How to Troubleshoot Contact Lens Fitting

All contact lens fitting sessions start with an accurate refraction (prescription determination) and precise keratometry (corneal curvature) readings. Evaluate the patient's visual needs and determine which lenses are best for the patient. Clear and consistent vision is the goal of every contact lens fitting.

Things You'll Need

• Sodium fluorescein
• Contact lens trials
• Slit lamp
• Keratometer
• Phoropter
• Loose lenses

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Instructions

Soft Spherical

• 1

  Choose a soft spherical lens for single vision prescriptions with less than 3/4 diopters of astigmatism correction. Pick the appropriate base curve according to the keratometry readings.

• 2

  Evaluate the movement of the lens, the coverage of the lens on the cornea and the centration of the lens. Choose a flatter base curve if the lens is fitting too tightly and is moving less than 1/4mm when the patient blinks. If the lens is too loose choose a steeper base curve.

• 3

  Select a different brand of contact lens or a different material if the patient is exhibiting any discomfort after a one week trial period. Also, switch the patient to a hydrogen peroxide based cleaning system to ensure that sensitivity to preservatives in the solution is not part of the problem.

Soft Toric

• 4

  Assess the rotation of the toric lens. Lens rotation is the only additional factor that comes into play. The lens must sit properly in order for the patient to achieve clear consistent vision. With the lens in place on the patient's eye, imagine the cornea as a clock face with 12 o'clock being the superior most part of the cornea, look for markings at 3 o'clock and 9 o'clock, or a series of markings at the 6 o'clock position.

• 5

  Choose a different axis lens if these markings do not center well. Use the "Left Add Right Subtract" or LARS principle. For example, if the lens is rotating to the left by 10 degrees, then add 10 degrees to the axis of the lens for the next trial. Adjust the lens a few degrees manually with your finger to center it. Check the patient's vision to see if these adjustments help.

• 6

  Choose a different brand of toric contact lens. If the lens is decentered by more than 20 degrees or if the patient has discomfort after the one to two week trial period choose a different brand.

Soft Bifocal

• 7

  Start with the lowest bifocal power that provides adequate near vision. The best candidates for soft bifocals are patients with a little hyperopic correction in the distance.

• 8

  Do not allow the patient to try the lenses in the office. Set up the trials empirically based on your exam findings and send the patient home with the lenses for at least a week. It is ideal for the patient to start the trial period when the patient's visual demands are less, like over a weekend. There is a learning curve that has to take place with this type of fit. The brain has to get used to a new way of connecting with the eyes.

• 9

  Determine which of the patient's eyes is dominant. If the patient is complaining of decreased near vision with the first set of trials, strengthen the power of the bifocal in the lens of the non-dominant eye. Also, see if it helps to add plus power to the distance correction without losing acuity in the distance.

• 10

  Over-refract with loose lenses only. In bifocal fits, small changes go a long way.

• 11

  Provide your patient with reasonable expectations. These lenses, for some, offer a compromise in vision. At some point in the fitting process the patient may have to give up clarity in her near vision to see better at distance or vice versa. If the patient is aware of these limitations at the onset of the fitting it can make the process much smoother, and minimizes the expectation of immediate perfect vision.

Basic Rigid Gas Permeable

• 12

  Pick your initial trial gas permeable lenses using the patients corneal curvature readings and spectacle prescription or order the initial trail empirically from the gas permeable manufacturer. Put this trial lens in position on the patient's eye. You may want to instill a drop of topical anesthetic for patient comfort. Assess the lens position. If the lens is decentering inferior, the easiest changes to make are choosing a flatter base curve or minimizing the center thickness of the lens. If the lens is a plus lens order your next trial lenticulated. Also, if the patient has more than 2.5 diopters of astigmatism, you may need to opt for a bi-toric lens instead of a standard spherical lens. If the lens is decentering superior, choose a steeper base curve or again try increasing the center thickness of the lens. If the lens is moving laterally, choose a larger diameter lens, steepen the base curve or choose an aspheric design.

• 13

  Evaluate the fit of the lens by instilling one drop of sodium flourescein. Check the pattern of the dye under the lens. You want the dye to be evenly distributed under the lens. If the pattern shows apical clearance and peripheral seal off, select a flatter base curve. Conversely, if there is apical bearing, select a steeper base curve. If the pattern shows mid peripheral bearing, choose a smaller optical zone diameter.

• 14

  Assess how the lens moves when the patient blinks. If there is greater than 1/4 mm of movement on the blink, steepen the base curve. If the lens adheres, flatten the peripheral curves. If the patient complains of reduced or fluctuating vision, rule out flexure. Do this by taking corneal curvature readings over the gas permeable lens. If there does appear to be residual astigmatism, use a flatter base curve, increase the center thickness of the lens, reduce the optical zone diameter, or switch to a lower Dk material.

Rigid Gas Permeable Multi-Focal

• 15

  Decide whether a simultaneous aspheric design (similar to a progressive spectacle lens) or a segmented design (similar to a flat top bifocal spectacle lens) is better for the patient. The simultaneous aspheric works best for patients with a lower ADD power, patients that require better intermediate vision and patients whose lower lid is below the lower limbus. The segmented multi-focal works best for patients with larger pupils, those with critical near demands and whose lower lids rests at the lower limbus.

• 16

  Start 0.5 diopters stronger than the patient's spectacle bifocal power when choosing the first diagnostic lens for either lens design,

• 17

  Choose a flatter bast curve if there are bubbles under the lens, specifically with the simultaneous design. These lenses require good centration and minimal lag when the patient blinks. Perform all over refractions with loose lenses.

• 18

  Check translation by lifting up the lid as the patient looks down; the lens should push up. If the lens is not translating, increase the diameter of the lens. If the segment is riding too high, increase prism or decrease the segment height. If the lens is rotating too much, flatten the base curve or increase the prism. With the segmented design, translation or the lens moving up when the patient looks down is the most crucial element of a successful fit.