FP1263 : Verion Versus Slit Lamp Manual Marking in Toric IOL Implantation

Dr.Neeraj Agrawal, A13164, Dr.Zervin Baam

Purpose: To compare the accuracy of manual axis marking using the slit lamp compared to the VERION™Image Guided System

Method:This is a prospective, observational study which we carried out on 100 patients undergoing toric IOL implantation. Pre-op reference marking was done on slit lamp. On-table incision axis & IOL axis markings were done with the help of the reference marking. VERION™ Digital overlay was switched on and patient registered. Manual markings were compared with VERION™ overlay markings by the operating surgeon and also by an observer viewing a live view of the eye on an external monitor. Angular or lateral deviation was noted. Implantation of Toric IOL was done using the VERION™ Digital Marker.

Result:100 patients were enrolled in the study. Average deviation of incision axis was 2.59°. Average deviation of IOL axis was 3.03°. 5 patients had lateral deviation measuring <0.5mm. At the one month follow-up visit, 90 patients had uncorrected vision of 6/6p or better. 3 patients had 6/12 uncorrected vision.

Conclusion: Manual marking method is almost comparable to the VERION™ Image Guided System, and can be an acceptable method of marking the toric axis.

INTRODUCTION

Astigmatism contributes a significant proportion of refractive errors in patients who undergo cataract surgery. The prevalence of significant corneal astigmatism (≥ 1.5D) ranges from 15% to 29%, as reported by different studies.^1-4Correction of pre-existing astigmatism may be done by implanting a Toric IOL after the completion of the Phacoemulsification of the nucleus and aspiration of the remaining cortex. Since a Toric IOL has an axis, it has to be aligned accurately within the capsular bag in order to achieve effective astigmatic correction. Improper alignment may occur due to wrong alignment from the beginning or due to post-operative IOL rotation.^5,6One of many methods may be used for alignment of the Toric IOL. Reference marking of the horizontal or vertical meridian can be done manually under the guidance of different methods including slitlamp-assisted marking with a horizontal or vertical slit beam, slitlamp-assisted marking with a pendulum-attached marker or a non-pendular marker by a surgeon under direct visualization. With the guide of the reference marks, the operating surgeon can mark the intended axis of incision as well as the axis of implantation using a Toric Axis Marker intra-operatively.

The VERION™ Image Guided System consists of the VERION™ Reference Unit and the VERION™ Digital Marker. The VERION™ Reference Unit enables surgeons to quickly determine an optimized surgical plan for toric IOL procedures. The VERION™ Digital Marker optimizes toric IOL implantation by providing real-time positioning guides, automatically compensating for cyclo-rotation and eliminating the need for manual eye marking during toric procedures. However, it may not be economically viable for a majority of ophthalmic surgeons practicing on their own. Hence, through this study, we intended to determine the average error introduced while marking the axis using the conventional slitlamp-assisted method, while comparing it with the VERION™ Digital Marker.

PATIENTS AND METHODS

 Our study was a prospective, observational study including 100 patients who had significant astigmatism (>1.25D) and who were willing for toric IOL implantation. Patients having any co-existing ocular co-morbidity were excluded. Keratometry was done for all patients using the Bausch & Lomb Keratometer. The patients underwent toric IOL planning using the VERION™ Reference Unit.The incision location, the axis of implantation and the toric IOL power were decided pre-operatively. Just before the surgery, these patients underwent reference marking using an Epsilon Vann pre-op marker. This marker makes 3 marks on the limbus (temporal, superior and inferior). After the patient was shifted on the operating table, the patient registration was done on the VERION™ Digital Marker. The cases which would fail to register with the VERION™ Digital Marker were excluded from the study. The surgeon would then use the reference markings and mark the planned incision axis and the axis of implantation using an ASICO Beveled Degree Gauge and a Nuijts-Solomon Toric Axis Marker. Following this, theVERION™ Digital Marker overlay was switched on and the marked axes were seen over the VERION™ overlay. The deviation of the axes was noted as compared to the VERION™ axes by the operating surgeon in the operating microscope, and by an observer on the VERION™ monitor. The amount of deviation as well as its orientation (clockwise, anti-clockwise or lateral) was noted. Angular rotation was noted in terms of degrees whereas lateral deviation (wherein both the manual marks were on one side of the VERION™ axis) was noted using a Castroviejo caliper. Following this, the surgeon would go ahead with the Phacoemulsification procedure as per his or her convenience. In each case, the toric IOL was implanted using the VERION™ Digital Marker. All the patients were followed up on the first post-op day as well as at 1 month post-op. During each post-op visit, uncorrected and best-corrected visual acuity was checked along with slit-lamp examination to check the deviation of the toric IOL axis from the pre-operative planned axis of implantation. Refraction was done at the 1 month post-op visit.

