Socrative Flashcards
A prism ballast GP lens requires how much prism for proper orientation?
0.75 to 1.50D (She says in most cases)
In against-the-rule astigmatism, the short/ steepest corneal meridian:
At or near 180
In with-the-rule astigmatism, the longest/flatest corneal meridian:
At or near 90
What is the term for the condition in which there is loss of vision without any apparent disease to the eye?
Amblyopia
is the absence of an iris
Aniridia
What should be suspected when there are large fluctuations in a patient’s refractive error?
In diabetics, the sudden shift in blood sugar levels can cause changes in the refractive error
Corneal edema, a sensation of soreness. injection, foggy vision and ghost images usually indicate:
A lens that prevents tear exchange and elimination of corneal debris and metabolic waste products may cause corneal edema which could be due to a tight-fitting lens
What does it mean when we say the soft lens must equilibrate on the eye?
The polymer of the lens must reach the same temperature as the tear film 98.6 degrees
Punctal occlusion may be most beneficial for?
Tear deficient dry eye, occlusion of the lacrimal drainage apparatus simply increases tear volume by slowing the rate of outflow.
In a GP lens, a poorly finished transitional zone between the optic zone and the lens edge can be evaluated by:
Profile analyzer which helps in evaluating the quality of the peripheral blends of a GP lens.
A patient will have a much greater awareness of a loose lens and may experience a constant foreign body sensation when wearing a lens that…
Is too loose
Soft lenses fit steeper than K
A soft lens that is fit steeper than K will vault the cornea centrally and seal off around the periphery. Vision will fluctuate with each blink
It is important that the practitioner inform the patient not to use lotions, creams, make-up, sprays and all cosmetics (before/after) lens insertion.
before
Things to be documented with a patient:
the care system the patient is using and any systems they had problems with, as well as lens parameters and materials are all vital pieces of information to have documented in the patient’s permanent record.
With a rigid contact lens in place, a fluorescein pattern shows a concentration of fluorescein inferiorly and superiorly beneath the lens. Which one of the following types of astigmatism is represented by this pattern?
With the rule astigmatism: the flattest corneal curvature is horizontal and steepest curvature is vertical.
Fluorescein will be absent or minimal where the cornea is (flatter/steeper), and pool or collect where the cornea is (flatter/steeper).
Flatter
Steeper
Astigmatism that is inside the eye and not on the cornea.
lenticular/residual astigmatism
The base curve of a rigid lens was ordered 7.84mm and was received measuring 7.94mm. this lens is ________than ordered.
0.50 flatter
Every 0.05mm of radius equals approximately 0.25 diopters. The lens ordered was 43.00D, but was received as a 42.50D
Which of the following modifications to a gas permeable lens can be made in the office?
Blending of peripheral curves
Polishing lens surface
Addition of minus power
Which of the following modifications to a gas permeable lens can not be made in the office?
Changing the base curve
Application of fluorescein should be used in…
Evaluations of gas permeable lens fit
The main purpose of a rigid lens wetting solution is to:
Convert the hydrophobic surface of a rigid lens to one that is temporarily hydrophilic
If a soft contact lens is not properly neutralized, how does residual hydrogen peroxide affect the cornea?
It is likely to cause epithelial damage
contact lenses that have a non-spherical back surface are called:
Aspheric lenses
Lenses that have central base curves that are spherical.
Tricurve and spherical lenses
A lens that refers to the removal of plastic on the lower portion of the lens to aid in positioning of a bifocal or toric GP lens.
Truncated lens
A technician can perform a preliminary evaluation of soft contact lens movement by:
Observing the movement of the lens edge in relation to the position of a conjunctival vessel
Observing movement and lens lag in upward and lateral gaze with a penlight
Having the patient look up and blink
In a GP wearer, an arcuate stain on the cornea may be due to:
Poorly blended secondary curves
Failure to close the lids completely when blinking results in:
3 & 9 o’clock staining.
To aid in the positioning of a GP prism ballast lens riding too low and slipping underneath the lower lid:
Truncation would help provide a flatter, thicker surface to interact with the lower lid, enabling the lens to rest in the proper position.
The slit lamp illumination that gives an overall view of the cornea but limits detail is:
Diffuse
Two narrow illuminations
Sclerotic scatter and specular reflection
Up until the recent introduction of silicone hydrogel lenses the Dk/t of previous hydrogel lenses was limited by:
Water content and center thickness
Which edge design is recommended for a +15.00D aphakic GP lens?
