MT1 Flashcards
Leonardo Da Vinci
The first to describe neutralizing cornea with a new refractive surface. Drew schematic eye and described how an image one was formed.
Descartes
Described how placing a tube of water on the eye would give perfect vision. Came up with telescopes
Young
Father of optics. First to describe and measure astigmatism. Described how accommodation occurred by changing the lens. First to give scientific reason for color vision. Designed the hydradiascope.
hydradiascope
25 mm tube closed at one end by a biconvex lens filed with cold water and placed at orbital lens. Designed to study accommodation.
John Herschel
First to take a photograph onto glass. Described a contact lens with a posterior surface (fit cornea) and anterior surface (designed for RE)
Muller
Master glass blower and made artificial eyes. Made a CL for a patient with a exposure following malignant lid tumor. Wore this for 21 years. New one made every 12-18 months. Had no RE power.
When was the first CL invented
1888
What three people invented CL
Fick, Muller, Kalt,
Fick
First published work on CL. Experimented from molds from cadavers. Muller and Zeiss gave him Cl.
Muller CL maker
First to describe why contact lens created corneal edema.
Kalt
Developed first lens for keratoconus. Used base lens citing on keratometric measurements. 11m lens design. Made from segments from the bottom of test tubes.
Muller Company
Scleral lenses from blown glass. Had a greater patient tolerance since no sharp edges remained
Zeiss company
Ground glass scleral lens. First to produce a commercially available diagnostic set.
Dallos
First to make impression of living eyes using negocoll. First to describe toric and lenticular lens design.
When did PMMA become material of choice for Cl
1938
Feinbloom
The first to use plastic for cl. The central portion is glass and the scleral portion is plastic. First to describe bifocal cl.
Gyorffy
First to make completely plastic scleral contact lens.
Obrig
First to suggest using fluorosceine dye with cobalt blue to evaluate fitting relationship
Bier
First to describe a scleral lens that incorporated a transitional curve between the cornea and sclera portions to provide limbal clearance.
First way to make molding CL
Used negocol to mold the eye. Removed and made cl off of mold. Then you would modify the lens based off of the mold.
England
Deisgned first CORNEAL CL made of PMMA. However, patient was rejected.
Tuohy
Patient first Corneal CL. A mono curve design. Must be first 1.50D flatter than flat K.
Butterfield
Designed the first multi curve contact lens to better contour the true shape of the cornea.
Dickson, neil, Sohnges
Developed the Microlens. 9.5 mm in diameter with average thickness of .2 mm.
Wichterle
First soft CL. Used a wichterle’s spin cast system. Morrison and National patient development got rights.
Food and Drug
CL became a drug.
Bausch and Lomb
First hydrogel lens approved by FDA for the US market.
Heat disinfection
First way to clean CL
First chemical disinfection
- Solution sensitivity.
Lens care today
Multi-purpose solutions, hydrogen peroxide, UV systems
RGP material
PMMA–>CAB–>silicone acrylate–>fluorosilicone acrylate
Hyatt
invented celluloid plastic
History of CL plastics
PMMA–>CAB–>polystyrene–>fluropolymers–>silicone
PMMA
Very durable. Doesn’t change shape. Good weight and wetting. Howevery does not have oxygen transmission.
Corneal edema and PMMA
Central corneal clouding due to decreased oxygen transmission. The basal layer has greatest metabolism and decreased oxygen causes it to separate from bowman’s. This is a great corneal abrasions. Occurs from overwear syndrome.
Spectacle Blur
Wearing Contact lens causes the cornea to warp and then when the patient puts on their glasses they cannot see.
Endo changes with PMMA
polymorphism and polymegaism
Hypoxia and Cornea
The endothelium releases lactic acid in response to hypoxia. This is what hurts the endothelium.
Cellulose Acetate Butyrate (CAB)
A great failure but a great step.
Silicone Contact lenses
Pure silicone lenses have the highest oxygen permeability in a cl. Only used with pecs with aphasia. Has a surface TX that is hard to support with an adults tear film. DK=340
DK
How much oxygen can get through a cl
Polymer
All other Cl are polymers (made of many different parts)
Silicone Fluorine
Used for oxygen premeability
Methacrylic acid/ Hema
Wetting agents
Methylmethacrylate
mechanical and optical stability
Oxygen Transmissiblity
A material oxygen tranmission is known as its Dk/t. t=lens thickness. DK=oxgen permeability.
