Coaxial centration

Even very small amounts of subclinical decentration during excimer laser vision correction can degrade retinal image quality. Problems associated with ablation decentration include coma aberration, causing ghosting and monocular diplopia. Japanese researchers compared refractive outcomes, higher-order aberrations and contrast sensitivity of myopic wavefront-guided aspheric LASIK using two centration techniques, coaxially sighted corneal light reflex or line of sight. At the three-month postoperative point, the study of more than 500 eyes showed that centration on the coaxially sighted corneal light reflex resulted in better safety, effectiveness and contrast sensitivity than line-of-sight centration. Higher order aberrations and coma were statistically significantly higher in the line-of-sight group. The line-of-sight group also had a significantly greater change in contrast sensitivity. Centration on the coaxially sighted corneal light reflex was safer for myopic eyes with P-distances greater than 0.25mm. Therefore, the researchers suggest that to avoid suboptimal refractive outcomes and diminished visual quality, surgeons should determine the difference in the pupil centre and the coaxially sighted corneal light reflex and consider centring the excimer laser ablation on the coaxially sighted corneal light reflex once the difference is 0.15mm or larger.

S Okamoto et al, JCRS, 'Comparison of wavefront-guided aspheric laser in situ keratomileusis for myopia: Coaxially sighted corneal-light-reflex versus line-of-sight centrationâ€, Volume 37, No. 11, 1951-1960.'