CORNEAL THICKNESS AND ENDOTHELIAL DAMAGE AFTER INTRACAPSULAR CATARACT EXTRACTION
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A C T A O P H T H A L M O L O G I C A V O L . 5 8 1 9 8 0
Department o f Ophthalmology (Head: N. Ehlers), h h u s Kommunehospital, University o f Aarhus, Arhus, Denmark
CORNEAL THICKNESS AND ENDOTHELIAL DAMAGE AFTER INTRACAPSULAR CATARACT EXTRACTION
In a prospective study corneal thickness and specular microscopic findings of corneal endothelium are reported in 37 patients undergoing intracapsular cataract extraction. Central endothelial cell loss was estimated six months after the operation and was found to correlate significantly to the immediate post-operative increase in central corneal thickness. A subgroup of patients showing slight endothelial dystrophy prior to the operation showed a signifi- cantly higher increase in corneal thickness fourth day after the operation. Six months after the operation a significant residual increase in corneal thickness was found for this group, while the rest of the patients had returned to near pre-operative levels. No correlation was found between cell loss and residual corneal thickness increase at this time. Six months after the operation a vertical difference in cell density was found. This difference could be correlated to the age of the patient, presumably indicating a less complete redistribution of the cell population in older patients.
Key words: cataract extraction - cell loss - corneal thickness - endothelium - specular microscopy.
The damage exerted on the corneal endothelium during cataract extraction has been the subject of several specular microscopic studies (Bourne & Kaufman 1976; Cheng et al. 1977; Forstot et al. 1977; Hirst et al. 1977; Rao et al. 1978; Drews & Waltman 1978; Rao et al. 1979; Galin et al. 1979; Abbott & Forster 1979). A working hypothesis has been that the amount of the endothelial trauma, i.e. the cell loss is somehow related to the function of the endothelium and therefore to corneal hydration. The information yielded by the endothelial reflex on this respect is, however, still unsettled.
Received December 15th. 1979.
Corneal thickne.n and endothelial damage
The post-operative endothelial cell density varies with time and location on the cornea. Evidence is now accumulating that the gradual decrease in cell density seen months after the operation (Hirst et al. 1977; Rao et al. 1978; Galin et al. 1979) is caused by a redistribution of the cell population (Rao et a1 1978; Sugar 1979), tending with time to even out imbalances in cell density created during surgery. This implies that a lowered central cell density is an inaccurate index of total cell loss in the early phases after the operation.
This study reports the immediate effect of endothelial damage on corneal thickness following intracapsular cataract extraction. In order to improve estima- tion of the cell loss, post-operative cell densities were not estimated until six months after surgery.
Subjects and Methods
A total of 45 subjects with senile cataract entered the study. This group comprised all patients consecutively admitted to the eye department during a two months period where indication for intracapsular cataract extraction was found. Patients with co-existing eye diseases such as glaucoma, uveitis or corneal diseases were excluded. Generally patients were not advocated surgery if endothelial dystrophy was revealed in routine slit lamp examination. Not seldomly, however, the specular microscopic examination revealed a guttate endothelium in the endothelial reflex which was not readily detected in ordinary slit lamp examination. In such cases surgery was not abandoned and the patients were included in the study.
T h e operational procedure was intracapsular cryoextraction with corneal incision and zonulysis. For irrigation a Ringer solution was used. The wound was closed with running 10-0 nylon suture. The operations were performed by a number of surgeons. No regard was paid to the particular surgeons experience. Occurrence of vitreous loss or other pre-operative complications did not exclude the patient from the series.
Prior to surgery the central endothelium of all patients were photographed with a non-contact specular microscope (Olsen 1979). The central corneal thickness was measured the day before and on each of four days after surgery using a modified Haag-Streit pachometer (Ehlers & Sperling 1977). All measurements were single determinations taken as the closest 5 I. position on the scale reading of the pachometer, and were done by the author shortly after noon. The standard error of single determinations with the present method has repetitively been found to be 5-6 p (about l%), estimated from a large (>20) number of measurements of several subjects.
