Vector planning for astigmatism
Managing astigmatism to avoid LASIK surprises
Incorporating Vector Planning in which both corneal and refractive parameters are used in creating an ablation treatment plan could help to avoid debilitating visual symptoms after LASIK and other refractive surgery procedures, according to Prof Noel Alpins FRANZCO, FRCOphth, FACS.
“Treatment based solely on refractive parameters can result in excess corneal astigmatism, causing any one or more of symptoms of glare, starbursts, haloes and reduced contrast sensitivity (known as GASH),” Dr Alpins told delegates attending the 37th Congress of the ESCRS in Paris.
Dr Alpins presented a case study of a 34-year-old man who presented to his practice after undergoing bilateral LASIK with another surgeon in 2016. He had been treated with the latest generation Schwind Amaris 1050 laser. He reported symptoms of glare, ghosting, starbursts and haloes with a loss of contrast sensitivity. Preoperatively, the patient had myopic astigmatism with a BCVA of 20/20 in each eye with regular topography and no such pre-existing symptoms.
Postoperatively, his UCVA was 20/20 in each eye with no refractive error, but he could drive at night only by shining his cell phone flashlight in his eyes to reduce the pupil size and mitigate the effect of his GASH symptoms. He had more than 1.00D of corneal astigmatism remaining in each eye postoperatively because he had undergone LASIK treatment based on traditional 100% refractive parameters.
“While he had 20/20 vision in each eye he would definitely be classed as a 20/20 unhappy patient. The preoperative ocular residual astigmatism (ORA) was 0.99D in the right eye and 1.24D in the left eye. The key point is that he had a high ORA, which is quite a common finding of up to 46% of eyes in some studies and which puts the patient at risk for GASH,” he said.
Treating such a patient by using 100% refractive parameters, as is done in around 95% of LASIK cases around the world, the surgeon can calculate ahead of time how much astigmatism will remain on the cornea afterwards, said Dr Alpins.
“Had he been my patient, I would have treated him with Vector Planning, which means we are treating somewhere between the refractive cylinder and the corneal astigmatism by taking an optimised view of it. The treatment breakdown is around 60% by refractive and 40% by corneal parameters, essentially generating a balance between the refractive cylinder and the corneal astigmatism and thereby reducing the risk of GASH,” he said.
Dr Alpins said that refractive surgeons could avoid similar surprises in their own LASIK surgeries by using the free Vector Planning and ORA calculator tools at www.ISRS.org.