Lesson 19 - Soft Contact Lenses

Question 1

Spherical lens

Answer 1

The simplest contact lens design—a spherical lens—has a single power. The front and back surfaces of spherical lenses have the same power. These correct myopia and hyperopia. Spherical lenses are made in daily (single-use) wear, two-week, monthly, and quarterly lens modalities. Some are FDA approved for extended wear (meaning some people are successful wearing these overnight) or daily use. Some come clear, some come with a light blue handling tint, and some are colored lenses to change eye color.

Question 2

Toric lens

Answer 2

Just as glasses can correct for astigmatism with a cylinder component, a toric contact lens can correct myopia, hyperopia, and presbyopia, but also corrects astigmatism starting at -0.75 diopters of cylinder.

Just as with the astigmatic curvatures of a spectacle lens, the front surface of a toric lens is flatter in one direction and steeper in another. Here’s the tricky thing about a toric contact lens: It has to stay aligned on the cornea while the person is blinking. It can’t move around, or the astigmatic correction will be in the wrong place.

For this reason, some toric lenses typically contain a prism ballast weight, making them thicker at one end of the lens. Gravity keeps the thicker portion of the lens at the bottom of the eye when the person blinks.

Another toric design has double thin zones, meaning that the lens is thinner at opposite edges. The lens stays in place because it’s wedged under the upper and lower eyelids.

Question 3

Multifocal or aspheric soft lens design

Answer 3

These soft contact lenses have the most complicated design of all. They correct the distance prescription as well as address the power needed for reading close up.

Sometimes they are also called aspheric design lenses.
Their design is similar to a target, with concentric rings so that the center portion is for near for distance vision and outer rings progressively change in power for distance or near viewing. Since most of the center distance power lies over the pupil area, the brain has to decipher whether it needs to utilize the distance or the near power of the lens. Sometimes these multifocal designs are called simultaneous vision multifocal designs. As you can imagine, not everyone can be successful wearing these lenses. Many people don’t get clear vision in the distance or at near since there are so many powers in front of the pupil.

Some manufacturers have tried to decrease the size of the center portion to allow a greater reading portion; however, this gives rise to blurred distance vision as a tradeoff. More designs are coming out every few months.

Aspheric designs gradually change power from the center to the edge and used to correct low amounts of astigmatism. Be careful not to confuse these with toric or multifocal designs.

Question 4

Like spectacle lenses, the soft contacts come in what designs?

Answer 4

Like spectacle lenses, the soft contacts come in spherical, toric (corrects for astigmatism), and multifocal designs.

Question 5

Hydrogels

Answer 5

These are gel materials that contain varying amounts of water and also vary in their oxygen permeability—in other words, how well they allow oxygen to pass through the lens to the eye.

Question 6

What are the two main materials for soft contact lenses today? What are their pros and cons?

Answer 6

Silicone hydrogel and hydrogel soft contact lenses are the main two materials for soft contact lenses today.

The primary advantage of silicone material is that it allows more oxygen transmission from the lens to the cornea than hydrogel lens materials. The advantage of hydrogel lens material is that it stays wetter longer than silicone materials. The lens material chosen should depend on the eye health of the person.

The hydrogel may be a better option for some clients with drier eyes. The original hydrogel lens material is a less expensive option compared to the silicone version. Although hydrogel lenses have less oxygen transmissibility than silicone hydrogel lenses, silicone hydrogel lenses don’t wet as well and tend to collect more deposits on the surface than hydrogel lenses. Therefore, if a person tends to have poor tear film quality or a drier eye, the hydrogel lenses tend to perform better in the long run. If the person has to wear their lenses longer hours and is lucky to have very wet eyes, they would do well with silicone lenses.

Question 7

Oxygen permeability (Dk)

Answer 7

Dk stands for Diffusionskonstante, (a German term). We use the Dk value to indicate the oxygen permeability of lens materials. The higher the Dk, the more oxygen is transmitted through that particular lens material.

Question 8

Thermal conductivity

Answer 8

Thermal conductivity is the ability of that lens material to spread heat produced by the cornea.

Question 9

Transmissibility (Dk/t)

Answer 9

The oxygen transmissibility through a specific lens thickness (t)

Question 10

Durability and stability

Answer 10

The lens materials can be compared by their durability and stability.

Durability - the strength and ability of the material to maintain its structure over time.

Lens stability - the ability of the lens material to maintain its shape and dimensions over time.

Question 11

Wetting angle

Answer 11

A measurement used to describe the wettability of that contact lens material. For those of you who love science, it is the angle measured of a droplet of water on the contact lens surface. If the wetting angle is 90 degrees, then the surface of that material is not very wettable, because the drop won’t spread well over the material. If the wetting angle is low, then that material is more wettable, because that water drop will spread over the surface of the material better.

Question 12

Water content/resistance to dehydration

Answer 12

The water content of the lens material will tell you how much oxygen can go through the lens to the cornea. If the water content of the lens material is high, there will be less atmospheric oxygen getting to the cornea. Hydrogel lenses actually have higher water content than silicone lenses and are better for drier eyes, but less suitable for long hours of wear. The silicone materials have lower water content and allow more oxygen to the cornea, so they are better for longer hours of wear. But remember, silicone lenses don’t wet well, so if you have a dry eye, you should wear low water content hydrogel lenses and not for many hours!

