Corneal endothelium of 121 normal corneas was studied with the clinical specular microscope, and the relationship between cell density, cell morphology, and age was examined. Our observations indicate a decrease in cell density with age in homomegethous endothelium but no such correlation in a polymegethous endothelium

Aquavella, J. V.

Blatt, H. L.

Rao, G. N.

English

Publications of the IAS Fellows

Reports
Endothelial cell density in relation to mor-
phology. HERBERT L. BLATT, GULLAPALLI N.
RAO, AND JAMES V. AQUAVELLA.
Corneal endothelium of 121 normal corneas was studied
with the clinical specular microscope, and the relation-
ship between cell density, cell morphology, and age was
examined. Our observations indicate a decrease in cell
density with age in homomegethous endothelium but no
such correlation in a polymegethous endothelium.
A number of investigators have used cell density
as a quantitative description of the corneal en-
dothelium. Different studies on normal corneal
endothelium11 2 have shown a decrease in endo-
thelial cell density and an increase in pleomor-
phism with age.
In earlier reports,3' 4 we described two dis-
tinctly different types of endothelial cell morphol-
ogy, which we designated as "homomegethism"
and "polymegethism."
The categorization of these two types was based
on the degree of density in cell size in the en-
dothelium of a given cornea. A cornea with an
endothelium having cells of obviously different
sizes is considered to have polymegethous en-
dothelium. The largest cell in this endothelium is
several times bigger than the smallest cell. In con-
trast, a homomegethous endothelium demon-
strates cells which are of relatively uniform sizes.
In one of the earlier studies5 designed to exam-
ine the relationships between endothelial cell
morphology and corneal deturgescence, we also
noted an apparent relationship among the three
factors: endothelial cell morphology, cell density,
and age. Although the expected decrease in endo-
thelial cell density with age was seen in homo-
megethism, no correlation between cell density
and age was found in the polymegethous group.
We undertook further investigation of this hy-
pothesis, and the results are presented in the
present communication.
Materials and methods. A total of 121 corneas
were included in this study. These subjects were
selected from either candidates for cataract ex-
traction or volunteers from the hospital staff. None
of the volunteers had a history of any ocular
pathology. In the surgical patients, the unaffected
eye was selected for inclusion in the study.
All subjects were given a complete eye exami-
nation, and any eye showing evidence of anterior
segment pathology was excluded. Pachometry was
obtained on all eyes included in the study group.
The corneal endothelium was then examined
and photographed with a Syber clinical specular
microscope. At least 10 photographs were ob-
tained of the endothelium from the central cornea
in each eye. Eyes showing evidence of cornea gut-
tata were excluded from this study. The endothe-
lial cell densities were determined from at least
five different specular photomicrographs of the
central cornea, and the mean values were ob-
tained for each cornea. The methodology used in
determining the cell density was the same as de-
scribed earlier.2
On the basis of the subjective evaluation of the
endothelial cell morphology which was described
in earlier studies, all the corneas were classified
under two different categories. Of these 121
corneas, 60 were classified as homomegethous
(Fig. 1) and 61 as polymegethous (Fig. 2). In seven
of the volunteers, the endothelium of two corneas
was found to belong to two different morphological
categories.
All these data were subjected to statistical anal-
ysis, the results of which are included in the Re-
sults section.
Results. The mean endothelial cell densities for
each subject were calculated. These values were
then plotted as a function of the subject's age. The
relationship between the cell density and the age
for the 60 subjects in the homomegethous group
were then plotted as shown in Fig. 3. Linear re-
gression equation describing the curve which best
fits these data is shown in the upper right hand
corner of the figure. The standard error of esti-
mate for this equation was ±306. The limit lines
on either side of the curve represent 1 standard
error of the estimate.
The data obtained from the 61 polymegethous
corneas were plotted in a similar fashion, and the
