contact lenses made of a soft,
water-absorbing plastic
1960
Otto
Wichterle
Drahoslav
Lim
Czech
chemists
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11. Contact Lens Theory 1 – Course 1
A Danish manufacturer developed a way for contact lenses to be made in a
continuous wet state. This would allow fewer distortions in the
manufacturing process. Lenses could be made with high precision and
repeatability. He sold the rights to Johnson & Johnson.
1980 - tinted daily-wear soft contact lens
1981 – extended -wear
(overnight) soft
contact lenses
1982 - bifocal daily-
wear soft contact
lens
1983 - tinted RGP
contact lens
1971 United States allowed the commercial distribution of contact lenses
1978
- toric contact lens
1979
- rigid gas permeable (RGP) contact
lenses
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12. Contact Lens Theory 1 – Course 1
1996 – disposable contact lenses with ultra-violet absorber
1997 – 1-Day Acuvue launched in the market and modern age begins
1991 - planned replacement contact lens
- daily-wear 2-week replacement contact lens
1992
- disposable tinted
contact lenses
1993
- J&J conducts trials for
1-Day Acuvue
1995
RGP contact lenses with
low silicone content
1986 - extended-wear (overnight) RGP contact lens
1987
- first disposable soft contact lenses
(Johnson & Johnson)
- soft contact lenses that change the eye
color appearance
1987
- RGP contact lenses made of fluoro-
silicone acrylate
- multipurpose lens care products
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13. What else has happened in the contact lens
world in the last 20 years?
What is new this year?
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14. Contact Lens Theory 1 – Course 1
2.Contact lens definition, design, classification and
terminology
How do we define the contact lenses ?
- as corrective lenses that are worn in contact
with the eye
- as thin plastic discs designed to fit over the
cornea held in place by the natural layer of
tears on the surface of the eye
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15. Contact Lens Theory 1 – Course 1
What are contact lenses used for?
- to correct vision
problems caused
by refractive errors
- hyperopia
- myopia
- astigmatism
- to correct vision
problems caused
by aging
- presbyopia
- to preserve
binocularity
- less magnification
- as surface protection
to the damaged eye
and recuperation of
the cornea
- cosmetic use - to
change eye color
appearance
- correction after
cataract surgery
when lens implant is
not advisable
- in occlusion
therapy to treat
- diplopia
- amblyopia
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16. Contact Lens Theory 1 – Course 1
What type of contact lens designs are available?
2.1 SCLERAL LENS DESIGN
- lens entirely covers the cornea and a significant part of
the sclera
2.2 CORNEAL LENS DESIGN
- lens floats on the tear film over the cornea
2.3 SEMI-SCLERAL LENS DESIGN
- lens covers the cornea and a small portion of the sclera
adjacent to it
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17. Contact Lens Theory 1 – Course 1
2.1 Scleral lenses
Scleral contact lenses are
designed to cover the entire
sclera and bridge over the
cornea.
TYPES
 Hard (PMMA)
 RGP (Rigid Gas Permeable)
 Hybrid
Designed with a:
- corneal section
- transition section
- scleral section or haptic
section
Fitting methods
a) Impression method
– an impression of the
eye is taken and copied
b) Performed lenses
– use of many diagnostic
lenses to find the right
one
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18. Contact Lens Theory 1 – Course 1
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19. Contact Lens Theory 1 – Course 1
Characteristics
- first lens used in the history of contact lenses
- correct refractive errors and protect some type of
diseased corneas
- large hard contact lens, molded to fit patient’s own
cornea and sclera
- between 1930's to 1970's lenses were made of a
hard, unbreathable contact lens material known as
PMMA
- modern scleral lenses are gas permeable, which
ensures that the eye receives an adequate supply of
oxygen
- are the largest contact lenses with diameters
ranging from 15 – 21mm
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20. Contact Lens Theory 1 – Course 1
Scleral lens in the eye
(marcoeyes.tumblr.com)
Front view Side view
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21. Contact Lens Theory 1 – Course 1
2.2 Corneal lenses (Rigid lenses)
Rigid contact lenses cover only
part of the cornea.