Oxygen permeability
D=diffusion. Inherent ability of material that allow oxygen to diffuse through holes or voids in plastic
K=solubility. Degree to which oxygen is absorbed within or on a material
Diffusion
Physical spaces within the material
Solubility
Absorbed within a material.
What material do we use today
Flurosilicone acrylate
Measurement of oxygen transmission in vitro
polygraphic technique.
Measurement of oxygen transmission in vivo
- Equivalent oxygen percentage. Lens placed on a rabbit. 2. Can also measure overnight corneal swelling. (no cl to get a baseline and then with a cl) More swelling with lower DK. 3. Biochemical corneal changes 4. epithelial mitosis 5. corneal sensitivity 6. Limbal vascular response
Oxygen Flux
The actual amount of oxygen that diffuse through a contact lens and is available to cornea
Oxygen availablility
The driving force of oxygen through a contact lens. Reduced at higher altitudes.
Oxygen tension
Driving force of oxygen through a contact lens
Minimal lens and TF thickness
Lens=100 TF=10-20
Why does cornea wet?
Due to micorvilli that holds mucin material
Ways to measure wetting properties
Sissile drops, captive bubble, wilhelmy plate
Plasma treatment
Should use on all gas perm. lenses. Gets rid of waxy material. Cleans the lens and increase wetting. Will then ship wet.
HydraPEG
A coating that makes contact lens more hydrophilic. Only lasts about 2 months.
Dimensional stability
Base curve radius stability. PMMA is more stable. How well contact lens keeps shape
Flexural/Fracture resistance
The lens should not fluxuate. Should hold shape with blinking.
Flexural resistance measurement
In vitro: Lab. mesaurements.
In vivo: residual astigmatism
CL hardness
How many scratches the lens gets. Polish scratches for comfort.
Lens specific gravity
The weight of the lens. Solubility diffusion lens are the heaviest. AKA those made of fluorine are more heavier.
Index of refraction of lens
Only use material with high n for multi-focal cl. (allows more add power to be derived) Styrene was used but low DK so not popular.
Machining Properties of lens
Should be able to maintain the lens. UV resistance and heat resistance.
Optium solution
Very good product. hard to get though
Lanoline based products
Lenses won’t wet with left over debris. Must wash hands with non cold cream based soap.
Progent and unqiue PH
Best cl invention for cleaning.
Gas permeability lenses schedule
Begin with 4 hours on Day 1. Increase wearing 2 additional hours a day.
Steps to GP lens fitting
- lens diameter 2. Base curve radius 3. lens power
Average corneal diameter
11.8 mm
Why measure average corneal diameter on obliique
As cornea longer horizontally than vertically.
If HVID (horizontal visible iris diameter) 11.4 mm or less?
9.0 mm diameter lens
If HVID 11.5 mm or greater
9.5 mm diameter lens
How much clearance do you want on flat K
20 microns
Which meridian will have more tears?
The vertical as it has more bend so more tears can come in.
How much tears under cl on horizontal
19 in the middle and 6 on the side.
Base curve evaluation
The center of the lens should vault the central cornea. The lens should and on the mid peripheral cornea along the horizontal meridian (3+9 o’clock). The lens should have unobstructed vertical movement.
Where will the lens land on the eye
At the point of highest elevation. Will naturally life at 12 and 6.
HVID greater than 12.2
large
HVID 11.4-12.1
Normal
HVID less than 11.4
small
+ numbers/red on cornea topography
Higher than spherical
- numbers/blue on cornea topograph
lower than spherical
Difference between horizontal and vertical height on cornea
Take both the numbers. DO not worry about negative or positive. Just add them.
If we place a rigid lens on flat K how many times will it be correct?
50% of the time
Cornea eccentricity
Amount of cornea flattening that occurs
Eccentricity of sphere
- As flatter eccentricity increases.
