December 2019

ASCRS NEWS

Eyeworld Journal Club
Review of “Effect of Hypothermic Perfusion on Phacoemulsification in Eyes with Hard Nuclear Cataract: a Randomised Trial”


by Cassandra C. Brooks, MD, Kevin Jackson, MD, Mark F. Goerlitz-Jessen, MD, Pratap Challa, MD


Pratap Challa, MD
Residency Program Director
Duke University
Durham, North Carolina


Kevin Jackson, MD, Mark F. Goerlitz-Jessen, MD, Cassandra C. Brooks, MD, and Pratap Challa, MD.
Source: Pratap Challa, MD

Although it has been debated in the past, the concept of cooling irrigation fluid for phaco has garnered little attention in the past decade. I asked the Duke residents to review this December JCRS study, which analyzes the potential benefits of colder infusion for hard cataracts.

—David F. Chang, MD EyeWorld Journal
Club Editor

 

Introduction

Cataracts affect approximately 24.4 million people in the United States and are expected to be responsible for vision loss in almost 40 million people by 2030. Cataract surgery is one of the most common procedures performed today with 3.6 million surgeries performed in the United States in 2015.1,2 Phacoemulsification has become the most common method of cataract extraction due to its efficiency, safety profile, and use of a small incision. However, phacoemulsification can have undesired effects when excessive ultrasound energy is used, which is more likely as a cataract becomes more mature.3
Unfortunately, excess ultrasound energy can affect nearby ocular structures via dissipated vibrational energy and thermal damage. The undesired effects attributed to excess ultrasound energy include thermal injuries to the incision and damage to the corneal endothelium. Thermal injuries to the incision lead to difficult wound closure, wound leakage, damage to corneal stroma, fistula formation, and high postoperative astigmatism.4 Damage to the corneal endothelium during surgery can acutely and chronically impair endothelial cell function in corneal transparency given the limited regenerative capacity of endothelial cells.5 Due to the potential for these adverse effects, surgeons continuously seek ways to minimize damage caused by ultrasound energy from phacoemulsification while preserving its efficiency.6

Overview of study

In this study, Wan et al. hypothesized that intraocular hypothermia during phacoemulsification may reduce postoperative inflammation and endothelial cell damage. The study was composed of an animal trial with 40 rabbits (40 eyes) and a randomized clinical trial with 80 patients (80 eyes) with a hard nuclear cataract (grade III–V, Lens Opacities Classification System III) that underwent phacoemulsification by one surgeon at a single institution.
The preoperative visual and corneal characteristics for the clinical trial were obtained, though not provided. Phacoemulsification for the animal study was performed with an energy of 50% and a phacoemulsification time of 20 seconds in total (phacoemulsification for 5 seconds, pause for 5 seconds, repeated four times) while phacoemulsification energy and time were recorded at the conclusion of each operation in the randomized clinical trial. Real-time intraocular temperature was obtained using a thermometer with thermocouple probes inserted into the anterior chamber (AC) as well as the corneal incision. The animal study evaluated intraocular perfusion temperature of 4˚C, 10˚C, and 24˚C while the randomized trial evaluated intraocular perfusion temperatures of 4˚C and 24˚C.
Postoperative ophthalmic evaluation included the patient’s best-corrected visual acuity (BCVA), slit-lamp examination of the anterior and posterior segments, intraocular pressure (IOP), and a dilated fundus examination. Additionally, anterior segment OCT, fundus OCT, corneal endothelial cell count, central corneal thickness (CCT), and AC inflammatory cell count were obtained on the 1st and 7th postoperative day. Subjects were followed for 30 days after surgery.

Results

In both the animal and clinical studies, the authors found a statistically significant difference between the 4°C and 24°C groups at postoperative day 1 with regard to CCT and AC inflammation, with the 4°C group having a lower CCT and grade of AC inflammation. In the animal trial, there was no difference between the 4°C and the 10°C groups. The clinical trial also found the 4°C group had a higher endothelial cell density and hexagonal morphology when compared to the 24°C group at postoperative day 1, which was statistically significant.
Interestingly, none of the statistically significant differences seen at day 1 remained significant at postoperative day 7 or 30 in either the animal or clinical model. The differences between the 4°C and 24°C group did not translate into clinically or statistically significant differences in postoperative visual acuity or surgical complications, such as transient IOP elevation or macular edema.

