The use of intravitreal air in the treatment of retinal detachment was described by Rosengren (1938, I951), and Norton, Aaberg, Fung, and Curtin (I969) applied this technique to the treatment of giant tears. The method described in this paper differs from that of Rosengren in several features.A series of forty patients is divided into two broad groups:(A) Those appearing de novo at the Outpatient Department and undergoing a first operation for retinal detachment.(B) Relapsed detachments following some other previous operative technique. Eight aphakic patients previously described in detail (Chawla, I973) are included.The method described is used in all cases in which tears lie superiorly between the 8 and 4 o'clock meridians. If additional inferior tears exist, some other manoeuvre must be included. Method EXAMINATIONThe patient is admitted to the ward, and examination is undertaken with the binocular indirect ophthalmoscope. The periphery of both eyes is examined using transpalpebral indentation of the sclera; no local anaesthetic drops are instilled into the conjunctival sac. The patients are not compelled to rest in bed unless a functioning macula is in imminent danger of detachment. Double padding is never used.Slit-lamp examination is essential to determine the state of the vitreous. If narrow anterior chamber angles are suspected, gonioscopy is performed.In the preoperative state, a large amount of subretinal fluid is an advantage for two reasons:(i) Subretinal fluid can be released with greater safety. (2) Removal of fluid at operation makes way for the requisite I to 3 ml. air to be injected. Thus rest in bed may be unhelpful. OPERATIONThe patient is operated upon as soon as possible under general anaesthesia. A 360°limbal conjunctival incision is made and the rectus muscles are secured with 5/o silk stay sutures. The sclera is examined; any thinning and the position of the vortex veins are noted.Cryopexy to the areas of tear(s) is performed; the monitoring of each application prevents overfreezing. The onset of iceball formation is clearly seen. The cryoprobe must not be removed from the sclera until it has defrosted, thus avoiding scleral cracking (Shea, I969) and rupture of vortex veins during posterior applications.

SUMMARY The 'fishmouth phenomenon' seen in some previously treated retinal detachments is associated with large horseshoe tears and scleral buckling techniques. A method of treating patients with this complication is described in which scleral buckling with implant or explant is not used. The technique utilises intravitreal air tamponade with cryopexy and gives good results. The incidence of patients developing the fishmouth phenomenon as a complication of primary simple retinal detachment surgery is much lower when an intravitreal air technique is used than the expected incidence following a primary scleral buckling operation.The objective of this paper is to describe the management of difficult large posterior horseshoe-tear retinal detachments which develop the aptly named 'fishmouth phenomenon', in which a second surgical procedure is required following a failure of scleral buckling with scleral silicone implant or explant and/or encircling silicone tape.The prognosis for reattachment of the retina in routine retinal detachment surgery for primary rhegmatogenous detachments, by different surgical techniques, is now well documented. The results from different series indicate reattachment in 90 to 95 % of patients (Kreiger et al., 1971;Chignell, 1977;and Curtin, 1976). The reduced chance of a successful first surgical procedure in more complicated detachments, for example, detachments due to macular holes (Leaver and Cleary, 1975) and in secondary detachments is also recognised.Results of operations for detachment where the primary process of detachment involves retinal lesions with large posterior tears suggest that the larger the tear the worse the prognosis (Lincoff et al., 1977). At the worst a giant tear may extend through almost 3600 and is virtually unmanageable with present surgical techniques. Difficulties are encountered in routine scleral buckling procedures with large horseshoe tears when the buckle causes the operculum of the tear to elevate as the rolled edges of the tear come closer together. This compromising effect is greater with circumferential buckles than with radial buckles. If further tightening of an encircling tape is attempted at this time, it

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