Citation: Jin KH, Kim TG. Relationship between early structural changes at cornea incision
sites and surgical outcomes after phacoemulsification. Int J Ophthalmol 2019;12(7):1139-1145
DOI:10.18240/ijo.2019.07.14
·Clinical Research·
Relationship between early structural changes at cornea incision sites and surgical outcomes after phacoemulsification
Kyung Hyun Jin1, Tae Gi Kim2
1Department of Ophthalmology, Kyung Hee University Medical Center, Kyung Hee University, Seoul 02447, Korea
2Department of Ophthalmology, Kyung Hee University Hospital at Gangdong, Kyung Hee University, Seoul 05278, Korea
Correspondence to: Tae Gi Kim. Department of Ophthalmology, Kyung Hee University Hospital at Gangdong, # 892, Dongnam-ro, Gangdong-gu, Seoul 05278, Korea. tk1213@hanmail.net
Received:
Abstract
AIM: To assess the early structural changes at clear corneal cataract incision sites and surgical outcomes using anterior segment optical coherence tomography (AS-OCT).
METHODS: We evaluated 80 eyes of 59 patients who underwent phacoemulsification with a clear corneal incision. All incisions were evaluated 1wk, 1, and 3mo postoperatively using AS-OCT and analyzed regarding angle, length of the incision, maximal corneal thickness at the incision, and if present, corneal endothelial gap length and incision gap area. The patients were divided into two groups according to whether or not an endothelial gap was present at 1wk postoperatively (endothelial gap, group 1; no endothelial gap, group 2). We analyzed the difference in patient and surgical factors between the two groups, and compared the surgical outcome and the refractive outcome.
RESULTS: An endothelial gap was observed in 56 (70.0%) of 80 eyes at 1wk postoperatively but not at 3mo postoperatively. The mean patient age was significantly higher in group 1 than in group 2. The longer the length of the corneal incision and the steeper the incision angle, the greater the length and area of the endothelial gap. In group 1, the mean change in mean keratometry of the anterior cornea was significantly greater than in group 2, and the spherical equivalent (SE) and mean numerical error indicated significant myopic changes at 1wk postoperatively.
CONCLUSION: The risk of an endothelial gap increases with patient age and a long corneal incision and steep incision angle. The presence of an endothelial gap after surgery may affect the early postoperative corneal curvature and SE.
KEYWORDS: corneal incision structure; phacoemulsification; corneal curvature; corneal endothelial gap; anterior segment optical coherence tomography
DOI:10.18240/ijo.2019.07.14
Citation: Jin KH, Kim TG. Relationship between early structural changes at cornea incision sites and surgical outcomes after phacoemulsification. Int J Ophthalmol 2019;12(7):1139-1145
INTRODUCTION
Modern techniques in cataract surgery aim to achieve better uncorrected visual acuity (UCVA) and rapid postsurgical recovery. The clear corneal incision (CCI) technique, first introduced by Fine[1] in 1992, is commonly used in phacoemulsification cataract surgery. Its advantages include shorter procedural times, more rapid postoperative wound recovery, minimizing induction of astigmatism, and less bleeding[2]. However, there have been several reports suggesting that CCIs are associated with an increased risk of postoperative infection because of postoperative wound leak and dehiscence[3, 4, 5, 6, 7, 8, 9]. Recently, anterior segment optical coherence tomography (AS-OCT), which allows visualization of the ultrastructure of the cornea in real time, has enabled qualitative analysis of structural changes in the cornea. It is important to identify the morphologic changes associated with CCIs and preoperative factors conducive to rapid visual recovery and to decrease the risk of intraocular infection caused by wound leak. Several studies have used AS-OCT to assess the short-term and long-term architectural changes at CCI sites after cataract surgery[10, 11, 12]. However, to our knowledge, there have been no studies comparing the structural changes after CCI with the surgical outcomes after cataract surgery.
The purpose of this study was to investigate the early structural changes associated with CCI using AS-OCT, to identify surgical factors that might contribute to architectural changes at the wound site, and to assess whether these postoperative changes affect the early visual outcome and refractive change after cataract surgery.
SUBJECTS AND METHODS
Ethical Approval All procedures were compliant and consistent with the tenets of the Declaration of Helsinki. Informed consent was obtained from all individual participants included in this retrospective study.
