LETTER TO THE EDITOR
JOURNAL OF OCULAR PHARMACOLOGY AND THERAPEUTICS Volume 00, Number 00, 2016 ª Mary Ann Liebert, Inc. DOI: 10.1089/jop.2016.0030
Re: Immediate Intraocular Pressure Tendency Following Intravitreal Delivery of Dexamethasone Implant; Alago¨z et al. J. Ocul. Pharmacol. Ther. 32:44–49, 2016. Osman C xekic¸ and Semra Akkaya Turhan
aqueous outflow volume is a counterbalance mechanism for acute rises of IOP in nonglaucomatous eyes (*0.3 mm3/ min),5 about 3 min are enough to dispose extra volume in case of dexamethasone implant; however, more than 5 h are needed4 in case of triamcinolone acetonide if the additional effect of increased aqueous outflow by IOP increase is disregarded. It seems that elevated postinjection IOP normalizes quickly after intravitreal delivery of tiny dexamethasone device, whereas it takes some more time in the others depending on their relatively higher volume.
e read with great interest the article ‘‘Immediate intraocular pressure changes following intravitreal dexamethasone implant’’ written by Alago¨z et al.1 In their study, although only a transient hypotonia occurred in the presence of vitreous reflux, the median short-term intraocular pressure (IOP) unaltered in eyes without reflux. Specifically, an immediate IOP more than 25 mmHg was never observed in any of the dexamethasone device implanted eyes.1 These results are critically important when similar previous studies with other intravitreally injected agents are considered. Although some comparisons to 0.05 mL of antivascular growth factor injections and IOP changes take part in their article, we think this difference needs to be further discussed by also including another commonly used intravitreal steroid, triamcinolone acetonide, with a volume of 0.1 mL. Immediate IOP elevations up to 59.3 mmHg were observed shortly after intravitreal ranibizumab (0.05 mL) delivery.2 More than one-third of the eyes achieved IOP greater than 30 mmHg just after bevacizumab (0.05 mL) injection.3 One hundred percent of the intravitreal triamcinolone (0.1 mL)injected eyes had immediate IOP of more than 35 mmHg.4 Acute and sustained rise in IOP immediately after intravitreal drug application is commonly overlooked although it may be associated with the impairment of optic nerve perfusion. As volume expansion is blamed for acute IOP elevations after intravitreal drug application,1 calculating previously mentioned injected drug volumes and converting them into the same unit in mm3 will help all of us better understand and interpret the impact of volume on the results. The standard dose of bevacizumab and ranibizumab is 0.05 mL that equals to 50 mm3 volume, whereas 0.1 mL triamcinolone acetonide has a volume of 100 mm3. As cylinder (rod)-shaped dexamethasone implant (0.7 mg) has a given1 width (2r) of 0.45 mm and height (h) of 6.5 mm, its volume (pr2h) can be calculated as *1 mm3. According to these results, at immediate postinjection period, triamcinolone adds 2.5%, bevacizumab or ranibizumab adds 1.25%, whereas dexamethasone implant adds only 0.025% extra volume to the vitreous (assuming the average vitreous volume *4,000 mm3). In other words, vitreous volume expansion after dexamethasone implant is about 50–100 times less than that of the other mentioned intravitreal drugs in the absence of vitreous reflux after drug injection. As the increase of
References 1. Alago¨z, N., Alago¨z, C., Yılmaz, I., et al. Immediate intraocular pressure changes following intravitreal dexamethasone implant. J. Ocul. Pharmacol. Ther. 32:44–49, 2016. 2. Gismondi, M., Salati, C., Salvetat, M.L., Zeppieri, M., and Brusini, P. Short-term effect of intravitreal injection of Ranibizumab (Lucentis) on intraocular pressure. J. Glaucoma. 18:658–661, 2009. 3. Lemos, V., Cabuqueira, A., Noronha, M., et al. Intraocular pressure in eyes receiving intravitreal antivascular endothelial growth factor injections. Ophthalmologica. 233:162– 168, 2015. 4. Kotliar, K., Maier, M., Bauer, S., et al. Effect of intravitreal injections and volume changes on intraocular pressure: clinical results and biomechanical model. Acta Ophthalmol. Scand. 85:777–781, 2007. 5. Brubaker, R.F. Clinical measurements of aqueous humor dynamics: implications for addressing glaucoma. In: Civan, M.M., ed. The Eye’s Aqueous Humor: From Secretion to Glaucoma. San Diego: Academic Press; 1998; p. 234–284.
Received: February 28, 2016 Accepted: March 11, 2016 Address correspondence to: Prof. Osman Cxekic¸ Department of Ophthalmology Marmara University Medical School Pendik _ Istanbul 34890 Turkey E-mail: [email protected]
Department of Ophthalmology, Marmara University Medical School, Istanbul, Turkey.