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Correcting astigmatism with toric multifocal IOL: a clinical approach
Session Title: Intraocular correction of presbyopia : multifocal IOLs, Monovision
Session Date/Time: Tuesday 08/10/2013 | 14:00-16:00
Paper Time: 14:34
Venue: Elicium 1 (First Floor)
First Author: : B.Gjerdrum NORWAY
Co Author(s): : E. Stųle Vinciguerra
Correcting corneal astigmatism with toric multifocal IOL“s requires high accuracy, as both over correction, under correction and unintended rotation of the lens easily could end up with no effect or even negative effect on the astigmatism
The purpose of this work was to reduce the rate of excimer laser enhancement for patients with multifocal IOLs.
Laser enhancements of RLE treatments haves in our clinic proven to make patient less satisfied with their treatment. It also leads to increased chair time, as well as increasing the risk of unwanted side effects and complications.
The work has been done in the private refractive surgery clinic Memira, in Stavanger, Norway.
The clinic performs both excimer laser treatments, and RLE treatments.
Up until late 2010 correcting astigmatism in RLE was done solely by using spherical multifocal IOLs and correcting residual astigmatism with excimer laser.
ReSTOR Toric was introduced in the autumn of 2010.
With Our first few surgeries with this lens corneal astigmatism was based Zeiss IOLMaster cylinder, hereafter called "IOLMasterCyl". The treatments failed to correct astigmatism in a satisfying way as most eyes turned out with an overcorrection.
The method for assessing the corneal astigmatism was adjusted and careful registration of pre and postoperative data was performed to keep track of the results This was performed for a series of 44 patients implanted with ReSTOR Toric in both eyes and 14 patients with toric in one and spherical in the fellow eye (a total of 116 eyes) in the period from September 2010 to July 2011
Measurements of preop astigmatism with both topography (Orbscan IIz) and Zeiss IOLMaster was performed at least two times consecutively for each eye to ensure repeatability.
Corneal astigmatism was found by looking at topography k-values in 4 meridians (axial keratometric, 3mm zone) and calculating the difference between the flattest k-value in the steep meridian, and the steepest k-value in the flat meridian, hereafter called "LDK (Least Difference K-values)"
Lens calculations were performed with The online Alcon Toric Calculator and surgical induced astigmatism set to zero based on experience.
All treatments were performed using the same surgical approach same surgeon:
Pre-operatively two ink marks were placed at the corneal periphery according to the axis of implantation with the patient sitting up using the beam of the biomicroscope as a guide for the correct axis. A main incision of 2,2 mm at the corneoscleral junction was placed temporal in both eyes. Two side ports of 1,2 mm were placed in the upper and lower temporal quadrants at the corneoscleral junction .
The results was analysed by recording pre- and postoperative data at 3month follow up .The postop refraction was compared with IOLMasterCyl and the LDK as well as topography SimK
The comparison of postop refraction and different preop. k-readings showed that the best correlation between postop cylinder refraction was achieved with LDK (Least difference K-values)
By calculating the difference between IOL cylinder power at the cornea plane and the postop refractive cylinder, a close approximation to the actual corneal astigmatism is found1). This assumed actual corneal cylinder is compared with two different methods of preop cylinder calculation (LDK and IOLMasterCyl). The following table shows the distribution of the deviation from the actual corneal astigmatism the two methods give. A positive value indicates an overestimation of the corneal astigmatism.
The most important source of error is if the actual axis of implantation differs from the planed axis. Also repeatability of the preop corneal mesurements as well as enlargement of the insicion for high power lenses which could induce more astigmatism
Deviation from actual1) corneal cylinder :
+>=+0,75: LDK :9% / IOLMasterCyl: 20%
<+0,75 >=+0,50: LDK:13% / IOLMasterCyl: 29%
<+0,50>=+0,25: LDK:25% / IOLMasterCyl: 20%
<+0,25 >=-0,25: LDK:42% / IOLMasterCyl: 28%
<-0,25 >=-0,50: LDK:6% / IOLMasterCyl: 3%
<-0,50: LDK:4% / IOLMasterCyl: 1%
LDK+0,24 (stdev0,41) / IOLMasterCyl: +0,40 (stdev 0,40)
The results show that most corneas have some degree of asymmetric astigmatism and by assessing the topography and "least difference k-values (LDK)" the accuracy of cylinder correction with toric multifocal IOLs is increased significantly as compared to using IOLMasterCyl
The LDK method estimates the corneal cylinder within ±0,25 for 42% of the eyes as opposed to 28% for IOL master.
Furthermore IOLMasterCyl overestimated the corneal astigmatism with 0,75 or more in 20% of the eyes, while this only happens for 9% of the eyes when calculating LDK
When the LDK method was used and these k-values was put into the Online Alcon calculator an the proposed cylinder was used, the average postop cylinder refraction for 142 eyes was 0,32 (regardless of axis) with a standard deviation of 0,26
For these 142 eyes the rate of laser enhancement turned out to be 15% after 2 years, but astigmatism playing a part in only 3%
The LDK method is a quick an effective way, that with some training usually takes no more than a couple of minutes extra to perform. However, care should be taken to ensure the repeatability of the topography measurements
The initial work has been performed with the implanting of ReSTOR Toric, but later use of Lentis Mplus Toric multifocal has showed that the method also applies with another lens. The main purpose of this work has been to find a method that can easily be used in a clinical everyday setting and with standard optometric equipment.