The manual process: Time consuming and potentially unreliable ink marking
Prior to surgery the toric lens orientation in the capsular bag has to be determined, ideally using a topographic device or other mediums capable of measuring the curvature values of the cornea. Calculations are then made by the pre-op device itself or manually by the surgeon. To transfer the results of these calculations into the OR the surgeon has to manually mark the reference points with blue ink on the sclera of the patient to ensure adequate alignment with the pre-operative data.
As well as being time consuming, there are a number of factors that could influence accuracy. Firstly, the patient is normally seated for ink marking, while during the surgery itself the patient is supine. This change of position causes the eye to rotate up to 20 degrees. Another concern is that the ink may dissolve or smear from the lachrymal fluid. Both of these factors make it even more difficult for the surgeon, who needs to picture an imaginary line between the marks against which to align the toric lens.
As a deviation of only 5 to 10 degrees already has a significant impact on the outcome, the result could be that the patient will still require glasses post-surgery.
No blue dot marking is required with IOLcompass Pro available through Leica Microsystems, as the software uses the pre-operative reference image to recognize patterns of the limbus and scleral blood vessel structures. Upon surgeon confirmation, the templates are automatically aligned to the live surgical image.
With many IOL guidance software systems the surgeon needs to purchase a topography device from the same manufacturer, regardless of data accuracy or cost. Alternatively, IOLcompass Pro is fully compatible with some of the leading topographers on the market and provides full data connectivity.
The surgeon is free to choose the topography device he trusts most, allowing him to work with the precise data from this device throughout the entire procedure. In addition, he is also able to select any intraocular lens available on the market, according to his preference.
Manual: Even slight deviations can impact on surgical outcome
Achieving the highest level of accuracy through all steps of a cataract surgery from performing the clear corneal incision/limbal relaxing incision (CCI/LRI), to capsulorhexis, to the centration of the IOL and alignment of the toric lens, demands a high degree of skill and surgical experience. Even the smallest deviations, for example in the positioning of the corneal incision, may have an impact on the final refractive outcome.
With IOLcompass Pro guidance templates support the surgeon through every step of the surgery. This includes positioning of the CCI/ LRI, where the exact position and size of the incisions is displayed to enable a precise start to the procedure, with the impact of surgically induced astigmatism (SIA) already taken into account.
During capsulorhexis the template displays the individually planned shape and size of the capsulorhexis to position the IOL along the optical or visual axis. This might make the utilization of a mendez-ring obsolete if used during surgery. To facilitate IOL centration and toric alignment the surgeon can confirm the positioning against a topography overlay which shows the exact curvature of the cornea. An optimized target axis targets toric alignment with the lowest predicted residual astigmatism.
During the surgical steps of incision, capsulorhexis, lens excision and final IOL placement the surgeon has to take into account that the eye moves. It is rather complicated to continually adapt to the changing position and naturally can lead to inaccuracy.
With latest IOL Guidance systems like IOLcompass Pro the surgeon does not need to worry about eye movement and cyclotorsion. Sophisticated auto-registration algorithms align to patterns of the limbus and scleral blood vessel structures and track to the live surgical image in real-time for highly stable and reliable IOL guidance templates throughout the surgery.
Fig. 3, 4: Templates can be directly injected into the eyepiece and displayed on a HD screen.
Manual: No support to adapt the plan
During any surgery an unexpected but necessary change of plan can occur. For the surgeon who uses the manual IOL workflow this change can affect the originally calculated outcome, meaning manual recalculation or adaptation. The outcome of the surgery thus depends fully on the experience of the surgeon.
Even when using an IOL guidance system it is not always possible to adjust the surgical plan in response to changes due to rigid system pre-settings. The software of IOLcompass Pro, however, responds dynamically to changes, immediately recalculating predicted refractive outcome and proposing an adjusted surgical plan, which the surgeon can accept or freely adapt as required. Optimized templates are then transferred immediately to the surgical field of view on a screen or injected into the microscope eyepiece.
Footnote: IOLcompass Pro is manufactured by TrueVision Systems Inc. and distributed by Leica Microsystems.