Ординатура / Офтальмология / Английские материалы / Modern Cataract Surgery_Kohnen_2002

microscopy (Konan Camera Research Institute, Inc.) was performed only once on the third postoperative visit (1 month after surgery).

Statistical analysis was performed with the SPSS statistics software package SPSS/Pc4.0 for Windows® (SPSS Inc., Madrid, Spain). Normality of the data in each group was confirmed by normal probability plots. Statistically significant differences between data samples means that they were determined by the t-test; p values 0.05 were considered significant. Correlation between different parameters was studied using the Pearson correlation test.

Results

The mean ultrasound time was less in the phaco-out group (1.12 0.69 min, range 0.1–2.3) using a mean ultrasound power of 20.5 6.7% (range 6–32%) compared the phaco stop and chop (1.3 0.74 min, range 0.28–2.7) using a mean power of 25.3 7.9% (range 11–42%), but this was not statistically significant (p 0.515 and p 0.089 respectively, independent samples t-test) (fig. 1).

The mean preoperative best-corrected visual acuity (BCVA) was 20/63

20/125 (range 20/400–20/32) in the phaco-out group, and 20/63 20/100 (range 20/400–20/25) in the phaco stop and chop group. In the first postoperative visit, the mean BCVA was 20/32 20/80 (range 20/400–20/20) in the phaco-out group and 20/32 20/63 (range 20/400–20/20) in the phaco stop and chop group. At the last visit (3 months after surgery) the mean BCVA was 20/2520/100 (range 20/100–20/20) in the phaco-out group and 20/25 20/80 (range 20/200–20/20) in the phaco stop and chop group. The differences were not statistically significant (table 1, fig. 2).

Corneal edema (table 2, fig. 3) was observed clinically by the slit lamp biomicroscopy during the first postoperative visit in 5 eyes (33.3%) of the phaco-out group, 2 eyes (13.3%) edema grade ‘ ’ and 3 eyes (20%) edema grade ‘ ’. In the phaco stop and chop group, edema was present in 5 eyes (33.3%), all edema grade. Two weeks after surgery, edema was still present in 2 eyes (13.3%) of the phaco-out group, all grade ‘ ’. Edema grade ‘ ’ was also present in 1 eye (6.7%) of the phaco stop and chop group. One month after surgery there was still no clinically significant edema present in either group. Again these differences were not statistically significant (table 1).

The mean preoperative intraocular pressure (IOP) (measured by the applanation Goldmann tonometry; Haag-Streit) in the phaco-out group was 15.6 2.9 mm Hg (range 10–22). In the phaco stop and chop technique the mean preoperative IOP was 15.67 3.66 mm Hg (range 8–23). In the first postoperative visit the mean IOP was 19.67 4.01 mm Hg (range 12–30) in the phaco-out group, and 19.73 4.63 mm Hg (range 10–30) in the phaco stop and chop

Fig. 1. a Phaco time (min). b Phaco power (%).

technique. Three months after surgery the mean IOP was 15.53 2.97 mm Hg (range 8–18) in the phaco-out group, and 14.87 2.53 mm Hg (range 10–18) in the phaco stop and chop group. The increase in IOP during the first visit was statistically significant compared to the preoperative value in both groups (p 0.001 and p 0.01 in the phaco-out and phaco stop and chop respectively, Student’s t-test), but there was no difference between the two groups throughout the follow-up (table 1).

Table 1. Comparison of the different evaluation parameters between both groups

Table 1. (continued)

p 0.05 is considered not statistically significant.

a Cannot be computed because the standard deviations of both groups are 0.

Fig. 2. Evolution of BCVA. A Preoperatively; B postoperatively, visit 1; C postoperatively, visit 4.

