Toric iol

TORIC IOL

Dr. Ankit Gupta

INTRODUCTION

• Postoperative emmetropia – for myopic and hypermetropic errors by spherical lenses.

• For corneal astigmatism1. Spectacle correction2. Contact lens3. Arcuate keratotomies4. Limbal relaxing incisions5. Opposite clear corneal incisions6. Toric IOLs7. lasik

TORIC INTRAOCULAR LENSES

• First – Shimizu et al in 1994 , non-foldable 3 piece toric iol made from PMMA with oval optic and loop haptics.

• Postoperative rotational stability of toric iol also depends on the iol material and iol design.

IOL MATERIAL

• IOL biomaterial is of great influence on the postoperative rotation.

• STAAR toric IOL and the MicroSil toric IOL were made from silicone material and showed relatively high postoperative misalignment rates.

• Currently available toric IOLs are usually made of acrylic material.

• After implantation of the toric IOL in the capsular bag, the anterior and posterior capsules fuse with the IOL which prevents IOL rotation.

• Hydrophobic acrylic IOLs showed the highest adhesive properties, followed by hydrophilic acrylic IOL, PMMA IOLs and finally silicone IOLs.

IOL DESIGN

• The overall IOL diameter has been shown to be a major factor in the prevention of IOL rotation.

• Chang compared two different sizes of the same toric IOL: the STAAR model with a diameter of 10.8 mm and the STAAR model with a diameter of 11.2 mm. The longer STAAR model was found to have a much better rotational stability compared to the shorter STAAR model.

• Currently available toric IOLs however have a total IOL diameter ranging from 11.0 mm to 13.0 mm.

• Regarding the IOL haptics design, two different IOL designs are available: plate haptic IOLs and loop haptic IOLs.

• Buckhurst et al. hypothesize that loop haptic IOLs have a better early rotational stability compared to plate haptic IOLs due to the longer haptics and consequently more contact between haptics and capsular bag.

• Prinz et al. recently compared plate-haptic and loop-haptic acrylic IOLs and did not find a significant difference in rotation.

• This indicates that for acrylic IOLs, plate and loop haptics demonstrate equally good rotational stability.

SUCCESSFUL OUTCOME

• Good patient selection• Preoperative workup• IOL calculation• Good surgery with centered IOL.

PATIENT SELECTION FOR TORIC IOL

• Ideal patient – with regular corneal astigmatism between 1 to 3D.

• Toric IOLS have been successfully implanted in cases with post keratoplasty astigmatism after complete suture removal.

RELATIVE EXCLUSION CRITERIA

• Irregular astigmatism• Post refractive surgery• Corneal dystrophies• Corneal edema• Problems encountered during surgery

(including pupil damage, posterior capsule integrity , vitreous loss ,poor iol centration and discovery of zonular instability)

PREOPERATIVE WORKUP

• Refraction• Keratometry• Surgically induced astigmatism• Biometry• Marking techniques

KERATOMETRY

• Various methods of keratometry: IOLMaster automated keratometry, manual keratometry, autokeratorefractometry, corneal topography, or a combination of these techniques.

• Keratometry measurements obtained by automated keratometry, manual keratometry and corneal topography have been shown to have a high repeatability and are generally well comparable between Devices.

SURGICALLY INDUCED ASTIGMATISM

• Surgeon specific criteria• Total astigmatism should include the SIA.• SIA may be calculated with the help of online

calculators (www.doctor-hill.com)

BIOMETRY

1. Axial length measurement should ideally be done with IOL master or lenstar however immersion scan may also be used

2. Only corneal astigmatism should be used for IOL calculation.

3. Various companies providing toric IOLs have their online IOL calculators which calculate power according to surgeons comfort and also suggest the steepest axis for incision making thereby giving least residual astigmatism.

MARKING TECHNIQUE

• Accurate marking of the alignment axis should be performed with the patient in an upright position in order to prevent cyclotorision in the supine position.

• Firstly the horizontal axis is marked preoperatively at the slit lamp with the coaxial thin slit turned to 0-180 degrees. Marking is done with either sterile ink or a needle or a bubble marker.

PREOP MARKING

• Intraoperatively, the preoperative horizontal marks are used to position an angular graduation instrument. The actual alignment axis is marked using a toric axis marker.

INTRAOP MARKING

NEWER TECHNIQUES

• Newer techniques have become available for intraoperative toric IOL alignmen :-

1. Iris finger printing technique2. Intraoperative wavefront aberrometry3. Real time eye tracking

SURGERY

• Phacoemulsification technique with 1.5 to 3.4 mm limbal incision depending on the toric iol.

• A well centered capsulorrhexis with 360 degree overlap of the IOL optics should be achieved.

• After the phacoemulsification is completed and the foldable toric IOL is inserted through the limbal incision.

ALLIGNMENT OF TORIC IOL

• First, gross alignment is achieved by rotating the IOL while it is unfolding, until approximately 20 to 30 degrees short of the desired position.

• Final alignment of the toric iol is done after the removal of the viscoelastic substance.

• In the event of a complication during surgery which may affect the stability of the toric IOL, such as zonular damage, vitreous loss, capsulorrhexis tear, or capsular rupture, conversion to a standard non-toric IOL may be required.

POST OPERATIVE AXIS MEASUREMENT

• Clinically – using a slit lamp with a rotating slit. Since the IOL marks are located at the periphery , full mydriasis is required.

• Objective method – wave front aberrometry combined with corneal topography.

DISADVANTAGES OF TORIC IOLs

• Improper alignment or rotation of the iol after surgery may result in more residual astigmatism than predicted.

• For every 1 degree the toric iol axis is off from the true postoperative axis of astigmatism, there will be a 3.3% loss of toric correction.

• Astigmatism more than 4D at corneal plane still remains dificult to correct with toric iol.