Objective 5 Flashcards Preview

CL2: LOG 6 > Objective 5 > Flashcards

Flashcards in Objective 5 Deck (52)
Loading flashcards...
1
Q

The only contraindication to the fitting of soft toric lenses that differs from any other soft lens is if a patient has irregular corneal astigmatism. In this case, the patient would need to be fit with:

A

RGP lenses

2
Q

The biggest challenge in fitting a soft toric lens is

A

stabilization

3
Q

Given the following information, calculate the power would you order? For the purposes of this case studies, assume axis availability is in ten-degree increments. The patient’s refraction has been compensated for vertex distance.
Patient’s refraction: OS -4.50 –2.25 X 170
Trial Lens: -4.50 –2.00 X 170
Lens orientation: ten degrees to the left of six o’clock from your viewpoint
What lens power would you order?

A

-4.50 –2.00 X 180

4
Q

Patient’s refraction: OD -3.00 –4.00 X 175
Trial Lens: -3.00 –4.00 X 180
Lens orientation: ten degrees to the right of six o’clock from your viewpoint
What lens power would you order?

A

-3.00 –4.00 X 160

5
Q

Patient’s refraction: OD -3.25 -2.00 x 175
Trial Lens: -3.25 –2.00 X 180
Lens orientation: twenty degrees to the right of six o’clock from your viewpoint
What lens power would you order?

A

-3.25 -2.00 x 150

6
Q

Given the following information, calculate the power would you order? For the purposes of this case studies, assume axis availability is in ten-degree increments.
Patient’s refraction: OS –1.00-1.75 X 160
Trial Lens: -1.00 –1.75 X 160
Lens orientation: twenty degrees to the left of six o’clock from your viewpoint
What lens power would you order?

A

-1.00 –1.75 X 180

7
Q

Patient’s refraction: OS +1.75 –2.00 X 010
Trial Lens: +1.75 –2.00 X 010
Lens orientation: 15 degrees to the left of six o’clock from your viewpoint
What lens power would you order?

A

+1.75 –2.00 X 30

8
Q

In general, which type of toric lens is best for stability on patients who have against-the-rule or mostly corneal astigmatism?

A

Back Toric

9
Q

You have ordered a lens for a patient in whom the diagnostic lens of –2.50 –1.50 X 180 positioned at 7:00. If you have made the proper calculations where should the new lens position on the patient’s eye?

A

At 7:00 o’clock

10
Q

Name at least three methods of stabilizing a toric soft lens.

A

Truncation
Dynamic stabilization
Prism
Back surface asphericity or toric curves can be added to match the corneal shape

11
Q

If a patient has extremely tight lids, which method of toric stabilization would you choose as a first lens of choice?

A

Dynamic stabilization

12
Q

How long should a soft toric lens be allowed to equilibrate on the eye before evaluation?

A

Twenty minutes

13
Q

You have a diagnostic lens on a patient’s right of +3.00 –1.50 X 170. After time is allowed for the lens to equilibrate, the lens positions at 135. What would you do?

A

Try a different brand. Orientation of a lens more than thirty degrees off axis indicates instability.

14
Q

A patient presents in your office who has worn RGP lenses, but because she is no longer working she wants to wear lenses on an occasional basis.
Spectacle correction: OD –7.00-3.00 X 85 OS –7.00 –1.00 X 90.
What type of lens would you consider fitting this patient with in each eye and why?

A

Toric SCL should be used.
RE the cyl is “1.00 or more” and “is more than 1/3 of the sphere”
LE the cyl is “1.00 or more”

15
Q

When calculating orientation of a toric soft lens, how many degrees does a clock hour represent?

A

The correct answer is: 30 degrees

16
Q

How is dynamic stabilization of a soft toric lens achieved?

A

The lens is made thinner superiorly and inferiorly so that the thinner portions tend to rotate and come to rest under the upper and lower eyelids.

