Results of corneal pachymetry after small-incision hydrogel lens implantation and scleral-step incision poly(methyl methacrylate) lens implantation following phacoemulsification

Results of corneal pachymetry after small-incision hydrogellens implantation and scleral-step incision poly(methyl methacrylate) lens implantation following phacoemulsi6cation M. Amon , M.D., R. Menapace, M.D.,

w.

Scheidel, M.D.

ABSTRACT In a prospective study we used the change in central and peripheral (12 o'c1ock position) corneal thickness after two cataract surgery techniques as a parameter of tissue trauma. We looked at whether our findings indicated a difference in corneal thickness in the two groups and thus, as postulated in the literature, in the prospective endothelial cellioss. In 32 eyes (Group A) we performed small incision surgery (3.5 mm to 4.0 mm scleral-step incision) with hydrogel intraocular lenses implanted in the bag. In 30 eyes (Group B) we performed a 7.0 mm scleral-step incision with in-the-bag implantation of conventional poly(methyl methacrylate) intraocular lenses. Increases in corneal thickness (centrally and peripherally) were correlated after different postoperative periods. After 48 hours Group B showed a slightly higher increase in corneal thickness than Group A. Similar findings were observed at five days. In Group B the peripheral thickness did not show as high an increase as the central thickness after 48 hours. In all other cases the peripheral thickness increased more than the central thickness. After one month all eyes regained their preoperative thickness. We did not find a statistically significant difference in central and peripheral corneal thickness between the two groups. The results show that neither of the two surgical techniques greatly influenced the increase in corneal thickness and, consequently, the prospective endothelial cellloss.

Key Words: corneal thickness, endothelial ce]] loss, hydro gel intraocular lens, poly(methyl methacrylate) intraocular lens, sderal-step incision

The endothelium maintains corneal transparency by its pump function , actively removing fluid from the stroma.! The efficiency of the pump depends on the number of working units and their functional state. Pump function may be impaired in a variety of ways2; for example, in diseased states,3 if the cells are damaged,4 or if the physiologie milieu is al-

tered. 5 While it is understood that the cornea swells when more fluid leaks into it than is removed from it, it is not entirely dear how functional units are related to cell density, which is not significantly related to corneal thickness in normal eyes .6 -8 During surgical procedures the cells and cell junctions may be damaged, resulting in increased

Presented in part at the Symposium on Cataract , [OL and Refractive Surgery, ws Angeles, March 1990. Reprint requests to Michael Amon, M.D. , 1st University Eye Clinic Vienna , Spitalgasse 2, 1090 Vienna , Austria 466

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ingress of ßuid and reduced removal. 9 The increase and decrease in corneal thickness (dCT) may reßect the damage inßicted at surgery and the number of residual cells capable of dehydrating the stroma. lO Since a correlation between the corneal thickness increase in the immediate postoperative period and the percentage of endothelial cell loss one and six months after cataract surgery is postulated in the literature, 10 we examined the changes in central (dCTc) and peripheral (dCTp, 12-0'clock position) corneal thickness after two types of cataract surgery as a parameter of tissue trauma with resulting endothelial cellioss. Presuming that different scleral-step incision lengths and different lens implantation techniques may affect corneal thickness and thus the prospective endothelial cellioss, we looked for a difference in the corneal thickness change after small-incision hydrogellens implantation and 7 mm scleral-step incision poly(methyl methacrylate) lens implantation following phacoemulsification.

MATERIALS AND METHODS Thirty-two eyes had small incision surgery (3.5 mm to 4.0 mm scleral-step incision) and implantation of a folded hydrogel intraocular lens (IOL) in the bag (Group A). Thirty eyes had a 7.0 mm scleralstep incision and in-the-bag implantation of a conventional poly(methyl methacrylate) (PMMA) IOL (Group B). After capsulorhexis all eyes had phacoemulsification. Only eyes with a central endothelial cell density exceeding 2,000 cells/mm 2 were included in the study. Eyes with cornea guttata or polymegatism were excluded. The surgical techniques of the two procedures have been previously described. 1l - 14 In all operations the same physiological irrigating solution was used. In Group A the lens was inserted with a Faulkner folder through the 3.5 mm incision; in Group B the lens was implanted with a conventional forceps. All surgical procedures were done by the same surgeon. Only eyes with uncomplicated senile cataracts were accepted in the study. We randomized the nucleus density by the clinical aspect at the slitlamp and the phacoemulsification time among the eyes was comparable. Eyes with significant intraoperative trauma responsible for complications were excluded. Postoperative treatment consisted of four dexamethasone drops and four indomethacin drops daily for six weeks. Eyes with increased intraocular pressure postoperatively were excluded. The mean age of the patients in Group A was 73.9 years (73.9±9.2, range 50-80). There were 22 female and ten male patients. In Group B mean age was 73.4 years (73.4 ± 12.0, range 43-89). There were 20 female and ten male patients. The two

