Shared Flashcard Set

Details

Contact Lenses
State Board Exam
111
Medical
Undergraduate 1
07/30/2008

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Cards

Term
Who was the Italian Renaissance painter who described how a glass lens could change the optical power of the cornea?
Definition
Da Vinci
Term
In 1888 what two individuals independently tried to correct vision errors by placing glass lenses on the cornea?
Definition
Fick and Kault
Term
Who was the first scientist to develop a soft (hydrogel) contact lens?
Definition
Wichterle
Term
Who created the first all-plastic corneal lens made of PMMA?
Definition
Touhy
Term
In 1986 what substance was added to Rigid Gas Permeable contact lenses to make them more wetable?
Definition
Flourine
Term
If a yound patient is not wearing spectacles or contact lenses, and thier distance vision is blurry, but their near vision is clear, what is their refractive state?
Definition
Myopia
Term
What type of contact lens is designed specifically to correct astigmatism?
Definition
Toric
Term
What lens material is stable, has good machining properties, but allows little to no oxygen through the cornea?
Definition
PMMA- Poly Methacrylate
Term
What lens material (when made available as a spherical contact lens) is comfortable, but does not compensate well for corneal astigmatism.
Definition
HEMA- Hydroxyethyl Methacrylate
Term
What type of contact lens material was recently FDA approved for 30-day continous wear?
Definition
Silicone Hydrogel
Term

What are the three most important parameters of an RGP lens?

Definition
  1. Diameter
  2. Base Curve
  3. Power
Term
Consider an RGP with a base curve, and a peripheral curve. What is another name for the base curve diameter?
Definition
Optic Zone
Term
In an RGP contact lens, when the junction between two curves is too sharp, we smooth it out during lens modification. This smoother junction is called?
Definition
Blend
Term
The keratometer is an optical instrument designed to measure what?
Definition

The radius of curvature of the cornea

Term

The keratometer does not measure?

Definition
Total astigmatism
Term
In keratometery, how much of the patients cornea is being examined?
Definition
3-4 mm of the central cornea
Term
List four reasons why a clinician would want to use a keratometer.
Definition
  1. Contact Lens Fitting
  2. Corneal cylinder can be used to determine the spectacle RX.
  3. To help determine if the patient has kerataconus
  4. Distorted mires could indicate pathology
Term
What instrument is more accurate than the keratometer when measuring corneal curvature?
Definition
Computerized corneal topographer
Term
Which topographical map takes peripheral corneal flattening into consideration?
Definition
Tangential Map
Term
Why would we consider fitting a keratoconic patient with an RGP lens?
Definition
The vision is usually superior to spectacles
Term
Which computerized corneal topographical map predicts flourescein patterns when fitting RGP's?
Definition
Elevation Map
Term
Name four reasons why a clinician would use a computerized corneal topographer over a keratometer.
Definition
  1. Pre and post refractive surgery measurements
  2. More accurate than keratometer for fitting RGP's
  3. Helps when fitting keratoconics with RGP's
  4. Easier to assess cornea with irregular astigmatism due to disease or trauma
Term
Define "Flat K" ?
Definition
The flattest principal meridian with the smallest dioptric value, also referred to as "on-K".
Term
What are the three most important instruments used to fit both RGP and soft contact lenses?
Definition
  1. Biomicroscope
  2. Phoropter
  3. Keratometer
Term
Whta type of glands are embedded in the tarsal plate of the eyelid?
Definition
Meibomian Glands
Term
The glands of Krause and Wolfring are what type of eyelid glands?
Definition
Accessory Lacrimal Glands
Term
List the six important functions of the tear film?
Definition
  1. Keeps the eye moist and lubricated
  2. Traps debris and washes it away
  3. Primary sourceof O2
  4. Smooth refractive surface
  5. Contains antibacterial substances-lysosomes
  6. Helps to maintain corneal hydration
Term
Name the three layers of the tear film and the structures responsible for the production of each, starting with the outermost layer.
Definition
  1. Lipid- Meibomian Glands
  2. Aqueous - Main lacrimal gland and accessory lacrimal galnds Krause & Wolfring
  3. Mucin - Goblet Cells
Term
Name the five Corneal layers starting with the outermost layer.
Definition
  1. Epithelium
  2. Bowman's layer
  3. Stroma - lamellae
  4. Descemet's membrane
  5. Endothelium
Term
The corneal epithelium is made up of what three type of cells?
Definition
  1. Squamous cells
  2. Wing cells
  3. Basal layer of columnar cells
Term
Name two important functions of the cornea.
Definition
  1. Refraction of light
  2. Transmissions of light
Term
 Name three ways the cornea may receive oxygen.
Definition
  1. Diffusion from aqueous humor
  2. Conjunctival and episcleral capillaries located in limbus
  3. Atmospheric O2 diffused through the tear film
Term
Lamellae are found in which corneal layer?
Definition
Stroma
Term
What are the two types of a biomicroscope?
Definition
  1. Dissecting microscope
  2. Illumination system
Term
Name the three reasons to use a biomicroscope.
Definition
  1. Observation of normal ocular sturctures
  2. Observation of abnormal ocular structures
  3. Contact lens fitting
Term
Name five types of illumination used while performing biomicroscopy.
Definition
  1. Direct
  2. Diffused
  3. Indirect
  4. Retro
  5. Sclerotic Scatter
Term
Name four types of direct illumination
Definition
  1. Parallelpiped
  2. Optic section
  3. Specular reflection
  4. Conical beam
Term
What is the most common form of direct illumination?
Definition
Parallelpiped
Term
A V-channel Gauge is used to measure what parameter of an RGP contact lens?
Definition
Total Diameter
Term
 A hand magnifier is used to measure what parameters of an RGP contact lens?
Definition