Lens that is too flat
Will fit too high. Have low central clearence
How much central clearance do you want
20 microns (10-25)
Lens that is too steep
Excessive apical clearance. May have bubbles and drift low.
Normal cornea ____ in the periphery
Flattens
Peripheral curves
Allows cl to move over eyes as pt. moves eye. Fit will change with cl gaze. Can ask lab to make peripheral curves more flat or steep.
Step 3 of corneal fit
Overrefraction.
WTR Astigmatism
Horizontal meridian: touch at 3 &9
Vertical meridian: clearance at 12 and 6
ATR Astigmatism
Horizontal: clearence at 3 & 9
Vertical: clearance at 12&6
Where does cl clear?
Clear at the power meridian
Base curve radius
primary radius on the POSTERIOR surface of the lens
On flat K lifts off of the _____ meridian
power axis
fluroscene staining
Darker=lens closer to cornea
Green=more clearance.
What type of astigmatism is ideal for RGP
WTR. Can move vertically
How much tears do we want along horizontal meridian with WTR
About 20 microns
How much TF do we want along periphery with WTR
7 microns
How much do we want in vertical with WTR
40 microns. Allows it to move.
Atlas
Takes cornea topography and allows you to superimpose a cl. Can adjust cl so it has 20 microns of clearance
Secondary and periphery curves
Has increased clearance. Allows eye to move
Posterior optical zone
Shows you have far the optical zone extends. The chord diameter over which the base curve extends. Not to edge of lens. Only goes to peripheral curves
Sagittal Depth
Distance between the flat plane of a given diameter and the highest point of a concave surface of the CL
The larger the OZ the _____ the sagital depth
greater
The smaller the OZ the ____ the sagital depth
Smaller
Secondary curve width
.2-1 mm.
Peripheral curve width
.1-.4 mm.
Secondary curve radius
Flatter radius of curvature adjacent to the base curve. .7-1.50 mm flatter than the base curve radius.
Peripheral curve radius
The outer most curve on the posterior surface. It is designed to clear the peripheral cornea and limbus. Always 11.50 mm
What is the peripheral curve radius
11.50 mm
Peripheral curve types
- Spherical radius
- Aspheric radius-gradually flatten the cornea and easy to duplicate
- Tangent angle-cornea periphery described as a straight line.
Do you read cl based off of front or back vertex power?
Must ask the lab what they do
SAM
Steeper add minus
FAP
Flatter add plus
Lens thickness
Need to avoid bending with blinking.
Specific gravity with plus vs. minus
plus=more ant=rides down more
Minus=more post=rides up more
Anterior Optical Zone
Radius of curvature of the anterior lens surface which determines the Refractive power. Has both a radius of curvature and a diameter. Normally lab determines.
Lenticular Flange
An increase or decrease in the anterior edge thickness to aid in lens positioning. Creates more or less lid interaction.
Myo-flange
An increase in peripheral lens thickness to aid in raising low riding lenses (i.e. plus lens design) Plus power lens with minus periphery. Allow greater lid/lens interaction.
Hyper-flange
A decrease in peripheral lens thickness to aid in lowering high riding lenses (i.e. high minus lens) The decrese in edge thickness results in less lid interaction. Occurs with any lens greater than -3D.
Lenticulation
Where there is anterior optical zone curve and then lenticular curve (myo, hyper, or plano)
Edge Design
Represents the junction between the anterior and posterior lens surface. The edge profile is instrumental to the overall comfort of the lens.
Edge Design zones
Anterior zone, apex, posterior zone
Prism Ballast
Incorporates a thicker inferior portion of the lens periphery. Use to orient lens (i.e. bifocal). Top portion thinner than bottom. No prism effect. Allows the upper lid to squeeze the lens downward by watermelon effect. (upper lid pushes down)
Truncation
The removal of inferior portion of a lens to aid in the meridional orientation of a lens. Used in some toric and bifocal lens designs. More stability when rest at bottom of lid. Not very common today
Fenestrations in CL
Holes need to help with CL removal. Used to be used to allow more oxygen in but not down today.