linear regression equation was calculated (Fig. 4).
As shown, the slope of the curve was much less
steep than in the homomegethous groups, and the
standard error of the estimate was larger, 427 vs.
306 in homomegethous corneas.
The correlation coefficients between age and
cell density were determined for each of the two
groups. In the homomegethous group, the rvalue
was —0.615 and is highly significant (p < 0.001). In
the polymegethous group, on the other hand, the
r value was not significant at —0.211 (p < 0.1). As
can be seen in the homomegethous group, the
numerical value of the correlation was highly sig-
nificant. The fact that it has a negative sign indi-
856 0146-0404/79/080856+04$00.40/0 © 1979 Assoc. for Res. in Vis. and Ophthal., Inc.
Volume 18
Number 8 Reports 857
Fig. 1, Specular photomicrograph ofcorneal endothelium demonstrating homomegethism in a
62-year-old white man. Cell density = 2867/mm2.
Fig. 2. Specular photograph of corneal endothelium demonstrating polymegethism in a 64-
year-old white man. Cell density = 2700/mm2.
cates that the correlation was inverse, which
showed a decrease in cell density with increasing
age. According to the sign of the correlation co-
efficient calculated for the polymegethous group,
cell density tended to decrease with age. How-
ever, since the numerical value of the coefficient
was well below the level required for statistical
significance, this tendency was not particularly re-
liable. That is, the probability of finding a low cell
density in a young person having a polymegethous
endothelium is not much different from the prob-
ability of finding high cell density in an older sub-
ject having this type of endothelial cell mor-
phology.
We determined the group mean standard error
for each of the two morphological categories by
averaging the standard errors of each subject's
mean cell density. Since the group mean standard
error included all individuals in the category, age
was not an interacting factor. Sample size was also
not a factor; therefore the magnitude of the stan-
dard error depended on the existence of real vari-
ation in cell density. The results are given in Table
Table I. Mean standard errors of
individual endothelial cell densities
Homomegethism Polymegethism
± 63.2 ± 79.9
(28-107) (26-294)
p < 0.01 by t test
I. The range in size of the individual standard er-
rors and the mean standard error for the entire
group was notably smaller in the homomegethous
groups. The difference between the values in the
two morphological categories was highly signif-
icant, according to the t test.
Discussion. Endothelial cell density forms only
one of the many components in the endothelial
cell morphology. The relationship between cell
density and cell morphology is not clearly under-
stood. Previous studies indicated that cell density
decreases with age, with an increase in the degree
of pleomorphism, '• 2 From our studies3' 4 of nor-
mal corneal endothelium, we observed that there
858 Reports Invest. Ophthalmol. Visual Sci.August 1979
3500
3000
I
ul 2500
Ui
UJ
o
UJ
o
2000
1500
HOMOMEQETHISM
ECD - 3 1 2 4 - ( 1 1 4 3 K AGE)
STD. ERROR » ±306
10 20 30 40 60
AGE (YEARS)
60 70 80 90
Fig. 3. Relationship between cell density and age in homomegethous group. ECD, Endothe-
lial cell density.
3500
3000
SJ 2500
o
2000
1500
POLYMEQETHISM
ECD - 2752 • (5.34 x AGE)
STD. ERROR = ±427
10 20 30 40 60
AGE (YEARS)
60 70 60 90
Fig. 4. Relationship between cell density and age in polymegethous group. ECD, Endothelial
cell density.
Volume 18
Number 8 Reports 859
is a great variation in the endothelial cell mor-
phology in the normal corneas, and we divided the
endothelium into two morphological categories,
homomegethous and polymegethous. Upon fur-
ther analyzing our data, we5 observed that those
corneas with homomegethous endothelium tend
to show a decrease in cell density with age but that
corneas with polymegethism do not essentially fol-
low this rule. From our present study, it can be
clearly seen that cell density certainly decreases
significantly with age when the endothelial cells
are regular in size and arrangement. However, if
the endothelial cells are irregular in size and ar-
rangement, the endothelial cell densities did not
correlate with age. This study also demonstrated
that a polymegethous endothelium shows a sig-
nificantly greater variation in cell density within
the central cornea regardless of age. These findings
give a more quantitative basis to our categorization
