Alignment is critical for astigmatism correction. Cyclotorsion of varying degrees occurs when a person changes position from upright to supine, so it is important to accurately mark the eye or record distinguishing landmarks so that the proper meridian of astigmatism can be identified during surgical treatment.
There are a number of methods to achieve toric intraocular lens (IOL) alignment at the end of cataract surgery. It is recommended that the alignment marks on the lens be left at least 10–15 degrees short (counterclockwise) of the final meridian so that if the IOL rotates slightly during viscoelastic removal it will still remain short of its final resting position to facilitate a slight clockwise rotation into the correct position. Otherwise, if the lens overshoots the final meridian, it will require a large amount of rotation.
In order to safely rotate the IOL in the capsular bag after the viscoelastic has been removed, volume must be maintained with irrigation. This can be accomplished with a variety of one- and two-handed techniques, and instruments have been developed specifically to facilitate toric IOL alignment. Examples of some of these methods are listed below.
One-handed:
- Microhook and anterior chamber maintainer through a paracentesis
- Donnenfeld irrigating positioner: attaches to irrigation line of the phaco machine (developed by Dr. Eric Donnenfeld and available from Accutome)
- Friedman irrigating IOL manipulator (see video): cannula attaches to a syringe of balanced salt solution (BSS) (available from Rhein Medical; I have no financial interest in this instrument)
- Silicone I/A tip rotated downward to aspirate the IOL surface and rotate the lens (personal communication, Dr. Robert Cionni)
Two-handed:
- Bimanual I/A with appropriate handpiece for rotating a lens
- Coaxial I/A with a microhook