Investigating the effect of clear corneal incisions on the principle meridians of the cornea

Session Details

Session Title: Corneal Astigmatism Assessment. Surgery Equipment

Session Date/Time: Saturday 05/09/2015 | 11:00-13:00

Paper Time: 12:10

Venue: Main Auditorium

First Author: : C.Hamer UK

Co Author(s): :    P. Buckhurst   N. Habib   H. Buckhurst   C. Purslow           

Abstract Details

Purpose:

Providing the most effective correction with toric intraocular lenses (IOLs) requires accurate alignment with the post-surgical steepest corneal meridian. During cataract surgery clear corneal incisions cause a meridional flattening effect on the cornea and it is generally accepted that if these incisions are placed away from the steepest corneal meridian then an axis shift will occur. The present investigation aims to compare the predicted change in the steepest meridian axis with the actual change that occurs following cataract surgery.

Setting:

Royal Eye Infirmary, Plymouth, UK.

Methods:

A prospective interventional study recruited 96 subjects (53 females, 43 males, aged 74.9±7.8 years) who all underwent small incision suture-less cataract surgery with a clear corneal incision (2.8mm) placed superior-temporally. Scheimpflug tomography was conducted pre-operatively and at 3-6 months post-operatively. The true location of the corneal incision was assessed post-operatively via slit lamp examination. Vector analysis was used to compare the predicted and actual postoperative steepest meridian axis change.

Results:

The mean location of the superior-temporal corneal incision was 7.6 ± 56.9° from the steepest corneal meridian. The median pre-operative corneal astigmatism was 0.74D (IQR 0.45, 1.10D). The median predicted and actual shift in steepest axis towards the incision was 11.24° (IQR 6.43, 24.62°) and 2.05° (IQR -9.23, 13.85°), respectively. No correlation was found between the predicted and actual corneal axis change (Ƭ=0.25, p= 0.713). The predicted shift in meridian position significantly overestimated the actual change found (p<0.001).

Conclusions:

The use of vector analysis calculations caused a large overestimation of the post-surgical axis shift towards the incision. The actual change measured was significantly smaller. Using the predicted axis position rather than the pre-surgical axis position could significantly reduce the effectivity of the toric IOL correction.

Financial Interest:

One of the authors receives consulting fees, retainer, or contract payments from a competing company, One of the authors research is funded, fully or partially, by a competing company