Fixation of a toric IOL to the iris in the absence of adequate capsular support

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Introduction.
In case of failure of the ligamentous-capsular apparatus of the lens (LCA), there are two main ways of fixing the IOL: to the sclera and to the iris [1-3]. The literature describes such disadvantages of scleral lens suturing as the technical complexity of the operation, the likelihood of decentration and tilt of the IOL, the risk of vitreous prolapse, retinal detachment, endophthalmitis, and bleeding. [4, 5]. Fixation of the lens to the iris is characterized by less technical complexity, a low risk of complications and a more optimal position of the IOL.
Incorrect IOL position (tilt and decentration) does not allow achieving maximum functional results, causing optical aberrations and reducing visual acuity [6]. The effect of IOL tilt and decentration on visual function depends on the IOL design [6]. Aspheric aberration-correcting IOLs are known to result in greater visual problems with tilt or decentration compared to aspheric neutral IOLs [7, 8]. With regard to toric IOLs (TIOLs), tilt and decentration can lead to significant residual astigmatism [9]. In addition, the need to position the TIOL along the calculated axis causes additional difficulties during its fixation in the absence of adequate capsular support.
Known methods for fixing an IOL to the iris, despite their advantages over scleral lens fixation, have a common drawback - the lack of control of thread tension when tightening the knot, which does not allow standardization of the suture application stage and can lead to disruption of the position of the IOL, rough contact with the reactive structures of the anterior segment eyes.
Goal of the work.
Development of a universal method for suture fixation of TIOL to the iris both for preventive purposes in case of weakness or defects of the ligamentous-capsular apparatus of the lens (LCA), and in cases of reposition of the dislocated “TIOL-capsular bag” complex in the long-term period with the ability to control the tension of the thread when forming a suture loop .
Materials and methods.
Through mathematical modeling, we have determined that for most TIOLs with an S-shaped haptic with a total size of 13 mm and an optic diameter of 6 mm, the axis of the cylinder, indicated by marks on the optical part of the IOL in the area of its interface with the haptic elements, corresponds to the axis of suture fixation of the TIOL, provided that the seams will be located at a distance of 3 mm from the pupillary edge of the iris with a pupil diameter of 2.5 mm (Fig. 1), that is, on a circle with a diameter of 8.5 mm relative to the center of the pupil.
 
Rice. 1. Tecnis IOL model, straight line - the axis of the TIOL cylinder, corresponding to the axis of suture fixation, the dotted line indicates the optimal distance for suture fixation.
To carry out the proposed method of suture fixation of TIOL to the iris, it is necessary to perform standard markings on the limbus of the axis of the TIOL cylinder and two 1.2 mm paracenteses in the projection of these marks in a plane parallel to the iris. The TIOL is positioned in the correct plane and centered. Then, through both paracenteses, two iris retractors are passed towards each other so that each retractor is fixed externally by the cornea in the area of one paracentesis with a hook at its end, and in the opposite paracentesis - with a retractor sleeve (Fig. 2). Rice. 2. Diagram of the location of two iris retractors in the anterior chamber passing through paracenteses
Against the background of drug-induced miosis, the fixing suture is placed on a circle passing 3.0 mm from the pupillary edge of the iris with a pupil diameter of 2.5 mm, which corresponds to the maximum safe anatomical zone. In the area of one of the haptic elements, a 13 mm needle with a ¼ curvature with a 10-0 polypropylene thread is passed transcorneal, then through the iris and anterior lens capsule, under the haptic part of TIOL and then in the reverse order. The needle is inserted and punched out on both sides of the retractors at an equal distance with a total distance in the range of 1.4-1.8 mm for correct positioning of the IOL and to prevent pupil deformation in the postoperative period. The Siepser sliding knot [10] is formed so that the iris retractors are pulled into the suture loop. Similar actions are carried out with the opposite haptic element. Then the iris retractors are removed by removing the coupling and pulling them out by the hooks, while suture loops are formed with dosed thread tension and the optimal “IOL-iris” distance, which is ensured by a certain thickness of the retractors.
6 patients were operated on using this method. Three patients underwent suturing of the lens as a preventive fixation of TIOL in case of initial weakness of the SCA, and three more patients underwent lens suturing for the purpose of repositioning the dislocated “TIOL-capsular bag” complex in the long-term period. In all cases, there was an intracapsular position of the IOL with varying degrees of MCA failure.
Research results and discussion.
Lack of control of thread tension when suturing the IOL to the iris leads to significant differences in the fixation sutures. These seams can be classified into three types depending on the degree of thread tension. The first type (Fig. 3) is characterized by weak tension and sagging of the thread, a long injection/puncture distance, and a large distance from the iris before IOL, large range of motion of the “IOL-capsular bag” complex, absence of significant deformation of the iris and ovalization of the pupil, preservation of the diaphragmatic function of the iris.
 
