We all know that TORIC Intra Ocular Lenses are meant for regular astigmatism. However, from my experience of working with TORIC IOLs for a decade suggests that there are often patients with not an absolute regular astigmatism. In other words such patients have a fair amount of irregularity in an otherwise healthy cornea. Infact, it is very common to find patients with varying amounts of irregular astigmatism, and complete regular astigmatism as per the topography picture, may be very rare.
The question therefore is, do such patients benefit from a TORIC IOL during cataract surgery? My thought is that you may follow the following guideline to choose a TORIC IOL in a seemingly irregular cornea :
Guideline 1 : See the data in the central 3 to 4 mm of the corneal topography of the anterior cornea. Some patients with Form Fruste Keratoconus, and PMD will have irregularity beyond this zone. If you feel that the central 3mm or 4mm is fairly regular, chances are that the patient will benefit from a TORIC IOL. Symmetry in the central zone of cornea is critical for choice of TORIC IOLs.
Guideline 2 : Does the patient benefit from regular prescription glasses. Glasses cannot correct irregular astigmatism, and if these patients do benefit from glasses, or has a history of comfort with glasses, such patients may benefit from TORIC IOLs. Patients, who have worn contact lenses, and have discontinued for atleast four weeks before biometry, and still has irregular cornea on the central zone of the cornea, are very poor candidates for TORIC IOLs during cataract surgery.
Guideline 3 : A regular astigmatism is one which has a symmetric profile. However, in patients where this symmetry is skewed, also known as SRAX, this should be less than 22 degree of asymmetry. In other words, if you draw a straight line and another line that follows the asymmetric profile, the angular difference between the two lines should be less than 22 degree.