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Here are a couple of cases where one might think toric, but it's actually the wrong decision, and one where toric was just the ticket, though preliminary data would not have predicted it. CASE I - Dr. Bergenske Right Eye:
This looks like a case for SPE... ...spherical power effect bitoric! It appears from the K's and refraction that a spherical lens would correct the refractive cylinder, which is apparently all corneal. Due to the high degree of toricity, it is reasonable to expect a toric base would be needed. A lens was ordered empirically to be slightly flatter than flat K and with about 1 diopter less toricity than the corneal cyl: Base: 43.25 x 46.25. Power: -3.75/-6.75. (Cylinder power specified has same magnitude as base curve cyl in diopters "K.") Diameter: 9.5. This should provide a fit that looks like and acts like a spherical lens on an eye with a low degree of with the rule cylinder, with minimal apical clearance and modest vertical movement. It didn't. The lens fit like a suction cup, with significant central pooling and seal off superior and inferior. There was little movement and less comfort. What went wrong? Let's look at the topography:
Although the K readings accurately indicated the amount of cylinder, they were misleading on the toricity of the peripheral cornea. For some eyes the toricity does not extend throughout the cornea. This type of eye is best fit with a spherical or aspheric base lens. The patient was successfully fit with a lens 43.25/9.5/-3.75. CASE II - Dr. Bergenske A patient presented with complaint of decreased correct visual acuity in the right eye, following LASIK and several enhancement procedures. Refraction was +0.50 - 3.50 x 35 for best acuity of 20/40. Simulated K's from topography were 39.87 and 46.12. One might be tempted to think toric here also, but let's have a closer look at the topography:
This pattern is typical of pellucid marginal degeneration. By obtaining pre-op topography also, it was confirmed that the patient had this condition prior to the LASIK, but it just got a lot worse when the cornea was thinned. Again, although the refractive and K data say "toric," the topography says "no way toric." This patient was successfully fit with a 10.0mm 43.50 base spherical lens. CASE III - Dr. Bergenske
This patient was initially fit with a 44.25 spherical base lens. Acuity and comfort were good, though the lens rode high. The patient returned with complaint of poor vision with spectacles after removal of the lens. The post lens refraction was -3.00 sphere. The left eye was similar. Let's go to the topography:
This patient has considerably more peripheral toricity than central readings would indicate. The spherical lens had an excessively flat fitting relationship with the vertical meridian, leading to sphericalization of the central cornea. The solution here is to fit with a toric base lens that will create a better fitting relationship and prevent the corneal molding that is occurring with the spherical lenses. The right eye was refit with an SPE: 44.00 x 46.00, -2.50/-4.50. This centered better, and the post lens refraction was stable, giving good acuity with the current spectacles.
CASE I - Dr. Quinn
Should this patient be fit with a sphere or toric gas perm lens?
CASE II - Dr. Quinn
All maintain a 0.75 difference in fitting relationship between horizontal and vertical meridians to mimic fitting the "ideal" cornea.
Order: BC: 41.00 (8.23mm)/ 43.25 (7.80mm) BVP: -1.00/ -3.25 Difference in base curve: 2.25D Difference in lens powers: 2.25D Conclusion: Spherical Power Effect Design Spherical Power Effect (SPE)
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