The study
included 80 eyes of 59 patients who underwent cataract surgery by
phacoemulsification through a
Surgical
Technique All eyes underwent
phacoemulsification and implantation of an intraocular lens through a
sutureless CCI. All procedures were performed under topical anesthesia by the
same surgeon (Jin KH) and comprised creation of a self-sealing
Patient Examinations Examinations were performed preoperatively and at 1wk and 1mo postoperatively. Before and after surgery, all patients underwent the following examinations: uncorrected and corrected visual acuity testing, automated refraction using the Nidek ARK-1s (Nidek Technologies, Gamagori, Japan), measurement of intraocular pressure, slit-lamp examination, and fundus evaluation. Corneal curvature and astigmatism were analyzed using a Scheimpflug rotating camera (Pentacam, Oculus, Wetzlar, Germany). AS-OCT (Cirrus OCT, Carl Zeiss Meditec, Jena, Germany) was used to visualize the structure of the wound. The mean numerical error (MNE) was defined as the difference between actual postoperative spherical equivalent (SE) and predicted postoperative SE. MNE is widely used to compare how much refraction measured after refractive surgery, including cataract surgery, is matched to the target refraction. A negative predictive error indicates more myopic results i.e. tendency towards over correction, and vice-versa.
AS-OCT Assessment The CCIs were visualized on radial AS-OCT scans at 1wk, 1 and 3mo postoperatively to evaluate the length and area of the endothelial gap, incision angle and the maximal corneal thickness at the incision site. The incision angle was measured between the corneal surface tangent at the external wound opening and the line connecting the internal and external wound openings. The length and area of the endothelial gap were calculated using ImageJ software (National Institutes of Health, Bethesda, MD, USA; Figure 1). The patients were divided into two groups according to whether or not an endothelial gap was present at 1wk postoperatively. Patients with an endothelial gap were classified as group 1 and those without an endothelial gap were classified as group 2.
Figure 1 Representative AS-OCT image of corneal incision site A, B: AS-OCT images show a clear corneal incision site postoperatively. C, D: The incision site parameters are defined as follows: 1) maximal corneal thickness at the incision site (red line); 2, 3) endothelial gap length and area; 4) incision angle; and 5) incision length (yellow line). The incision angle was measured as the angle between the tangent of the corneal surface at the incision and the line connecting the internal and external wound openings.
Statistical Analysis The statistical analysis was performed using the independent samples t-test in SPSS version 18.0 software (SPSS Inc., Chicago, USA). The Pearson correlation was used to analyze the relationship between preoperative factors and the length and area of the endothelial gap. A P-value less than 0.05 was considered to be statistically significant.
RESULTS
The study included 80 eyes in 59 patients of mean age 68.8±12.9 (range 52-82)y. No intraoperative complications were encountered and there were no reports of hypotony, shallow chamber, or endophthalmitis during the 3mo of follow-up.
Structural Analysis of Clear Corneal Incision Site Using AS-OCT An endothelial gap was observed in 56 (70.0%) of 80 eyes at 1wk, 3 eyes (3.8%) at 1mo, and 0 eyes at 3mo postoperatively (Table 1). The average length and area of the endothelial gap at 1wk were 148.54±73.55 µm and 9684.86± 11 932.89 µm2, respectively. These values decreased to 6.58±33.52 µm and 238.12±1228.37 µm2, respectively, at 1mo after surgery. No endothelial gap was observed at 3mo after surgery. The mean patient age was significantly higher in group 1 than in group 2, but there was no significant difference in sex ratio, endothelial cell count, axial length, mean incision length or angle, or preoperative cataract grade between the two groups (Table 2).
