Test Your GP Fitting Skills – page 1

Case 1 – Discussion Item 1

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

Corneal Measurements

Ocular Measurements (OU)
Corneal diameter
Pupil
Fissure width

OD -2.00 -0.75 x 180
OS -2.25 -1.00 x 180
OD 43.50/44.25 @ 90
OS 43.25/44.25 @ 9011.5mm
4.0mm
10.5mm

Discussion Item 1: A GP lens is well suited for this patient because:

a) Refractive cylinder matches corneal cylinder select

b) With-the-rule astigmatism select

c) Her mother wears GP lenses select

d) The amount of astigmatism is better corrected with GP spherical lenses as compared to hydrogel spherical lenses select

e) All of the above select

Go to Discussion Item 2 >>


Spectacle Rx

Corneal Measurements

Ocular Measurements (OU)
Corneal diameter
Pupil
Fissure width

OD -2.00 -0.75 x 180
OS -2.25 -1.00 x 180
OD 43.50/44.25 @ 90
OS 43.25/44.25 @ 9011.5mm
4.0mm
10.5mm

a) While it is desirable to have the refractive and corneal cylinder match as close as possible, in most cases it isn’t necessary. The tear layer behind the posterior lens surface will optically negate the corneal cylinder. Of more importance is that the refractive cylinder should be equal to or less than the corneal cylinder. If it is greater, the residual amount will need to be offset by utilization of a toric design. back


Spectacle Rx

Corneal Measurements

Ocular Measurements (OU)
Corneal diameter
Pupil
Fissure width

OD -2.00 -0.75 x 180
OS -2.25 -1.00 x 180
OD 43.50/44.25 @ 90
OS 43.25/44.25 @ 9011.5mm
4.0mm
10.5mm

b) With-the-rule astigmatic patients are well suited for GP lenses due to the ideal lens movement along the steeper vertical meridian. During the blink cycle the GP lens follows the path of least resistance, which is the steepest curved meridian. While against-the-rule patients can also be fit with GP lenses, beware of post blink movement horizontally which may result in excessive lens decentration. back


Spectacle Rx

Corneal Measurements

Ocular Measurements (OU)
Corneal diameter
Pupil
Fissure width

OD -2.00 -0.75 x 180
OS -2.25 -1.00 x 180
OD 43.50/44.25 @ 90
OS 43.25/44.25 @ 9011.5mm
4.0mm
10.5mm

c) When parents are successful GP wearers it is often desirable to also fit their children in this lens modality. back


Spectacle Rx

Corneal Measurements

Ocular Measurements (OU)
Corneal diameter
Pupil
Fissure width

OD -2.00 -0.75 x 180
OS -2.25 -1.00 x 180
OD 43.50/44.25 @ 90
OS 43.25/44.25 @ 9011.5mm
4.0mm
10.5mm

d) It is not unusual to see first-time wearers with this amount of astigmatism fit in spherical hydrogel lenses (usually to save expense of going into soft toric lenses). Fortunately this compromised vision can easily be corrected with a GP lens. back


Spectacle Rx

Corneal Measurements

Ocular Measurements (OU)
Corneal diameter
Pupil
Fissure width

OD -2.00 -0.75 x 180
OS -2.25 -1.00 x 180
OD 43.50/44.25 @ 90
OS 43.25/44.25 @ 9011.5mm
4.0mm
10.5mm

e) All of the above are excellent reasons to recommend GP lenses to this patient. back