17
Q

What type of toric soft lens would you order given the following parameters?
Ks: 42.00 @ 180 / 45.00 @ 090
Spectacle Rx: -2.00 -3.00 x 180

A

Back toric

18
Q

It is important to remember that the scribe mark does NOT represent the

A

axis

19
Q

If you are midway between axis selections, use the LARS principle again, but now it relates to the _____.

A

eye – Left (eye) Add – Right (eye) Subtract. This allows the 5 degrees nasal torque produced by the lids with the blink, causing the rotation to work with you, rather than against you.

20
Q

When using LARS, be sure to add or subtract the amount to be compensated from the :

A

refracted axis, NOT the trial lens axis.

21
Q

Most disposable toric soft lenses are available with the sphere power in quarter diopter steps up to +/- 6.00D and ____ diopter steps thereafter. Most cylinder powers are available from –0.75 D or –1.00 D in half diopter steps and up to –2.25 D or –2.75 D. Most cylinder axis are available in ______ increments around the clock.

A

half, ten-degree

22
Q

Generally a diameter of ____mm or larger is used, depending on the brand. Larger lenses offer superior stability, which is crucial in toric lenses.

A

14.5mm

23
Q

_______ lenses can be ordered with any parameters, including diameter changes.

A

Custom

24
Q

If the spherical portion of the refractive error is fairly ___, greater amounts of cylinder can be tolerated without the benefit of a ____ lens. For instance if a patient’s Rx is -7.00 -1.00 X 180, it is likely that a _____ soft lens will provide adequate vision.

A

high, toric, spherical

25
Q

______ percent of patients with refractive error have 1.25 D or more of astigmatism.

A

Twenty-five

26
Q

If you are considering a spherical soft lens for a patient with a toric cornea, try a _____ thickness spherical lens if possible.

A

standard

27
Q

Thin design lenses do not cover as much _____. This theory was much more useful in the past when thicker lenses were more prevalent. The advent of ______ toric lenses came after thin lens designs which would not mask the same amount of astigmatism.

A

astigmatism, low cylinder

28
Q

One diopter of cylinder is likely the limit of the _____ rule; consequently, anything one diopter or more should be considered for fitting with a ____ lens.

A

one-third toric

29
Q

If a patient is subjected to a dusty work environment or is involved in high contact sports, the lens of choice may be ___.

A

soft

30
Q

When _____ astigmatism is present, the horizontal and vertical meridians are not ninety degrees apart. A soft ____ lens will not stabilize properly and the powers on the lens are designed to be ninety degrees apart.

A

irregular, toric,

31
Q

Many factors contribute to the stability of soft toric lenses. Corneal topography and the _____ have the most effect. The shape and tautness of the lid, movement of the eye with the blink (____ phenomenon) and lateral movements, the size of the lid aperture and whether the blink is partial or complete all become important. Other contributing factors are lens ____, water content and lens _____.

A

eyelids, Bell’s, materials, thickness

32
Q

Prism ballast - The lens is weighted ___ using a prism.

A

inferiorly

33
Q

Truncation - The bottom portion of the lens is ____ and this design is generally used in combination with prism ballast. The reason a truncation is added is to reduce the amount of ____ and thickness caused by the prism. This method is _____ used today except in custom designs.

A

cut off, weight, rarely

34
Q

Dynamic stabilization - The lens is made thinner ______ and _____ so that the thinner portions tend to rotate and come to rest under the upper and lower eyelids.This method is a good choice for patients with ____ lids.

A

superiorly, inferiorly, tight

35
Q

_____ surface asphericity or toric curves can be added to match the corneal shape more closely and therefore offer more stability.

A

Back

36
Q

Each lens manufacturer has a way of marking toric soft lenses so that the fitter can judge the relative position of the axis of the lens on the patient’s eye. These marks are generally placed on the _____ part of the lens to avoid weakening the material. Look for them at the __ o’clock or at the 3 and 9 positions.

A

thickest, 6

37
Q

Toric lenses must be made ____ than sphere designs to accommodate the extra power curve. With this in mind, consider the amount of ____ being transmitted to the cornea. Higher water content lenses and ____ wearing schedules must be considered in order to maintain __________.