Total diameter and/or Optic zone

Term
A Radiuscope is used to give an accurate measurement of what RGP contact lens parameter?
Definition
Base Curve
Term
What would be the best instrument to use to measure the optic zone diameter of an RGP contact lens?
Definition
Hand Magnifier
Term
What instrument is often used in the clinic to measure the base curve of an RGP contact lens?
Definition
Contact meter
Term
What instrument is often used in the clinic to measure the power of an RGP contact lens?
Definition
Lensometer
Term
What instrument would you use to verify the center thickness of an RGP lens?
Definition
Thickness Gauge
Term

When using a Radiuscope to determine an accurate base curve radius of an RGP contact lens, it is important that the concave surface of the lens is what?

Definition
Dry
Term

You would use a lensometer to measure which RGP parameter?

Definition
Power
Term
When measuring the base curve of an RGP lens with a Radiuscope, what is required in order to get a proper reading?
Definition
That the concave surface of the lens is dry
Term
What are the three important areas during the preliminary evaluation case history?
Definition
  1. Reasons for CL wear
  2. Medical History
  3. CL history
Term
Why are we interested in the patient's medication?
Definition

Many types of medications can cause dry eye

Term
Name two ways to obtain refractive data.
Definition
  1. Corneal Topography
  2. Refraction
Term
What three areas are examined during Biomicroscopy?
Definition
  1. Externals
  2. Conjunctiva
  3. Cornea
Term
What prismatic correction can be achieved with some contact lenses?
Definition
Vertical prism
Term
What three anatomic measurements are taken during the preliminary evaluation?
Definition
  1. Corneal diameter
  2. Pupil diameter
  3. Palpebral aperture height
Term
What is needed to perform a Schirmer Tear Test?
Definition
Strips of filter paper
Term
What is needed to perform a Phenol Red Test?
Definition
70 mm cotton thread soaked in phenol red dye
Term
What tear film test is performed using flourescein dye, a cobalt blue filter and the biomicroscope?
Definition
Tear Break Up time (TBUT)
Term
What is the three point touch of a contact lens?
Definition

Contact lens must be touching

  1. Upper Sclera
  2. Cornea
  3. Lower Sclera
Term
What are the four criteria that must be met when evaluating contact lens fit.
Definition
  1. Adequate movement
  2. Stable Vision
  3. Good Centration
  4. Undistorted Keratometer mires
Term
 Name three methods of contact lens manufacturing
Definition
  1. Spin Casting
  2. Lathe Cutting
  3. Cast Molding
Term

A contact lens can get lost behind the eye

 

True or False

Definition
False
Term

Only patients between the ages of 18 and 35 can effectively wear contact lenses.

 

True or False

Definition
False
Term

Contact Lenses are considered Medical devices

 

True or False

Definition
True
Term
What are the two broad catergories of contact lenses?
Definition
  1. Soft
  2. Rigid
Term
What are the two categories of Rigid contact lenses?
Definition
  1. Hard (PMMA)
  2. RGP (CAB)
Term

PMMA allows little to no oxygen to reach the cornea

 

True or False

Definition
True
Term

RGP's are more comforatble to wear than soft lenses

 

True or False

Definition
False
Term

Soft lenses are hydrophobic

 

True or False

 

Definition
False
Term

Soft lenses have a larger diameter than RGP's

 

True or False

Definition
True
Term

Hypoxia causes corneal edema

 

True or False

Definition
True
Term
The amount of oxygen passing through the CL is determined by what two factors?
Definition
  1. Lens thickness
  2. Lens material
Term

The Dk value of a soft lens is dependant on the water content of the lens

 

True or False

Definition
True
Term

The thicker the CL, the greater the oxygen transmissibility

 

True or False

Definition
False
Term

Low water content soft lenses have greater resistance to deposits

 

True or false

Definition

True

Term

Non-ionic soft lens materials easily attract lens deposits

 

True or False

Definition
False
Term

The spin casting method limits the ability to control the base curve

 

True or False

Definition
True
Term

Lathe cutting can only produce RGP's

 

True or False

Definition
False
Term

Cast molding is simple and reproducible

 