Special Considerations with CL
Pregnancy (vision will change), diabetes, allergies, HIV (concerned with ability to fight infection), Arthritis, refractive surgery, active eye dz, dry eyes, conjunctival injection, lid margin disease (CI for successful CL wearing. MGMT of condition prior) Photophobia
Spectacle vertex distance
12 mm
A contact lens will require a _____ focal length than spectacles with myopia
Longer. ADD. Less minus.
A contact lens will require a _____ focal length than glasses with Hyperopia
Shorter. MINUS. More plus.
When does vertex distance matter?
When it is greater than +/- 4D
Converting D –> R
D = 1.3375-1/radius in m
Lacrimal lens theory
Lacrimal lens=TF, fluid lens. Reference to flat k. Lacrimal lens shape determines the BC to cornea relationship.
When does SAMFAP not apply
When changing diameter or optical zone.
When does SAMFAP apply
when changing the base curve
Residual Astigmatism
When a non-flexing rigid contact lens is placed on the cornea, it can be assumed to mask or negate the corneal cylinder. Lenticular cal will come through though, therefore need consider potential for residual astimgatim.
Does Javal’s rule apply to cl?
No only glasses
Approximating power for corrective lens with residual astigmatism greater than .75D
Use equivalent sphere, proceed with caution, toric RGP, soft toric contact lens, over spectacles.
How would you ID clinically that there was residual astimgatim during your RGP fitting?
Not getting Vas that are expected. Do cal rxn and then see if pick up cylinder and does better
How would you clinically determine there was lens flexure?
Keratometry over rigid lens. Fix by asking maker to make lens thicker
What if manifest ref cyl=165 and kcyl=180
Both are considered WTR. Treat them as the same
What if manifest ref cyl=WTR and kcyl=obl
create obliquely crossed cylinders. Messy math. Rare and poor candidate for GP.
How close should cl compare to actual ors in phoropter? What could be wrong if its not this close?
Ideally within .25-.37 D. K’s off, manifest off, cl base curve off, cl power off, calculation error
What if cl way off from phoropter?
Vertify ors out of phoropter, verify cl, prescribe least minus possible, rely on true over rxn verified.
Who accommodates and converges more in CL’s than spectacles?
Myopes
Who accommodates and convergenes LESS in CL’s than spectacles
Hyperopes
A 4.00D myopes has to accommodate _____ D more in Cl’s than spec?
.25D
3 and 9 staining with Cl
Punctate epithelium staining. Trianglular shaped patches at 3 and 9 or 4 and 8. Shaped and position of PEE is dependent on the lens design and resting position. Conj. hyperemia localized in the horizontal meridian.
3 & 9 staining symptoms
patients may be asymptomatic, may have an itchy sensation usually increase with wearing the time and persists after lens removal. Increasing lens awareness throughout the day. Dry eye symptoms.
What causes 3 & 9 staining
Mechanical-related to the lens design or fabrication. Physiological-peripheral drying secondary to an unstable TF or edge thickness. May appear during the first few days of lens wear or after months of even years. Rarely disappears spontaneously more often increases in severity.
TX for 3&9 staining
Artificial tears, decrease overal diameter, blend peripheral edge lift, flatten peripheral edge life.
Vascularized Limbal Keratitis Symptoms
Moderate discomfort with some photophobia. Lens awareness and decreased wear time. Visualization of defect by the patient. Will tell you they have a white spot in their eye. This is 911.
VLK Signs
Elevated epithelial lesion bridging the limbus. Will have stromal involvement. Diffuse ill defined border. Semi-opaque. Conj. injection. Edema and staining. Corneal vascularization.
Early VLK TX
Reduced wearing time or stop wear. Begin lubricating drops. Redesign the lens (reduce diameter, flatten base curve, flatten peripheral curves) follow closely for recurrences
Late VLK TX
Signifigant pt symptoms of pain. Increase conj. injection. Erosion of the elevated mass. Discontinue lens wear for 1-3 weeks. Treatment with combination of antibiotic/steroid (tobradex). Redesign lens. Consider piggyback (SCL under GP) if unable to discontinue GP wear.
Post VLK neovascularization and scaring
Normally not a ton of scaring. If see BV and no prog. ask about it. It probably happened in the past. Pay attention to the periphery and decrease the lens diameter.