The mean preoperative laser flare cell meter count was 6.73 2.15 (range 4–11) in the phaco-out group, and 7.07 1.98 (range 5–12) in the phaco stop and chop group. In the first postoperative visit, the mean laser flare cell meter count increased significantly in both groups compared to the preoperative values (p 0.0001, Student’s t-test). The count started to decrease 2 weeks after surgery in both groups reaching its preoperative values 3 months after surgery (table 3, fig. 4). There were no significant differences between the two groups in all visits (table 1).

Table 2. Postoperative corneal edema

No eye had corneal edema at the first month follow-up visit.

Postoperative corneal edema

Fig. 3. Postoperative corneal edema.

The mean preoperative endothelial cell count (table 4, fig. 5) was 2,620 473 cells/mm2 (range 1,992–4,010) in the phaco stop and chop group, and 2,809 575 cells/mm2 (range 1,897–4,069) in the phaco-out group. Three months after surgery the mean endothelial cell count was 2,318 491 cells/mm2

Table 3. Laser flare cell meter readings

Fig. 4. Laser flare cell meter counts. A Preoperatively; B postoperatively, visit 1; C postoperatively, visit 2; D postoperatively, visit 3; E postoperatively, visit 4.

(range 1,607–3,745) in the phaco stop and chop group, and 2,523 602 cells/ mm2 (range 1,615–3,861) in the phaco-out group. The cell loss was statistically significant in both groups (p 0.0001, Student’s t-test), but the difference between groups was not statistically significant. The mean percentage cell loss was 11.85 5.14% (range 6.61–26.39%) after the phaco stop and chop technique and 10.65 5.4% (range 4.55–24.25%) after the phaco-out technique. Again this was not statistically significant (table 1).

Table 4. Endothelial cell changes

Regarding the corneal thickness, measured by Ophthasonic Ultrasonic Biometer (Tecknar Inc.), both groups showed a significant increase in corneal thickness. A maximum corneal thickness was reached at the first postoperative visit (p 0.0002 and p 0.001 in the phaco stop and chop, and the phaco-out groups respectively, Student’s t-test), and decreased gradually to reach the preoperative values by the third month (table 5). However, the difference between the two groups was not statistically significant (table 1).

Discussion

Removal of the nucleus by ultrasound can be performed using a number of techniques. Originally, Kelman [8] developed phacoemulsification in the anterior chamber in 1967, seeking for a procedure that reduces astigmatism and provides early rehabilitation. Many surgeons, seeking the same objective, performed thousands of Kelman phacoemulsification cases, and their results were reported [9, 10]. However, the corneal endothelium damage (many cases being impossible to accomplish with the instruments available by that time), the realization that very dense nucleus resisted ultrasonic fragmentation, and the need of an incision 3 mm to implant the intraocular implants available at that time limited the universal application of Kelman’s procedure.

Corneal problems have been significantly minimized by the advent of in situ, or what has become known as posterior chamber, phacoemulsification and the protective properties of viscoelastic substances [11, 12]. Phacoemulsification as the surgical procedure of choice increased from 12% in 1985 to 79% in 1992 [3]. The tremendous 7-year growth can be directly correlated with the introduction of continuous curvilinear capsulorhexis (CCC) in 1985 [13, 14].

Following the introduction of CCC, various endocapsular phacoemulsification techniques developed, from which surgeons can choose depending on their own skill, machine available and more important the type of cataract

Fig. 5 a Endothelial cell count (cell/mm2). b Percentage endothelial cell loss (%).

they are dealing with. The various endocapsular techniques include [7, 15–17]: technique of cut and suck for nuclei of moderate-low hardness, technique of cleavage for nuclei of moderate hardness (chip and flip), and techniques of nucleofracture for nuclei of moderate-high hardness, Sheperd’s cross technique,

divide and conquer by Gimbel, crack and flip by Fine, phaco chop by Nagahara, and stop and chop by Koch.

