Maternal Corneal Thickness During Pregnancy

Robert N. Weinreb, M . D . , Arthur Lu, M . D . , and Charles Beeson, M.D.

We measured central corneal thickness in 89 pregnant women. It was increased 16 \xm (P = .01) compared to the control eyes of 18 non-gravid and 17 postpartum women. There was no significant difference (P = .79) in corneal thickness between the nongravid and postpar­tum groups. When comparing subjects by week of gestation, there was no trend over time in corneal thickness (analysis by linear regression). Intraocular pressure was lowered during pregnancy, but it did not correlate with corneal thickness for either the pregnant or nonpregnant group.

PREGNANT WOMEN often cannot tolerate con­tact lens wear.12 It has been hypothesized that this may be related to changes in corneal sensi­tivity resulting from increased corneal thick­ness or altered tear composition.35 Millidot3

described five pregnant women with increased corneal thickness who also had decreased cor­neal sensation. Manchester6 examined 27 women in the third trimester of pregnancy and again six weeks postpartum. Using an optical pachymeter, he demonstrated that corneal thickness decreased 0.2% after delivery. In this study, we compared the central corneal thick­ness throughout each trimester of pregnancy with corneal thickness in nonpregnant control subjects.

Subjects and Methods

Pregnant women and nonpregnant female control subjects seen in the Obstetrics and Gynecology Clinic at our institution for routine

Accepted for publication Dec. 7, 1987. From the Department of Ophthalmology, University

of California at San Diego, La Jolla, California. Reprint requests to Robert N. Weinreb, M.D., Univer­

sity of California at San Diego, Department of Ophthal­mology (T-014), La Jolla, CA 92093.

examinations were enrolled in this study. The study was approved by the Human Subjects Committee and informed consent was ob­tained. Eighty-nine consecutive pregnant women and 35 nonpregnant control subjects were examined. The control group consisted of 18 nongravid and 17 postpartum subjects. Post­partum subjects were evaluated within six weeks after delivery. The average age was 23 years for the pregnant group and 27 years for the nonpregnant group.

One drop of 0.5% proparacaine hydrochlor-ide was administered to each eye for topical anesthesia. While the patient was seated, three separate readings of central corneal thickness were obtained with an ultrasound pachymeter. The mean of the three readings was calculated for each eye. To avoid possible diurnal varia­tions of corneal thickness, readings were taken between 11:00 A.M. and 3:00 P.M. Intraocular pressure was then measured with a pneu-matonometer.

Corneal thickness of pregnant and non­pregnant subjects was compared by unpaired f-tests. Corneal thickness of nongravid and postpartum subjects also was compared by un­paired f-tests. Linear regression was used to analyze corneal thickness of pregnant subjects according to weeks of gestation. The relation­ship between corneal thickness and intraocular pressure was examined with Pearson correla­tions. P < .05 was considered significant.

Results

In nongravid control eyes, corneal thickness was R.E.: 535.5 ± 34.8 n.m (mean ± S.D.) and L.E.: 533.4 ± 36.5 ^m. In the postpartum group, corneal thickness was R.E.: 532.5 ± 27.0 jxm and L.E.: 532.7 ± 26.8 urn. The difference between these two groups for either the right or left eye was not statistically signifi­cant.

In the pregnant subjects, mean corneal thick­ness was R.E.: 550.7 ± 34.1 |xm and L.E.: 550.8 ± 34.1 |xm (Table 1). Differences between preg-

258 ©AMERICAN JOURNAL OF OPHTHALMOLOGY 105:258-260, MARCH, 1988

Vol. 105, No. 3 Corneal Thickness During Pregnancy 259

TABLE 1 CENTRAL CORNEAL THICKNESS (MEAN ± S.D.) WITH PREGNANCY

PREGNANT SUBJECTS CONTROL SUBJECTS (N = 89) (N = 35)

R.E. L.E. R.E. L.E.

Corneal thickness (n.m) 550.7 ± 34.1 550.8 ± 34.1 534.0 ± 30.9 533.0 + 31.7 Intraocular pressure (mm Hg) 14.8 ± 2.3 14.6 ± 2.4 16.1 ± 2.4 16.2 ± 2.5

nant and control subjects were statistically sig­nificant for both right and left eyes (P < .02). The mean corneal thickness in the right eye was highly correlated with corneal thickness in the left eye (P < .01). Corneal thickness did not correlate with age.

We then divided the pregnant subjects into three groups based on weeks of gestation. Sub­jects examined during the first 13 weeks of gestation were included in the first trimester group, those between 13 and 27 weeks were in the second trimester group, and those after 27 weeks were in the third trimester group. By linear regression, there was no trend over time in corneal thickness in either eye (Table 2). From these data, we found that corneal thick­ness increases by 3% (16 |j,m) during pregnan­cy, independent of the stage of gestation, and returns to baseline levels within a few weeks after delivery.

