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examination showed unstable axis location. We then educated the patient on her refractive correction options. We discussed the use of custom soft toric (ex. Art Optical Intelliwave®), GP (standard or sclera), or trying various brands of soft toric contact lenses. The decision was made to try standard diameter GP lenses. We then discussed the benefits of bitoric GP lenses such as crisper, more stable vision and that they would be more economical long-term due to the ease of maintenance and longer wearing life. We also made her aware that there would be a period necessary to adapt to the increased lens awareness. Topography was then done and showed keratomy readings to be 46.1/48.5 @098 OD and 45.9/ 48.5 @080 OS. Figure 1. Right Eye axial map
Figure 2. Left Eye axial map
depicting limbus-to-limbus With- depicting limbus-to-limbus With- the-Rule astigmatism. the-Rule astigmatism. The axial topographical map revealed with-the-rule astigmatism and it was calculated that nearly all of the patient's refractive cylinder was corneal, so we opted for a spherical power effect fit. This finding along with the amount of cylinder present made her a great candidate for bitoric GP lenses. We empirically fit these lenses using the Mandell-Moore Bitoric Lens Guide rather than using a diagnostic set. Using this method, we ordered an Art Optical bitoric of -5.25/- 7.25 BC: 7.37/7.03 OD and -5.25/ -7.50 BC:7.4/7.03 OS. The diameter was 9.5 and the optic zone was 8.1 OU with Boston EO material. The patient was instructed to return to the clinic to have the lenses dispensed and evaluated in two weeks.

Figure 3. Left Eye slit map photograph using fluorescein to assess the lens-to-cornea
fitting pattern. The patient returned to the eye clinic September 20th, 2012 to have the ordered bitoric lenses fit and assessed. The lenses were rinsed, inserted, and allowed to settle. Initial visual acuities with the lenses were 20/20-2 OD and 20/20-1 OS. The slit lamp exam findings showed center alignment, movement to be about 1 mm, fluorescein pattern was aligned, good edge lift, and excellent surface quality. The over-refraction was plano OU. The patient was educated that the lenses were to be worn daily and disinfected with Clear Care® solution. The GP bitoric lenses were dispensed, and she was instructed to return to the clinic in 1-2 weeks for a contact The patient returned October 4th, 2012 after wearing the GP bitoric lenses for two weeks. The patient noted lens awareness, but that the awareness had gradually decreased while wearing the lenses 8 hours a day over the two weeks. She also noted a marked improvement in her vision with the GP bitorics in comparison to her previous soft toric lenses. Her initial visual acuities were 20/20 OD and 20/15-1 OS at distance, and at near her visual acuities were 20/25-2 OD and 20/15-1 OS. During the slit lamp evaluation, the lenses were noted to be sitting slightly superior to center. Good movement, edge lift, surface quality, and an aligned fluorescein pattern were also observed. Further biomicroscopy was done and revealed normal lids, lashes, and cornea. The patient was made aware the comfort of GP lenses should continue to improve over the coming weeks and that if the comfort doesn't improve or she notes a decrease in vision to return to the clinic to assessed for mini scleral or scleral lenses. Discussion
The objective in fitting a bitoric lens is to achieve a close alignment of the contact lens on the eye and create an appearance in the fluorescein pattern as if the fit were a spherical lens on a mildly astigmatic eye. Making the lenses slightly flatter in the vertical meridian will promote more vertical lens movement and increase tear flow beneath the lens. This will likely provide an upper lid attached fit, which will be a more comfortable fit. The diameter used for these contact lenses was determined to ensure complete pupil coverage in both bright and dim conditions. Most lens designs range from 9.2 to 9.8mm in diameter.1,5 In designing and ordering the patient's lenses, we used the Mandell-Moore Bitoric Lens guide to input her refraction and keratometry values. We then determined the base curve by fitting 0.25 diopters flatter than her flat "K" measurement and 0.50 diopters