FP1760 : Comparative analysis of coaxial phacoemulsification with 2.2- and 2.8-mm clear corneal incisions

Dr.KOMAL SALUJA,Dr.Harinder Singh Sethi

 

Abstract

Purpose: To compare the intraoperative efficiency and postoperative visual outcome of coaxial phacoemulsification using 2.2- and 2.8-mm clear corneal incision coaxial phacoemulsification.

Setting: The study was conducted at Vardhaman Mahavir Medical College and Safdarjung Hospital, New Delhi which is a tertiary health care centre.

Study design: This is a prospective, randomized, comparative interventional study.

Materials and methods: A total of 140 eyes of patients undergoing cataract surgery were enrolled according to the inclusion–exclusion criteria and randomly divided in two groups of 70 such that Group I—Patients underwent phacoemulsification through 2.8-mm clear corneal incision. Group II—Patients underwent phacoemulsification through 2.2-mm clear corneal incision. Postoperative assessment was done at 1 day, 1 and 6 weeks to note best-corrected visual acuity (BCVA), ophthalmic examination, corneal topography, central corneal thickness and corneal endothelial cell count.

Statistics 1. Quantitative variables were compared using Mann–Whitney test and Wilcoxon ranked-sum test. 2. Qualitative variables were compared usingFisher’s exact test. p value of\0.05 was considered statistically significant.

Results There is steady trend in decrease in postoperative astigmatism with time, more so in 2.8 mm group; however, differences were not found to be statistically significant. 2.2 mm group had larger increase in CCT and ECC compared to 2.8 mm group which was not statistically significant (p = 0.296).

Conclusion Reducing the incision size from 2.8 to 2.2 mm does not result in any significant reduction in the amount of surgically induced astigmatism. Also, both the incision sizes have similar intraoperative efficacy when compared in terms of postoperative decrease in corneal endothelial cell count and increase in central corneal thickness.

Keywords 2.2-mm clear corneal incision _ 2.8-mm clear corneal incision _ Coaxial phacoemulsification

Introduction

Internal wound architecture has been important in the evolution of cataract surgery. Careful attention to wound construction can create wounds that need not be sutured. Separating the external and internal wounds by making these incisions of partial thickness and forming a tunnel creates a structure where application of force to the eye will result in wound apposition rather than gape and loss of intraocular contents.There is a definite trend nowadays toward the reduction and elimination of the corneal consequences of cataract surgery through reducing the incision size, aiming not only to decrease the incidence of wound leak and postoperative infection[1, 2] but also to gain the optical advantages of small incision size cataract surgery to preserve corneal optical performance. Corneal refractive

changes following cataract surgery are related to the location and size of the corneal incision. Smaller incision has advantages of manipulating the cornea with minimal stress and injury to the surrounding tissues [3–5], thus giving an optically and morphologically better incision and better optical outcomes [6, 7]. A significantly better control of astigmatism has been demonstrated related to the reduction in corneal incision size for over 3 mm to less than 2 mm, resulting in a reduction in surgically induced astigmatism (SIA) and corneal aberrations [3–5]. Improvements in technology connected with cataract surgery have made it possible to decrease significantly the size of corneal incision created during phacoemulsification.

The reduction in incision size provides many advantages by reducing the need for suturing, leading to more wound stability, a decrease in regular and irregular astigmatism (by avoiding corneal wound burn) [8] and a decrease in corneal aberrations [3]. In addition, smaller incisions has several advantages such as rapid visual restoration with a significant decrease in postoperative intraocular inflammation and endophthalmitis [9], fewer wound-related complications, shorter surgical time and faster postoperative rehabilitation [1, 10]. Smaller incisions also yield a lower incidence of vitreous loss, iris inclusion and intraoperative floppy iris syndrome; less wound leakage, inward [11, 12] or outward with subsequent macular edema; and fewer cases of expulsive hemorrhage [3, 10]. Theoretically, among other factors, the smaller the incision, the more stable the anterior chamber with improved surgical control during capsulorhexis, hydrodissection and phacoemulsification [13]. In this study, therefore, we make an attempt to compare the surgical and visual outcome in terms of various intraoperative and postoperative variables using 2.2- and 2.8-mm coaxial phacoemulsification incisions.

