[The hydrogen-ion concentration in the anterior chamber of the rabbit eye after experimental chemical burns with calcium hydroxide and the effect of various buffers]

Corneal calcification after chemical eye burns caused by eye drops containing phosphate buffer

PURPOSE

Chemical burns with calcium containing corrosives as well as irrigation with phosphate buffer solutions after eye burns bear the risk of corneal calcification. The aim of this study was to evaluate the correlation between the occurrence of corneal calcification after chemical injuries and the usage of phosphate buffer containing local therapeutics.

METHODS

We reviewed the data of 179 patients who have been treated in the University Eye Clinic Aachen, Germany, between 1941 and 2000. Only when the corrosive did not contain calcium and when the initial irrigating solution did not contain phosphate buffer, respectively, were patients included in the study. The cases were analyse, if the patient was treated with phosphate buffer containing eye drops/ointment during the first 7 days of hospitalization or as an out-patient, and if corneal calcification was visible by slit-lamp examination during the follow-up. Statistical analysis was performed using Fischer's exact test.

RESULTS

152 eyes were included. From 63 eyes treated with phosphate buffer containing eye drops, 31 eyes (49%) developed corneal calcification. From 89 eyes treated without phosphate buffer containing eye drops, only 23 eyes (26%) developed corneal calcification. The two-sided p-value of Fischer's exact test is 0.0036.

CONCLUSION

During follow-up after chemical eye burns, eye drops containing phosphate buffer double the risk of corneal calcification. We recommend avoiding these agents in order to prevent the burned cornea from additional opacity. Substances containing phosphate buffer are listed in this article.

Effect of different irrigating solutions on aqueous humour pH changes, intraocular pressure and histological findings after induced alkali burns

PURPOSE

To evaluate the effects of hypo-osmolar tap water and isotonic saline solution on the intracameral pH, intraocular pressure and histological changes in alkali burned rabbit eyes.

METHODS

Four groups of four rabbit corneas each were burned with 2 N sodium hydroxide, and then rinsed with 0.5 l or 1.5 l of saline solution or tap water, respectively. Changes in pH were monitored with an intracameral microelectrode. Intraocular pressure (IOP) was monitored by a transducer placed in the vitreous cavity. After enucleation, histology was performed.

RESULTS

The pH increased after 1.5 min following alkali application. Irrigation with different solutions affected the maximum pH levels reached. Following the tap water rinse, the maximum rise was significantly lower than after the saline solution rinse. The maximum rise following rinsing with 1.5 l of tap water showed a significant delay. The increase in IOP was 23 +/- 10 mmHg without differences between the groups; the original pressure was recovered after 18 +/- 9 min. Histology of the eyes revealed a significant oedema in all corneas. Other ocular structures appeared unchanged.

CONCLUSIONS

The hypo-osmolarity of tap water led to remarkable corneal oedema. Enlargement of the diffusion barrier and intracorneal dilution inhibit elevated intracameral pH levels. The difference in maximum pH levels reached may influence the degree of subsequent intraocular structure injury. Therefore, the use of iso-osmolar saline solution proves to be less efficacious than tap water as an irrigation agent for ocular burns.

[Aqueous humor pH in experimental lye burns and influence of different treatment measures (author's transl)]

300 rabbit corneas were burned for 1 minute by applying a filter paper of 10 mm diameter soaked in different concentrations of NaOH. The aqueous humor pH was then measured at certain time intervals and after different treatment methods until the physiologic pH of 7.6 was reached. The results were statistically analysed. Group 1, 2 and 3 were burned in 1n NaOH, 3n NaOH, and 6n NaOH respectively without any treatment. In these groups a "therapeutic" pH-level of 8.5 was measured on an average 0.5, 2.5 and 5 hours after the burn (Table 1 and Fig. 2). Group 4 and 5 again were burned with 6n NaOH. In group 4 the burn was followed by constant irrigation with physiologic saline solution by means of the Morgan Therapeutic Lens (Fig. 1a and b). With this regimen a pH of 8.5 was reached after 2.5 hours (Table 1 and Fig. 3). In group 5 the physiologic saline solutions was replaced by a buffer solution (Isogutt) and a pH of 8.5 was measured after only one hour (Table 1 and Fig. 3). Based upon these results it is felt that severe lye burns should be treated by constant irrigation with a buffer solution for several hours. A treatment that can easily be performed by use of the Morgan Therapeutic Lens.