[Inhibition of secondary increase of intraocular pressure following cyclokryocoagulation (author's transl)]

Cyclocryotherapy for glaucoma. Evaluation of techniques

Clinical results of cyclocryotherapy reported by various authors have been contradictory. This is partly due to considerable differences in technique. In this paper, details of the technique of cyclocryotherapy are reviewed in order to determine the most effective protocol of treatment. Parameters such as temperature, duration, probe placement, diameter of the tip, pressure exerted on sclera, extent of ciliary body freezing, additional cyclocryotherapy and preparation of patient for treatment are discussed.

Mediation of the ocular response to cyclocryocoagulation

The possible roles of prostaglandins and a neural pathway in the disruption of the blood-aqueous barrier in the rabbit eye after cyclocryocoagulation were studied. Both the preoperative IV administration of the prostaglandin inhibitor acetylsalicylic acid and the application of retrobulbar and topical anesthesia reduced IOP and decreased breakdown of the blood-aqueous barrier, as measured by protein in the aqueous humour. These results imply that the acute response of the animal eye to cyclocryocoagulation is mediated partly by prostaglandins and partly by a neural component resistent an inhibitor of prostaglandin synthesis. When administered together, acetylsalicylic acid and ocular anesthesia yielded a further reduction in postoperative reactions and protein concentrations in the aqueous humour, but were unable to abolish the ocular response completely. The dual ocular mediation to cyclocryocoagulation is apparently due to the combined thermal and mechanical injury caused to ocular structures which synthesize prostaglandins and receive sensory innervation from the trigeminal nerve. The considerable breakdown of the blood-aqueous barrier in cyclocryocoagulation allows leakage of different molecular weight proteins, in equal ratio, into the aqueous humour.

Cyclocryokoagulation. Sequelae of induced alterations and effect of a prostaglandin-inhibitor on the breakdown of the blood-aqueous barrier

Histopathological changes following cyclocryokoagulation in a group of rabbits pretreated with acetylsalicyclic acid (ASA) were studied and compared with similar changes in a control group. As observed clinically, macroscopical and histological differences were only noted in the early phase after the procedure. In this phase, all operated eyes revealed an immense vascular response with edema, exudation and extravasation of blood cells. The treated animals, however, showed some reduction of tissue edema than the animals not treated. At a later stage there is an necrosis of the stroma with reduction of small vessels and tissue cells. The reparative process, tending to restore both epithelial and stromal lesions, begins already in the 3rd. week after cyclocryokoagulation. Neither the epithelial nor the stromal alterations differed significantly in any of the operated eyes at this stage. This indicates that ASA mainly affects an obviously prostaglandin-mediated acute vascular response. The disruption of the epithelial barrier may be aggravated by the subsequent stromal alterations, but does not seem to be influenced by ASA.