flatter than her steep "K" measurement, which we obtained via the Medmont® topographer.1-4 For this patient, we discussed many treatment options. The use of GP toric lenses was deemed best for initial use in this case. The three GP torics considered were front torics, back torics, and bitorics. Front torics are useful for patients with spherical corneas and astigmatism. The spherical correction is on the back of the lens, while the astigmatic correction is on the front.1,2 Back torics have spherical correction on the front of the lens with the astigmatic correction on the back. The back toric lens can induce additional astigmatism in the flatter meridian of the eye, so use of these lenses should be confined to patients who follow the "two- thirds principle". The "two-thirds principle" is determined by dividing the refractive cylinder at the cornea by 1.5 and then adding that value to your flat "K" measurement. This will give you an appropriate steep "K" value.1 Back torics are best utilized in cases of against-the-rule astigmatism.1,2 Finally, a bitoric lens has a toric anterior surface that compensates for any residual astigmatism created by the toric posterior surface. There are two type of fits with the bitoric lenses. There is a spherical power effect fit where the lens acts optically as a spherical lens because the difference in base curves between the front and back surfaces cancel out any toricity regardless of the rotation of the lens. There is also a cylinder power effect fit where the front and back base curves do not completely equal the difference in the lens powers, so rotation does have an effect on vision. This type of lens design must be prism ballasted to maintain the proper axis although the saddle principle with these lenses decreases the chance the lens will rotate.1,2,4,5 Custom soft toric lenses were also an option for this patient, but due the high cost and possibility of rotation still occurring, this alternative was not used. Scleral and corneoscleral lenses were discussed as an option for this patient if lens awareness was still noticeable in the weeks after the follow-up exam. Due to their larger diameter, these lenses rest almost exclusively on the conjunctiva which is much less sensitive than the cornea. These lenses are also less likely to become decentered or dislocated.1,6 Bitoric lenses show limited success when the keratometric axis differs 15 degrees or more from the spectacle cylinder axis.1-3 Spherical GP lenses would be a more practical option of treatment in these circumstances. Corneal topography that exhibits a symmetric pattern and astigmatism that is limbus-to-limbus is a good indicator for success in using a bitoric lens Conclusions
Bitoric lenses are a very viable option for refractive correction in patients with the suitable amount of astigmatism. The lenses can considerably decrease the amount of rotation seen with soft torics to provide stable vision for the patient. It is important to inform a new GP patient on the adjustment period for increased lens awareness, so their expectations of comfort are appropriate. References
1. Bennett, Edward, and Vinita Henry. Clinical Manual of Contact Lenses. 3rd ed. Philadelphia: Lippincott, Williams & Wilkins, 2009. 336-344. Print. 2. Heiting , Gary. "Toric Contact Lenses for Astigmatism." (2011) All about vision, Web. 23 Nov 2012. <http://www.allaboutvision.com/contacts/torics.htm>. 3. Raul Martín Herranz, Guadalupe Rodríguez Zarzuelo and Victoria de Juan Herráez (2012). Contact Lens Correction of Regular and Irregular Astigmatism, Astigmatism - Optics, Physiology and Management, Dr. Michael Goggin (Ed.), ISBN: 978-953-51-0230-4, InTech, Available from: <http://www.intechopen.com/books/astigmatism-optics-physiology-and-management/contact-lens-correction-ofregular-and-irregular-astigmatism> 4. Silbert, Joel. "Optometric Management." Optometric Management. (2007): 5. Anderson , Bruce. "GP Lens Institute." GP Lens Institute. (2012): 6. Visser , E, R Visser , H Van Lier, et al. "Eye & Contact Lens: Science & Clinical Practice." Eye & Contact Lens: Science & Clinical Practice. 33.1 (2007): 13-20. <http://journals.lww.com/claojournal/Abstract/2007/01000/Modern_Scleral_Lenses_Part_I Clinical_Features.3.asp>.

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