UNIVERSITY OF MISSOURI-ST. LOUIS

SCHOOL OF OPTOMETRY

LABORATORY PROGRAM OPTOMETRY 553/563

CONTACT LENSES I

FITTING SOFT CONTACT LENSES

Introduction

Soft contact lenses may be manufactured by three methods or a combination of these methods. (Spincasting, cast-molded or lathe-cut) These will be discussed in more detail in the contact lens course. Today you will be fitting a partner with soft contact lenses. These lenses will be ordered and dispensed at a future lab time.

Fitting Procedure

  1. Determine lens power by taking the patient’s spherical equivalent of their spectacle Rx, corrected for vertex distance.
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  2. Lens Selection
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    Many labs suggest starting with a base curve radius 4-5D flatter than low "K". Another method to use is to fit the middle base curve available. Most of these type lenses are available in approximately 3 base curves, for example: 8.2mm, 8.6mm, 8.9mm. In this example, you would choose the 8.6mm. If you find it to be too flat, change to the 8.2mm and if too steep, change to the 8.9mm. Another method is to use the following as a guide for selection base curves:

    Low K >345D Steeper BCR

    Low K 41-45D Middle BCR

    Low K<41D Flatter BCR

    Diameter: A 13.8 or 14.0 diameter is fairly standard. HVID’s of about 10 or 11mm are fairly average. Eyes with a small HVID may need to go to a smaller diameter and eyes with a large HVID, a larger diameter.
  3. Select lens thickness. The best lens is the one with the least mass which provides full corneal coverage, taking into consideration individual patient factors such as comfort, overall corneal oxygen requirements and patient’s dexterity. In powers of –2.00 or less, and if handling and durability are a problem, the standard thickness lens should be used.
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  4. Bring your predicted power and diameter to the laboratory instructors for diagnostic lenses.
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  5. Insert the lens and allow 10-15 minutes for adaptation
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  6. Evaluate lens performance and complete the fitting form.
    1. Lens Centration & Movement – The optimal lens is the one with the flattest base curve which centers consistently and does not move excessively as a result of blinking or exaggerated eye movements. Remember, lenses may tighten; therefore, if in doubt go to the flatter lens.
    2. Quality of the keratometer mires and retinoscopic reflex.
    3. Patient comfort
  1. If criteria met, over-refract with sphero-cylinder and best sphere.
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  2. Complete order form indicating BCR, Diameter, Power, Lab name and Type of Lens.

Example: BCR Diameter Power Lab Type

8.6 13.8 -3.00 Ciba Cibasoft

Note: We are using Cibasoft lenses from Ciba Vision for this lab today. We use all types of lenses in clinic. We have changed the laboratory slightly from years past and I wanted to try ordering and dispensing lenses this year. Ciba was kind enough to supply the lenses.