groups were almost age, sex, and refractive error matched. Corneal thickness (JLm) was determined preoperatively and postoperatively after 48 hours, five days, ten days, and one month. Measurements were obtained using a Konan wide-field contact specular microscope focusing the corneal epithelium and shifting backward until the endothelium was in focus. All measurements were obtained by the same trained observer measuring corneal thickness twice and taking the mean value. Central corneal thickness was determined first and then peripheral corneal thickness was measured at the 12-0'clock position, approximately 1 mm from the limbus. For peripheral observations the patient had to look down slightly to obtain a perpendicular position for the conus. Eyes with uncertain pachymetry results because of the impossibility of focusing the endothelium exactly were excluded (two eyes in each group). Corneal thickness increase was taken to be the postoperative value minus the preoperative value of the operated-on eye. Corneal thickness increase at various postoperative periods in the two groups were correlated. For statistical analysis the Wilcoxon test was used to compare dCT in the two groups and the t-test was used to compare dCTc and dCTp in the same group; P< .05 was determined to be significant.

Table 1. Mean corneal thickness increase (~CT ± SD) in Groups A and Band difference in corneal thickness increase (~CTPH) between the groups. Group A SD

~CT ±

Interval

Group B SD

~CT ±

Difference ~CTPH

Preoperative (CT) c

542.2±46.1

535.4±37.3

P

649.4±56.0

640.4±40.5

127.1 ± 57.6

150.0± 76.1

22.9

143.2±77.3

146.3±75.5

3.1

c

86.7±51.7

96.0±50.8

9.3

P

91.1±48.3

128.9±98.9

37.8

c

23.9±38.5

29.4±39.6

5.5

P

31.7±55.5

36.9±52.6

5.2

2 days pos top c

P 5 days

10 days

30 days -3.6±36.1 -14.6±29.3

c p

-15.7±45.0

20.0±32.7

CT = corneal thickness; c = central; p = peripheral

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Table 2. (~iCaTerence between CTp and CTc in each group (CTpcH, CTpcP) and difference in increase in CTp to CTc in each group ... pcH, ~CTpcP). Diff. CTpcH (CTpH-CTcH)

Diff. CTpcP (CTpP-CTcP)

Preoperative

107.2

105.0

2 days postop

121.8

5 days postop 10 days pos top

Interval

Diff. ~CTpcH (~CTpH -~CTcH)

Diff. ~CTpcP (~CTpP-~CTcP)

105.2

16.1

-3.7

105.6

133.9

4.4

32.9

112.7

115.0

7.8

7.5

RESULTS Sixty-two eyes were included in this study. Mean corneal thickness preoperatively is shown in Table 1. Mean preoperative central and peripheral thickness (CTc, CTp) was not significantly different between Group A and Group B. Preoperative difference between central and peripheral corneal thickness was almost the same in both groups (Table 2). Figure 1 shows the changes in central and peripheral corneal thickness in both groups during the follow-up period. The graph shows that the corneal thickness ßuctuation in both groups was almost the same. The minimum and maximum corneal thickness values were also similar. Mean values measured preoperatively and postoperatively at 48 hours, five days, ten days, and 30 days and their differences are recorded in Table 1. After 30 days all eyes regained their preoperative thickness. . Incre~se in central corneal thickness was slightly hIgh er In Group B; the highest difference was 22.9 /-Lm two days after surgery (Table 1). Increase in

peripheral corneal thickness was also higher in Group B; it showed the highest difference, 37.8 /-Lm, five days after surgery. In all measurements peripheral corneal thickness showed a higher increase than the central cornea with one exception. Two days postoperatively cen~ tral thickness was higher than peripheral thickness in Group B (Table 2). It seems remarkable that ACTp was very definite two days postoperatively in Group A a.nd five days postoperatively in Group B (Table 2). ThlS occurred because ACTp was not very high in Group B five days postoperatively. No evident differences in the clinical aspect ofthe corneas were found at the slitlamp examination. Statistical analysis showed no significant difference between the corneal thickness in the two groups. DISCUSSION We have not found any significant correlation between corneal thickness and endothelial cell