Intraocular pressure in pregnant subjects was lower than in control eyes (Table 1). There was no correlation between corneal thickness and intraocular pressure.

Discussion

Our data indicate that central corneal thick­ness is 3% higher in the eyes of pregnant

TABLE 2 CENTRAL CORNEAL THICKNESS (MEAN ± S.D.) OF

PREGNANT SUBJECTS

TRIMESTER

First (n = 19) Second (n = 26) Third (n = 44)

CORNEAL THICKNESS (nM)

R.E.

549.3 ± 35.9 546.7 ± 29.5 554.0 ± 36.5

L.E.

551.5 ± 34.9 545.3 ± 28.4 554.1 ± 37.4

women compared with the control eyes. This difference is statistically significant. The in­crease in corneal thickness did not change dur­ing the gestation period and it returned to baseline level within a few weeks after deliv­ery.

These observations support the hypothesis that hormonal changes during pregnancy lead to retention of water in the cornea, with a concomitant increase in corneal thickness as well as alteration in corneal topography. In response to the rapidly growing fetus and placenta and their increasing demands, the pregnant woman undergoes numerous, in­tense metabolic changes.7 Increased reten­tion of water is a normal, physiologic alteration of pregnancy, which is under the influence of ovarian, placental, and steroid hormones. At term, an additional 3.0 L of water accumulates subsequent to an increase in maternal blood volume and in the size of the uterus and breasts.7 The return to baseline of corneal thick­ness after delivery can be explained by the mobilization and excretion of water at this time.

Although previous reports on the relation­ship between intraocular pressure and corneal thickness are contradictory, they raise the pos­sibility that changes in corneal thickness also could be related to changes in intraocular pres­sure. In the presence of well-functioning corne­al endothelium, it has been suggested that decreased intraocular pressure is associated with increased corneal thickness.8 In our study, and in others,910 intraocular pressure was re­duced during pregnancy. However, we found no correlation between corneal thickness and intraocular pressure.

Changes in corneal thickness and topogra­phy may account for intolerance to contact lens wear experienced by many pregnant women.15

Hence, one may wish to delay fitting new contact lenses until several weeks postpartum,

260 AMERICAN JOURNAL OF OPHTHALMOLOGY March, 1988

w h e n corneal th ickness has r e tu rned to its basel ine va lue .

A C K N O W L E D G M E N T Char les Berry, P h . D . , p rov ided statistical

consul ta t ion and ass is tance.

References

1. Davidson, S. I.: Reported adverse effects of oral contraceptives on eyes. Trans. Ophthalmol. Soc. U.K. 91:561, 1971.

2. Sarwar, M.: Contact lenses and oral contracep­tives. Br. Med. J. 5497:1235, 1966.

3. Millidot, M : The influence of pregnancy on the sensitivity of the cornea. Br. J. Ophthalmol. 61:646, 1977.

4. Riss, B., and Riss, P.: Corneal sensitivity in pregnancy. Ophthalmologica 183:57, 1981.

5. Weinreb, R. N., and Lu, A.: Maternal ocular adaptations during pregnancy. Obstet. Gynecol. Surv. 42:471, 1987.

6. Manchester, P. T.: Hydration of the cornea. Trans. Am. Ophthalmol. Soc. 68:425, 1970.

7. Pritchard, J. A., MacDonald, P. C , and Gant, W. F.: Williams Obstetrics, ed. 17. Norwalk, Conn., Appleton-Century-Crofts, 1985, p. 188.

8. Ehlers, N.: On corneal thickness and intraocu­lar pressure. I. A clinical study on the thickness of the corneal stroma in glaucomatous eyes. Acta Oph­thalmol. 48:1107, 1970.

9. Horven, I., and Gjonnaess, H.: Corneal inden­tation pulse and intraocular pressure in pregnancy. Arch. Ophthalmol. 91:92, 1974.

10. Paterson, G. D., and Miller, S. J. H.: Hormo­nal influence in simple glaucoma. Br. J. Ophthalmol. 47:129, 1963.

OPHTHALMIC MINIATURE When I was in my twenties, I said, I had a job as an 'expert ' on modern

painting with a well-known firm of art auctioneers. We had sale-rooms in London and New York. I was one of the bright boys. People said I had a great career, if only I would play my cards right. One morning, I woke up blind.

During the course of the day, the sight returned to the left eye, but the right one stayed sluggish and clouded. The eye specialist who examined me said there was nothing wrong organically, and diagnosed the nature of the trouble.

"You've been looking too closely at pictures ," he said. "Why don' t you swap them for some long horizons?"

I went to Africa, to the Sudan. My eyes had recovered by the time I reached the airport.

Bruce Chatwin, The Songlines New York, Viking, 1987, p. 16