Owing to the great development of phacoemulsification techniques and machines, as well as the availability of various forms of foldable intraocular lenses, phacoemulsification is the technique of choice by most surgeons nowadays. However, we should not ignore the fact that in certain situations the surgeon will find himself obliged either to perform an ECCE procedure from the very beginning or to switch from phacoemulsification to ECCE during the procedure. These difficult situations include very deep anterior chamber, where the surgeon will need to keep the tip in an almost vertical position, limiting the depth of field of the microscope and the surgeon will have less control and all of the intraoperative maneuvers will be more difficult. Another factor is difficult visual control of the peripheral lens structure due to miosis, as in cases of dystrophic iris; doubts regarding the strength of the zonules or the integrity of the posterior capsule. Performing phacoemulsification in these cases carries the risk of further intraoperative complications, and switching to ECCE is a viable alternative to decrease the incidence of complications.

In this study we are making use of the great improvement in the phacoemulsification techniques, machines as well as the viscoelastic materials to compare the results of performing phacoemulsification in the anterior chamber (phaco-out), against phacoemulsification using the phaco stop and chop technique and study the effect of both procedures on corneal endothelial cells, and the intraocular postoperative inflammatory reactions.

Several studies have evaluated the functional behavior of the corneal endothelium, IOP, and intraocular inflammatory response after cataract surgery. Carlson and Bourne [18] observed that the barrier function of the endothelium was transiently decreased following cataract surgery but appeared to recover by the third month. Sawa et al. [19] also reported a recovery of the barrier function 3 months after cataract surgery. Comparative studies evaluating the percentage of cell loss with ECCE and phacoemulsification have been reported. Davidson [20]

reported a mean endothelial cell loss of 10.7 11% after ECCE and 10.0 12.9% after phacoemulsification and posterior chamber IOL implantation. Ravalico et al. [21] reported endothelial cell loss of 8% after phacoemulsification. In our current study both the phaco-out technique and phaco stop and chop technique resulted in endothelial cell loss in the same range that was reported by these authors, the mean endothelial cell loss was 10.65% after phaco-out, and 11.85% after phaco stop and chop technique. Thus both techniques affected corneal endothelial cells to the same extent with no significant difference (p 0.536, independent sample t-test), a point favoring the safety of the phaco-out technique described. We attribute this to the proper use of viscoelastics throughout the procedure, to fill the anterior chamber and protect the endothelium during the delivery of the nucleus to the anterior chamber and performing the phacoemulsification [22].

On clinical examination, corneal edema was more evident with the phacoout technique during the first 2 weeks after surgery after which there was no clinically detected corneal edema in both groups (table 2). Thus in our study, corneal edema, although it was present more with the phaco-out technique, its effect did not interfere with the visual outcome of both procedures. This finding could be related to the short distance between the cornea and ultrasound probe in the phaco-out technique in comparison to the phaco stop and chop technique.

Corneal thickness, measured by the ultrasonic pachymetry, correlated well with the postoperative clinical corneal edema. There was a significant increase in the corneal thickness in both groups during the first 2 weeks after surgery; corneal thickness was more evident in the phaco-out group. However, this did not affect the final outcome in both groups. There was no significant difference between the mean preoperative value and 3 months after surgery.

Even when considering the postoperative inflammation measured by the laser flare cell meter, in both groups there was a significant difference between the preoperative and the first postoperative visit means, that decreased with time to return to the preoperative values at 3 months. This agrees with the fact that intraocular inflammation usually responds well to the postoperative steroidal and nonsteroidal anti-inflammatory agent [23]. However, the difference between the two groups was not statistically significant throughout the follow-up. This further supports the safety of the phaco-out technique.

The final visual outcome in both groups was satisfactory. The mean BCVA improved from a mean value of 20/63 20/125 (range 20/400–20/32) in the phaco-out group, and 20/63 20/100 (range 20/400–20/25) in the phaco stop and chop group to 20/25 20/100 (range 20/100–20/20) in the phaco-out group and 20/32 20/80 (range 20/200–20/20) in the phaco stop and chop group 3 months after surgery.