of endothelial cell morphology. Relative uniformity
in cell size and arrangement seen in homomege-
thous corneas is a reflection of uniform cell density
throughout the endothelium. The morphological
irregularities seen in polymegethism are associated
with some degree of regional differences in cell
density and cannot be considered a simple effect of
age.
From the Department of Ophthalmology, Park Ridge
Hospital, Rochester, N. Y. Presented in part before the
ARVO meeting in Sarasota, Fla., April-May 1978. Sub-
mitted for publication Feb. 5, 1979. Reprint requests:
James V. Aquavella, M.D., 1160 Chili Avenue, Roches-
ter, N. Y. 14624.
Key words: endothelium, density, morphology, homo-
megethism, polymegethism, age
REFERENCES
1. Laing, R.A., Sandstrom, M.M., Berrospi, A.R., and
Leibowitz, H.M.: Changes in the corneal endothe-
lium as a function of age, Exp. Eye Res. 22:597, 1976.
2. Bourne, W. M., and Kaufman, H.E.: Specular mi-
croscopy of human corneal endothelium in vivo, Am.
J. Ophthalmol. 81:319, 1976.
3. Rao, G. N., Shaw, E.L., Arthur, E.J., and Aquavella,
J.V.: Endothelial cell morphology and corneal de-
turgescence, Ann. Ophthalmol. (in press).
4. Shaw, E.L., Rao, G.N., Arthur, E.J., and Aquavella,
J.V.: The functional reserve of the corneal en-
dothelium, Ophthalmology 85:640, 1978.
5. Arthur, E.J., Rao, G.N., and Aquavella, J.V.: Auto-
mated pattern analysis of corneal endothelium. Pre-
sented before the ARVO Eastern Section Meeting,
Gainesville, Fla., November 1977.
Permeability of retinal capillaries in rats
with inherited retinal degeneration.
EDWARD ESSNER, RICHARD M. PINO, AND
RICHARD A. GRIEWSKI.
The permeability of retinal capillaries in RCS rats with
inherited retinal degeneration ivas investigated with
horseradish peroxidase used as a tracer. Five-week-old
rats showed typical degeneration of photoreceptor cells
and accumulation of outer segment debris, but retinal
capillaries were not permeable to peroxidase. At 10 weeks
of age, capillaries in the inner retina appeared normal,
but many in the outer retina were leaky. Peroxidase ac-
tivity in these latter vessels was demonstrable in the basal
laminae of endothelial cells and pericytes and in vesicles
on the luminal and abluminal sides of the endothelium.
Tracer also permeated the intercellular spaces in the sur-
rounding area. The number of leaky capillaries in the
outer retina increased during the course of the dys-
trophy. The site of the leak in permeable capillaries has
not yet been established; it may be due to an alteration of
the endothelial cell junctions or of transcellular vesicular
transport. In the choriocapillaris, peroxidase permeated
Bruch's membrane and the basal infoldings between ad-
jacent pigment epithelial cells; tracer progression along
the intercellular spaces was blocked at the zonulae oc-
cludens at the apicolateral border. The RCS rat may be
a useful model for studying the morphological basis of
changes in capillary permeability associated with retinal
degeneration.
Retinal dystrophy in the Royal College of Sur-
geons (RCS)1 rat is a recessively inherited disorder
characterized by progressive degeneration of the
photoreceptor cells, beginning by about the third
postnatal week.2 This process continues with a
progressive thinning of the outer nuclear layer
until almost all the photoreceptor cells have de-
generated and have been replaced by a layer of
debris. Gerstein and Dantzker,3 using the tryp-
sin-digest method, found that photoreceptor de-
generation in RCS (tan-hooded) rats was accom-
panied by degenerative changes in the retinal
capillaries. In this report we demonstrate that the
retinal capillaries of RCS rats become leaky to in-
travenously injected horseradish peroxidase dur-
ing progression of the dystrophy.
Materials and methods. RCS-p + (pigmented)
rats4 and normal, Long-Evans Blue rats of both
sexes were used in this study. They were reared
in cyclic light (12 hr light-12 hr dark) at a room
illumination of approximately 10 to 15 ft-cd from
overhead fluorescent lamps. Room temperature
was controlled at 21° C, and the rats were fed
Purina Chow. Animals were sacrificed at 5, 10,
15.5, and 28 weeks of age. For enzyme tracer stud-
0146-0404/79/080859+05$00.50/0 © 1979 Assoc. for Res. in Vis. and Ophthal., Inc.


Endothelial cell density in relation to morphology

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Endothelial cell density in relation to morphology

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