Table 1 Frequency of endothelial gaps and their length and area after surgery
Variables |
Postop. 1wk |
Postop. 1mo |
Postop. 3mo |
Incidence of endothelial gap, eyes (%) |
56 (70.0) |
3 (3.8) |
0 |
Endothelial gap length (µm) |
148.54±73.55 |
6.58±33.52 |
0 |
Endothelial gap area (µm2) |
9684.86±11932.89 |
238.12±1228.37 |
0 |
Table 2 Demographic and preoperative data for the two groups
Variables |
All patients |
Group 1 |
Group 2 |
P |
No. of eyes (%) |
80 (100) |
56 (70.0) |
24 (30.0) |
|
Sex (M:F) |
34:46 |
23:33 |
11:13 |
0.794 |
Age (y) |
68.8±12.9 |
71.8±11.7 |
61.9±13.4 |
0.002 |
IOP (mm Hg) |
13.71±2.41 |
13.72±2.48 |
13.68±2.28 |
0.951 |
Endothelial cell count (cells/mm2) |
2678.82±429.87 |
2719.30±276.09 |
2586.80±658.9 |
0.231 |
Axial length (mm) |
23.75±1.45 |
23.85±1.56 |
23.52±1.16 |
0.388 |
Mean incision length (µm) |
1678.61±320.29 |
1770.78±324.27 |
1587.52±298.28 |
0.400 |
Mean incision angle (°) |
34.00±6.65 |
33.74±6.84 |
34.62±6.32 |
0.852 |
Cataract grade |
3.34 |
3.36 |
3.28 |
0.615 |
Values are presented as mean±SD unless otherwise indicated; P value by independent t-test.
The maximum corneal thickness was significantly greater in group 1 (1024.19±105.63 µm) than in group 2 (924.50±105.32 µm) at 1wk postoperatively (P=0.001; Figure 2). However, there was no difference in maximum corneal thickness between the two groups at 1 and 3mo postoperatively.
Figure 2 Change in maximum corneal thickness after phacoemulsification The bar graph shows a significant increase in maximum corneal thickness in group 1 at 1wk after surgery when compared with group 2. aP<0.05, independent t-test.
Correlation of Length and Area of the Endothelial Gap with Incision Length and Angle The length and area of the endothelial gap correlated significantly with corneal incision length and angle at 1wk postoperatively (Figure 3). The longer the corneal incision length and the steeper the incision angle, the greater the length and area of the endothelial gap. This finding was statistically significant.
Figure
Changes in
Corneal Curvature At 1wk postoperatively, there was a
statistically significant increase in the mean keratometric value (Kmean)
of the anterior cornea with respect to preoperative corneal astigmatism in
group 1 (Figure
Figure 4 Mean corneal curvature (Kmean)
and mean changes in Kmean in groups 1 and
There was a significant difference in the mean change in anterior corneal Kmean between groups 1 and 2 at 1wk postoperatively (Figure 4B) but not at 1 and 3mo postoperatively. The mean Kmean changes in the posterior cornea were not significantly different between the two groups at any time during follow-up (Figure 4D).
Changes in
Corneal Astigmatism In group 1, there was a statistically
significant increase in anterior corneal astigmatism with respect to
preoperative corneal astigmatism at 1wk and 1mo but not at 3mo postoperatively
(Figure
Figure 5 Mean corneal astigmatism and
mean changes in corneal astigmatism in groups 1 and
The mean changes in anterior corneal astigmatism increased in groups 1 and 2 at 1wk and 1mo postoperatively, with no statistically significant difference between the groups (Figure 5B). The mean change in posterior corneal astigmatism was greater in group 1 at 1wk postoperatively, but there was no statistically significant difference in the mean changes in astigmatism between the two groups (Figure 5D). At 3mo postoperatively, anterior and posterior corneal astigmatism decreased to preoperative values in both groups.
Postoperative Visual Outcomes and Refractive Error Preoperatively, there was no significant difference in mean UCVA between groups 1 and 2 (Table 3). Mean UCVA and BCVA improved significantly after cataract surgery in both groups, with no significant difference between the values for these two parameters at any follow-up assessment. However, there was a significant difference in SE between the two groups at 1wk after cataract surgery. There was a significantly greater myopic change in group 1 than in group 2 at 1wk postoperatively but not at 1 or 3mo postoperatively.
