GP Fitting Case 1 - Discussion Item 6

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 6: Based on the performance of this fluorescein pattern, what changes would you employ?

a)	Larger diameter select
b)	Smaller diameter select
c)	Steeper base curve select
d)	Flatter base curve select
e)	No change select
Back to beginning of this case >>

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) Since this lens is obviously fitting quite flat increasing the overall lens diameter would be an option, improving the fit by increasing the sagittal depth. Importantly though, is how the size presently compares to the overall corneal diameter - which should be evaluated before simply increasing the size of the lens. 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) Decreasing the lens diameter without significantly changing the base curve relationship would be the worst thing to do here. One would need to steepen the present base curve by 1.50D to 2.00D if the lens was made much smaller. 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) This fit can be improved by simply steepening the base curve from 0.50D to 1.00D. This would be adequate to improve centration and increase the vaulting over the central cornea. Steepening the base curve in this example is the best choice. 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) An excessively flat lens can never be improved by making it flatter. This is not a consideration. 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) Some change must be made to this fit. A decentered, flat fitting lens like this will result in patient awareness (or discomfort), unstable vision and possibly spectacle blur upon lens removal. back

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This page was last updated Wednesday, March 03, 2010.

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