The Topolyzer Vario (Alcon Laboratories, Inc., Fort Worth, Texas) diagnostic device maps the cornea and provides asphericity and pupil centroid shift data. This article describes numerous functions of the Vario, how it enables customized corneal topography-guided laser procedures, and how it facilitates accurate toric IOL placement.
IMAGE CAPTURE, CENTRATION, AND TOPOGRAPHIC DATA
The Vario captures two 2-D images of the anterior segment, one of the cornea and tear film and one of the pupil and iris, 2.6 milliseconds apart. The corneal topographic Placido-ring image is referenced to the corneal apex and locates the pupil center and the limbus. An automatic measuring release ensures that the image centration has a peripheral standard deviation of only 4 μm.
The device measures elevation points on the corneal surface in steps, which are then used to draw 11 contour (Placido) rings from the corneal apex by edge recognition and interpolation. The software creates a map of the cornea from these contour rings. Less space between the rings indicates steeper areas, and wider space between the rings indicates flatter areas of the cornea (Figure 1). A steeper radius of curvature means a higher refractive power.
Each ring in the topographic picture has an inner and outer edge, and each space between the rings has an edge. This total of 22 edges represents 22,000 measuring points. The Vario also has a built-in keratometer for adding true keratometric marks to the corneal image. Furthermore, the device can display corneal data in a range of maps for a complete picture of the anterior segment: sagittal, tangential, dioptric, and Zernike and Fourier polynomials for viewing aberrations. These maps are displayed in average halfmeridian curvature values (3, 5, and 7 mm).
The pupil-recognition software can measure pupil centroid shift, allowing centration of the laser ablation according to the patient’s visual needs. For example, a professional truck driver who mainly drives at night may benefit from centering the laser treatment on the dilated (scotopic) pupil. Sometimes, the previous-generation Topolyzer Vario did not recognize the pupil because of lighting issues that caused too many artifacts in the image. These problems have been solved in the new Topolyzer Vario.
Recognition of the pupil edge is important when the topography and pupil margin are used to drive and center the laser treatment. No other topographic device has pupil recognition, and the Topolyzer Vario can capture the pupil in both dilated and undilated positions (Figure 2) using continuous pupil recognition. Raising or dimming the device’s light intensity enables the capture of the pupil in a physiologically constricted position (photopic pupil size) or dilated position (mesopic pupil size). These image captures are repeated three times to average the measurements.
Pupil centroid shift is calculated and shown in millimeters in both x- and y-directions, plotted graphically. Additionally, the pupillometer allows the surgeon to test the pupil’s reaction under defined phototopic and mesopic conditions. Users may obtain the minimum, maximum, and mean diameter of the pupil and the standard deviation for the specified measuring conditions.
Q-value information is useful when planning an aspheric correction; the amount of asphericity determines whether it should be maintained or ablated to enhance depth of field and contrast sensitivity. The Vario measures asphericity with eccentricity or Q value, at various diameters on the cornea, or at various degrees peripherally (10°, 15°, 20°, 25°, and 30°) from the corneal apex. The asphericity maps display eccentricity, asphericity, or sagittal curvature.
TIPS FOR CAPTURING IMAGES
For topography-guided custom ablation treatment (T-CAT), the surgeon must know where the pupil is. If you capture an image of the pupil undilated on the Vario but then dilate the pupil before the eye goes under the laser, the treatment will most likely be decentered. Therefore, the pupil must be of a similar size when you capture the topography and when you treat the eye.
Undilated pupils show fewer iris markings, and these markings change significantly when the pupil is dilated (See Positioning Toric IOLs). If an eye lacks significant iris markings, the Vario image can be digitally enhanced by third-party software such as Adobe Photoshop (Adobe Systems, Inc).
Once it has captured the topography, the Vario can transfer the eye’s treatment parameters to either the Allegretto Wave Eye-Q or the WaveLight EX500 excimer laser (both Alcon Laboratories, Inc.). Then the T-CAT software calculates the treatment pattern, which can be reviewed and changed before applying the treatment.
HOW I USE THE TOPOLYZER
For T-CAT ablations, I create four topographic maps of the eye, average them for consistency, and export them to the laser’s laptop. Target refraction and other patient data are then entered into the computer, and the T-CAT nomogram is applied. I compare the T-CAT ablation pattern with the total wavefront and the Allegro Analyzer (A-CAT) and Custom Q treatment (F-CAT) ablation patterns. If these maps are consistent, I treat the patient.
My results with the Eye-Q excimer laser, the iFS femtosecond laser (Abbott Medical Optics Inc., Santa Ana, California), and the Topolyzer Vario are better than those I achieved with my previous Topolyzer Vario (Figure 3). Although I currently have performed topography-guided LASIK in only 114 eyes with the new Topolyzer Vario, compared with 2,158 eyes with the previous system, the scattergram of results for eyes treated with the newer system is excellent.
Even with corrections of up to -12.00 D, 94% of patients achieve ±0.50 D of their intended correction by 1 month postoperative. Even more impressive, 87% achieved 20/20 UCVA within 3 months postoperative, and 40% had achieved 20/16 by that time. Such outcomes are nearly unheard of with traditional laser vision correction.
Jerry Tan, FRCS(Ed), FRCOphth, is the owner and Medical Director of Jerry Tan Eye Surgery Pte Ltd., Singapore. Dr. Tan states that he is a WaveLight Ambassador. He may be reached at tel: + 65 6738 8122; e-mail: email@example.com.
• The Vario software enables customized topography-guided laser vision correction.
• This is the only topography system with iris recognition.
POSITIONING TORIC IOLS
The dual-image capture system of the Topolyzer Vario can be used to orient a toric IOL and align it with the iris markings. I use the Vario image of the large pupil to locate where the iris markings are, and then I superimpose the topography over the iris, mark the location of the iris markings, and overlay the toric IOL markings. This strategy has improved my results with toric IOLs. I do not have to sit the patient up to mark his or her eye preoperatively at the slit lamp. All I bring to the operating theater is a composite image of the iris with its markings and the toric IOL diagram.