Analysis

The findings of this study suggest that perfusion with a 4°C fluid may be safe and protective against inflammation in the early postoperative period. Cooling perfusion fluid appears to blunt the overall fluctuation in temperature changes in the AC that can be associated with phacoemulsification in hard cataracts. However, this reduction in temperature variability does not appear to translate into clinically relevant benefits at one month postop.
One limitation of the study is the overall short duration of follow up, making it unclear whether the initial findings might translate into long-term differences in visual outcomes or complications. Also, we found ourselves interested in a few additional pieces of information in order to better interpret the overall findings. First, it would be helpful to have the data from the preoperative animal and clinical measured corneal parameters to determine whether there was a statistically significant difference between the groups prior to phacoemulsification. While the paper indicates this data was collected, it is not made available. This would enhance the analysis of whether the postoperative results were significant by comparing pre- and postoperative values within and across each of the test groups. Additionally, it would help us better interpret how the statistically significant endothelial cell count difference between the 4°C and 24°C groups reported at postoperative day 1 changed by postoperative day 7, at which time there was no longer a statistically significant difference between the groups. This possibly suggests a delayed cell dropout in the 4°C group but would be better understood in the setting of the preoperative data. Second, when analyzing the temperature differences seen in a figure in the study, it is unclear why the authors are demonstrating the data as a linear progression when comparing AC temperatures before and during phacoemulsification to incision temperature during surgery. The data for incision temperatures prior to surgery is also not included. This data may be better represented as a table with the addition of the incision temperature before phacoemulsification.
There are a few technical aspects of lens insertion and phacoemulsification in these cases that should be considered as well. From a surgeon’s perspective it may be important to account for differences in acrylic IOL unfolding due to changes in fluid temperature.7 The rate of lens unfolding could impact the final lens position, thereby altering refractive outcomes. Prolonged unfolding may also lengthen surgical times, which could impact postoperative inflammation. Furthermore, it is unclear whether ophthalmic viscosurgical devices (OVDs) were utilized and, if so, whether it was cohesive or dispersive. OVDs have been shown to protect the corneal endothelium from temperature fluctuations associated with phacoemulsification.8 Interpreting the data in the setting of a specific OVD would add context and value to the analysis.
Finally, it would have been interesting to learn whether there was a difference in patient comfort intraoperatively and during the early postoperative period. A study in patients undergoing photorefractive keratectomy (PRK) found a trend toward increased pain amongst patients receiving chilled versus room temperature saline, but this was not found to be statistically significant.9 It is unclear what the effect of hypothermic perfusion on patient comfort would be during cataract surgery and future applications of this technique should evaluate the patient experience.

Conclusion

The authors of this study present an interesting and thoughtful idea by which surgeons may be able to reduce postoperative inflammation in cataract patients. While the impact of tissue hypothermia has certainly proven to be effective in a number of disease states and procedures, there is still work to be done to understand its impact on phacoemulsification. We agree that additional studies with larger sample sizes and longer follow-up periods are needed to understand the long-term impact of this technique. Furthermore, understanding how intraocular hypothermia may impact the patient’s subjective intraoperative and postoperative experience is an important perspective to be explored. We appreciate this unique contribution to the literature and look forward to the development of improved phacoemulsification techniques for the benefit of our cataract patients.

References

1. Cataract Data and Statistics 2010. National Eye Institute 2019.
2. Lindstrom R. Thoughts on cataract surgery. Review of Ophthalmology. 2015.
3. Zeng M, et al. Torsional ultrasound modality for hard nucleus phacoemulsification cataract extraction. Br J Ophthalmol. 2008;92(8):1092–1096.
4. Bissen-Miyajima H, et al. Thermal effect on corneal incisions with different phacoemulsification ultrasonic tips. J Cataract Refract Surg. 1999;25:60–64.
5. Joussen A, et al. Effect of irrigating solution and irrigation temperature on the cornea and pupil during phacoemulsification. J Cataract Refract Surg. 2000;26(3):392–397.
6. Fundamental of Ultrasonic Phacoemulsification Power 2019. American Academy of Ophthalmology 2019.
7. Jung GB, et al. Physicochemical and surface properties of acrylic intraocular lenses and their clinical significance. J Pharma Investig. 2017;47(5):453–460.
8. Suzuki H, et al. Efficacy of Ophthalmic viscosurgical devices in preventing temperature rise at the corneal endothelium during phacoemulsification. Cur Eye Res. 2016;41(12):1548–1552.
9. Neuffer MC, et al. Prospective comparison of chilled versus room temperature saline irrigation in alcohol-assisted photorefractive keratectomy. Nepal J Ophthalmol. 2013;5(2):154–160.

Contact information

Challa: pratap.challa@duke.edu

Review of “Effect of Hypothermic Perfusion on Phacoemulsification in Eyes with Hard Nuclear Cataract: a Randomised Trial” Review of “Effect of Hypothermic Perfusion on Phacoemulsification in Eyes with Hard Nuclear Cataract: a
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