Six months after the operation the patients were asked to attend the clinic for reexamina- tion. The central endothelium was photographed as described above and in addition an area 2-3 mm superiorly to the center of the cornea was photographed by directing the gaze of contralateral eye. Again corneal thickness was measured. Intraocular pressure was measured with an applanation tonometer attached to the slit lamp. Seven patients did not show up for the reexamination. One patient was excluded because of post-operative glaucoma. Age range of the remaining patients, 16 men and 21 women, was 57-87 years with a mean of 73.6 years. These 37 patients are reported on in the following. Unless specified otherwise statistical analyses were based on distributional methods. For comparison of means Students t-test was employed.
Pre-operative and post-operative central cell density of operated eye was (mean f SD) : 254 1 (f 423) and 1894 (f 50 1) cells/mm*, respectively, with a mean cell loss of 25.1 (k 16.4) %. Pre-operative central corneal thickness of operated eye was 0.530 (k 0.03 1) mm. No correlation was found to pre-operative cell density (r = 0.16, P > 0.3). The immediate increase in central corneal thickness was 0.085 (+ 0.066), 0.073 (f 0.050), 0.059 (k 0.027) and 0.054 (k 0.028) mm the first, second, third and fourth day after the operation, respectively. For each day this increase was found to correlate significantly to the central cell loss (r = 0.73, 0.59, 0.56 and 0.58, P < 0.00 1, for day one through day four, respectively). The strongest correlation was thus found on the first post-operative day (Fig. 1). Dotted line in Fig. 1 indicates regression line y on x calculated using the method of least squares for thickness increases below 250 p. Intersection on ordinate is not significantly different from the origin.
Six of the patients turned out to have guttae in the endothelium as revealed on the pre-operative photographs of the central endothelium. These changes were
Central cell loss (%I 7c
. . .. . . . . =
' . . . ., ' . . .. . . '
JO 100 150 200 2 5 0 300 350 400
A CCT (Am) first day after operation Fzg. 1.
Correlation between first day post-operative increase in central corneal thickness (CCT) and central endothelial cell loss estimated six months after cataract extraction. Dotted line
indicates regression line y on x. (r = 0.73, P < 0.001).
Corneal thickness and endothelial damage
0 I I
A CCT I y m l
g u l l e l e endof hel ium
1 2 3 4 days 180
Fig. 2. Mean post-operative increase in central corneal thickness (CCT) in 31 patients with normal endothelium and 6 patients with minor dystrophic changes in the endothelium. Asterisks indicate significant (P < 0.05, by Student's t-test) difference among the groups on day four and persistent elevated thickness six months after surgery for the group with guttate
endothelium. Vertical bars indicate standard errors of the mean.
bilateral. Mean pre-operative corneal thickness of this group was 0.540 (+ 0.017) mm, not significantly different from the rest of the patients. The post-operative increase in corneal thickness for this group was larger than in the patients with normal endothelial reflex and became significantly different fourth day after the operation (Fig. 2). The mean cell loss of 29.7 (+ 20.1) 5% for this group was however not significantly different from the rest of the patients.
For the total group neither pre-operative cell density visible pleomorphology of the cells, pre-operative corneal thickness, age nor sex was significantly related to the thickness increase or central cell loss.
Six months after the operation central corneal thickness was almost normalized in the normal group. Mean residual thickness increase was 0.006 (+ 0.018) mm, not significantly different from zero. In the group of pre-operative indothelial guttae the residual thickness increase was 0.018 (+ 0.020) mm, which is close to, but significantly (P < 0.05) different from zero. In these patients the endothelial changes had worsened in all cases, that is, the defects in the endothelial reflex were larger and more numerous than before the operation (Fig. 3). No guttai-like changes were found in those eyes with previous normal endothelial reflex (Fig. 4).
No correlation was found between cell loss and residual corneal thickness at this time in the entire group (r = 0.22, P > 0.1). All corneas were clear. Corneal thickness of unoperated eye showed a mean change of -0.001 (+ 0.012) and -0.003 (k 0.012) mm in the normal and guttae-group, respectively.
The superior counts found six months after the operation were as a group lower that the central counts. Mean decrease from central to superior counts was 18.8