Types
 HARD (PMMA)
 RGP (Rigid Gas Permeable)
 Hybrid
Designed with a:
- optic zone
- transition zone (blending zone)
- peripheral zone(s) - one or
multiple peripheral curves
Fitting methods
1. Fitting on K
2. Fitting steeper than k
3. Fitting flatter than k
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22. Contact Lens Theory 1 – Course 1
Hard corneal lens
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23. Contact Lens Theory 1 – Course 1
Characteristics
- fitted with a high level of precision
- made of a hard contact lens material and
designed to fit over patient’s cornea
- manufactured in a great variety of designs
and materials
- diameters HARD lenses 8.0 -8.7mm
RGP lenses 9.0 – 9.6mm
- made to create a smooth refractive surface
for the eye with irregularities secondary to ocular
trauma, corneal transplant, corneal dystrophy and
keratoconus
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24. Contact Lens Theory 1 – Course 1
Corneal lens in the eye
(marcoeyes.tumblr.com)
Front view Side view
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25. Contact Lens Theory 1 – Course 1
2.3 Semi-scleral lenses
(Soft lenses)
Semi-scleral contact lenses are
shaped relative to the eye
topography to achieve central
contact and edge contact with
tear film clearance in between
Diameter of the lens extends
beyond limbus.
Type – Soft -Hydrogels
-Silicone hydrogels
Designed with a:
- optic zone
- peripheral zone(s) - one or
multiple peripheral curves
Method of fitting
• Three point touch
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26. Contact Lens Theory 1 – Course 1
Soft contact lens
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27. Contact Lens Theory 1 – Course 1
Characteristics
- are made from soft, flexible materials called
hydrogels (watery gels) or the newer materials
called silicone hydrogels
- water content 38% - 79%
- diameters 13.8 – 14.5mm
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28. Contact Lens Theory 1 – Course 1
Semi-scleral lens in the eye
(marcoeyes.tumblr.com)
Front view Side view
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29. Contact Lens Theory 1 – Course 1
Contact lens designs
1 HARD DESIGN
- spherical lenses - provide spherical correction
- used to correct hyperopia and
myopia and up to 3D of corneal
astigmatism
- toric lenses - provide both a spherical and a cylindrical
correction
- used when is a large amount of corneal
astigmatism and a spherical lens design can
not be fitted properly
- front toric design will require a method of
stabilization
- bifocal lenses - provide correction for presbyopia
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30. Contact Lens Theory 1 – Course 1
2 SOFT DESIGN
- spherical lenses - provide spherical correction
- can correct corneal astigmatism up
to max 1.50D when spherical
equivalent rule can be applied
- toric lenses - contains both a spherical and cylinder
component to correct prescriptions which
have astigmatism
- use a mechanism of stabilization so that its
position in the eye is maintained
- are thicker in one meridian or have
modified thickness profiles to enable the
lens to maintain correct orientation
- bifocal lenses - provide correction for presbyopia
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31. Contact Lens Theory 1 – Course 1
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How are contact lenses
made?
What differences
would be?
Are there any similarities
with the way eyeglasses
are made?

