GP Fitting Case 1 - Discussion Item 2

After reading the Patient History, read the Discussion Items below. To test your understanding of this case, click on the word "select" to read the reasoning behind each choice.

Patient History: 16 y/o female student has never worn contact lenses. She plays no extra curricular sports, and her mother wears GP lenses. No contraindications for lens wear.

Spectacle Rx	OD -2.00 -0.75 x 180 OS -2.25 -1.00 x 180
Corneal Measurements	OD 43.50/44.25 @ 90 OS 43.25/44.25 @ 90
Ocular Measurements (OU)
Corneal diameter	11.5mm
Pupil	4.0mm
Fissure width	10.5mm

Discussion Item 2: When designing a lens empirically or selecting the first diagnostic lens, which parameter would you choose first?

a)	Diameter select
b)	Base curve select
c)	Power select
d)	Peripheral curves select
e)	Material select
Go to Discussion Item 3 >>

Spectacle Rx	OD -2.00 -0.75 x 180 OS -2.25 -1.00 x 180
Corneal Measurements	OD 43.50/44.25 @ 90 OS 43.25/44.25 @ 90
Ocular Measurements (OU)
Corneal diameter	11.5mm
Pupil	4.0mm
Fissure width	10.5mm

a) More than one fitting philosophy will usually work for most patients. A lid attachment philosophy is great for patients whose upper lids cover the superior limbus, as is the situation in this case. Larger diameters in the range of 9.4mm - 9.8mm will usually achieve lid attachment. Therefore in this case diameter would be the 1st parameter selection to make. TIP - If making changes in fit by altering diameter, change the diameter at least 0.3mm to make any significant change. back

Spectacle Rx	OD -2.00 -0.75 x 180 OS -2.25 -1.00 x 180
Corneal Measurements	OD 43.50/44.25 @ 90 OS 43.25/44.25 @ 90
Ocular Measurements (OU)
Corneal diameter	11.5mm
Pupil	4.0mm
Fissure width	10.5mm

b) This is usually the second parameter to be selected. Larger diameter, lid attachment philosophy lenses (9.4mm - 9.8mm) require a base curve fit flatter than K to achieve an alignment fit while smaller intrapalpebral philosophy lenses (8.8mm - 9.2mm) require an on K or steeper than K base curve selection to achieve the desirable lens to cornea relationship. TIP - If making changes by altering base curve, alter at least 0.50D (0.10mm) for a significant change. back

Spectacle Rx	OD -2.00 -0.75 x 180 OS -2.25 -1.00 x 180
Corneal Measurements	OD 43.50/44.25 @ 90 OS 43.25/44.25 @ 90
Ocular Measurements (OU)
Corneal diameter	11.5mm
Pupil	4.0mm
Fissure width	10.5mm

c) The lens power cannot be selected until the diameter and base curve is determined. The power can then be calculated using the rule of thumb - Steeper Add Minus and Flatter Add Plus (SAM/FAP). back

Spectacle Rx	OD -2.00 -0.75 x 180 OS -2.25 -1.00 x 180
Corneal Measurements	OD 43.50/44.25 @ 90 OS 43.25/44.25 @ 90
Ocular Measurements (OU)
Corneal diameter	11.5mm
Pupil	4.0mm
Fissure width	10.5mm

d) Today it is not necessary to design the peripheral curves. Your CLMA member laboratory can provide standardized parameters to complete the data necessary for the posterior optical zone, peripheral curves, edge shape, center thickness and the anterior control of power and lens mass. The CLMA member laboratory will use standardized parameters based on philosophies established by your colleagues and peers. They are tried and proven averages, which will be successful for the greatest percentage of patients fit. back

Spectacle Rx	OD -2.00 -0.75 x 180 OS -2.25 -1.00 x 180
Corneal Measurements	OD 43.50/44.25 @ 90 OS 43.25/44.25 @ 90
Ocular Measurements (OU)
Corneal diameter	11.5mm
Pupil	4.0mm
Fissure width	10.5mm

e) Today, the choice of material doesn't affect the parameters of a lens chosen. Instead the material choice is based upon oxygen demands, wetting characteristics, etc. back

GP Lens Design Database - Online Symposium Schedule

Newsletter Sign-up - Order Educational Materials

Contact GPLI - Site Map - Home

Questions about fitting GP lenses? Send an e-mail to our panel of experts.

Copyright ©1999–2010 Contact Lens Manufacturers Association.
All rights reserved.
This page was last updated Wednesday, March 03, 2010.

Printing Note: If you're printing pages from this website and find that the right side is cut off, try this: With older printers, you could choose the "landscape" (horizontal) setting rather than the "portrait" (vertical) setting when printing. But most newer printers let you scale down web pages before you print. For example, if you have an HP laser printer, when you choose "Print" from the menu, you can then choose "Preferences," where under the "Effects" tab you can change the 100% setting to, say, 95%. You may also see a "ZoomSmart" feature that lets you choose "scale to fit."