A

thicker, oxygen, reduced, corneal integrity

38
Q

Trial lens fitting allows examination of the lenses in ___. Waiting at least ____ minutes before looking at the lens on the patient will allow the lens to equilibrate with the tears and allow time for ______.

A

situ, twenty, stabilization

39
Q

It is important to remember that when a lens is ______, the entire lens is moved toward the eye and not just the spherical meridian. When dealing with spherical soft lenses, this is not an issue because the power is the same in all meridians. With soft ___ lenses, two separate powers are cut on the ____ surface of the lens, incorporating the sphere and the cylinder. This necessitates one extra step to assure proper _____ powers.

A

vertexed
toric
front
vertex

40
Q

While there is no hard and fast rule stating which type of lens should be used for which type of astigmatism, it has generally been found that ____ toric lens designs provide greater stability for patients who have ______ astigmatism or when astigmatism is mostly corneal.

A

back

against-the-rule

41
Q

Front Surface Toric
This lens has a _____ surface curvature which is spherical. The _____ surface has two different radii of curvature generated at 90° to each other. This design typically requires _____ or thin zones for proper lens orientation.

A

posterior
anterior
prism ballast

42
Q

Back Surface Toric
This lens has an ____ surface curvature, which is spherical. The _____ surface has two different radii of curvature generated at 90° to each other.

A

anterior, posterior

43
Q

Bitoric lenses have different radii of curvature on both the _____ and ____ surfaces. The curves of each side are generated at 90° to each other.

A

posterior and anterior

44
Q

The LARS rule states that if a lens orients off axis but is stable in rotation:

A

it can be calculated and compensated for.

45
Q

The letters stand for Left Add - Right Subtract. When viewed through a slit lamp, if the markings orient to the fitter’s left then:

A

the equivalent amount of axis must be added to the refracted axis.

46
Q

A toric contact lens axis is generally available in ____ increments. In this case you would have to round to the nearest __ degrees. Would you order the axis at 150 degrees or 160 degrees? Many fitters would order 160, as this is closer to 180, but the actions of the lids now come into play. Remember we are discussing a right eye fit and the OTHER use of LARS relates to exactly that.

A

ten degree 10

47
Q

In this example, the right superior and inferior lids push all tears ____ to drain through the Canal of Schlemm. Lid action also twists the bottom of the contact lens ___ toward the inner canthus with the blink. The lids twist or torque a right eye contact lens nasally to the right and a left eye contact lens, nasally to the left. In other words, when the patient blinks, there is a discernible movement _____. This is always from the ________point of view. As a result of this interaction of the lids, this patient’s lens should be ordered at axis 150 for the right eye.

A

nasally
nasally
nasally
practitioner’s

48
Q

Be sure that you are using your own ____ or ____ and not the patient’s when estimating rotation.

A

left or right

49
Q

When using LARS, be sure to add or subtract the amount to be compensated from the _____ axis, NOT the trial lens axis.

A

refracted

50
Q

The same tests should be used for evaluating a soft toric lens as used in spherical lenses. These include:

A

Assessing movement with the blink, centration, excursion movements, over lens keratometry and recovery tests (push-up). In addition to these, the orientation evaluation

51
Q

In a successful patient returning for follow-up, if stability has recently become a problem, Consider:

A

Consider: the cleanliness of the lens. Some substances, such as hand lotion or hairspray, can be absorbed into the lens matrix causing instability. This has become much less of a problem with the advent of inexpensive disposable toric lenses.

52
Q

Once the lens is fitting properly, if the patient continues to have _____ issues with the toric lenses, it would be appropriate to perform a cross cylinder _____ to determine if the final problem has to do with the sphere power and the axis of the cylinder. If a major change is indicated, then refer the patient for an over refraction with the _______ then calculate the new lens powers using the cross cylinder formulas or you could use one of the many online cross cylinder calculators.

A

visual acuity issues
over refraction
prescriber