Lenticular myoflange, this minus carrier design increases edge thickness and enables a low-riding high plus lens to center better.
The LARS principle provides us with a means of:
Compensating for axis rotation of a soft lens, “LARS” stands for Left Add Right Subtract. If a soft toric lens orients with its markings rotated to the fitter’s left, the number of degrees of rotation must be added to the patient’s refractive axis (not the axis of the diagnostic lens) in order to counterbalance the lens so it will align with the patient’s correct corneal cylinder axis in the eye. If the diagnostic lens orients with iits markings rotated to the fitter’s right, the number of degrees of rotation must be subtracted from the patient’s refractive axis when ordering the patient’s lens.
two methods of stabilizing the rotation of rigid bifocal contact lenses?
Truncation and Prism Ballast
These lenses must be stabilized in order for the proper segment to align correctly with the pupil.
Translating or alternating gas permeable bifocal lenses
The bottom portion of the lens is removed, producing a ledge that interacts with the lid, aligning the lens in its proper position.
Truncation
the bottom portion of the lens is made thicker than the top portion.
Prism ballast
Inferior punctate staining may be a sign of:
Lagophthalmos, the inability of the upper lid to close completely prevents the inferior cornea from being bathed with tears that rest along the lower lid. As much as one-third of the population has a slight lagophthalmos during sleep.
Corneal Edema characteristics
Reports of smoky vision and spectacle blur are common in patients with severe corneal edema. The contact lens professional may also notice a steepening of the keratometer readings for those patients
What Rx would be ordered for a gas-permeable lens fit on K?
K’s 43.00 @ 180/44.00 @ 090
Rx -3.00 +1.00 x 090
-2.00D
To determine the Rx of a gas permeable lens, first put the Rx in minus cylinder form: -3.00 +1.00 x 090 becomes -2.00 -1.00 x 180
Next, drop the cylinder. When fitting a lens on K order the sphere power corrected for vertex distance when the Rx is in the minus cylinder: -2.00D
If a patient with exophthalmic eyes due to thyroid disease requires a toric lens:
It may dehydrate excessively due to the lid retraction and dry eye condition that often accompanies thyroid disease
Stability will be difficult to maintain since there are no lid forces to keep the lens in position
bifocal designs that represent a translating design (not mentioned in any review?)
Crescent design
If an adapted contact lens wearer complains of a sudden onset of discomfort, the technician should suspect:
A damaged contact lens
A change in corneal curvature creates…
a gradual decrease in lens comfort
tight lens syndrome
a gradual decrease in lens comfort
Ph value of human tear
7.4
Tear Ph higher than 7.4 is
alkaline
Tear Ph lower than 7.4 is
acidic
To correct a flat fitting gas permeable lens, you could:
Enlarge the optical zone: only if there is no change in lens diameter.
Decrease in sagittal vaulting
creates a flatter lens to cornea relationship
decreasing overall lens diameter
decreases sagittal depth
tear break up time is done by:
instilling fluorescein, having the patient blink once to spread the fluorescein across the cornea and timing the interval between the blink and the development of the first dry spot (tear break-up) on the cornea.
Given the following information, which set of lens specifications would best simulate a lid attachment rigid lens fitting?
K’s 42.00 @ 180/43.00 @ 090
Rx -2.00 -0.87 x 180
Upper lid positioned 2mm below the superior limbus
A
41.50 -1.50 9.5
B
42.50 -2.50 8.5
C
43.00 -2.50 9.5
D
43.00 -3.00 8.2
A 41.50 -1.50 9.5
“Lid attachment” lenses are designed to fit with the upper edge of the lens positioned under the upper eye lid. To achieve this positioning, a flatter than K, larger diameter (over 9.0mm) is generally used.
Which type of slit lamp illumination will allow you to determine corneal thickening, thinning and distortion and depth of foreign bodies or opacities in the cornea?
Optic section
The tolerance for the overall lens diameter according to the ANSI standards is
+/- 0.05 mm
Carole’s GP contact lenses are fit on flat K. her refraction is -5.00+2.00x090. What is the power of her contact lenses?
-3.00D
Reason: Convert to minus, when a rigid lens is fit on K, no compensation is needed for the resulting tear film so the lens power remains -3.00D.