32. Contact Lens Theory 1 – Course 1
Contact lens terminology
1. Base curve - the curvature of the back
surface of a contact lens
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33. Contact Lens Theory 1 – Course 1
BCOR – Back Central Optic Radius or
BOZR – Back Optic Zone Radius
- the curvature of the central portion of the back
surface of a contact lens
- designed to conform the optic zone of the cornea
- can be measured in mm or diopters
- uses refractive index of keratometer to convert
Optic Zone BCOR
- is the central area of a
lens with the specific OZ
optic power ordered
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34. Contact lens theory 1- Course 10
FCOR – Front Central Optic Radius or
FOZR – Front Optic Zone Radius
- is the front curve of the lens (or anterior curve) -
the curvature of the central portion of the front
surface of a contact lens measured in mm and
diopter
BCOR
FCOR
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35. Contact lens theory 1- Course 10
PC - Peripheral Curve(s)
- one or more curves surrounding the central base curve
- is a flatter radius at the edge of a contact lens
- allows for greater comfort and greater tear exchange
(have to consider that the corneal surface is aspherical
and flattens towards the periphery)
- rigid lenses have very specific peripheral curves, some
soft lenses have as well, but harder to measure
PC - width (Peripheral curve width)
- refers to the measurement of one side of the curve
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36. Contact lens theory 1- Course 10
Secondary curve (SC) – the first curve that follows after
the optical zone (OZ)
Transition zone – the junction between OZ- SC,
SC - PC and between all other
peripheral curves
Blending – is the smoothing out of the transition zone
(terminology associated with rigid contact
lenses)
Total diameter (TD) – is the total diameter of the lens
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37. Contact lens theory 1- Course 10
(www.slideshare.net)
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38. Contact lens theory 1- Course 10
Bevel
- usually refers to the front contact lens surface
- is applied on high minus lenses to reduce edge
thickness
- conforms closely to the radius of the back surface
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39. Contact lens theory 1- Course 10
Contact lens design
Front view Cross-section view
Junction
Back Optic
Zone Diameter
Peripheral curve width
Ct
TD
Back Optic Zone Radius
Back Peripheral Curve Radius
Front Optic Zone Radius
Ct – central thickness
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40. Contact Lens Theory 1 – Course 1
Sagithal depth or height or vault
- is the distance between a flat surface and the
back surface of the central portion of the lens
Considerations
For the same lens diameter
a. as sagittal depth increases the lens will vault
the cornea and the effect will be that the
lens will fit more steeply or tightly
b. as the sagittal depth decreases the lens will touch
cornea and the effect will be that the lens will fit
flatter or looser2020-09-30 Tatiana Mighiu 40

41. Contact Lens Theory 1 – Course 1
(www.oculist.com)
(www.clspectrum.com)
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42. What lens design is it? Soft
Contact lenses
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43. What lens design is it? Corneal
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44. Contact Lens Theory 1 – Course 1
3. Converging radius into diopter
Formulas to be used:
Where: n = 1.3375 keratometer standard refractive
index
r = radius of curvature (m)
BCOR (back central optic radius) = the curvature
of the back surface of the contact lens (dpt)
Ex: 43.5D =>7.76 mm
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1.3375 – 1.00
BCOR (dpt) = ──────────
r(m)
1.3375 -1.00
r = ───────────── (m)
BCOR(dpt)

45. Contact Lens Theory 1 – Course 1
4. Contact lens vertex distance compensation
In order to dispense contact lenses, the powers higher
than +/- 4.00D in each principal meridian of a spectacle
Rx, have to be compensated for vertex distance.
Formula to be used:
MOST IMPORTANT
FORMULA IN CONTACT
LENS DISPENSING
Where: F - compensated power (dpt)
Ft - total power of the lens (dpt)
(as in spectacle prescription)
d - vertex distance (mm)
(in contact lens calculations, if not otherwise
specified d = 12mm is used)
Ft
F = ———
1 – d(Ft)
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46. Contact Lens Theory 1 – Course 1
QUESTIONS
1. Why do I have to convert radius of curvature from millimeters in
diopters and vice versa?
2. Why compensation needs to be done?
3. Why only powers over +/-4.00D need to be compensated?
4. Do I have to compensate one or 2 meridians?
5. How do I know which are the principal meridians?
6. How accurate the resulting answer needs to be?
7. How do I now my solution is correct?
8. What to do if I do not know how to solve this type of problems?
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47. Contact Lens Theory 1 – Course 1
ANSWERS
1. Because measurements of corneal curvature are done on most
instruments in diopters and lenses are ordered in “mm”.
To easily determine if a base curve is flat, steep or median.
Median BC = 43.50D, less than 40.00 are considered very flat and more
than 46.00D very steep
2. Because the spectacle refraction is done with the testing lenses being
placed 10-14mm in front of the eye where normally eyeglasses sit, but
contact lenses fit on the cornea
3. Because significant powers changes occur for powers over +/- 4.00D and
need to be accounted for.
