A C T A O P H T H A L M O L O G I C A V O L . 5 3 1 9 7 5

Department of Ophthalmology, (Heads: P . Brcendstrup, S . E . Lorentzen, M. S. Norn R- K. Nsrskov), Kommiinehospitnlet, Copenhagen, Denmark

CORNEAL THICKNESS AFTER CATARACT EXTRACTION WITH AIR

IN THE ANTERIOR CHAMBER

BY

M. S. NORN

A total of 135 patients had the corneal thickness measured prior to cataract extraction. The chamber was reestablished by air in 86, while the remainder acted as controls. On the second postoperative day the corneal thickness had increased by 12.7 o/o in the air-inflated group, and by 17.60/0 in the control group. On the sixth postoperative day the increases in thickness were 7.2 and 11.1 O/o respectively. On follow-up control 6 to 12 months later the corneal thickness was as before the operation. Epithelial oedema was significantly more frequent in the control group.

The conclusion is drawn that an air bubble in the anterior chamber has no uafavourable effect on the corneal endothelium. On the contrary, it seems to protect the endothelium from postoperative damage.

Key words: cornea - corneal endothelium - corneal thickness - pachymetry - air in chamber - cataract extraction.

Some surgeons prefer to fill the anterior chamber with air at the conclusion of an operation (cataract extraction, corneal grafting), while others advise against inflation with air.

Adherents of the procedure of air inflation in the chamber attach importance to the re-establishment of the anterior chamber immediately after the opera-

Received June 1, 1975.

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M. S. Norn

tion. Those opposed to this procedure fear pupillary block with consequent secondary glaucoma caused by the air bubble.

The air bubble may have an unfavourable effect on the corneal endothelium by impairing its vitality or its permeability. Leibowitz et al. (1974) in rabbit experiments showed that scattered endothelial cells might be damaged when air was introduced into the chamber. Conversely, von Bahr (1956), in short rabbit experiments, found no alteration of the corneal thickness when aqueous humour was replaced by air.

On the other hand the air bubble may protect the endothelium from post- operative damage of the high-protein secondary aqueous humour, of fibrin, blood, and a possibly prolapsing vitreous body. The air bubble further prevents any penetration of fluid into the region it covers.

The corneal thickness, measured with a Haag Streit pachymeter, is a sensitive indicator of alterations in endothelial permeability, e.g. after corneal grafting (Ehlers 1974).

It therefore seems natural, in an attempt to find whether the air bubble has a favourable or harmful effect, to perform pachymetry in relation to cataract extraction both with and without air inflation into the anterior chamber.

Method and Material

Cataract extraction was performed with a limbus-based conjunctival flap and five corneo-scleral knotted silk sutures 8-0, as described previously (Norn 1973).

At the conclusion of the operation, atmospheric air was inflated into the anterior chamber with a syringe with a blunt canula. The chamber was thereby re-established. W e aimed at inflating just so much air that the air bubble had B diameter of not less than 6-8 mm. W e endeavoured to avoid a rise in pressure or air in the posterior chamber.

All the author’s cataract operations from October 1972 to August 1974 were included consecutively in the material under review. Air was inflated at the end of operation every other month.

A total of 86 operations were performed with air inflation and 49 without. The corneal thickness was measured with a Haag Streit pachymeter mounted

on a Haag Streit slit lamp no. 900, as described previously (Norn 1973). The measurements were undertaken the day before, and on the second and the sixth day after operation. Finally, the patients were summoned to a follow-up with measurement 6 to 12 months after the operation.

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Corneal Thickness with Air in Chamber

Ten per cent of those who had air inflated and 100/0 of the controls failed to appear for follow-up examination (14 patients, of whom five had died and three lived abroad, while the remaining six were too weak to come to the hospital unit for a control).

Results

A few days after operation the cornea was seen to have increased considerably in thickness. The increase was greatest in the control group. The percentage increase in proportion to the preoperative value is shown in Table I. The highest value was measured on the second postoperative day, and a somewhat lower value on the sixth day. On measurement 6 to 12 months after the operation the thickness did not differ significantly from the preoperative measurement.

A significant difference in corneal thickness was noticed between the patients with air inflated into the chamber and the control group, both on the second postoperative day (P < 0.01) and on the sixth postoperative day (P < 0.05, Students t-test).

Likewise, oedema of the corneal epithelium was most frequently present in the control group, 51 Q / o on the second postoperative day as opposed to 260/0 in the air-inflated group (P < 0.01), 22 O/O on the sixth day as opposed to 8 O/O

(P < 0.05). At the follow-up, epithelial oedema was found in only one case from each group.

Within the air-inflated group 33 (38 O/o) still had an air bubble in the chamber on the second postoperative day. In four of these the bubble was a small one situated behind the iris plane.

On the sixth day air was present in one case only. There was no instance of pupillary block.

Table 1. The mean percentage increase of the corneal thickness after cataract extraction f SEM in 86 patients operated on with air inflated into the anterim chamber and 49 patients

without air inflation.

1 Air Controls I I I

2nd postoperative day 12.7 f 1 .1 17.6 k 1.7 Gth postoperative day 7.2 f 0.9 1 1 . 1 f 1.4 After 6-12 months i(0.2 f 0.8 $0.1 f 1.1

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M. S. Norn

Discussion

The two series are comparable, all the operations having been performed by the author, according to the same technique, and within the same period.

The two series showed no difference with regard to incidence of complica- tions (few cases of haemorrhage in chamber, vitreous-cornea contact, loss of vitreous, and flat chambers in both groups).

The investigation showed that the postoperative increase of the corneal thickness is lessened if air is inflated in to the anterior chamber. The effect is seen even after absorption of the air bubble.

The air bubble seems to have no unfavourable influence on the vitality of the endothelium. On the contrary, it seems to protect the endothelium from the harmful effects of the operation.

The favourable effect of the air bubble can possibly be intensified by using a more slowly absorbable, non-toxic gas (perhaps SF,). This would, however, probably add to the risk of air bubble-induced pupillary block.

References

v. Bahr, G. (1956) Corneal thickness. Its measurement and changes. Amer. /. Ophthal.

Ehlers, N. (1974) Graft thickness after penetrating keratoplasty. Acta ophthal. (Kbh.)

Leibowitz, H. M. Laing, R. A. & Sandstrom, M. (1974) Corneal endothelium. Arch.

Norn, M. S. (1973) Pachometric study on the influence of corneal endothelial vital staining. (Corneal thickness after cataract extraction studied by vital staining with trypan blue). Actu ophthul. (Kbh.) 51, 679-686.

42, 251-266.

52, 893-903.

Ophthal. 92, 227-230.

Author’s address: M. S . Norn, M.D., Eye Department, DK-1399 Copenhagen, Denmark.

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