Spherical and Toric Soft Contact Lenses

Question 1

Contraindications: Conjunctival Abnormalities

Answer 1

Elevated areas such as pterygiums and pingueculas can be irritated when rubbed by the edges of a larger diameter soft contact lens.

Question 2

Contraindications: Giant Papillary Conjunctivitis

Answer 2

Soft lenses if not taken care of can leave surface deposits on the lens. Over time, these deposits lead to an allergic reaction in the conjunctival area of the eyelid. The result is discharge that can adhere to the contact and can cause it to move when blinking.

Question 3

What are some factors to keep in mind when choosing soft contact lens materials?

Answer 3

Water content, ionic charge and oxygen permeability.

Question 4

Soft Lens Classifications: Group 1

Answer 4

1. Water Content: Low
2. Percentage: <50%
3. Non-ionic

Question 5

Soft Lens Classifications: Group 2

Answer 5

1. Water Content: High
2. Percentage >50%
3. Non-ionic

Question 6

Soft Lens Classifications: Group 3

Answer 6

1. Water Content: Low
2. Percentage: <50%
3. Ionic

Question 7

Soft Lens Classifications: Group 4

Answer 7

1. Water Content: High
2. Percentage: >50%
3. Ionic

Question 8

What are some advantages to a low water content soft lens?

Answer 8

1. Environmentally Stable
2. Resistant to protein deposits
3. More Wettable
4. Better for Dry eye patients

Question 9

What are some disadvantages to low water content soft lenses?

Answer 9

1. Low oxygen permeability
2. Less Flexible

Question 10

What are some advantages to a high water content soft lens?

Answer 10

1. Higher Dk
2. More Flexible

Question 11

What are some disadvantages to a high water content soft lens?

Answer 11

1. Fragile
2. Prone to deposits
3. Cannot be made thin

Question 12

Whats up. Whats up. Whats up. WHAT THE FUCK IS UP DENNYS

Question 13

Why is the ionic charge of a soft lens important?

Answer 13

Ionic lenses are more prone to wettability and maintain tear integrity. The main disadvantage is that the lens is more prone to deposits.

Question 14

What are the advantages to a Silicone based soft lens?

Answer 14

They transmit oxygen well so they are highly permeable and they are also easier to handle.

Question 15

What are the disadvantages to a silicone based soft lens?

Answer 15

The stiffness means that greater care must be taken with fitting, which leads to comfort issues if not fit properly on the patient. They can also create a “dry eye” sensation for some patients.

Question 16

What is the Dk Value?

Answer 16

A measure of how much oxygen passes through the material and reaches the eye by diffusion. For manufacturing comparison, the Dk is factored for each material using a -3.00 lens. The higher the Dk, the greater the oxygen permeability.

Question 17

What is the three point touch?

Answer 17

Where the soft contact lens touches the cornea and two points on the sclera on either side. It provides stability and consistent movement for the patient.

Question 18

What happens to the fit of a soft lens if the three point touch is not achieved?

Answer 18

If the lens is too tight, the fitter may observe blanching of the conjunctival vessels or a scleral indentation. If the fit is too loose, the fitter may see bubbles under the contact lens surface.

Question 19

How does the fitter determine the appropriate diameter for a soft contact lens?

Answer 19

Measure the patients horizontal visible iris diameter (HVID) and add 2 mm to the measurement. The additional 2mm allows for clearance of the corneal limbus and give enough corneal coverage for lens movement.

Question 20

Why would you want to choose a larger diameter soft lens?

Answer 20

A larger diameter lens reduces irritation at the limbus, minimize lid interaction, and dip into the lacrimal lake to spread tears and hydration more effectively.

Question 21

Why would the fitter start with the flattest base curve possible on a soft lens?

Answer 21

The K’s are not as critical when fitting soft contact lenses, and it is easier to detect than a steep fitting lens, meaning it is easier to modify.

Question 22

What is the spherical equivalent formula for soft contact lenses?

Answer 22

Spherical equivalent=sphere power + 1/2 cylinder power

Question 23

What are the steps for determining power of a soft lens?

Answer 23

1. Convert RX to minus cylinder
2. If it is a toric RX, convert to spherical equivalent
3. If the spherial equivalent power is greater than 4 diopters, then adjust for vertex distance.

Question 24

Define Equlibration

Answer 24

When the lens becomes hydrated with the patients tears so that the lens is in its proper state

Question 25

What are 5 points a fitter checks for upon soft lens insertion?

Answer 25

1. Corneal Coverage 2. Dynamic Movement 3. Three point touch 4. Correct Visual Acuity 5. Subjective Comfort Assesment

Question 26

Corneal Coverage of soft contact lenses

Answer 26

The lens should be covered with good centration, determined by a slit lamp. Examine how the edge of the lens interacts with the limbus. The coverage should be around 1mm and if it is less than 1mm it should be determined if the diameter is too small or the base curve is too flat.

Question 27

Dynamic movement of soft contact lenses

Answer 27

Movement is crucial for flushing out debris and promoting tear exchange. It should be about 1mm in older modalities and about 0.4mm in newer modalities. Observed at 5 and 7 o clock when using indirect illumination

Question 28

What is lens lag?

Answer 28

When the eye looks up down left and right, the contact should follow that movement.

Question 29

Issues with visual acuity while fitting soft contact lenses

Answer 29

1. If visual acuity is blurry after the blink, then the lens is too steep 2. If visual acuity is blurry before the blink, then the lens is too flat. 3. If it is blurry without relation to blinking, then an over refraction should take place.

Question 30

What are some indications for Soft Toric lenses?

Answer 30

1. Lenticular Astigmatism 2. Against the rule and low oblique astigmatism 3. Normal to large palpabrae aperture 4. Axis close to 180 or 90 5.Spherical soft lens wearers that have a lower than desired visual acuity

Question 31

What are some contraindications for soft toric lenses?

Answer 31

1. Little to no spherical component to the RX 2. Steep Cornea 3. Poor Tear quality 4. Exophthalmic eye 5. High astigmatism greater than 2.75 diopters 6. Very tight lids

Question 32

What is the thin zone on a toric lens design?

Answer 32

This lens is thick in the center and thin on the edges. These thin edges tuck under the lid and maintain stability by using the watermelon seed principle

Question 33

What is the watermelon seed principle?

Answer 33

When the tension of the lid on the thin portion of the lens squeezes the thicker portion of the lens away from the lid