Materials and methods

This prospective, randomized, comparative interventional study conducted at a single tertiary center on patients undergoing cataract surgery. Inclusion criteria were age more than 40 years, presence of senile cataract in one or both eyes, Lens Opacification Classification System III grades II–III [14]. Patients with any central corneal pathology, glaucoma, any macular pathology, uveitis and previous intraocular surgery or ocular trauma were excluded from the study. A total of 140 eyes were enrolled and randomly divided in two groups of 70 such that:

Group I—Patients underwent phacoemulsification  through 2.8-mm clear corneal incision.

Group II—Patients underwent phacoemulsification through 2.2-mm clear corneal incision.

Preoperative assessment

A review of medical history.

Uncorrected visual acuity with Snellen’s chart.

Best-corrected visual acuity.

Intraocular pressure using NCT (noncontact tonometry.

Diffuse light examination.

Slit lamp examination.

Dilated fundoscopic examination (using direct and indirect ophthalmoscopy).

Corneal topography: The simulated keratometry values of the central 3 mm zone as keratometry readings were taken using Shin- Nippon corneal topographer (CT-1000, Shin-Nippon Commerce, Inc. Tokyo, Japan).

Central corneal thickness.

Corneal endothelial cell count: Central corneal thickness and endothelial cell count was done by Konan pachymeter (KONAN MEDICAL INC. _2008). Endothelial cell count was measured three times, and the mean of the three was used.

At surgery, the incision was given on the steeper corneal meridian, using a 2.8-mm metal tip knife in the coaxial phacoemulsification Group I and a 2.2- mm metal tip knife in the coaxial phacoemulsification Group II. Phacoemulsification was performed using Infiniti_ Vision System Ozil_ phacoemulsification platform (Alcon, Fort Worth, TX) by a single surgeon.

Intraoperative assessment

Size of incision (2.2 or 2.8 mm).

Site of incision.

Absolute phacoemulsification time (time spent for the phacoemulsification process).

Phaco power.

Effective phacoemulsification time (Defined as the time in seconds required if 100% power in continuous mode would have been used throughout the phacoemulsification process and is calculated by multiplying total phacoemulsification time in seconds by the average power percent used) [15].

Any complications such as corneal wound burn, posterior capsular rent, zonular dehiscence and iris damage.

Postoperative assessment

On the first postoperative day, the following parameters were assessed by blinded investigator:

Uncorrected visual acuity.

Intraocular pressure.

Diffuse light examination.

Slit lamp examination.

The patient was asked to come for follow-up after 1 and 6 weeks. On each of his/her visit, the following parameters were noted:

Uncorrected visual acuity (UCVA).

Best-corrected visual acuity (BCVA).

Intraocular pressure (IOP).

Diffuse light examination.

Slit lamp examination.

Dilated fundoscopic examination (using direct and indirect ophthalmoscopy).

Corneal topography.

Central corneal thickness.

Corneal endothelial cell count.

Complications example endophthalmitis

Categorical variables were presented in number and percentage (%), and continuous variables were presented as mean ± SD. Normality of data was tested by Kolmogorov–Smirnov test. If the normality was rejected, then nonparametric test was used.

Statistical tests were applied as follows:

Quantitative variables were compared using Mann–Whitney test (as the data sets were not normally distributed) between the two groups, and Wilcoxon ranked-sum test was used to compare pre with post.

Qualitative variables were compared using Fisher’s exact test. A p value of \0.05 was considered statistically

significant.