True or False

Definition
True
Term
What are three advantages to fitting spherical RGP's empirically?
Definition
  1. Eliminates fitting visit
  2. "Used" diagnostic lens is avoided
  3. The lenses manufactured at a lab may be just as effective as the best fitting diagnostic lens
Term
What are the  four advantages to fitting spherical RGP's with a diagnostic lens set?
Definition
  1. Fewer re-orders (an optimum lens-to-cornea relationship has already been achieved)
  2. Practitioner confidence in the fit
  3. Patient has a chance to experience how an RGP will feel on the first visit
  4. Ability to evaluate patient's vision on first visit
Term
What are the three advantages to having hundreds of spherical RGP's in stock?
Definition
  1. Convenience to patient (Patients receive replacement lens without delay)
  2. You can fit directly from stock
  3. Lens parameter changes can be made without delay
Term
What role does Sodium Fluorescein play when fitting spherical RGP's?
Definition
It is invaluable for assesing the lens-to-cornea fitting realtionship
Term
What two instruments are used to observe the Sodium Fluorescein pattern?
Definition
  1. Burton Lamp
  2. Biomicroscope
Term
What would you expect to see if there was apical clearance?
Definition
Even pooling of fluorescein in the center of lens
Term
What occurs during Apical bearing?
Definition
Direct contact between the lens and the cornea
Term
What refractive condition could account for a dumbell pattern?
Definition
Astigmatism
Term
 Would we always fit "on-K" for a patient with a spherical cornea?
Definition
No
Term

Why not fit a spherical RGP on a high astigmat?

Definition

Increased 3 and 9 o'clock injection, poor lens positioning, visual complaints, corneal curvature changes, failure to correct residual astigmatism.

Term
Name the seven types of astigmatism
Definition
  1. With the Rule
  2. Against the Rule
  3. Irregular
  4. Internal
  5. Residual
  6. Refractive
  7. Oblique
Term
In which form of astigmatism is the horizontal meridian the least curved (flattest) and the vertical meridian the most curved (steepest)?
Definition
With the Rule Astigmatism
Term
In which form of astigmatism is the horizontal meridian the most curved (steepest) and the vertical meridian the least curved (flattest) ?
Definition
Against the Rule Astigmatism
Term
What are the three common reasons for irregular astigmatism?
Definition
  1. Keratoconus
  2. Trauma
  3. Lasik
Term
What two factors can cause internal astigmatism?
Definition
  1. The toricity of the back surface of the cornea
  2. The tilt of the crystalline lens with respect to the optic axis of the cornea
Term
What is another term for internal astigmatism?
Definition
Lenticular Astigmatism
Term
What is another term for refractive astigmatism?
Definition
Total Astigmatism
Term
 What is the astigmatism that is still present after a contact lens has been placed on the eye?
Definition
Residual Astigmatism
Term
Name three types of toric RGP's.
Definition
  1. Front surface Toric
  2. Back surface toric
  3. Bitoric
Term
What type of RGP lens is used when there is small amount of corneal astigmatism but a large amount of total astigmatism?
Definition
Front surface Toric
Term
What type of RGP is used when the refractive astigmatism is approximately 40% greater than the corneal astigmatism?
Definition
Back surface Toric
Term
What type of RGP is used when there is a significant amount of corneal Astigmatism ( more than 3.00D)?
Definition
Bitoric
Term
What is the name of the bitoric lens guide?
Definition
The Mandell-Moore Bitoric Lens Guide
Term
What are the three most common modification procedures?
Definition
  1. Edge and Surface Polishing
  2. Repowering
  3. Peripheral curve blending or flattening
Term
What four types of tools are needed to modify an RGP?
Definition
  1. Box modification unit
  2. Suction cup
  3. Sponge tools
  4. Radius tools
Term

What type of polish can NOT be used and why?

Definition
Silvo, because it is ammonia based, so it will ruin the RGP.
Term
Soft hydrophilic lenses are also known as?
Definition
Hydrogels
Term
What are the six main classifications of hydrogel lenses?
Definition
  1. Daily wear/ flexible
  2. Extended Wear
  3. Planned Replacement/Disposable
  4. Tints
  5. Torics
  6. Bifocals
Term
What are the three main classifications of tinted hydrogel lenses?
Definition
  1. Visibility
  2. Enhancing
  3. Opaque
Term
What water content is best for patients with dry eye?
Definition
Low to Medium
Term
What five factors contraindicate hydrogel lens wear?
Definition
  1. Irregular corneas ( keratoconus,ocular trauma)
  2. Radial keratotomy
  3. Chronic allergies
  4. Chronic antihistamine use
  5. Giant Papillary Conjunctivitis  (GPC)
Term
What is a standard rule-of-thumb for fitting hydrogels?
Definition
Fit as flat as possible
Term
What might you observe while using the biomicroscope if the lens is too tight?
Definition
Conjunctival drag
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