Question 13

Modulus

Answer 13

Modulus refers to the ability of the lens material to keep its shape. A lens with a higher modulus will keep its shape better than one with a low modulus.

Question 14

Surface treatments

Answer 14

These are put on the surface of contact lenses to try to increase their surface wettability or decrease the rate at which deposits can coat the surface.

Question 15

Doctors typically ask patients to try wearing their lenses 10-12 hours a day for about a week on a trial basis. Based on the follow-up exam results, the doctor will determine a wearing schedule. This schedule may vary from year to year or even from season to season, depending on what factors?

Answer 15

The client’s medications

Health status changes, such as hormone changes or dehydration

The environment in which the client wears the contact lenses

Diet

Age

Tear film quality and water content of the lenses

Question 16

The contact lens modalities are single use daily wear, bi-weekly (every 2 weeks), monthly, quarterly, and yearly. The yearly contact lens modalities are not as popular anymore why?

Answer 16

The yearly contact lens modalities are not as popular anymore because the lenses don’t actually last a year and tear easily.

Question 17

You will use the data you obtained from what to help you decide which soft contact lens to fit on your patient?

Answer 17

You will use the data you obtained from the keratometer, the topography map, and the slit lamp evaluation to help you decide which soft contact lens to fit on your patient.

Question 18

Soft contact lenses and keratometry

Answer 18

Look at the flattest and the steepest curves. Remember this reading is only measuring the two perpendicular curves at central 3-3.5 mm of the cornea. The topographer will give you more information about the curvature of the entire corneal surface.

In general, if there is less than -0.75 diopters of astigmatism in the prescription, you should be able to fit a spherical soft lens on that eye. If there is greater than -0.75 diopters of astigmatism in the prescription, you should be able to fit toric or rigid gas-permeable lenses.

Question 19

Note that the higher the astigmatism correction in a soft toric lens, the… Therefore, you may want to offer the patient a what?

Answer 19

Note that the higher the astigmatism correction in a soft toric lens, the less stable it will be, since it can rotate out of alignment after each blink, so the vision will not be very sharp. Therefore, you may want to offer the patient a gas permeable rigid lens that has a spherical back surface that will smooth out the astigmatic corneal surface and allow sharper, more consistent vision than a soft toric lens.

Question 20

Remember that the soft lenses will lie over whatever shape the cornea has. If the corneal surface is the reason for the majority of the toricity of the cornea, the soft toric lens won’t be able to what? For this reason, a gas permeable rigid lens would be better. How will you be able to get good vision with a toric soft lens?

Answer 20

Remember that the soft lenses will lie over whatever shape the cornea has. If the corneal surface is the reason for the majority of the toricity of the cornea, the soft toric lens won’t be able to correct all the astigmatism well because there will be gap between the back surface of the lens and the cornea, called a lacrimal lens, since it will be filled with tears. For this reason, a gas permeable rigid lens would be better. If the corneal surface is relatively smooth and the amount of corneal toricity is similar to the refractive cylinder, then you will be able to get good vision with a toric soft lens.

Question 21

The parameters of soft contact lenses are what?

Answer 21

The parameters of soft contact lenses are manufacturer, brand name, base curve, diameter, power, Dk/l (oxygen permeability), water content, and material. Other parameters include center thickness, tint, and modality.

Example:

Manufacturer: Vistakon
Brand name: Acuvue Oaysis 1 day with HydraLuxe
Base curve: 8.5mm, 9.0mm
Diameter: 14.3
Power: -0.50 - +8.00
Dk/l (oxygen permeability): 121 x 10-9
Water content: 38%
Material: Senofilcon A

Question 22

List and describe the steps to check your patient’s lens fit

Answer 22

1. Check vision. Check the patient’s acuity for each eye. If they need extra power or less power to achieve their best visual acuity, change the power of their lens. You can use trial lenses.

A trial frame and loose lenses can be used to do a quick over-refraction to determine if more or less power is needed. Or, if you have been taught by the doctor how to use a phoropter to check acuities, you can use the phoropter. The NOCE-CLRE will not require you to know how to do an over-refraction or use a phoropter.

Spherical soft contact lenses come in 0.25 diopter increments usually. You can use the trial lenses that come in +0.25 and -0.25 diopter steps to find if your patient needs more or less power. Toric lenses usually come in 0.25 diopter sphere steps, -0.50 cylinder steps, and 10 degree axis steps; however, it’s best to consult with the contact lens manufacturer information to know which powers, cylinders, and axes are available.