Results

Mean age in Group I was 64.77 ± 11 years, with age ranging from 56 to 75 years. Mean age in Group II was 64.87 ± 12.26 years with age ranging from 56 to 75 years. Maximum patients in both groups were between 51 and 60 years of age. Of the 70 patients in Group I (2.8 mm), 32 patients were male and 38 were female while there were 34 male patients and 36 female patients in Group II (2.2 mm). Maximum patients in both the groups were female.Group I (2.8 mm) comprised 34 LOCSIII NS grade II patients and 36 LOCSIII NS grade III patients while Group II (2.2 mm) comprised 38 LOCSIII NS grade II patients and 32 LOCSIII NS grade III patients. Both the groups had comparable baseline parameters, and there was no significant difference between the two groups in terms of mean age (p = 0.993), preoperative keratometric astigmatism (KA) (p = 0.761), preoperative refractive astigmatism (RA) (p = 0.765), preoperative central corneal thickness (CCT) (p = 0.705), preoperative corneal endothelial cell count (ECC) (p = 0.873). Ref.Table 1. Mean phaco time in 2.8 mm group was comparable to 2.2 mm group. (p = 0.554). Ref. Table 2. The mean value of KA in 2.8 mm group eyes, preoperative and on day 1, week 1 and 6 were 1.7 ± 0.65, 1.32 ± 0.72, 1.14 ± 0.72 and 1.05 ± 0.67 diopters, respectively. It decreased by -0.38 ± 0.44, -0.56 ± 0.41 and -0.65 ± 0.4, respectively, on day 1, week 1 and 6, respectively, compared to preoperative value. Ref. Table 3. The mean value of KA in 2.2 mm group eyes, preoperative and on day 1, week 1 and 6 were 1.68 ± 0.72, 1.32 ± 0.75, 1.17 ± 0.76 and 1.08 ± 0.7 diopters, respectively. It decreased by -0.36 ± 0.44, -0.51 ± 0.43 and -0.6 ± 0.44, respectively, on day 1, week 1 and 6, respectively, compared to preoperative value. Ref. Table 3. The mean value of CCT in 2.8 mm group eyes, preoperative and on day 1, week 1 and 6 were 516.13 ± 31.73, 567.47 ± 33, 528.91 ± 31.99 and 525.19 ± 31.96 microns, respectively. It increased by 51.34 ± 8.1, 12.79 ± 5.53 and 9.06 ± 5.55, respectively, on day 1, week 1 and 6, respectively, compared to preoperative value. Ref. Table 4. The mean value of CCT in 2.2 mm group eyes, preoperative and on day 1, week 1 and 6 were 514.07 ± 32.4, 565.64 ± 33.53, 527.67 ± 32.3 and 524.29 ± 32.19 microns, respectively. It increased by 51.57 ± 7.7, 13.6 ± 7.28 and 10.21 ± 6.05, respectively, on day 1, week 1 and 6, respectively, compared to preoperative value. Ref. Table 4. Overall 2.2 mm group had a larger increase in CCT compared to 2.8 mm group which was not statistically significant (p = 0.296). It is also observed that CCT tends to return to its preoperative value 6 weeks after surgery. The mean value of ECC in 2.8 mm group eyes, preoperative and on day 1, week 1 and 6 were 2263.74 ± 106.38, 2079.44 ± 115.91, 2040.89 ± 113.16 and 2025.36 ± 115.88 cells/mm2, respectively. It decreased by 184.3 ± 42.52, 222.86 ± 38.48 and 238.39 ± 42.73 cells/mm2, respectively, on day 1, week 1 and 6, respectively, compared to preoperative value. Ref. Table 5. The mean value of ECC in 2.2 mm group eyes, preoperative and on day 1,week 1 and 6were 2260.87 ± 105.46, 2072.06 ± 108.79, 2036.59 ± 109.52 and 2021.51 ± 111.93 cells/mm2, respectively. It decreasedby 188.81 ± 38.75, 224.29 ± 39.43 and 239.36 ± 43.5 cell/mm2, respectively, on day 1, week 1 and 6, respectively, compared to preoperative value. Ref. Table 5. Over all 2.2 mm group had a larger decrease in ECC compared to 2.8 mm group which was not statistically significant (p = 0.919).

