A Comparative Study on Visual Outcome and Rotational Stability After Different Toric Intraocular Lens Implantation During Cataract Surgery—A Randomized Controlled Trial

Cataract is one of the leading causes of blindness which accounts for almost 51% of the world’s blindness. Pre-existing astigmatism of greater than 1.50 D is found in around 15-29% of cataract patients while 3-15% of cataract patients have pre-existing astigmatism of greater than 2 D. Notable astigmatism is often associated with poor visual acuity, escalating the dependence on prescription glasses and dwindling quality of vision by virtue of distortion and smearing of images. Hence reducing the astigmatism would lead to further improvement in the visual outcome after cataract surgery.For patients where both cataract and corneal astigmatism are present the lenticular component conferring to the astigmatism is eradicated by the surgery itself and the ultimate postoperative astigmatic error is governed by the corneal contribution. In such patients, if monocular intra ocular lens is implanted, the patient may require ancillary refractive surgeries like corneal incisions in steep meridian and femtosecond laser-associated astigmatic keratotomy. A number of these procedures are associated with complications such as delayed wound healing, lack of precision, and corneal epithelial defects to name a few. Therefore the preexisting astigmatism correction in cataract patients can be done by implanting toric intra ocular lens without need of any additional refractive surgeries.

Toric IOLs are made of acrylic hydrophobic or hydrophilic material, which have stable haptic design for rotational stability hence making it more predictable and more precise than corneal or limbal surgeries. It could also meet patients’ need of spectacle free vision. Factors determining better visual outcome with toric IOLs are accurate biometry values and rotational stabilitiy. It has been observed in few studies that, for around every 1⁰ of lens misalignment there is a loss of 3% of astigmatic power correction. Misalignment by 30⁰ causes total loss of astigmatic power of toric IOL and misalignment of greater than 30⁰ induces new astigmatism. These patients might require IOL realignment surgery. Toric IOLs shows greatest rotation in early post operative period usually within 1 hour of surgery and the rotation is minimal after 1 week post operatively. Factors associated with an increased likelihood of toric IOL rotation include inaccurate capsulorrhexis size and centration, long axial length, incomplete removal of viscosurgical devices and changes in intra ocular pressure. Various methods that can be used to evaluate the toric IOL alignment post operatively include slit lamp, retro illumination 14 | P a g e photographs, digital sequential photographs, software based analysis and optical coherence tomography.

The objectives of my study are

Primary Objective:

1.To compare and analyze the visual outcome among all cataract cases with astigmatism >1D cylinder undergoing different toric intraocular lens (IOLs) implantation during cataract surgery.

Secondary Objectives:

1.To evaluate rotational stability of different toric IOLs at 1 month, 3 months and 6 months post operative follow up.

2. To compare the residual error with digital marking and slit lamp marking for toric IOL implantation.

3. To assess the quality of life in all toric IOLs based on validated questionnaire

When patient presents to the OPD, BCVA, autorefractometry and keratometry will be recorded to look for any astigmatism. Further dilatation of eyes using eyedrop tropicamide and phenylephrine will be done and a detailed slit lamp examination will be performed to grade the cataract along with a detailed fundus examination. If significant grade of cataract is found and patient requires to undergo a cataract surgery then optical 21 | P a g e biometry will be done to determine the lens power and astigmatism present. Patient will then be admitted and planned for cataract surgery. Toric axis will be calculated using respective IOLs Toric calculator. Preoperatively on the day of surgery, patient will be seated with their eyes fixed at a distant light source (torch light) and the corneal light reflex is noted in both eyes. Lane’s preop bubble marker will be used to mark axes of 0⁰, 180⁰ and 270⁰ over the limbus. Intraoperatively, using Mendez ring the patient’s Toric axis is marked in supine position along with the incision site. Cataract surgery will be carried out and then the toric IOL will be implanted in the appropriate axis using markers provided in the toric IOL.

Patients will be reviewed post operatively after 1 month, 3 months and 6 months.