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Review
. 2019 Sep-Oct;8(5):385-390.
doi: 10.1097/01.APO.0000580144.22353.46.

Review on Centration, Astigmatic Axis Alignment, Pupil Size and Optical Zone in SMILE

Quan Liu  1 , Xiaonan Yang  1 , Limian Lin  1 , Manli Liu  1 , Haiqin Lin  1 , Fang Liu  1 , Yi Xie  1 , Dennis S C Lam  2   3
Affiliations
Review

Review on Centration, Astigmatic Axis Alignment, Pupil Size and Optical Zone in SMILE

Quan Liu et al. Asia Pac J Ophthalmol (Phila). 2019 Sep-Oct.

Abstract

The advent of "flapless" small-incision lenticule extraction (SMILE), employing all-in-one technology, has resulted in a revolutionary breakthrough in refractive surgeries. SMILE has been gaining popularity due to fewer potential complications, such as postoperative dry eyes and greater biomechanical stability, etc. However, attention must be given to 1) the centration on the corneal vertex, 2) the proper alignment of the astigmatic axis, and 3) the relationship between pupil size and treatment diameter, to achieve good SMILE results. There is no pupil-tracking system to ascertain the accuracy of centration during the SMILE surgery. To improve the centration accuracy, our center uses two corneal topographers (Pentacam and Sirius) to measure and determine corneal vertex. Proper predicted optical zone diameter is not clearly defined yet in SMILE. Some scholars insist that mesopic pupil size should be taken into consideration when setting the predicted optical zone. Meanwhile, the issue of "functional optical zone" still has many unresolved issues and warrants further studies.

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Conflict of interest statement

The authors have no conflicts of interest to disclose.

Figures

FIGURE 1
FIGURE 1
Schematic sketch of a selection of ocular axes. The axes are indicated by the following lines: solid brown (pupillary axis), dashed blue (visual axis), dark red (corneal vertex normal).
FIGURE 2
FIGURE 2
The “Centration Map”: The central point of the map of defines the pupillary center; the “X” marks (measurements taken under photopic condition; red cross: Pentacam data; black cross: Sirius data) represent the locations of the corneal vertexes measured by Pentacam and Sirius respectively.
FIGURE 3
FIGURE 3
The surgeon can see through the operating microscope the light reflex located at the corneal intercept (corneal vertex) when the patient is starring and fixating at the green blinking internal fixating light of the VisuMax machine.
FIGURE 4
FIGURE 4
Photo showing what could be seen through the microscope of the VisuMax system during the docking procedure in SMILE.
FIGURE 5
FIGURE 5
Using a horizontal slit beam to help mark accurately the cornea for eyes having astigmatism of ≥0.75D.
FIGURE 6
FIGURE 6
Manual manipulation of the cone to compensate for the cyclotorsion happened after the patient lying down in the supine position.
FIGURE 7
FIGURE 7
Photo showing a cyclotorsion of about 5 degree and adjustment of the cone is needed to make the horizontal marks on the eye in alignment with the horizontal axis of the reticule.
FIGURE 8
FIGURE 8
Infrared pupillometry.
FIGURE 9
FIGURE 9
Pupillary diameter measured by Sirius.
See this image and copyright information in PMC

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