Discussion

Surgically induced astigmatism

Any incision on cornea can potentially alter the optical power of the cornea. It has been generally recognized that a smaller corneal incision results in early stabilization of refraction and a shorter recovery time [1, 10]. The quality of incision influences cataract surgery outcomes as smaller incisions give lesser trauma to the eye. Small incision clear corneal phacoemulsification is associated with more wound stability with a decrease in regular and irregular astigmatism [3–5, 7, 16]. Hashemi et al. [17] compared 2.2- and 2.8-mm incisions groups by using vectorial analysis for surgically induced astigmatism. They concluded that there were no clinical or statistically significant differences between two techniques in minimizingthe effect of incision size on SIA (p = 0.479). Mean SIA in their study was 0.1 D in both groups at all follow-up visits and clinically insignificant p[0.05). They attribute this small amount of astigmatism to a steep uniplanar wound that produces little flattening effect on cornea. Also they created only two incisions 90_ apart (single side port, 1.2 mm) which might have had counter effects on each other. Luo et al. [18] compared three incision sizes, 1.8, 2.2 and 3.0 mm, and they concluded that change in astigmatism was not statistically significant when 1.8- and 2.2-mm incision groups were compared; however, the 2.2-mm incisions appear to result in less surgically induced astigmatism than 3.0-mm incision. They also reported that the mean chord length of the clear corneal incision was increased in each group after surgery. The study concluded that with appropriate equipment, smaller incisions may result in less astigmatism, but the particular system used will influence incision stress and wound integrity, and may thus limit the reduction in incision size and astigmatism that is achievable. It is important to note that in this study, a temporal clear corneal incision was used in all cases, irrespective of the steeper meridian. Our study suggests that while the change in keratometric astigmatism at week 6 of the surgery in 2.8 mm (0.65 ± 0.4) group was more than in 2.2 mm (0.6 ± 0.44) group, the results were not found to bestatistically significant (p = 0.670). This is true for reduction in refractive astigmatism also (p = 0.608) and is consistent with the findings of Hashemi et al. [17]. Site of incision placement is important as the clear corneal incisions tend to flatten the meridian of incision and steepen the meridian 90_ away. It has been shown by Nielson and coworkers [19] that this only has an effect on the direction of astigmatism, and not the total surgically induced astigmatism. Beltrame et al. [20] also found similar amounts of SIA in right and left eyes (superotemporal and superonasal),respectively. While all the incisions were given on the steeper meridian, no comparison was made in the two groups with regard to the direction of astigmatism. Additionally, as all the patients were operated by a single surgeon, the confounding factors due to dexterity of the surgeon can be equated out among the groups.

Endothelial cell count

In the general population, ECC decreases with age by 0.5–0.8% per year [21]. Phacoemulsification leads to endothelial cell loss and the process may continue for at least 10 years after surgery [22] or even throughout a patient’s life. The causes of this cell loss are corneal distortion, irrigation solution turbulence, trauma induced by instrument manipulation, nuclear fragments floating in the AC during phacoemulsification, possible IOL contact and free oxygen radicals. In this study, mean endothelial cell loss 6 weeks following coaxial phacoemulsification through 2.2-mm incision was 230 ± 43.5 and 240 ± 42.73 in 2.8- mm incision and not statistically significant, similar to as shown by Hashemi et al. [17] while comparing 2.2- and 2.8-mm incision sizes and Hayashi et al. [23] while comparing 2.0- and 2.65-mm incision sizes. Berdahl et al. [24] found more endothelial cell loss in their 2.8-mm incision versus 2.2 mm coaxial microincision cataract surgery (MICS) groups (p = 0.044). However, in a comparative study by Dosso et al. [25] between conventional phacoemulsification and coaxial MICS using 2.8- and 1.6-mm incisions, the difference in the endothelial cell loss was not significant and was independent of surgery time and ultrasound time that were significantly higher in the coaxial MICS group. It is suggested that the postoperative endothelial cell count is affected by factors other than only incision size. Use of a dispersiveCentral corneal thickness Hashemi et al. [17] found that the mean central corneal thickness (CCT) was 528 ± 32 and 535 ± 36 lm in the 2.8 mm group and 2.2 mm group, respectively; and the difference (7.0 lm) was not statistically significant (p = 0.35). Comparison of CCT readings with baseline values demonstrated significant differences only with day 3 after surgery in both groups. The thickness reached baseline measures one month after surgery (p = 0.85). Similar results were shown by Hayashi et al. [23] and the increase in CCT did not differ between the MICS group and SICS group. Also, Dosso et al. [25] found that these parameters to be similar between coaxial MICS and coaxial SICS. Mean central corneal thickness increased from 514.07 ± 32.4 to 565.64 ± 33.53 l in 2.8-mm incision group and from 516.13 ± 31.73 to 567.47 ± 33 l in 2.2-mm incision group on day 1 postoperatively. Both groups show reduction to baseline value of CCT in 6 weeks postoperatively, and the were not statistically significant. This is again consistent with the findings of Hayashi et al. [23], Hashemi et al. [17] and other researchers. The results of the current study also confirm the findings of other investigators that endothelial cell count is not correlated with CCT on a long-term basis. These data showed that CCT returned to preoperative values after 60 days, despite the endothelial loss, in agreement with data reported by Cheng et al. [26] and Glasser et al. [27], who showed that the functional reserve of a normal endothelium can maintain corneal thickness despite the significant reductions in cell density occurring with age or after intraocular surgery. Thethickness of the cornea increases immediately after surgery, when the pump and the barrier functions of the endothelium are compromised, and therefore, the measurement of corneal thickness reveals the extent of the surgically induced endothelial injury. At 1–2 months after surgery, endothelial cell count remains irreversibly changed, but cell function is usually re-established, and there is a proportional increase in endothelial cell size and reduction in corneal pachymetry to preoperative values [28]. Time taken by the surgeon to perform phacoemulsification was also comparable in the two groups. There was no difference in the incidence of the

