A patient presents with bilateral cataract and refractive errors of 
RE -1.00/-2.50 X 90 and 
LE -2.00 / -2.75 X 90. 
A right phacoemulsification and lens implant is planned. 

a. What would be the effect on this patient's astigmatism (increased or decreased) if:
i. a superior corneal incision was performed without suturing?
ii. a temporal corneal incision was performed without suturing?
assuming the astigmatism is mainly cornea.
 

b. What is the name of the instrument above?
 

 
Answer a
This patient has against-the-rule astigmatism in both eyes ie. the steepest axis is at
180 degrees. In the RE -3.50/+2.50 X180. Corneal incision causes central corneal 
flattening of its own meridian and some central corneal steepening at 90 degrees to
its meridian.
i. Increased. Incision near the 90 degrees causes central corneal flattening of its own meridian and some central corneal steepening at the 180 degrees.
ii. Decreased. Incision near the 180 degrees causes central corneal flattening of its own meridian and some central corneal steepening at the 90 degrees.

 

Answer b
Astigmatic keratotomy ruler (more specifically of the Thornton type).