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First, they will take a measurement to check the curve and diameter you are going to need in your lenses. Next, the eye doctor will take a measurement of your pupil and your iris. Finally, the eye doctor will make sure that your eyes make enough tears to keep your contacts moist.

?Lag? refers to the difference in distance from contact lens edge to limbus in the same location (nasal, temporal, superior, or inferior) when looking in primary gaze compared to peripheral gaze.

The 8.4mm base curve is still the likely best fit for the majority of eyes. In instances when the 8.4mm lens is too steep, the 8.8mm lens allows a flatter option. This is more likely needed in smaller eyes, and possibly in some very flat corneas.

Spherical Lenses Spherical contact lenses are an ideal choice for those who are nearsighted(myopia) or farsighted (hypermetropia). These are the common types of contact lenses prescribed for myopia or hyperopia.

Although traditional training and fitting guides recommend assessing lens movement on right and left gaze (known as lag, figure 5) and on up gaze (known as sag, figure 6), studies indicate that these measures have little predictive value in deciding if a lens fit is ideal or not,8,10 though movement on horizontal gaze ...

Yes they do matter. The BC, or base curve, is measured based on your cornea's curvature. If the base curve is too small, it'll squeeze your eye, and if it is too big, it won't stay on your cornea. These both may cause damage to your eye.

Contact lens materials are typically based on polymer- or silicone-hydrogel, with additional manufacturing technologies employed to produce the final lens. These processes are simply not enough to meet the increasing demands from CLs and the ever-increasing number of contact lens (CL) users.

Your eye doctor may measure the size of your pupil or your iris (the colored area of your eye) with an instrument called a biomicroscope or slit lamp or manually with a ruler or card. This measurement is especially important if you are considering specialized lenses such as Gas Permeable (GP) contacts.

When combined with your exam, it will add about 10 minutes, but may be longer for first time wearers or those being fit in multifocal contacts. A comprehensive eye exam takes 45 minutes to one hour.

Figuring out the proper base curve based upon Rx is fairly simple: Plus Power ? Use the Spherical Equivalent (Sphere power plus half the cylinder power) and add 4.00 diopter to that. Example ? Rx of +2.50, the base curve will be approximately 6.50.