Vector planning delivers superior outcomes for myopic astigmatism

Reviewed by Noel Alpins, MD

In eyes with myopic astigmatism undergoing LASIK, use of an ablation plan based on vector planning instead of the manifest refraction results in better astigmatic and visual outcomes, said Noel Alpins, MD.

“More than 60% of LASIK procedures involve correction of astigmatism, and commonly there is a difference between the astigmatic parameters measured on the cornea and the refraction,” said Dr. Alpins, medical director, NewVision Clinics, Melbourne, Australia.

Vector planning

Benefits of vector planning were demonstrated in a prospective study including 160 consecutive eyes. Eyes were eligible for inclusion if they had an ocular residual astigmatism (ORA, vectorial difference between corneal and refractive astigmatism expressed in diopters and degrees) >0.75 D and corrected distance visual acuity of 20/25 or better.

All procedures were performed by Maria Clara Arbelaez, MD, at the Muscat Eye Laser Clinic, Muscat, Oman, using the same excimer laser (Amaris Total-Tech, Schwind) and femtosecond laser for flap creation (LDV, Ziemer). The first 80 eyes were treated using vector planning, and in the second half of the series, LASIK was performed using the manifest refraction alone (“conventional LASIK”).

Treatment parameters for vector planning were calculated using the ASSORT program v5.50 (ASSORT PTY) and were designed with a 60% emphasis placed on the refractive astigmatism and a 40% emphasis placed on the corneal astigmatism. The 40/60 emphasis is based on previous studies that showed this to be the “sweet spot.”

An emphasis anywhere between 50/50 and 30/70 is considered to be optimum, Dr. Alpins noted.

3 months after surgery

At 3 months after surgery, there were statistically significant differences favoring the vector planning approach over conventional LASIK in analyses of percentages of eyes with manifest refraction spherical equivalent ≤ 0.13 D [(90% versus 68%; p = 0.003), ORA ≤ 0.75 D (43% versus 21%; p = 0.01), and corneal astigmatism < 0.75 D (75% versus 34%; p < 0.0001)].

Compared with conventional LASIK, the vector planning group had higher values for arithmetic mean refractive cylinder (0.10 D versus 0.08 D), but lower values for arithmetic mean corneal astigmatism (0.65 D versus 1.11 D) and arithmetic mean ORA (0.71 D versus 1.06 D).

The percentage of eyes achieving uncorrected distance visual acuity of 20/20 or better was also higher with vector planning compared with the conventional treatment group (96% versus 93%), although the difference was not statistically significant.

“When it comes to corneal astigmatism, less is more because corneal astigmatism affects visual outcomes,” he said. “Surgeons should evaluate the ORA preoperatively and recognize that eyes with high ORA, >1 D, are at high risk for a potential adverse result due to undercorrected corneal astigmatism or in some cases, increased corneal astigmatism postoperatively.”

More widespread adoption of a vector planning approach could increase patient uptake of LASIK by improving outcomes, he noted.

Authors of a literature review published in 2009 reported that 95.4% of patients were happy with their visual outcomes after LASIK [Solomon KD, et al. Ophthalmology. 2009;116:691-701].

“While that is a high satisfaction rate, the flipside is that 4.6% of patients were ambivalent or unhappy with their outcomes,” Dr. Alpins said. “This might be magnified by a factor of 9 when considering the collateral effect of these unhappy people and help to explain the flat-lined interest in LASIK in recent years.”

He added that vector planning has the potential to reduce the rate of patient dissatisfaction to 1% so that the demand for the procedure might flourish.

Noel Alpins, MD

E: alpins@newvisionclinics.com.au

This article was adapted from Dr. Alpins’ presentation at the 2017 meeting of the American Society of Cataract and Refractive Surgery. For more information on this topic, readers may refer to Dr. Alpins’ new book, Practical Astigmatism-Planning and Analysis, which will be published in September 2017. Dr. Alpins is the chief executive officer and has a financial interest in ASSORT Surgical Management Systems used for vector planning treatments and astigmatism analyses.