Given the following information, which of the following GP lens designs would you order to best correct this patient’s vision?
K’s 45.00 @ 180/42.00 @ 090
Rx -2.00-4.25x090
A
45.00 -2.00
B
42.00 -2.00-4.25x090 prism ballasted
C
42.00 -2.00
D
42.00/45.00 -2.00/-5.75 (drum readings)
D 42.00/45.00 -2.00/-5.75 (drum readings)
A bitoric lens design will provide the best lens orientation on against-the-rule corneal topography. The other answers are incorrect because the spherical base curves will not contribute to proper positioning of the lens on the against-the-rule cornea.
Which of the following preservatives produces the least toxic response of the eye?
A
Polyquad
B
Chlorhexidine
C
Sorbate or sorbic acid
D
Thimerosal
A polyquad
Clinical studies indicate that solutions preserved with polyquad can be used without as much risk of toxic or allergic reaction as the other preservatives listed.
When corneal epithelial cells suffer trauma, the first step toward resolution is:
Sliding and migrating of the adjacent remaining epithelial cells
Epithelial Cells are highly reproducible and quickly work toward covering any area that has suffered trauma. In the first twenty-four hours, the adjacent remaining epithelial cells slide and migrate over to cover the open area. During the next 48 to 72 hours, the epithelium will generate new cells to completely fill in the traumatized area.
best measure the convex curve of the rigid lens
Radiuscope
Given the following information, which of the listed rigid lens designs would you order to best correct this wearer’s vision?
K’s 42.00 @ 180/45.00 @ 090
Rx -3.00 -2.25 x 180
42.00/45.00 -3.00-2.25 (Rx form)
The base curves will parallel the K readings and the power in the lens will properly correct the astigmatism. A spherical lens design will rock on the 180 degree meridian causing discomfort and the chance of lens displacement or expulsion.
When the patient has Graves’ disease they can be fitted for soft lenses
True
contraindication for soft lenses
A
When the patient has Graves’ disease
B
When the patient has cylindrical keratometric readings
C
When the patient has irregular corneal astigmatism
D
When the patient has more than 1.50D of refractive cylinder
C When the patient has irregular corneal astigmatism
During the diagnostic evaluation of the following patient you note the lens rotates 10 degrees to your left. Which of the following lens parameters would you order for the patient?
Patient’s refraction -3.00-1.25x160
Diagnostic lens 8.4 -3.00-1.25x280 14.5
8.4 -3.00-1.25x170 14.5
To compensate for rotation of a diagnostic soft toric lens, add the amount of rotation if it rotates to your left and subtract the amount of rotation if it rotates to your right. The degrees of rotation are subtracted from the patient’s refractive axis, not the axis of the diagnostic lens.
A rigid lens shows two curves on the convex surface when measured with the radiuscope. On the lensometer, it shows one power. What type of lens is this?
warped
a warped lens will show two curvatures on the radiuscope that are close (usually within 0.15mm) but the power will read spherically, or close to spherical. A lens that has toric surfaces on the front, back or both, will all read two distinct powers on the lensometer
If a soft contact lens becomes adherent to the cornea, the patient should:
Irrigate the eye with saline or rewetting drops until the lens begins to move freely again
A lens adheres to the cornea when it is not:
wet enough or salty enough
The following ametropia frequently results in high riding rigid lenses:
High myopia
Due to the increased edge thickness of a high minus lens it will frequently “catch” under the upper lid causing it to ride high.
Gross corneal edema, which manifests itself clinically as central corneal haze, is verified by the slit lamp using sclerotic scatter illumination. What specific technique does the examiner use to see this condition?
the naked eye and an angle between the slit lamp beam and the eye of 90 degrees
First develops intracellularly (in the cells). In the beginning stages, the swelling (collection fo fluid) is easier to see without the microscope. When the condition worsens, it can be seen with the microscope, but it will be deeper into the cornea.
Epithelial edema
An instrument that allows simultaneous verification of lens diameter, optic zone width and peripheral curve width is
measuring magnifier
An instrument that allows simultaneous verification of lens diameter, optic zone width and peripheral curve width is
measuring magnifier
The average HVID for a patient is
11.5mm
To steepen the lens to cornea relationship of a gas permeable lens you could:
A
Increase overall diameter and decrease optic zone diameter
B
Increase overall diameter and increase optic zone diameter
C
Increase optic zone diameter and decrease overall diameter
D
Increase optic zone diameter and flatten base curve
B Increase overall diameter and increase optic zone diameter
decreasing the optic zone diameter, decreasing the overall lens diameter and flattening the base curve will … the relationship.
