| Objective: An experimental study was conducted to verify the effects of hyperbaric oxygen (HBO) of clinically adopted usual dosage on the retinas of foetus and newborn rabbits by means of morphological observation and stereological analysis.Methods: Ten New-Zealand white rabbits in 16 days' pregnance were devided randomly into Group A ( 3 rabbits received HBO supplement for ten days after the 16th day of pregnance) and Group B ( 7 rabbits as control group). The newborn rabbits were devided into group â…¡, group â…£ ( 17 and 11 rabbits whose mothers received HBO in pregnancy) and group â… ,â…¢, â…£,â…¤( 15,16,15 and 12 rabbits whose mothers didn't receive HBO in pregnancy). Group â… and â…¡ were raised in air for all 20 days; Group â…¢ received HBO first for 10 days, then were raised in air for the rest 10 days; Group â…£ were exposed to 80% oxygen for 10 days continuously and then in air for another 10 days. For group â… ~â…£, the rabbits' eyeballs were taken out on the 20th day after their birth; For group â…¤ and â…¥, on the same day they were born. The structures of rabbits' retinas of all groups were observed with optical microscope and electron microscope. For group â… ~ â…£, the numerical density of the surface area of the endothelial cells of new vessels extending from retina to vitreous (Ns) was measured and calculated; The volume density (Vvmi,p) , the surface area density ( Svmi,p ) of mitochondria in the internal segments of retinas, external and internal reticular layers, the volume density (Vvv,mi) and the surface area density (Svv,mi) of mitochondrion vacuoles of the three layers in group â… ~ â…£ were also measured and calculated.Results: 1. Morphological observation: The retinas of each baby rabbit of 20 days' age could be divided into 9 layers. The retinal structures of group â… and â…¡ were clear. There was no visible difference between them under optical microscope and electron microscope. For group â…¢, loosen external segments and localvacuolation in photoreceptor cells of retinas were found under optical microscope. Under electron microscope, enlarged and even partially dissolved or broken spaces between photoreceptor cell discoidals, swollen mitochondria of internal segments and more vacuolation were observed; The traumata of retinas for group IV were similar, but more serious. The retinas of group V and VI were immature with only thin photoreceptor cell layers formed and without obvious external reticular layers and outer limiting membrane. Observation with optical microscope and electron microscope showed no obvious difference in structure and cell morphology between the two groups. 2. Stereological analysis: ? Ns of group I ~IV: There was striking difference when each of group I, II and III was compared with group IV, but no significant difference of means between each pair within group I, II and III. (2) For baby rabbits in group I ~IV, there was no striking difference of Vvmi,p and Svmi,p of mitochondria in internal segments, external and internal reticular layers. However, the numerical density of mitochondria of the three layers decreased gradually from group I to IV with significant difference. (3) For group I ~IV, the Vvv,mi and Svv,mi differences of mitochondria vacuoles of the three layers showed striking significance; In group II, Vvv,mi and Sw,mi had no difference when compared with group I, but had striking difference with group IV. In group III, traumata of retinas were mainly shown in the striking significance in Vvv,mi and Svv,mi differences of retinal internal segments and mitochondrion vacuoles when compared with both group I and IV in internal segments.Conclusion: Hyperbaric oxygen therapy with normal pressure, normal oxygen- breathing time and normal number of treatment period usually adopted in the second and third trimester of pregnancy has no significant effects on the retina of foetus rabbit, but has traumata in the ultra microstructure of newborn rabbit's retina, if using the same dosage HBO in the neonatal period.
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