intraoperative and postoperative complications between the two groups. Complications that were observed and evaluated were corneal wound burns, posterior capsule rent, zonular dehiscence and damage to iris. This is compatible to the findings of the above mentioned studies.

Conclusion

Although it has beenwidely known that reduction in incision size leads to a better refractive outcome, reduction in incision size to 2.2 mm showed minimal advantage in astigmatic and other parameters when compared to 2.8-mm incision. It, however, has better wound stability and infection prevention, which were not considered in the current study.

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Table 1  Baseline parameters KA Keratometric astigmatism, RA refractive astigmatism, CCT central corneal thickness, ECC endothelial cell count

Variables	GROUP 1 (2.8mm)	GROUP 2 (2.2mm)	P value
Mean age +/- SD	64.77 ± 11	64.87 ± 12.26	0.993
Mean KA	1.68±0.72	1.7±0.65	0.761
Mean RA	1.65±0.71	1.68±0.63	0.765
Mean CCT +/- SD (um)	516.13 ± 31.73	514.07 ± 32.4	0.705
Mean CECC +/- SD (Cells/mm2)	2263.74 ± 106.38	2260.87 ± 105.46	0.873

Table 2 –Intraoperative parameters

Variables	GROUP 1 (2.8mm)	GROUP 2 (2.2mm)	P value
Effective Phaco time +/- SD   (seconds)	74.55 ± 54.1	78.63 ± 56.71	0.554

 

Table 3- COMPARISION OF PRE OPERATIVE AND POST OPERATIVE (DAY1,WEEK 1, & 6) KA (D) BETWEEN 2.8MM AND 2.2MM GROUP

PARAMETER	GROUP I 2.8MM	GROUP II 2.2MM	P VALUE
PRE OPERATIVE KA	1.7±0.72	1.68±0.65	0.761
KA  DAY 1	1.32±0.75	1.32±0.72	0.977
KA  WEEK 1	1.14±0.76	1.17±0.72	0.806
KA WEEK 6	1.05±0.7	1.08±0.67	0.799

 

Table 4- COMPARISION OF PRE OPERATIVE AND POST OPERATIVE (DAY 1,WEEK 1, & 6) CCT (μm) BETWEEN 2.8MM AND 2.2MM GROUP

PARAMETER	GROUP I 2.8MM	GROUP II 2.2MM	P VALUE
PRE OP CCT	516.13±31.73	514.07 ± 32.4	0.705
CCT DAY 1	567.47 ± 33	565.64 ± 33.53	0.745
CCT WEEK 1	528.91 ± 31.99	527.67 ± 32.3	0.819
CCT WEEK 6	525.19 ± 31.96	524.29 ± 32.19	0.868

Table 5- COMPARISION OF PRE OPERATIVE AND POST OPERATIVE (DAY 1,WEEK 1, & 6) ECC BETWEEN 2.8MM AND 2.2MM GROUP

PARAMETER	GROUP I 2.8MM	GROUP II 2.2MM	P VALUE
PRE OP ECC	2263 ±106.38	2260.87 ± 105.46	0.873
ECC DAY 1	2079.44 ± 115.91	2072.06 ± 108.79	0.658
ECC WEEK 1	2040.89 ± 113.16	2036.59 ±109.52	0.756
ECC WEEK 6	2025.36 ± 115.88	2021.51 ± 111.93	0.809