Soft Contact Lenses

Soft contact lenses are made of repeating units of high molecular weight chains called

polymers

The two major groups of soft contact lenses on the market today, based on their lens material, are ____________ contact lenses and ________________________ contact lenses.

hydrogel, silicone hydrogel

A major concern with the early designs of hydrogel contact lenses was ____________

hypoxia

Oxygen is transmitted through water channels in hydrogel contact lenses. One solution used to increase oxygen transmission in hydrogel lenses was to_____________ the water content of the lenses. Another solution was to develop _____________ lenses.

increase, thinner

advantages of high-water-content hydrogel contact lenses

Better comfort, Quicker adaptation, Longer wearing time & Easier to handle because they are thicker

List three disadvantages of high-water-content hydrogel contact lenses

Lenses are more fragile and prone to tearing, Water content may vary throughout the wearing time and affect vision, Lens deposits are more common, Lens dehydration may cause corneal desiccation & Less reliable to reproduce

What does the acronym USAN mean?

United States adopted name

List two examples of USAN nomenclature

Polymacon, Nefilcon A, Omafilcon B, Etafilcon A

Describe the biggest challenge that needed to be overcome during the development of silicone hydrogel lenses

Silicone is hydrophobic and does not combine well with hydrophilic hydrogel materials. Modifications were made by inserting polar groups into the material to improve the hydrophilic properties

Bausch & Lomb’s PureVision lenses and CIBA Vision’s Night & Day lenses were first-generation silicone hydrogel lenses approved for extended wear. What mechanism did these companies use to improve the wettability of their lenses?

Both companies used a plasma coating on their lenses to improve wettability because the silicone is hydrophobic

As water content increases in hydrogel contact lenses, the oxygen permeability ____________. As water content increases in silicone hydrogel contact lenses, the oxygen permeability ____________.

increases, descreases

Oxygen permeability

Referred to as the Dk of the material, May be measured in Fatt or Barrer units & Depends upon oxygen solubility and diffusivity of the material

Diffusivity

Measures how quickly oxygen moves through the material

Solubility

Measures how much oxygen the material can hold

Oxygen transmissibility

Referred to as the Dk/t, Units may be Barrer/cm & Impacted by oxygen solubility and diffusivity of the material, in addition to the thickness of the material

The stiffness of the contact lens material is referred to as its _______________.

modulus

Brand A has a modulus of 1.1 and Brand B has a modulus of 0.40. Which brand is most likely to feel more comfortable for the patient? Explain why.

Brand B has a lower modulus and is therefore less stiff of a material

List three different ways to improve the wettability of a soft contact lens

Increase the amount of water in a hydrogel lens, Add wetting agents to blister packs (e.g., polyvinyl alcohol or hyaluronic acid), Coat the surface of silicone hydrogels with a hydrophilic material, Add plasma treatments to silicone hydrogels to make them more hydrophilic

Surface friction of the contact lens impacts the ___________ of the lens on the eye.

comfort

The coefficient of friction is 0.423 for Brand A and 0.018 for Brand B. Which brand is most likely to feel more comfortable for the patient? Explain why.

Brand B is most likely to feel more comfortable for the patient because a lower coefficient of friction indicates there is less force on the contact lens during patient blinking

An instrument used to measure the percentage of transmission of different wavelengths is called a ______________________.

spectrophotometer

List five factors that describe the geometric components of a soft contact lens

Diameter, Sagittal depth, Thickness, Radius of curvature & Edge appearance