VLK vs. phlyctenular keratoconjunctivitis
Similar in appearance to VLK. VLK is mechanical and heals in 3-5 days. Phlyctenulosis heals in 10-14 days. Phlyctneulosis staph hypersensitivity
Salzmann’s Nodular Degeneration
Have blue-white opacities in periphery. Generally not inflamed unless associated with corneal degeneration.
BLK vs pseudopterygium
Pseudo-conj stick to ulcer on eye. Not very common.
Pterygium
can complicate lens
Pinguecula
Rarely progresses in size
Dermoid
Round
Papilloma
Diffuse
Dellen
Local saucer like depression in the peripheral cornea. Caused by localized dryness result in stromal dehydration. Occasional occurs with 3&9 staining. May scar and become vascularized.
Conjunctival xerosis or bitoto spot
White plaque area on conj. keratized cells. Can be associated with vit. A deficient (adult with gas perm. think gas perm). Patient are asymptomatic. Some minimal conj. injection towards the end of the day. Associated with long term conj. drying secondary to the bridging effect of the lens. Slightly elevated conj lesion. Located intra-palpebral. Keratinization of the conj. epithelium.
Conjunctival xerosis or bitot spot tx
Consider the lens design, follow for changes in patient symptoms or clinical appearance.
Lens Adhesion and patient symptoms
Happens with a flatter lens. Pt blink and it doesn’t move. Patient generally asymp. Patient may notice lens adherence in the morning.
Lens adhesion and signs
localized ring like corneal distortion (rarely stains with fluorosceine), adhesion usually located in the periphery with one edge crossing the limbus, retention of debris and mucus beneath the stationary lens, mild punctate staining, fern-like pattern upon manipulation.
Who does lens adhesion occur in?
25-80% of GP lens wearers in extended wear. Also occurs in DW. Patient dependent phenomenon. Lens suction does not play a role
What create GP lens adhesion
Created by a thinning of the post lens tear film during sleep which creates a thin highly vicious mucus rich tear between the lens and the cornea. Upon opening the force of the eyelid may be insufficient to initiate lens movement. The lens may remain bound until the mucus film is diluted and thickened by the tears. Can also be solution dependent.
What type of lenses are more often bound?
Flat, large, or loose.
TX for lens adhesion
Lens design changes may or may not stop the binding. Change lens care products, Treat dry eyes, adherence will not show signs every day on a given pt.
GP induced GPC
Can get GPC from GP. Can be due to mechanical reasons.
Atomic Force Microscopy
Assess surface roughness at a monoscopic level. Look at surface after rubbing.
What step of cleaning do pt. often miss?
Rubbing
Dimple Veil
Small circular indentation in the epithelium. Correlate with area of bubbles trapped beneath the lens. Pt. is asymp. unless over optical axis
Neurogenic ptosis
Caused, controlled or arising from the NS (congenital hornets)
Myogenic ptosis
Dysgenesis or abnormal function of the legator muscle. Congenital, MG
Mechanical ptosis
weight of the lids
Aponeurogenic ptosis
rupture of the tendon of the legator muscle/disinsertion or thinning of the legator muscle aponeurosis. Due to surgery or GP wear.
Aponeurogenic ptosis causes
forced lid squeezing-due to forced blink, rigid lens displacement of tarsus, blind induced lens rubbing, excessive forced used in soft lens handling.
Non-aponeurogenic CL ptosis causes
Edema, blepharospasm, papillary conjunctivitis caused by CL
Discontinuing CL wear and ptosis affect
Ptosis goes away but it has a rebound affect
CL induced ptosis risk factors
high myopia, pt. age, long term GP use.
DMV
May decrease ptosis. Less manipulation of the eyelid during ptosis.
Rigid lens corneal edema
Historical problem but decrease with new technology. Long term, low grade edema. Slow progression. Mild moderate CCC with centric like epithelial changes to adjacent Bowman’s layer.
Unexplained Red eye
Can be due to manufacturing compounds, surface debris toxicity, metharcylic acid toxicity. Can treat with surface treated GP or soft contact lenses.
