J.A. Oosterhuis

Clinical Aspects and Pathology of a Bengal Tiger's Eye

In the middle of 1961 the left eye of a Bengal tiger showed signs of a keratitis and of development of a buphthalmus. The bulbi, removed post mortal in September 1968, showed pathologoanatomically the results of a perforation of the cornea and the lens of the left eye. Some histologic details are discussed.

Experimental Transscleral Freezing at Temperatures Ranging from ––20 to ––160°C

The ophthalmoscopic and histologic aspects of cryocoagulation in 264 rabbit eyes were studied. Temperatures ranged from -20° to -160° C, times of freezing varied from 5 to 60 seconds. The periods of observation ranges from 30 minutes to 3 months after cold treatment. 1. Scleral thinning or scarring was not observed and there were no signs of overdosage: scleral lesions (except pigment migration) disappeared within two to four weeks after cold application. The condition of the sciera two weeks after intense cryocoagulation was invariably good enough to permit reoperation. 2. Choroidal lesions were reversible irrespective of temperature and time of freezing, with the exception of pigmentary changes and atrophy of the choriocapillaris. At -100°, -130° and -160° hyperaemia, haemorrhages and plasmatic exudation in the choroid were more intense than at higher temperatures. At -130° and-160° the vessel walls were damaged to such an extent that many choroidal and subretinal haemorrhages developed immediately after freezing. 3. After freezing at -40° and lower temperatures an irreversible atrophy of all the retinal layers developed. At -60°, and in particular at -100° and lower temperatures, retinal haemorrhages and oedema occasionally developed, which were sometimes so intense as to cause a rupture of the internal limiting membrane. 4. The early subretinal oedema located in the area of freezing developed most rapidly and was most intense after freezing at -100°; it caused numerous retainl tears in the treated area during the first few hours after cold application but was rapidly resorbed in the course of one day. At -130° development and resorption of the oedema occurred more slowly; it was still present in the stage of incipient chorioretinal adhesion. At -160° the late subretinal oedema developed one week after freezing, leading to retinal tears around the area of coagulation where a good chorioretinal adhesion had already been attained. The above mentioned complications interfered with a good chorioretinal adhesion. 5. Cold-induced lesions of the vitreous developed only at temperatures of -130° and -160°. Small vitreous haemorrhages were resorbed and vitreous clouding which was also ophthalmoscopically visible frequently cleared. Vitreous strands would sometimes interfere with good chorioretinal adhesion. 6. The intensity of the lesions induced by the Linde cryode is influenced by various factors :

Experimental transscleral freezing at temperatures ranging from −20 to −160°C

Summary and conclusionsThe ophthalmoscopic and histologic aspects of cryocoagulation in 264 rabbit eyes were studied. Temperatures ranged from -20° to -160° C, times of freezing varied from 5 to 60 seconds. The periods of observation ranges from 30 minutes to 3 months after cold treatment.1.Scleral thinning or scarring was not observed and there were no signs of overdosage: scleral lesions (except pigment migration) disappeared within two to four weeks after cold application. The condition of the sciera two weeks after intense cryocoagulation was invariably good enough to permit reoperation.2.Choroidal lesions were reversible irrespective of temperature and time of freezing, with the exception of pigmentary changes and atrophy of the choriocapillaris. At -100°, -130° and -160° hyperaemia, haemorrhages and plasmatic exudation in the choroid were more intense than at higher temperatures. At -130° and-160° the vessel walls were damaged to such an extent that many choroidal and subretinal haemorrhages developed immediately after freezing.3.After freezing at -40° and lower temperatures an irreversible atrophy of all the retinal layers developed. At -60°, and in particular at -100° and lower temperatures, retinal haemorrhages and oedema occasionally developed, which were sometimes so intense as to cause a rupture of the internal limiting membrane.4.The early subretinal oedema located in the area of freezing developed most rapidly and was most intense after freezing at -100°; it caused numerous retainl tears in the treated area during the first few hours after cold application but was rapidly resorbed in the course of one day. At -130° development and resorption of the oedema occurred more slowly; it was still present in the stage of incipient chorioretinal adhesion. At -160° the late subretinal oedema developed one week after freezing, leading to retinal tears around the area of coagulation where a good chorioretinal adhesion had already been attained. The above mentioned complications interfered with a good chorioretinal adhesion.5.Cold-induced lesions of the vitreous developed only at temperatures of -130° and -160°. Small vitreous haemorrhages were resorbed and vitreous clouding which was also ophthalmoscopically visible frequently cleared. Vitreous strands would sometimes interfere with good chorioretinal adhesion.6.The intensity of the lesions induced by the Linde cryode is influenced by various factors :a.The temperature of freezing: at -100° and lower temperatures secondary destructive lesions were observed.b.The time of freezing is important at the higher temperatures; at the low temperatures we observed very little influence of the time of application (5–60 sec) on the intensity of the lesions produced. We found in a previous experiment that the lesions caused by repeated short-time applications were more intense than those after long-time application.c.Scleral thickness.d.The degree of choroidal vascularization.e.The pressure exerted by the cryode on the surface of the eye has a very great influence on the severity of the lesions. This factor may be responsible for the variation in the results in our own experimental studies and for the difference between our results and those of some other investigators.7.The ophthalmoscopic appearance of the final scar on the rabbits eye was similar in all cold applications at -40° and lower temperatures. Only the pigment accumulation and the degree of atrophy of the choriocapillaris increased as the freezing temperature was lower. Histologically, the adhesion started before the fourth day and was consolidated in one month. The adhesion is good at a range of temperature from -20° to -80° and reaches its optimum at -80°. Our clinical experience of cryopexy in retinal detachment surgery confirms that this temperature, when applied for 5 to 20 sec or twice 5 sec, promotes a good chorioretinal adhesion and minimizes the risk of complications.