Recovery of the blood-aqueous barrier after topical chemical irritation in the rabbit eye

An acute irritative response in the rabbit eye, taking the form of a rise in the intraocular pressure (IOP), miosis, and breakdown of the blood-aqueous barrier, was elicited by topical application of 1% neutral formaldehyde. The peak rise in IOP was 22.1 ± 2.5 mmHg and occurred within 14.2 ± 1.9 min, after which IOP returned to normal values in 45.4 ± 5.2 min. An increased amount of i.v.-injected Evans Blue was found in the aqueous humour when injected 15 min after the irritation (119.0 ± 21.2 g/ml, compared with 2.1 ± 1.4 g/ml in intact eyes;P < 0.001), and the protein concentration in the aqueous humour was also increased, to 11.3 ±1.4 mg/ml (P < 0.001). When Evans Blue was injected 60 min after the irritation, no statistically significant difference was found from normal in the amounts (13.7 ± 7.8 g/ml) in the aqueous humour, although the protein concentration in the aqueous humour was again found to be elevated (7.9 ± 1.6 mg/ml,P < 0.01). Histologically, the Evans Blue was shown to leak through both the ciliary and the iris barriers at 15 min. At 60 min only occasional Evans Blue leakage was demonstrated between the nonpigmented epithelial cells and only minor fluorescence was seen in iris stroma. The histological findings were in good agreement with Evans Blue analyses in the aqueous humour. The miosis lasted over 60 min in the formaldehyde-treated eyes. After sympathectomy the rise in IOP was more rapid at the beginning of the response, suggesting greater sensitivity of the sympathectomized eyes to the irritative stimuli. However, the miosis had recovered by 60 min after irritation in the sympathectomized eyes. In the contralateral eyes changes in IOP and in the integrity of the blood-aqueous barrier were observed. The present results suggest that the breakdown of the blood-aqueous barrier after sensory nerve stimulation is transient and recovery rapid.