GP Lens Case Grand Rounds Troubleshooting Guide

Bitoric Empirical GPLI Calculator: Edward S. Bennett, OD, MSEd, FAAO, FSLS

Background

JH is an 18 year-old college freshman who is complaining of blur through her soft toric lenses. She has worn soft toric lenses for four years and has never been optimally satisfied with her vision but, upon initiating college at a large university, she found it more challenging to see information presented from the back of a classroom. She also feels her night driving is challenging as well, especially the glare presented from oncoming headlights.  

Test Procedures, Fitting/Refitting, Design, and Ordering

She is wearing monthly replacement lenses and admits to typically wearing them as long as 2 – 3 months. The lens powers and visual acuities are the following:

OD:  -4.00 – 2.25 x 180 20/25 -2
OS:  -3.25 – 2.25 x 180  20/25 -1

Slit Lamp Evaluation (with lenses on):  Both lenses exhibited good movement with the blink although the toric indicator line tended to shift between 5 – 10˚ with the blink OU.  In addition, Grade 2 mucoprotein deposition was present OU.

Manifest Refraction

OD: -4.25 – 3.25 x 003  20/20 +2
OS:  -3.00 – 3.75 x 180  20/15 -2

Keratometry

OD:  42.50 @ 180; 46.00 @ 090
OS:  42.75 @ 180; 46.00 @ 090

Based upon this information, bitoric GP lenses were recommended to provide an improvement in vision and she was agreeable to this option. Her information was inputted into the GPLI Toric and Spherical Lens Calculator and the following lens parameters were found:

The following lenses were ordered:

The Optimum Classic was selected as a viable low Dk rigid material which is a good option for daily wear myopic patients. Toric peripheral curves are typically recommended to ensure both central and peripheral alignment. The determination of the toric peripheral curves was based upon a tricurve peripheral curve system recommended by the author (i.e., add 1mm to the BCR for the SCR and add 2mm to the SCR to determine the PCR.(1)

Patient Education and Consultation

As the patient was unaccustomed to GP lens wear, a drop of topical anesthetic was applied immediately prior to lens insertion. Upon dispensing of the lenses, the visual acuity was the following:

OD: 20/15 -1  OR: +0.25DS  20/15-1
OS:  20/15 -2  OR: Pl – 0.25 x 175  20/15-1

Slit Lamp Evaluation: A slightly superior-central (i.e. lid attachment) fitting relationship was present with between 1 – 2mm movement with the blink. The fluorescein pattern was alignment centrally with slightly greater pooling peripherally.

The patient quickly demonstrated the ability to handle the lenses and was very pleased with the vision achieved with the lenses. She did note the awareness once the anesthetic had worn off but overall was quite pleased.

Follow-Up Care/Final Outcome

JH had totally adapted to all day lens wear by the one week visit. The vision and fitting relationship were unchanged from the dispensing. The patient was evaluated at three months and then every six months afterward.

Discussion/Alternative Management Options

This case demonstrates how important bitoric lenses are as an option for the highly astigmatic patient. The vision achieved was significantly better than the soft toric lenses she was accustomed to wearing. The fact that this success was achieved with empirical fitting is important as well. The first time she experienced GP lens wear was a very positive one visually which may actually decrease awareness concerns. Another option for her would have been a custom soft toric and that likely would have been more successful in correcting the level of refractive astigmatism she manifested as her standard lenses were only available in a maximum cylinder power of -2.25D.  However, the benefits of rigid lens optics for correcting astigmatism in combination with greater stability as compared to the impact on vision resulting from rotation of 3 to 4 diopter cylinder soft toric lens make a bitoric GP lens an important tool in the astigmatic correction toolbox.

As the cylinder power difference between the lens powers and the base curve radii resulted in a cylinder power effect bitoric design for the right eye it is important for the lens to rotate minimally or the cylinder difference (in this case the difference between -2.25 and -2.75 – or 0.50D) will rotate as well and possibly blur vision. Fortunately, when there is at least 2D of base curve toricity, these lenses tend to lock into place on the cornea and not rotate. A great resource on bitoric fitting is the GPLI webinar presented by Dr. Tom Quinn which can be found at: https://gpli.info/videos/webinar-2018-03.htm

References

1. Bennett ES, Sorbara L, Kojima R. Gas Permeable Lens Design, Fitting, and Evaluation. In Bennett ES, Henry VA (eds.): Clinical manual of Contact Lenses (5^th ed.), Philadelphia, Wolters Kluwer. 2020:134-185.