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Does size and shape matter for pupil expansion rings?

Poster Details

First Author: S.Bhattacharjee INDIA

Co Author(s):                  

Abstract Details



Purpose:

To determine the basis for selection of the size of pupil expansion rings - the pupil size desired by the surgeon, size of the eye or the shape of the device?

Setting:

Nayan Eye Associates, Kolkata, INDIA.

Methods:

The disposable Bhattacharjee pupil expansion rings are made of 5-0 Nylon, have notches at the corners and flanges at the sides, have a joint and are entirely disposed in a single 0.1 mm thin plane. Square (BSQ) and hexagon (BHX) designs of the Bhattacharjee pupil expansion rings were used alternately in a series of 54 eyes. The Square (BSQ) device is available in two sizes 6.5 and 7.0 mm while the Hexagon (BHX) is available in 6.0 and 7.0 mm sizes. Assuming that the white to white corneal diameter (WTW) would reflect the internal diameter of the anterior chamber, this was the basis for choosing the size of the ring. The WTW was measured using a Castroviejo calipers and the BSQ 6.5 & BHX 6.0 sizes were used if the WTW was less than or equal to 10.0 mm. The BSQ 7.0 & BHX 7.0 sizes were used when the WTW was more than 10.0 mm. Hardness of the cataract was noted and videos were analyzed to record difficulty in the steps of phacoemulsification or IOL implantation. Enlarged pupil size and capsulorhexis size were measured after cortical aspiration using an anterior chamber millimeter ruler.

Results:

Bhattacharjee rings were used in 54 eyes of 45 patients. The average preoperative dilated pupil was 4.3 mm. The average enlarged pupil size was 5.2 mm with BSQ6.5, 5.7 mm with BSQ7.0, 5.0 mm with BHX6.0 and 6.0mm with BHX7.0 models. The average capsulorhexis size was 4.8 mm with BSQ6.5, 5.0 mm with BSQ7.0, 4.6 mm with BHX6.0 and 5.0mm with BHX7.0 models. No intraoperative complications were noted because of the size of the capsulorhexis or the device even in hard cataracts. In hard cataracts the nucleus was chopped into multiple small fragments to avoid any stress on the capsule and zonules. There was no incidence of dislodgement of the ring or damage to the ring during the procedure. However, in smaller eyes, with shallow anterior chambers, the anterior chamber appeared cramped with difficulty in phaco probe movements.

Conclusions:

Though both the square and hexagon Bhattacharjee rings can effectively dilate the pupil, the hexagon has geometric advantages over the square and provides a larger pupil than a same size square. For a given size of capsulorhexis as an incircle, the hexagon requires a smaller circumcircle than the square. Hence, a larger hexagon can be accommodated in the anterior chamber resulting in a larger pupil. In this study and in general for all pupil expansion rings, the size of the device is the external side to side measurement. The longest diagonal in the deformed state would be much larger than that of the resting state. Moreover, the perimeter of a 7.0 mm square is larger than the perimeter of a 7.0 mm hexagon which means that the square has a longer longest diagonal compared to a hexagon. If only the pupil expansion desired by the surgeon is the criteria for choosing the size of the ring, these factors may lead to an error in judgment causing trauma to anterior chamber structures during manipulations. This is applicable to all closed ring pupil expansion devices and has to be borne in mind while making the choice of the size to be used. There is poor agreement and a weak correlation between the horizontal WTW diameter and the ciliary sulcus or anterior chamber diameter, although, there is statistically significant linear correlation. This statistically significant linear correlation was the basis for the WTW corneal diameter to be used as an approximate guide to gauge the angle to angle diameter of the anterior chamber in this study. The WTW corneal diameter is easily measurable and should be the primary criteria to choose the size of any pupil expansion ring. The amount of pupil expansion the surgeon desires should be secondary. FINANCIAL INTEREST: NONE

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