2. Check movement and corneal coverage. Using the slit lamp and a wide beam, check to see if the lens is covering the entire limbus and centers well over the cornea. Use an optic section and check for .5 mm movement of the lens with each blink. If the lens is not centered and sits low, your lens is too loose. If there is no movement with the blink, your lens is too tight.
3. Follow up. After the patient has had about a week to build up their wearing time with the lenses, you can bring them back to check how their cornea and adnexa are adapting to the contact lens fit. When they return for a fitting evaluation after one week, reassess their visual acuity, then use the slit lamp to assess the cleanliness of the lens if it is not a single-use lens, centration, and movement again. Now, you will also remove the lens and use a fluorescein stain to assess the health of the cornea and also evert the upper lids to assess whether there is any irritation of the tarsal plate or the upper limbal area. If there is staining of the cornea with the fluorescein dye noted or irritation of the tarsal plate, re-evaluate whether it is caused by the lens material, lens size, poor cleaning habits, or physiology of the patient’s cornea. Remember that you are responsible for consulting with the doctor any time you note any problems with the fit. The patient may not be a good candidate for contact lenses.

Question 23

There are many different ways to insert a contact lens. Other doctors may teach you another method. There’s no wrong way to accomplish this task, as long as the method you teach your clients allows them to insert their lens safely! What are the instructions for one method to offer patients?

Answer 23

1. If you’re right-handed, insert the right contact lens first. If you’re left-handed, insert the left lens first.
2. For the right eye, use your right hand’s middle finger to pull the lower lid down. Use your left middle finger to pull the upper lid up. With the lens on your right index finger, gently place the lens on the lower portion of your right cornea so the lower part of the contact lens is on the white part of your eye.
3. Look down and release both hands. Continue to blink while looking downward.
4. Once you have both lenses inserted, rinse the contact lens case with hot, running water for a few seconds and let it air dry, preferably upside down on a clean towel. You won’t need to refill the case with fresh solution until you’re ready to put your cleaned lenses away later on

Question 24

Instructions for removing their lenses.

Answer 24

1. Hold your eye open, using the same finger placement technique you used to hold your eyelids apart when you inserted the lens.
2. With your eye open, tip your chin downward as you look at your eye in a mirror positioned directly in front of you. You should be able to see some of the sclera below the cornea.
3. Now use your right index finger to touch the lower portion of the lens and tug it downward so about half the lens is off the cornea.
4. Without taking your forefinger off the lens after you’ve slid it downward, bring your right thumb upward to help pinch the lens from the sclera directly beneath the cornea. Remember that the white portion of the eye has no nerve endings, so it’s far more comfortable to pinch the lens off the white part of the eye than to pinch it directly off the cornea.

Ask your patients to insert and remove their lenses several times before they leave so you’re confident that they can do it easily and safely.

Question 25

Your clients should clean their lenses how often? Unless what?

Answer 25

Your clients should clean their lenses at least once a day, unless the lenses are designed specifically for one-day use. Some people clean their lenses in the evening, just after removing them. Other people clean them in the morning, just before inserting them in their eyes.

Question 26

What are the instructions for clients who are using a multipurpose solution?

Note: this cleaning technique uses a multipurpose disinfecting solution only. There are other disinfecting systems that require more than one bottle and that are hydrogen peroxide-based, so be aware that this technique is limited to multipurpose solutions only.

Answer 26

1. After removing the contact lens from one eye, put several drops of disinfecting solution in the palm of one hand and gently rub the lens back and forth in the palm of your hand—about four or five times on each side. Do not use tap water to clean the lenses, because it’s not sterile. (Doctors may recommend an additional cleanser to clean soft contact lenses, but multipurpose solutions are made to soak, clean, and rinse the lenses.) Note: Some disinfecting solution bottles say no-rub solution. However, still tell your clients to rub the lenses, because all lenses will become coated with oil and mucus, and simply soaking the lenses will not allow this coating to come off very well.
2. Refill the case with fresh disinfecting solution and place the clean contact lens in the correct side of the case. All contact lens cases are marked for the right and left side. Be careful not to mix up the lenses.
3. Now repeat with the other lens. Soak the lenses for least six hours.

Question 27

Some patients may have an allergy or sensitivity for multipurpose solutions. When this is the case, a hydrogen peroxide solution can be used.

What are the instructions for clients that are using a hydrogen peroxide solution?

Answer 27

1. This method is usually reserved for people who have allergies or sensitivities to multipurpose solutions.
2. The grey disc inside the kit is made from platinum and breaks down the hydrogen peroxide into water and oxygen after 6 hours. So the lenses need to soak for 6 or more hours.
3. After soaking, rinse the lenses with sterile saline before inserting the lenses to the eyes.

Question 28

Cleaning lenses well is a learned skill. Sometimes your clients may accidentally tear their lenses if they what?

Answer 28

Cleaning lenses well is a learned skill. Sometimes your clients may accidentally tear their lenses if they rub them too hard.

Question 29

In addition to teaching your clients to insert, remove, and clean contact lenses correctly, you’ll want to give them what tips?

Answer 29

Avoid exposing the lenses to any type of water when cleaning or wearing them.

Discard any remaining solution in the lens case before re-disinfecting. Always use fresh solution

Always wash your hands before handling lenses.

Keep the cleaning solution bottle tightly closed when it’s not in use.

Replace your lens case every one to three months.

Store your cleaning solution at room temperature and use it before the expiration date.

Keep cleaning solutions out of the reach of children.