Table 3 Preoperative and postoperative uncorrected and corrected visual acuity and SE in the two groups
Variables |
All patients |
Endothelial gap at 1wk |
P |
|
Group 1 |
Group 2 |
|||
Preop. |
||||
UCVA (logMAR) |
0.59±0.48 |
0.61±0.48 |
0.54±0.49 |
0.599 |
CVA (logMAR) |
0.45±0.42 |
0.48±0.43 |
0.38±0.38 |
0.338 |
SE (D) |
-1.49±3.83 |
-1.53±4.31 |
-1.41±2.40 |
0.913 |
Postop. 1wk |
||||
UCVA (logMAR) |
0.24±0.22 |
0.24±0.23 |
0.23±0.18 |
0.755 |
BCVA (logMAR) |
0.10±0.13 |
0.10±0.13 |
0.12±0.14 |
0.560 |
SE (D) |
-0.96±1.10 |
-1.15±1.14 |
-0.50±0.89 |
0.026 |
Postop. 1mo |
||||
UCVA (logMAR) |
0.18±0.14 |
0.19±0.14 |
0.16±0.13 |
0.427 |
BCVA (logMAR) |
0.06±0.08 |
0.05±0.07 |
0.07±0.10 |
0.484 |
SE (D) |
-0.85±0.99 |
-0.95±1.04 |
-0.58±0.80 |
0.158 |
Postop. 3mo |
||||
UCVA (logMAR) |
0.16±0.15 |
0.16±0.17 |
0.15±0.12 |
0.693 |
BCVA (logMAR) |
0.04±0.08 |
0.04±0.08 |
0.04±0.08 |
0.991 |
SE (D) |
-0.83±1.01 |
-0.82±1.06 |
-0.83±0.96 |
0.980 |
UCVA: Uncorrected visual acuity; BCVA: Best corrected visual acuity; SE: Spherical equivalent; Values are presented as mean±SD unless otherwise indicated. P value by independent t-test.
The MNE for the entire study group showed a mean myopic shift of -0.21±0.83 D at 1wk, -0.10±0.70 D at 1mo, and -0.08±0.75 D at 3mo postoperatively; all these values were not significantly different from the target diopter (P=0.131, P=0.242, and P=0.392, respectively). In group 1, MNE showed a myopic shift of -0.32±0.80 D at 1wk postoperatively that was significantly different from the target diopter (P=0.006). The MNE was -0.13±0.67 D at 1mo and 0.15±0.73 D at 3mo postoperatively; there was no significant difference between MNE and the target diopter at these assessments (P=0.181 and P=0.147, respectively). In group 2, the MNE was 0.05±0.83 at 1wk, -0.03±0.79 D at 1mo, and 0.11±0.78 D at 3mo postoperatively; these values were not significantly different from the preoperative target diopter (P=0.766, P=0.888, and P=0.543, respectively).
DISCUSSION
The self-sealing CCI technique is probably the most popular and widely accepted approach to performing cataract surgery. However, there is still a concern about the increased risk of endophthalmitis with this procedure when compared with scleral tunnel incision. Self-sealing of the wound provides a barrier that could lowering the risk of endophthalmitis. The recent introduction of AS-OCT has made it possible to record high-resolution images rapidly and easily in a non-contact and non-invasive manner. Understanding the morphologic changes at the incision site would help to prevent postoperative complications and improve wound management. AS-OCT has been used to assess the shape of the cataract incision, and there have been reports of problems with the incision, including detachment of Descemet’s membrane, increased corneal thickness, and a posterior corneal wound gap[12, 13, 14, 15, 16, 17]. In this study, we evaluated the structural changes at the CCI sites and the surgical outcomes after cataract surgery using AS-OCT.
All images in this study revealed swelling of the corneal stroma at the incision site 1wk after surgery. Fine et al[11] assumed that stromal hydration during surgery would cause wound swelling. However, Xia et al[18] maintained that the corneal swelling was caused mainly by tissue damage at the wound site during surgery, including the mechanical trauma induced by insertion of surgical instruments and direct damage by phacoemulsification power or transformed heat because wound swelling occurred even without stromal hydration. We believe that the corneal swelling is caused by both stromal hydration and mechanical damage.
