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Cataract Surgery | Jul 2011

Preoperative Corneal Edema

One of the most frequent causes of preoperative corneal edema is Fuchs endothelial dystrophy. This progressive, bilateral disease of the corneal endothelium can be subtle, presenting with only corneal endothelial guttata;1 however, the disease can eventually lead to corneal decompensation and decreased visual acuity. Corneal transplantation, usually with Descemet stripping automated endothelial keratoplasty (DSAEK), becomes the only option to improve vision.

DSAEK can be performed simultaneously with cataract extraction and IOL insertion when visually significant cataract is present. In patients with early-stage Fuchs endothelial dystrophy and visually significant cataract formation, cataract extraction alone may be preferable. Selection of patients who are likely to undergo successful phacoemulsification is crucial, as unexpected corneal decompensation leads to dissatisfied patients. Seitzman et al2 suggested that cataract surgery can be safely performed in patients with Fuchs endothelial dystrophy with a preoperative corneal thickness of less than 640 μm. Other sources advise that the decision to perform cataract surgery should not be based on corneal thickness measurements exclusively.3-5 Other preoperative evaluations such as endothelial cell density, symptoms of early morning decompensation, cataract density, and corneal thickness measurements should also be considered.

LOWER ULTRASOUND POWER

The ultrasound power necessary for phacoemulsification in routine cataract surgery induces an endothelial cell density loss of 6.3% to 12.8%.6-9 Therefore, decreasing ultrasound energy has become a primary goal in cataract surgery, especially in patients with a compromised cornea. A phaco strategy that combines cohesive and dispersive ophthalmic viscosurgical devices (OVDs), such as the soft-shell technique, further protects the corneal endothelium during cataract surgery.10

Newer phaco power modulation modalities, such as the Ozil Torsional (Alcon Laboratories, Inc., Fort Worth, Texas) and the Ellips FX (Abbott Medical Optics Inc., Santa Ana, California) technologies, help to reduce the amount of energy expended during phacoemulsification. The Ozil handpiece produces rotary oscillation of the phacoemulsification tip with a frequency of 32 kHz, rather than the forward-backward movement of the tip in longitudinal/conventional phacoemulsification. Three recent studies11-13 compared torsional and longitudinal ultrasound in normal eyes with different stages of cataract. In the torsional group, significantly less use of ultrasound power, lower cumulative dissipated energy (CDE), smaller increases of central corneal thickness at 1 and 7 days postoperatively, faster visual recovery, and less endothelial cell loss were seen. Patients with Fuchs endothelial dystrophy might benefit the most from the reported reduction in endothelial cell damage.

FUCHS ENDOTHELIAL DYSTROPHY AND CATARACT SURGERY

We recently generated a prediction model to calculate the risk of corneal decompensation after phacoemulsification in 52 eyes with Fuchs endothelial dystrophy and visually significant cataract. This randomized study assessed the pre-, intra-, and postoperative variables in these patients and evaluated the effect of torsional and longitudinal phacoemulsification on intra- and postoperative outcome parameters.

Eyes were randomly assigned to torsional (n=26) or longitudinal (n=26) phacoemulsification mode using a permuted blocks computer-based system that took into account the stage of Fuchs endothelial dystrophy, nucleus density grade, and age. Patients were evaluated preoperatively and at 1 day, 1 week, and 1, 3, and 6 months postoperative. We measured BCVA, performed anterior segment optical coherence tomography (OCT; Visante OCT Model 1000; Carl Zeiss Meditec, Jena, Germany) to evaluate corneal thickness at different locations, and used Scheimpflug imaging to calculate corneal volume.

Ultrasound time and CDE were measured intraoperatively. Ultrasound time and CDE were significantly lower for the harder nucleus density grades in the torsional group compared with the longitudinal group (P=.009 and P=.002, respectively). Differences in corneal volume and BCVA were not significant (P>.058).

Differences in corneal thickness were not significant with the exception of peripheral corneal thickness at the 6-o’clock position (opposite the incision site), which was significantly lower in the torsional group compared with the longitudinal group at 1 day postoperatively, with increases of 44 ±35 μm versus 74 ±46 μm, respectively (P=.010). A higher preoperative central corneal thickness (CCT) was associated with a larger postoperative increase in CCT at 1 day postoperative (r=0.460; P=.001) and lower BCVA at all follow-up visits (r>0.344; P<.015; Figures 1 and 2).

RISK FACTORS FOR POSTOPERATIVE CORNEAL DECOMPENSATION

Sixteen eyes (30.8%), eight in each group, required DSAEK due to corneal decompensation (Figure 3). Mean preoperative CCT, peripheral corneal thickness at the 6- and 12- o’clock positions, and corneal volume were significantly higher in patients who required DSAEK (Table 1; P<.022). After logistic regression analysis, only preoperative CCT was a significant predictor for DSAEK (P<.001). A higher preoperative CCT resulted in an increased risk of corneal decompensation postoperatively. All other preand intraoperative parameters, including torsional and longitudinal phacoemulsification, did not significantly contribute to the risk of corneal decompensation. The logistic regression model predicted that for each 10-μm increase in preoperative CCT, the odds of developing corneal decompensation increased 1.7 times (95% confidence interval; 1.251-2.217; P<.001). A preoperative CCT of 620 μm corresponds to an odds ratio of 1, meaning no increased risk of developing corneal decompensation.

CCT remained stable from 1 to 6 months postoperatively in the longitudinal (P=.057) and the torsional (P=.392) groups. Furthermore, BCVA did not change between 1 and 6 months after surgery in either group (P=.139 and P=.704, respectively). According to our analysis, it is safe to decide at approximately 1 month after cataract surgery whether DSAEK will be required in the future in patients with Fuchs endothelial dystrophy.

CONCLUSION

Although torsional phacoemulsification has been reported to reduce ultrasound time and CDE, which would appear to the beneficial in eyes with Fuchs endothelial dystrophy, there were no significant differences in our study in the postoperative outcome parameters between torsional and longitudinal phaco. The smaller increase in corneal thickness at the 6-o’clock position in the torsional group might be explained by less repulsion because it is exactly opposite the incision site. Logistic regression analysis showed that, for each 10-μm increase in preoperative CCT, the odds of developing corneal decompensation increased 1.7 times. Furthermore, CCT above 620 μm led to an increased risk for corneal decompensation after phacoemulsification in patients with Fuchs endothelial dystrophy.

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  8. Alio JL,Mulet ME,Shalaby AM,Attia WH.Phacoemulsification in the anterior chamber. J Cataract Refract Surg.2002;28(1):67-75.
  9. Walkow T,Anders N,Klebe S.Endothelial cell loss after phacoemulsification:relation to preoperative and intraoperative parameters. J Cataract Refract Surg.2000;26(5):727-732.
  10. Tarnawska D,Wylegala E.Effectiveness of the soft-shell technique in patients with Fuchs’endothelial dystrophy.J Cataract Refract Surg.2007;33(11):1907-1912.
  11. Liu Y,Zeng M,Liu X,et al.Torsional mode versus conventional ultrasound mode phacoemulsification:randomized comparative clinical study. J Cataract Refract Surg.2007;33(2):287-292.
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