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count on "unoperated-on" eyes in the literature. 6-8 Considering that changes in endothelial cell counts, which always happen after cataract surgery,15.16 do affect corneal deturgescence and therefore corneal thickness, a relationship between the change in corneal thickness and the endothelial cellloss seems reasonable.l° As postulated in the literature there is a correlation between corneal thickness increase in the immediate postoperative period and the percentage of endothelial cell loss one and six months after cataract surgery. Corneal thickness has become an early prognostic parameter of prospective endothelial cellloss. In our study we used the change in central and peripheral (12-0' clock position) corneal thickness after two cataract surgery techniques as a parameter of tissue trauma and resulting endothelial cellloss. We looked at whether there was a significant difference between corneal thickness in the two groups and thus in the prospective endothelial cell loss. Since Rao and coauthors 17 report a significant difference in the increase of corneal thickness between "polymegathous" and "homomegathous" corneas, we only accepted "homomegathous" corneas with at least 2,000 cells/mm 2 for our study. To compare the two groups a standard phacoemulsification technique l l - 14 was used by the same surgeon to achieve objective results. Irrigation during surgery was provided by the same solution in both groups so that differences in corneal thickness increase from different intraocular milieus were avoided. 5 Only the length of the scleral-step incision and the lens implantation technique were different in the two groups. Despite the lack of a significant difference in the corneal thickness changes between Group A and Group B, some aspects of our results are of interest. Corneal thickness returns to almost normal values within the first 30 days lO.18 so only measurements in the early postoperative period (within the first ten days) are important and make early prognostic results possible. The early corneal thickness values reßect the short-term changes caused by tissue trauma after surgery.18 The probability of high cell loss increases with corneal thickness. 10 Cheng and coauthors lO showed that a corneal thickness of more than 75 /.Lm two days and of 100 /.Lm five days postoperatively provide useful clinical indicators for high cell loss. In our results mean values for .lCT were much lower in both groups. There are no reports in the literature about differences between central and peripheral corneal thickness and .lCTc and .lCTp after cataract surgery. Our hypothesis was that the signs of tissue trauma would be higher at the peripheral (12-0'clock position) cornea where instruments are inserted and

the limbal ciliary plexus is disturbed. This was the reason for obtaining measurements ofthe peripheral cornea. In all measurements peripheral corneal thickness was higher than central corneal thickness. This has been weIl known about "unoperated-on" eyes. 19 With one exception .lCTp was higher than .lCTc; two days postoperatively central corneal thickness was higher in Group B. In this study it turned out that increases in central and peripheral thickness were slightly higher in Group B. In our opinion this was inßuenced by the length of the incision with disruption of the limbal ciliary plexus and resulting trophic problems. The fact that two days after surgery Group A had almost the same .lCTp as Group B, which was unusual in our results, might have been caused by stretching the scleral tunnel with resulting tissue stress during the implantation over the 3.5 mm to 4.0 mm pocket incision with the Faulkner folder in Group A. Since there was no significant difference in statistical analysis and clinical aspect and all corneas regained their preoperative thickness after 30 days, we concluded that the choice of one of these two techniques does not greatly inßuence the increase in corneal thickness and therefore the prospective endothelial ceIlloss. The corneal thickness changes are not primarily caused by the 'scleral-step incision length and the lens implantation technique. REFERENCES 1. Maurice DM. The cornea and sclera. In: Davson H , ed. The Eye. Orlando, fL, Academic Press Inc, 1984; vol B, 75-89 2. Waring GO In, Bourne WM, Edelhauser HF, Kenyon KR. The corneal endothelium; normal and pathologie structure and function . Ophthalmology 1982; 89:531-590 3. Olsen T. Transient changes in specular appearance of the corneal endothelium and in corneal thickness during anterior uveitis. Acta Ophthalmol1981; 59:100-109 4. Green K, Livingston V, Bowman K, Hull DS. Chlorhexidine effects on corneal epithelium and endothelium. Arch Ophthalmol1980; 98:1273-1278 5. Glasser DB, Matsuda M, Ellis JG, Ede!hauser HF. Effects of intraocular irrigating solutions on the corneal endothelium after in vivo anterior chamber irrigation. Am J Ophthalmol 1985; 99:321-328 6. Mishima S. Clinical investigations on the corneal endothelium (38th Edward Jackson Memorial Lecture). Am J Ophthalmol1982; 93:1-29 7. Kaufman HE, Capella JA, Robbins JE. The human corneal endothelium. Am J Ophthalmol1966; 61:835-841 8. Amon M, Grasl M, Scheide! W, et al. Bestimmung der präoperativen zentralen Endothelzelldichte von Spenderhornhäuten: Kritischer Vergleich zweier Methoden . Spektrum Augenheilkd 1988; 216:245-248 9. Khodadoust AA, Green K. Physiological function of regenerating endothelium. Invest Ophthalmol 1976; 15:96-101 10. Cheng H, Bates AK , Wood L, McPherson K. Positive correlation of corneal thickness and endothelial cell loss; serial measurements after cataract surgery. Arch Ophthalmol 1988; 106:920-922

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