The endothelial gap is the internal wound dehiscence of the corneal incision, which may allow for the inoculation of organisms into the aqueous humor, resulting in endophthalmitis and potential visual loss. Theoretically, surgically induced posterior astigmatism may occur due to internal wound dehiscence, which may affect visual outcomes after toric IOL implantation. In this study, an endothelial gap was seen in 56 eyes (70.0%) at 1wk postoperatively. This finding is similar to that of a previous study[12]. Further, we found that endothelial gaps were more common in older patients. Although the preoperative endothelial cell counts were not significantly different between groups 1 and 2, the observed difference in age between patients who did and did not have an endothelial gap may reflect an association between decreased endothelial cell function and aging. A longer incision length and a steeper incision angle correlated significantly with the length and area of the endothelial gap (Figure 3). The cause of the endothelial gap after cataract surgery is not clear yet. Fine et al[11]. found that wounds which did not receive stromal hydration were likely to develop internal gaping. Some authors suggested possible explanations for endothelial wound gaping, such as phacoemulsification method, instrument sizing or excessive ultrasound power, corneal stromal edema, and endothelial damage[19, 20, 21]. Other authors added intraocular pressure fluctuation as a factor[22, 23]. In our study, a longer incision length and a steeper incision angle correlated significantly with the length and area of the endothelial gap (Figure 3). Therefore, it is important to keep in mind, the possibility of an endothelial gap in elderly patients when the incision angle is small or the incision length is long. The maximum corneal thickness was significantly greater in group 1 than in group 2 at 1wk postoperatively. This finding may be attributable to the stromal edema caused by detachment of Descemet’s membrane and the endothelial gap. However, there was no difference maximum corneal thickness between the two groups thereafter, which could be related to the decreased likelihood of an endothelial gap at 1 and 3mo after surgery.
We found
that the Kmean of the anterior cornea was significantly increased in
group 1 but not in group 2 at 1wk postoperatively; there was also a significant
difference in the mean changes in Kmean in the anterior cornea
between the two groups at this time. A few studies have focused on the
structure of the wound at the posterior cornea and the change in corneal curvature
after cataract surgery[20, 24].
van Rij and Waring[20] reported that the
curvature flattened in the vertical and horizontal meridians in corneas that
had undergone experimental posterior wedge resection and suture. In the case of
wound retraction in the posterior cornea caused by an endothelial gap, which
cause the opposite effect of wedge resection and suture in previous study. This
could explain our present finding of a steepened Kmean in eyes with
an endothelial gap. In contrast, the Kmean decreased in patients
without an endothelial gap, although not significantly. We speculate that the
corneal swelling occurs mainly in the posterior stroma because the anterior
stroma is composed of tight interwoven anterior lamellae[24].
The decrease in anterior Kmean in group
In this
study, anterior and posterior corneal astigmatism increased significantly in
group
The visual outcome was favorable in both our study groups in terms of the final UCVA and BCVA measurements. It is possible that the corneal wound retraction was not sufficient to cause a statistically significant difference in UCVA or BCVA. However, the SE at 1wk showed more myopic change in group 1 than in group 2 and the difference was statistically significant. The results of the MNE analysis in relation to the target diopter showed a significant myopic shift in group 1 at 1wk postoperatively, which was presumably related to the increase in Kmean. There was no statistically significant difference in SE between the 2 groups at 1 and 3mo postoperatively. Therefore, an endothelial gap in the early postoperative period may be associated with an increase in anterior corneal curvature, but this relationship may not persist in the long term.
The main limitation of the study was its relatively small sample size, such that our findings cannot be generalized to all patients who underwent phacoemulsification. In addition, even though all the operations were performed by the same surgeon, cases may still exhibit differences in the corneal thickness, intraocular pressure, shape of wound, process of wound healing, and tissue response against trauma. Despite these limitations, the results that early structural changes after cataract surgery can affect corneal curvature and refraction are meaningful. Another limitation is that subgroup analysis of with-the-rule and against-the-rule astigmatism was not performed. In future large-scale studies, the study samples should be divided into subgroups according to with-the-rule and against-the-rule astigmatism.
In conclusion, in this study, an endothelial gap was more common in older patients and the length and area of the endothelial gap were correlated with increasing incision length and a steep incision angle. When an endothelial gap occurs early in the postoperative period, the anterior corneal curvature may increase and cause a change in SE. Therefore, if the incision length is long or the angle becomes steep in older patients, the appearance of an endothelial gap may lead to changes in initial postoperative refraction and this effect should be considered during surgery.
ACKNOWLEDGEMENTS
Conflicts of Interest: Jin KH, None; Kim TG, None.
REFERENCES