Choosing contact lenses

Short story - pick one with a high Dk/t :)

Given that you have to go to a High Street optometrist to buy lenses, it helps to crosscheck their sales pitch a bit.

Case in question is Specsavers offering me daily disposable varifocals, without indicating that the monthlies, though cheaper, are actually more breathable for my eyes.

My conclusions from surfing:

• A contact lens needs to deliver a high level of oxygen to the cornea.
• Silicon hydrogel lenses are currently the best mix of oxygen permeability and comfort. 
• Silicon lenses on their own allow oxygen to permeate but can stick to the cornea due to no water and leave deposits. 
• Hydrogel lenses on their own have a high water content but as water changes the refractive index lenses needed are thicker,cutting off oxygen.
• Contact lenses are given a "Dk" value, where D is the diffusion and k the solubility of oxygen. A consistent comparison parameter is "Dk/t" which is oxygen passing through a lens in a specific time period, taking into account the thickness t of the lens.
• Long story short..a higher Dk/t indicates a higher transmission of oxygen to your cornea.

How to find the Dk/t

• If the optometrist sells lenses under their own brand, ask them the underlying supplier and product. e.g. Specsavers sells Coopervision Biofinity multifocals as Easycare Opteyes.
• If they refuse to tell you and you still want to stick with them, you can find the underlying brand via lensdirect.
• Finally check the manufacturers published information to know the Dk/t value,and compare your options.