4. Only the meridian or meridians with powers over +/-4.00D
5. Transpose the power in the other (cyl) form and look at the spherical powers of
both transpositions. If over +/-4.00 transpose
6. FOR COMPENSATED RX AND BC in DIOPTER POWER ALWAYS ROUND YOUR FINAL
ANSWER TO 1/8D
FOR CALCULATED BC IN MILLIMITERS ROUND FINAL ANSWER TO 2 DECIMALS
7. Compensated MINUS power results in LESS minus
Compensated PLUS power results in MORE plus
8. ASK ME, a colleague, anybody can help you, as with these formulas start all CL
problems
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48. Contact Lens Theory 1 – Course 1
In class problem solving
Part A Converging radius to diopter to radius problems
1. Determine for the following contact lenses the base curves in
diopter power, if the base curves in millimeters are:
7.80mm
8.20mm
9.00mm
6.96mm
7.44mm
7.50mm
Round your answer to 1/8D
2. For the following corneal curvatures measured in diopters as 42.25D,
40.67D, 44.12D, 43.00D, 38.37D and 39,75D and determine the radiuses
of curvature in millimeters.
Round your answer to 2 decimals.
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49. Contact Lens Theory 1 – Course 1
Part B Vertex distance compensation problems
1. A patient was refracted at a 12.0mm vertex distance and was given a spectacle prescription of
- 6.25DOU. What would have to be the contact lens Rx used for the selection of a contact lens
power for this patient? Round your final answer to 1/8D.
2. What will be the contact lens Rx used to select the appropriate contact lens power for this
patient with a spectacle Rx of +6.25D OU, if the patient was refracted at 12.5mm? Round
your final answer to 1/8D.
3. What contact lens Rx has to be used in the selection of a contact lens powe for a patient, if his
spectacle Rx is - 3.75 - 3.50 x 180 OU and he was refracted at a vertex distance of 13mm?
Write your final answer in (-) cyl form and round to 1/8D. Place the spectacle Rx powers and
compensated powers on an optical cross
4. What is the contact lens Rx used in the selection of a contact lens power, if a spectacle Rx
refracted at 10mm is - 6.25- 3.50 x 180? Write your final answer in (-) cyl form and round to
1/8D. Place the spectacle Rx power and compensated powers on an optical cross
5. Determine the contact lens Rx for the following spectacle Rx +4.00 + 1.75 x 090 refracted at
11.5mm. Write your final answer in (-) cyl form and round to 1/8D. Place the spectacle Rx
power and compensated powers on an optical cross.
6. Determine the contact lens Rx for the following spectacle Rx +4.75 + 1.25 x 065
refracted at 11.00D. Write your final answer in (-) cyl form and round to 1/8D. Place the
spectacle Rx powers and compensated powers on an optical cross.
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50. Contact Lens Theory 1 – Course 1
Homework
Part A Converging radius to diopter to radius problems
1. Determine for the following contact lenses the base curves in diopter
power, if the base curves in millimeters are: 8.41mm
7.80mm
6.98mm
Round your answer to 1/8D
2. For the following corneal curvatures measured in diopters as 45.87D,
44.25D and 39.75D determine the radiuses of curvature in
millimeters. Round your answer to 2 decimals.
How are the above corneal curvatures? Flat, average or steep?
Enter your answers in the box below.
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Problem Unit FLAT AVERAGE STEEP
1 mm
Dpt
2 Dpt
mm

51. Contact Lens Theory 1 – Course 1
Homework cont.
Part B Vertex distance compensation problems
1. What will be the contact lens Rx if a spectacle Rx refracted at 12.5mm
is +6.25D?
2. Determine the contact lens compensated power for a spectacle Rx
of +4.75+ 2.50 x 150 refracted at 10 mm vertex distance?
3. Determine the contact lens Rx for a patient with
the following spectacle Rx.
OD - 4.75 – 1.25 x 065
OS - 3.75 – 2.00 x 090
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