a. 
A patient with a known history of stable and medically controlled right glaucoma shows deterioration of his visual field despite normal intraocular pressure as measured with a Goldman tonometer. He had had a right LASIK performed 9 months earlier. Suggest two possible reasons for the deterioration in relation to the LASIK procedure.

b. 
How may corneal astigmatism affect the intraocular pressure measurement with a Goldman tonometer ?

 
Answer a
1. Ischaemia of the optic nerve head. A suction with high vacuum power is applied to the globe during the cutting of cornea to form a flap. This causes transient ischaemia of the globe. In vulnerable patient, there may be damage to the optic nerve fibre resulting in some visual loss.
2. The intraocular pressure measurement may be mistakenly low following LASIK operation due to thinning of the cornea.
 

Answer b
Corneal astigmatism may result in false pressure readings. The error has been calculated at 1 mm for every 4 D (underestimated for with-the-rule; overestimated for against-the-rule).