Cataract surgery in patients with highly liquefied or vitrectomized vitreous is challenging due to its unique anatomical structures. To solve this problem, previous researchers, such as Li et al. 5 and Yu et al.10 has reported modified methods which had certain effectiveness in improving the safety of surgery and reducing complications, but there are still some limitation for their methods. In the current study, we reported with encouraging results that prechop technique had an advantage in treating patients with highly liquefied vitreous compared to conventional phaco chop during cataract surgery.
As demonstrated in previous studies, both vitrectomy and high myopia increase the risk of nuclear sclerotic cataracts.21,22 The severity of nuclear sclerosis is greater in vitrectomized eyes than typical cataract eyes.23 Phacoemulsification for these patients showed increased risks of complications due to alterations in anatomy and showed higher dependence on the surgeon’s experience. These patients share some common anatomical features including loss of support from the vitreous body, weakened zonules, intraoperative miosis, and increased mobility of the lens-iris diaphragm during cataract surgery. In conventional phacoemulsification, notable fluctuation of ACD and movement of the posterior capsule were observed. These changes increased the difficulty of operation and risks for broken zonules and posterior capsule rupture.1,24
Previous studies reported the safety of conventional phacoemulsification in post-vitrectomy cataract patients. 25,26 However, the phaco time and energy use were not thoroughly investigated. Manual prechop was recommended in recent years as an effective procedure to reduce energy use, especially for hard nucleus cataracts.17 In this study, we found that the prechop technique is safe and effective for high myopia-related and post-vitrectomy cataract patients. For cataracts with a hard nucleus, the prechop technique is preferred because of the reduced phaco time and CDE.
Intraoperative complications occurred in three eyes in the conventional phacoemulsification group, while no complication was observed in the prechop group. This observation indicates that the prechop procedure might have better safety. After manual prechop to split the nucleus, the fragments of nucleus are brought to the pupil and iris plane, while the lens-iris diaphragm moves further backward. In this way, the removal of nucleus fragments by phacoemulsification is done near the pupil plane with no extra forces against the capsule and zonules. It is unnecessary for the phaco tip to bury deeply into the nucleus. Shallow penetration provides proper protection to the posterior capsule and avoids unexpected rupture. Furthermore, when the pupil iris plane diaphragm moves backward, the handpiece needs to turn vertically to perform the phaco-chop and phacoemulsification deep in the capsule. This procedure places persistent pressure on the corneal flap, which might result in decreased maneuverability and problems with the water tightness of the incision. By proper manual prechop, the phaco procedure is done at the pupil-iris plane, thus reducing the difficulty of operation and incidence of complications.
It has been reported by previous studies that prechop could reduce energy use and corneal damage in phacoemulsification for patients with age-related cataracts.27 In this study, we retrospectively analyzed the intraoperative parameters of patients with high myopia-related and post-vitrectomy cataracts. For cataracts with NO scores < 5, these two methods did not differ significantly in phaco time or energy use. But for hard nuclear cataract with NO grading ≥ 5, less phaco time and CDE resulted from the prechop technique. The correlation between phaco time and NO or CED scores was also weaker in the prechop group, though the difference was not statistically different. This result may be due to a small sample size. The average energy was generally controlled by the surgeon to reduce heat damage to the corneal endothelium. The correlation between average energy and NO score was weak in both groups. The results of this study indicate that, for soft nuclear cataracts both phaco-chop and manual prechop work well for phacoemulsification. For hard nuclear cataracts, the prechop technique is preferred for its reduced phaco time and CDE as well as better surgical safety.
There are some limitations in the current study. First, the sample size was relatively small, especially for hard nuclear cataracts. Further prospective studies with larger sample size are still needed. Moreover, there might be a concern over the distance to corneal endothelium when removing cataracts at the pupil-iris plane. In patients with high myopia and previous vitrectomy, the movement of lens-iris diaphragm increases with deepening of the anterior chamber. This helped keeping the phaco probe further away from the corneal endothelium. A similar technique was reported by Yu et al., who recommended phacoemulsification in the anterior chamber for post-vitrectomy cataract. 10
In conclusion, the results of our study are encouraging that the prechop technique was found to have less intraoperative complications, reduced phaco time and CDE compared to standardized phaco-chop during cataract phacoemulsification surgery. It might be a good alternative for cataract surgery for patients with highly liquefied vitreous, such as in high myopia-related and post-vitrectomy cataract, especially those with hard nucleus.