Fig 3. First type of seam. A – photograph of the anterior segment of the eye, illustrating the weak tension of the fixation sutures, B – optical coherence tomography of the vitreolenticular interface, visualizing the tilt and decentration of the IOL.
In the second type (Fig. 4), there is a moderate tension of the thread, an optimal injection/puncture distance, no sagging of the thread, an optimal distance from the iris to the IOL, minimal mobility of the IOL-capsular bag complex, absence or minimal deformation of the iris, absence of ovalization of the pupil, preservation of the diaphragmatic function of the iris.
 
Rice. 4. Second type of seam. A, B – photograph of the anterior segment of the eye, illustrating the suture of adequate tension, C – optical coherence tomography of the vitreolenticular interface, visualizing the correct position of the IOL.
In the third type (Fig. 5), the injection/puncture distance may be different, there is a pronounced tension of the thread, a tightly tightened loop, no distance from the iris to the IOL, lack of mobility “IOL-capsular bag”, deformation of the iris, ovalization of the pupil, impaired diaphragmatic function irises.
 
Rice. 5. Third type of seam. A, B – photograph of the anterior segment of the eye, illustrating a tightened suture, deformation of the iris and pupil, coloboma, performed to prevent pupillary block, C – optical coherence tomography of the vitreolenticular interface, visualizing a tight fit of the IOL to the iris.
Inadequate fixation of the IOL to the iris in the first type can cause consequences such as decentration and tilt of the IOL, dysphotopsia, pseudophacodonesis, iris chafing syndrome, UGG syndrome. With the third type of suture, complications such as ovalization of the pupil, impaired diaphragmatic function of the iris, iris chafing syndrome, pupillary block, and UGG syndrome can be observed. IOL decentration and tilt.
The method we described for fixing an IOL to the iris allows us to form an optimal type 2 suture, reduce trauma to eye tissue, reduce the risk of postoperative complications, and is applicable to S-shaped lenses with any type of optics, including toric and multifocal IOLs.
In all of our patients operated by this method, the optimal centered position of the IOL was noted; the position of the lens cylinder axis corresponded to the calculated one. The early postoperative period proceeded without complications against the background of standard drug therapy. The results of the OCT study revealed the absence of decentration and tilt of the IOL, as well as the optimal “iris-IOL” distance of 250-450 µm. During the entire observation period (2 months), a stable position of the IOL and no complications were noted (Fig. 4 B).
In this method, iris retractors installed in the anterior chamber play the role of a thread tension limiter when tightening the knot and help to accurately position the fixing sutures, and, accordingly, the lens along the axis of the cylinder, which makes it possible to standardize the process of fixing TIOL to the iris.
The use of iris retractors is justified by mathematical modeling to calculate the optimal tension of the suture thread, which takes into account the thickness of the iris (0.5 mm), the parameters of the cross section of the IOL (square with a side of 0.49 mm, Tecnis model), the possibility of varying the width of the IOL haptics depending on from the lens model (0.98 mm segment equal to two haptics), the minimum required distance from the iris to the IOL (0.25 mm), parameters of two iris retractors (1.1 mm - corresponds to retractors occupying the entire width of the paracentesis), variability of the injection distance /puncture (interval 1.4-1.8 mm) (Fig. 6). The resulting suture loops after removal of the iris retractors will reliably fix the TIOL in the desired position, while maintaining the “iris-TIOL” space, which eliminates pupil deformation and does not disrupt the diaphragmatic function of the iris, which is confirmed by the data of a postoperative OCT study (Fig. 4 B ).
 
Rice. 6. Mathematical modeling scheme for calculating the optimal suture thread tension.
Conclusion.
The method we propose for fixing an IOL to the iris is universal both for preventive purposes in case of weakness or defects of the IAS, and in cases of repositioning of the dislocated IOL-capsular bag complex for S-shaped lenses with any type of optics, including toric ones. The advantages of the method are the ability to control the tightening of the thread when forming a loop, strict positioning of the axis of suture fixation of TIOL, and minimizing the risk of complications.

About the authors

Elena V. Egorova

Eye Microsurgery named after Academician S. N. Fedorov, Novosibirsk Branch

Email: evva111@yandex.ru
ORCID iD: 0000-0002-2901-0902

MD, Deputy Director for Medical Work

Russian Federation, Novosibirsk

Maksim A. Talalaev

Eye Microsurgery named after Academician S. N. Fedorov, Novosibirsk Branch

Author for correspondence.
Email: i@stomelic.ru
ORCID iD: 0000-0003-1869-2108

Ophthalmologist

Russian Federation, Novosibirsk

References

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