Can I use the "LARS" method to compensate for axis rotation of
ACUVUE TORIC?
Yes, you can use the "LARS" method to compensate for axis rotation of ACUVUE® TORIC. However, with the orientation marks in the horizontal meridian, 'left' vs. 'right' rotation can be confusing. Therefore, thinking "clockwise" and "anti-clockwise" may be easier. Clockwise means adding to the refractive axis, and anti-clockwise means taking away from the refractive axis.
Example: Spectacle Rx: -3.00-1.25X 10. After stabilisation, the initial ACUVUE® TORIC diagnostic lens orientates anti-clockwise 20 degrees. The compensated lens should be: -3.00-1.25 X 170.
Why are the ACUVUE® TORIC orientation marks at 3 and 9 o'clock?
The dual thin-zone design of ACUVUE® TORIC provides the highest oxygen transmissibility of any disposable toric hydrogel contact lens. For your patients, this means healthier corneal physiology. Since the thin zones are in the vertical meridian, the thicker portions in the horizontal meridian lend themselves to carrying the orientation marks. This also provides the eye care professional with the ability to observe orientation and lens stability without manipulation of the eyelids.
While the vast majority of ACUVUE® TORIC fits rotate minimally (less than 10 degrees), the lens may rotate more on a given eye. However, the rotation will remain the same for each subsequent lens, providing the eye care professional with the ability to simply adjust the correcting axis and prescribe the ACUVUE® TORIC with confidence that the lens will continue to orientate itself just like the initial diagnostic lens.
Is there a specific top and bottom to the ACUVUE® TORIC, or can it be inserted either way?
By comparison, prism-ballast lenses do have a "top" and "bottom." When the lens placed on the patient's eye with the area of maximum thickness, or prism, in the inferior (6 o'clock) position, it quickly settles. If the lens is not applied in this way, it will often orientate correctly after several blinks.
Inserting ACUVUE® TORIC with the orientation marks in the horizontal meridian may hasten the settling time, however it is not necessary to place it in the eye in any particular orientation. No matter which way the lens is placed upon the cornea, the lens should orientate properly within a short time.
Should patients expect good comfort initially when a toric soft lens is applied?
A few patients may notice greater "awareness" when switching from one brand of toric lens to another. Similar to first time toric lens wearers changing from a spherical design, some patients changing from a prism ballast design to a thin-zone design may experience increased awareness ("old shoe/new shoe" analogy). The Eye Care Professional should assure the patient that they should feel completely comfortable with their contact lenses within forty-eight hours.
Should we assume that the lens rotates nasally or temporally when we insert our first diagnostic lens, or should we just pick the axis closest to the spectacle Rx?
You cannot assume that a soft toric lens will rotate at all. So your first diagnostic lens choice should be as close as possible to the spectacle Rx. Do not make any assumptions about a clockwise or anti-clockwise rotation before inserting the first diagnostic lens.
Which way do I adjust the rotation: from my observation point or the patient's?
The adjustment for any toric lens is made from the observer's position.
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If I need to adjust for vertex compensation, should I adjust that amount in the cylinder component of the Rx as well as teh sphere?
The most accurate way to adjust for vertex distance in a toric prescription is to draw an optical cross and consider the total power in each principal meridian.
Example: -5.00 - 1.25 X 180 spectacle Rx. (assume 12 mm vertext distance) The -5.00 vertex compensation is -4.75. The vertex compensation for the -6.25 in the other meridian is -5.75. Thus, the resulting contact lens Rx would be -4.75 - 1.00 X 180.
Both meridians do not always require compensation.
Example: -1.00 - 4.50 X 180. In this example, the -1.00 meridian does not need to be compensated due to its low power, but the other meridian is -5.50 total power and would be reduced to -5.00, Final CL Rx of -1.00 -4.00 X 180.
Do I need to perform a spherocylindrical over-refraction?
If the lens axis is stable and the rotation is consistent with the refractive cylinder axis, it is not routinely necessary to perform a cylindrical over-refraction with today's soft toric lenses. However, if rotation is observed, it is safe to assume that any resultant cylinder is being induced by the rotation. It is therefore recommended that after a spherical over-refraction is performed, the rotation be compensated based on the amount of rotation observed.
Example: To determine if the appropriate amount of astigmatic power in the contact lens was selected, it may be valuable to test 0.50D of cylinder power on axis and 90 degrees away from the axis. If the patient accepts the 0.50D on axis, then they may need additional cylinder power. If they prefer their vision with the 0.50D 90 degrees away, they may benefit from a reduction in cylinder power.
Once I've compensated for the axis rotation of the diagnostic lens, where should I expect the patient's new lens to orientate?
With ACUVUE® TORIC, in which the stabilization system is independent of the optical system, you should expect the patient's new lens to orientate in the same manner as the diagnostic lens, even after you've compensated for axis rotation.
What are the benefits of a disposable toric soft lens?
The benefits of disposability are similar for spherical or toric patients. More frequent replacement of soft lenses has been demonstrated clinically to reduce the incidence of contact lens associated Papillary Conjunctivitis (CLAPC). In addition, more frequent replacement has also been shown to improve patient comfort and performance due to cleaner, more wettable surfaces.
An additional consideration with torics, which unlike sphericals do not rotate in the eye, is that certain areas of the lens build up deposits more quickly than others. An uneven build up of deposits may impact on the rotational stability of the lens.