RESULTS

 100 patients undergoing toric IOL implantation were included in this study. The average pre-op corneal astigmatism by the Bausch & Lomb Keratometer was 2.04 ± 0.58 D. Intra-operatively, the mean deviation of the manually marked incision axis as compared to the VERION™ overlay was found to be 2.59° (S.D. 3.47°). The mean deviation of the manually marked IOL axis from theVERION™ overlay was 3.03° (S.D. 5.05°). The following table shows the number of patients with each type of deviation.

During the post-op follow-up, the average rotation of the IOL from the intended axis of implantation was noted on slit-lamp, the details of which are given in the following table:

At the one-month post-op follow-up visit, refraction was done. 90 patients had uncorrected vision 6/6p or better. 3 patients had vision 6/12. 5 of the patients needed a cylindrical refractive correction. 2 of these were having 3D of astigmatism pre-operatively.

DISCUSSION

 For a successful toric IOL implantation, accurate alignment of the toric IOL in the capsular bag is a must. Unsatisfactory outcomes may be a result of misalignment of the toric IOL intra-operatively or due to post-operative rotation of the toric IOL in the bag. With advancements in cataract surgery, there has been a constant endeavour to minimize the amount of error, in order to achieve the best post-operative refractive outcome. There are a number of ways in which an error might be introduced during a toric IOL procedure. One of them is while making the reference marks on the cornea to assist the surgeon. With the advent of technology, newer modalities of toric IOL alignment have been introduced into the market. One of the more common ones is the VERION™ Image Guided System. This system aims to help the operating surgeon in the alignment of the toric IOL during surgery. However, due to its expense, it may not be accessible to a majority of operating ophthalmologists. Considering theVERION™ Image Guided System to be a gold standard with respect to toric markings, through this study, we aimed to estimate the relative error introduced during the marking of the reference marks by the conventional slitlamp-assisted method.

It is known that for every 1° misalignment of the toric IOL, the effective correction of astigmatism reduces by approximately 3%.⁹In our study, the average error while marking the incision axis was 2.59° and while marking the implantation axis, was 3.03°. This relates to an approximate 10% reduction of astigmatic correction, while using the manual method of marking, while compared to the VERION™ Image Guided System. In cases having pre-op astigmatism which is lesser than 2.5D, such an error may be considered to be insignificant enough such that the patient may not require cylindrical correction after the surgery. This is reflected in our results. Only 5 patients out of 100 were having a significant post-op cylindrical correction, needing a glasses prescription. Out of these 5 patients, 2 were having significant pre-op astigmatism (≥ 3D).

The VERION™ Image Guided System is an excellent tool for toric IOL implantation. However, from our study, we realize that the conventional method of slitlamp-assisted marking can be comparable to it in cases having astigmatism ≤2.5D. However, in patients having higher degrees of astigmatism, it becomes imperative to keep the errors to a minimum, as the slightest misalignment of the toric IOL will translate to a significant post-operative refractive error. In these cases, using the VERION™ Image Guided System will be beneficial to the patients.

One of the drawbacks of our study is our implicit assumption that the VERION™ Image Guided System is a gold standard for accurate alignment of the toric IOL. An unknown machine error may exist, which may be a cause of misalignment of IOL axis in rare cases.

Other similar studies mainly concentrate on post-operative outcomes using different methods of toric IOL alignment. To the best of our knowledge, there is no study which aims to determine the error of manually marked axis intra-operatively.

To conclude, manual marking method is almost comparable to the VERION™ Image Guided System and can be an acceptable method of marking the toric axis.

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