A flatten
B loosen
C tighten
D Steepens
B loosen
If a patient with exophthalmic eyes due to thyroid disease requires a toric lens:
It may dehydrate excessively due to the lid retraction and dry eye condition that often accompanies thyroid disease
Stability will be difficult to maintain since there are no lid forces to keep the lens in position
Tom’s spectacles with a power of -12.00 +0.50 x 090, sit 10mm in front of his cornea. The likely soft contact lens prescription for Tom would be:
-10.50D
In the conversion of a prescription from the spectacle plane to the corneal plane, additional plus power is needed. Usually a standard table
The following soft lens is placed on a patient’s eye:
14.0/8.8 -4.00
An over-refraction is performed resulting in -0.75D sphere. Which of the following lens parameters would you order for the patient?
14.0/8.8 -4.75
When applying the results of an over-refraction to a soft lens, first put the over-refraction in minus cylinder. Then determine the spherical equivalent and add this to the existing power.
The best technique to evaluate the movement of a thin hydrogel lens is:
Push up test
While observing in the slit lamp, the examiner takes his/her thumb and presses on the patient’s lower lid and pushes upward to move the lens. If the lens moves up freely and descends back into place freely, it is a good fitting lens. If the lens is difficult to move or drops slowly into place after it is moved, the fit may be too tight. The other forms of checking lens movement are not as accurate with some thin hydrogel lenses.
Transient keratometric mire distortion is usually due to:
Pre-ocular tear film
While prolonged rigid lens wear, prolonged soft lens wear and irregular corneal astigmatism may all cause mire distortion, the mire distortion will remain constant. Of the choices listed, only the tear film results in transitory mire distortion which can be cleared up if you ask the patient to blink.
Which type of lens would best satisfy this patient’s visual needs given the following information?
K’s 43.00 @ 160/44.00 @ 075 3+ distortion
Rx -2.00 +1.00 x 075
Spherical GP
The 3+ distortion is most probably due to irregular astigmatism and is best corrected with a rigid lens option
If a patient has 1.50D of refractive cylinder and keratometer readings of 44.00 @ 180/44.50 @ 090, you would expect a spherical gas permeable lens to:
Result in residual astigmatism
The rigid back surface of a lens will only correct the astigmatism that is found on the surface of the cornea. Therefore, when there is significantly more astigmatism in the refraction than on the surface of the cornea, residual astigmatism will result. Since there would appear to be a great deal of residual astigmatism, even though the lens is rigid, the patient would not realize their best correctable vision.
FDA group I soft lenses
Have a water content less than 50% and a non-ionic surface
Non-ionic surfaces do not carry an electrostatic charge and stay cleaner than ionic surfaces. Ionic surfaces, since they are negatively charged, attract positively charged tear lipids and proteins and coat more readily.
Cleaners that contain isopropyl alcohol should not be used on rigid lenses because they:
May cause parameter changes, brittleness, cracking
Aliphatic alcohols, such as ethyl, methyl and isopropyl alcohol will damage GP materials and are approved for use with PMMA and soft lens materials only. Benyzl alcohol is the only alcohol that is FDA approved and safe to use in GP solutions.
Dry eyes are a common side effect of:
Oral contraceptives, Accutane and antihistamines
In an alignment lid attachment GP fit, the fluorescein pattern should show:
A thin, even layer of fluorescein and less than 180 degrees of bearing in the mid-periphery
What is an essential characteristic of an ideal wetting solution?
they should be formulated so that they can be instilled directly into the eye without causing irritation or sensitization
hey should be made isotonic which means they try to mimic the normal tear pH and are neither acidic nor alkaline. Solutions must also be adequately preserved to be dispensed in a sterile manner.
When verifying a rigid lens on a radiuscope, you notice that the mires are not in focus in all principal meridians. This might indicate a:
Warped lens, back toric lens or front toric lens
A front toric lens will show a spherical posterior curve on the radiuscope and a sphero-cylindrical Rx on the lensometer.
Fluorescein is not used for
Corneal striae
