Shadowphotogrammetry of IOL Injectors and Clear Cornea Incision Size

Abstract

 

Purpose:

 

To examine and compare the metrology of various intraocular lens (IOL) injectors used in cataract surgery and find the relationship between injector tip and incision contours.

 

Methods:

 

The tips of eleven different types of IOL injectors from nine manufacturers underwent shadowphotogrammetric analysis using images from two orthogonal orientations from a modified optical comparator (BP-30S, Topcon, Tokyo, Japan). Three parameters were analyzed using computer software (Canvas 9): tip diameter (or ellipse major and minor axes), tip angle, and cone angle. The contour (perimeter) of each tip was calculated to determine the ideal incision needed for surgery. The contour of each injector was compared. Unused injectors were also compared to used injectors (after cataract surgery on rabbits) in order to determine whether there was a difference between the dimensions as a result of surgery.

 

Results:

 

Tip diameter ranged from 1.58 to 2.58 mm, tip angle from 34.4° to 66.5°, and cone angle from 0.64° to 10.8°. The tip diameters correspond to contours of 4.96 to 8.10 mm; the contour of a 1.8 mm incision is 3.6 mm. Apart from the Monarch III D and the i-Sert that have an elliptically shaped tip, all others were round. In most cases there was no difference between the pre-insertion and post-insertion values for any of the dimensions. The i-Sert and Nex-IJ did show a difference in dimensions before and after surgery caused by deformation of the plastic as a result of the surgery.

 

Conclusions:

 

None of the IOL injectors tested can be inserted through a 1.8 mm incision without tearing the wound. The measurements of the injectors and data from surgery show that the initial incision size needs to be 1.27±0.11 times larger than the tip diameter for insertion.  

 

Keywords: cataract • intraocular lens • small incision cataract surgery