Intravitreal use of triamcinolone acetonide: an experimental clinical procedure

The frequency of application of intravitreal injection of triamcinolone acetonide for the treatment of intraocular oedematous and neovascular diseases, initially suggested by Robert Machemer and colleagues in the late 1970s (Machemer et al. 1979), has increased exponentially over the last 3 years. According to recent estimates, the number of injections performed in the USA alone last year was about 250 000, and close to a million injections were performed worldwide. The increasing clinical application of intravitreal triamcinolone acetonide is also reflected in the present issue of Acta Ophthalmologica, in which five articles deal with the intraocular use of triamcinolone acetonide for the treatment of branch retinal vein occlusion (Krepler et al. 2005), macular hole (Ozdemir et al. 2005), therapy-resistant uveitis (Angunawela et al. 2005; Larsson et al. 2005), and proliferative diabetic retinopathy (Kytö et al. 2005). One of the most interesting aspects of the intravitreal triamcinolone acetonide injection may reflect a change in a paradigm, in that the vitreous cavity has begun to be regarded as a drug reservoir. Given that the eye represents about 1/10 000 of the whole body, an intraocular application of just 25 mg may have an equivalent dosage of a 0.25 kg if it were to be injected intraglutearly. This may exemplify the extremely high concentrations of triamcinolone acetonide that can be achieved in the eye with this new technique, almost without systemic side-effects (Degenring & Jonas 2004). The absence of side-effects allows the use of intraocular triamcinolone acetonide in patients with diabetes mellitus in whom steroids normally lead to a deterioration of metabolic control. The rule of thumb has been that for diseases with an intraretinal macular oedema, intravitreal triamcinolone acetonide temporarily increases visual acuity as much as macular ischaemia and the tissue destruction by the underlying disease allow it (Jonas et al. 2005a). Another interesting point about intravitreal triamcinolone acetonide is that it has become one of the leading competitors among a series of fairly new drugs which, intraocularly delivered, aim to treat macular diseases such as exudative age-related macular oedema, diffuse diabetic macular oedema and retinal vein occlusions (D'Amico et al. 2003; Gragoudas et al. 2004). Taking into account the specific side-effects of intravitreal triamcinolone acetonide (i.e. secondary ocular hypertension in about 40% of the eyes injected, including development of a secondary open-angle glaucoma) (Jonas et al. 2005b) and an increased cataractogenesis (Gillies et al. 2005), the major advantages of triamcinolone acetonide may be its prolonged action of about 6–8 months if used in a dosage of about 20 mg (Jonas et al. 2004) and, even more importantly, its unbeatably low cost. The latter is the reason why randomized, controlled trials have been, and probably will be, performed without major financial backing from industrial resources. However, despite the positive reports about the high anatomic success rate of intravitreal triamcinolone acetonide and the improvement in visual function it brings to some patients, and despite the feasibility of the technique and the low costs of the drug and its application, we ought not to forget that the intravitreal use of triamcinolone acetonide should continue to be regarded as an experimental clinical procedure for most diseases until more randomized, controlled trials and longterm studies have enabled us to better weigh the benefits and risks of this new treatment modality.