Cataract surgery is one of the most frequently performed surgeries worldwide. The main aim of cataract surgery is to restore visual function by removing the optically degraded crystalline lens using phacoemulsification and to implant a clear artificial intraocular lens (IOL).
In the past decade, technological advances in IOL optics, as well as in the procedures and tools used in cataract surgery, have improved significantly with increasing predictability of the refractive correction.1,2
Likewise, patient expectations are more and more demanding with regard to spectacle independence after surgery. Sophisticated IOL designs have therefore been developed to provide a complete visual restoration after cataract surgery, including toric IOLs that allow a satisfactory refractive correction in eyes with significant amounts of corneal astigmatism.3
The accurate alignment of a toric IOL is essential to achieve the intended astigmatism correction.4 A toric IOL misalignment of 11.5º could lead to a residual astigmatism that is 40% of the initial astigmatic power, and 3º of misalignment might result in values that are 10% of the initial power.4
In a standard setting, the cornea is marked manually before surgery to identify the steep meridian using a manual marking instrument. During surgery, the axis of the implanted IOL is rotated to the position of the marks. This manoeuvre requires surgical experience, can be biased by ocular cyclorotation, and is time consuming. For this reason, new systems allowing a digital control of toric IOL alignment without manual marking have been developed, such as the Callisto eye Z Align from Carl Zeiss Meditec.
The Callisto eye Z align is a markerless toric IOL alignment system that uses an eye tracker and intraoperative measurements to mark and project parallel lines for toric IOL placement and positioning.
This system is included in the Zeiss Cataract Surgery Suite platform that allows a highly efficient workflow for cataract surgery with toric IOL implantation. This workflow proceeds as follows: an image of the eye is taken along with the keratometric measurement by the IOLMaster 700 biometer; the FORUM data management receives the biometric data; the reference image is matched by the Callisto eye Z align facilitating the alignment of the patient eye and tracking the image in real time; and the target axis is displayed as an overlay on the live image seen through the OPMI Lumera wide field microscope.
This type of intraoperative digital control of toric IOL alignment overcomes the major limitations of the implantation of toric IOLs using manual marking,5 which are the need for specific instruments and mounting of those; the intensive patient cooperation, the risk of corneal injury through the marker, imprecise broad marks due to diluted ink and significant errors due to cyclorotation of the eye when the patient changes from sitting to lying position.6 The marks must be done before surgery because of their potential for blurring during the surgical procedure.
Furthermore, the manual marking could cause a lack of self-confidence, especially in non-experienced surgeons. Therefore, the Callisto eye system is an advancement for a better workflow, more accurate results, and higher safety during cataract surgery with implantation of toric IOLs.
We have done a non-randomised clinical prospective study to assess the efficiency of the Callisto eye in cataract surgery with toric IOL implantation and to compare it with the efficiency using manual marking for IOL alignment. A total of 57 eyes with visually significant cataract undergoing phacoemulsification surgery with implantation of a toric IOL (Zeiss AT TORBI, Alcon SN60T1-9 and bifocal OCULENTIS Comfort IOLs) were enrolled in the study. All eyes had regular corneal astigmatism of 1.5 D or more. Exclusion criteria were previous ophthalmic surgery, maculopathies, corneal pathologies, diabetes mellitus, manifest glaucoma, pseudoexfoliation, and strabismus. Two groups of eyes were differentiated according to the tool used for intraoperative IOL alignment: 29 eyes in which the Callisto eye Z align was used (Callisto group) and 28 eyes in which a marker instrument (bubble marker) was used to determine the zero degree axis for IOL alignment (manual group). The study adhered to the tenets of the Declaration of Helsinki.
An external time tracking software (SWAN) was used to measure the time requirements for the important steps of surgery in each group. In both groups, the time dedicated to marking of the axis and IOL alignment was recorded. The time of axis marking included the device assembling and corneal ink marking in the manual group, and the time for biometric data import from FORUM to Callisto and reference image matching in the Callisto group. The IOL alignment time was also measured in both groups. In the manual group the time dedicated to the different toric axis control measurements during surgery was also recorded.
The results of this study confirmed the higher efficiency of cataract surgery with toric IOL implantation using the Zeiss Cataract Surgery Suite platform, allowing a faster surgical procedure and consequently an optimised surgical workflow. Specifically, in our series, significantly more time was needed to perform the axis marking with the manual procedure than with the Callisto eye-assisted method (93.0 vs 16.3 seconds, p<0.001). Likewise, the time required for toric IOL alignment was significantly longer with the manual procedure (98.3 vs 37.2 seconds, p<0.001). As a consequence, the overall surgery time was significantly longer with the manual marking procedure than the surgical procedure with the Callisto eye Z system (1110.0±382.2 vs 727.2±198.4 seconds, p<0.001).
The Callisto eye Z align from Carl Zeiss Meditec is a valuable tool to increase excellence in cataract surgery with toric IOL implantation. It is one component of the Zeiss Cataract Surgery Suite platform promoting an optimised workflow during surgery. The Callisto eye Z align uses biometric data as a reference and allows the toric axis to be mirrored over a reference image for precise intraoperative IOL alignment. This high level of accuracy supports the predictability of the refractive outcomes. Additionally, this improved precision is even less time consuming and should help to minimise risks. Therefore, the Callisto eye Z align is an efficient assistant system for the cataract surgeon that streamlines the surgical process and enables a precise implantation and alignment of toric IOLs.
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3. Kessel L, Andresen J, Tendal B, Erngaard D, Flesner P, Hjortdal J. Toric intraocular lenses in the correction of astigmatism during cataract surgery: a systematic review and meta-analysis. Ophthalmology 2016; 123: 275–86.
4. Viestenz A, Seitz B, Langenbucher A. Evaluating the eye’s rotational stability during standard photography: effect on determining the axial orientation of toric intraocular lenses. J Cataract Refract Surg 2005; 31: 557–61.
5. Elhofi AH, Helaly HA. Comparison between digital and manual marking for toric intraocular lenses: a randomized trial. Medicine (Baltimore) 2015; 94: e1618.
6. Prickett AL, Bui K, Hallak J, et al. Cyclotorsional and non-cyclotorsional components of eye rotation observed from sitting to supine position. Br J Ophthalmol 2015; 99: 49–53.
Dr Wolfgang J Mayer
Dr Wolfgang Mayer is affiliated with the Centre for Refractive Therapy, LMU Munich, Germany.
The authors have no financial disclosures relating to the content of this article.