A well-dilated pupil is one of the requirements for safe and successful phacoemulsification surgery. Therefore, it is important to find a method for proper pupil dilation for an cataract doctor when faced a small pupil cataract surgery. Techniques for intraoperative mechanical dilatation of the pupil must be effective, safe, quick, practical, and economical. In this study, we compared 6 methods for pupil dilation.
The results of this study showed that all these methods could achieve proper pupil dilation and improve the safety of the surgery, without affecting the visual acuity and intraocular pressure.
The pupil maintained dilated better in group III-VI than in group I-II because the intraocular instrument can hold the iris. In group I and II, the pupils may resume to a smaller size, making the surgery more difficult to perform, while the costs for patients in group III-VI were higher with the use of intraocular instrument.
Procedures of surgeries in group III-VI were more complicated because of the use of intraocular instrument. More incisions were required to use the iris hooks in group III[7]. Compared with the iris hooks, the advantage of the Malyugin Ring, the OASIS pupil dilator and the B-HEX pupil expander was that there is no need for another incision. The OASIS iris expander in group IV was thicker and harder than Malyugin Ring in group V and the B-HEX pupil expander in group VI, and thus its manipulation would be more complicated. The B-HEX pupil expander was easy to fall off from the pupil sometimes in practice. We thought it maybe because the B-HEX pupil expander was very thin and with weak elasticity. The Malyugin Ring was more reasonably designed and much simpler to operate in our practice.
Before the Malyugin Ring, OASIS iris expander and the B-HEX pupil expander were used, there had been other pupil dilators, such as Morcher pupillary dilator[8, 9], Graether pupillary dilator[10, 11], Perfect the pupil dilator[11, 12], and Siepser pupil dilation etc.. These pupil dilators were designed to be implanted through the main incision in cataract phacoemulsification, fixed at the pupil margin to dilate the pupil, and removed from the main incision at the end of the surgery. Their common disadvantage was that the volume was large and some materials were hard. It was time-consuming to implant them into the eyes and remove them out. The doctors would need a much longer time to study using them and tissue damage is relatively severe. Hence, they were not widely applied. The lightweight, square linear design of Malyugin ring[13]-[14, 15] and OASIS iris expander cleverly avoided these drawbacks. Additionally, they both have an independent disposable micro implantation-removal system, and thus their volumes are quite small when implanted. The Malyugin ring is relatively thin and elastic, and each corner has a circle for the fixation of iris. The OASIS iris expander is relatively thick and hard, and each corner had a triangular bracket for the fixation of iris. The B-HEX pupil expander[16] is designed six side ,not the same to the Malyugin ring and the OASIS iris expander. The B-HEX pupil expander is more softer than the Malyugin ring and don’t need a disposable injector which increases the cost of production.
Corneal endothelium damage was severer in group I, II, IVandVI than in group III and V. There were no statistically significant differences in the corneal endothelium cell density and ACD among the 6 groups before surgery, so we think it might be attributed to less intraocular operations in group III and V[17].
The pupil diameter was largest in group II, which may affect the visual quality. The iris was radially cut open in group II, which will inevitably injure pupillary sphincter, thereby disabling the pupil contraction. The pupillary sphincter was pulled in an evenly dispersed fashion in the other five groups, which could minimize the damage of pupil sphincter in the process of pupil dilation, thereby effectively keeping the function of pupil sphincter intact and facilitating the recovery of postoperative visual quality.
This study compared the six pupil dilation methods for phacoemulsification in eyes with small pupil. Each method has its own advantages and disadvantages. Doctors should choose the suited method for each individual case. The limitation of this study is that the number of cases was limited, and the sample size used for statistical analysis was small .