Macular edema is the commonest cause of visual loss in diabetic patients. Damaged tight junction between endothelial cells and pigmented epithelial cells lead to water and electrolytes leakage. According to the Early Treatment Diabetic Retinopathy Study (ETDRS), macular laser blocked further visual loss in half of patients. However, it was unable to restore the vision and not effective in the treatment of cystoid macular edema. Complications of intravitreal triamcinolone injections include hemorrhage, endophthalmitis and retinal detachment. Subtenon injection of steroids appears to offer a better choice, less invasive and deliver same therapeutic dose for the management of diabetic macular edema and intermediate uveitis [1-3]. the purpose of this study was to assess the efficacy of posterior subtenon (SBT) capsule injection for the treatment of cystoid diabetic macular edema in pseudophakic patients.

This comparative prospective controlled study treated 100 eyes. Fifty two patients were males and forty eight were females, aged between 41 and 74 years (mean 67.3). Inclusion criteria included pseudophakic diabetic patients complaining from cystoid diabetic macular edema without retinal-vitreous traction. Patients were informed about the procedures and the study aim. They signed informed consent form to participate according to the declaration of Helsinki (1983). In all the patients the best corrected visual acuity in logarithm of the minimum angle of resolution (log MAR) was reported using Snellen chart, as well as intraocular pressure (IOP) applanation tonometry, anterior and posterior segment biomicroscopy. Central subfield thickness (SFT) was evaluated by optical coherence tomography (OCT 2000, Topcon, Japan). Exclusion criteria included previous ocular surgery other than cataract, glaucoma, ocular hypertension and uveitis. The patients were divided equally and randomly using computer software into two groups; IVT group and SBT group.

Procedures

Procedures for the IVT injection, the surface anesthesia with topical 0.4% benoxinate hydrochloride was performed, followed by skin sterilization with 5% povidone iodine. A paracentecis was done. A volume of 0.05 ml containing 2 mg TA (Kenacort, Bristol-Myers Squibb, Sermoneta, Italy) was injected via the inferotemporal parsplana (3 mm posterior to the limbus) using a 27-gauge needle. For the posterior SBT injection, 1 ml of a 40 mg/ml of triamcinolone acetonide (Kenacort, Bristol-Myers Squibb, Sermoneta, Italy) was given in the inferotemporal quadrant. The patients were direct to look in the extreme superonasal field of gaze. The conjunctiva and the Tenon's capsule were incised and penetrated with 23 G cannula. A paracentecis was done. Topical gatefloxacin and dexamethasone eye drops were used postoperatively for one week. The BCVA log MAR, IOP and SFT were reported one week, one month and three months postoperatively.

Statistical analysis

The data were statistically evaluated using SPSS 16.0 software. The ANOVA test and paired t test were used for comparison between the two groups. A “p<0.05” was considered significant.

The eyes treated with an IVT of TA displayed significant improvement in visual acuity, both after one month (0.35 ± 0.1 ) (Log MAR 0.45 ± 0.05; p<0.001) and after three months ( 0.3 ± 0.1 ) (Log MAR 0.5 ± 0.08; p<0.001) of treatment when compared to the baseline values (0.14 ± 0.1) (Log MAR 0.85 ± 0.1). Significant improvement was displayed also in eyes treated with an SBT injection, again after one month (0.35 ± 0.09) (Log MAR 0.45 ± 0.07; p<0.001) and after three months (0.3 ± 0.09) (Log MAR 0.49 ± 0.06; p<0.001) when compared to the baseline values (0.13 ± 0.09) (Log MAR 0.86 ± 0.1). There was no statistically significant difference in visual acuity between both groups during follow-up visits (Table 1). The SFT of the eyes treated with IVT injection were significantly reduced both after one month (225 ± 14 μm; p<0.001) and after three months (230 ± 10 μm; p<0.001) when compared to the baseline values 385 ± 12 μm. The eyes treated with SBT injections displayed significant improvement after one month (220 ± 15 μm; p<0.001) and after three months (235 ± 12 μm; p<0.001) of treatment when compared to the baseline values of 383 ± 18 μm. The improvement in SFT was statistically insignificant between the two groups (Table 2). The IOP of the eyes treated with IVT injection was significantly increased after one month (18.8 ± 1.8 mmHg; p=0.03), three months (17.2 ± 1.2 mmHg; p=0.02) when compared to baseline value (16.6 ± 1.6 mmHg). Glaucoma medication was used to control the IOP. The eyes treated with SBT injection displayed significant increase of the IOP only after one month (17.4 ± 1.4 mmHg; p=0.01). IOP after three ms was (16.6 ± 1.6 mmHg) comparable to baseline value (16.4 ± 1.4 mmHg) (p=0.1). The mean IOP was significantly higher in IVT group than in SBT group after one month. However, it was statistically insignificant after three months of treatment (Table 3).

Table 1: Visual acuity (log MAR) (mean ± standard deviation) of studied groups.

Table 2: Central subfield thickness (SFT) (mean ± standard deviation) (μm) of studied groups.

Table 3: Intraocular pressure (IOP) (mean ± standard deviation) (mmHg) of studied groups.

Macular edema is the main cause of loss of visual acuity in diabetic patients. Damaged tight junction in-between endothelial cells and pigmented epithelial cells, lead to water and electrolytes leakage. According to the Early Treatment Diabetic Retinopathy Study (ETDRS), macular laser blocked further visual loss in half of patients. However, it was unable to restore the vision and not effective in the treatment of cystoid macular edema. The diabetic retinopathy presents with features of chronic inflammation such as; vasodilatation, increased blood flow, tissue edema and an increase in the vascular permeability. All experimental data such as; leukostasis in diabetes with adhesion of activated molecules to the endothelium, increased production of prostacyclin, vascular endothelial growth factor (VEGF) and macrophage cellular component confirm the involvement of pro-inflammatory molecules in the early stages of diabetic retinopathy. Corticosteroids inhibit the initial arachidonic acid cascade, down-regulate the cytokines and support the blood-retinal barrier [1,2]. The complications of intravitreal TA were endophthalmitis, intraocular hemorrhages, retinal detachment and IOP elevation in 20% to 80% of patients [1].

The subtenon TA was used in the management of cystoid macular edema and intermediate uveitis. Correct injection makes it possible to deliver the drug in the macular area [1]. This work proved that intravitreal injection of TA and the subtenon injection of TA improved the visual acuity and an equally reduced the retinal thickness. A statistically significant rise of the IOP in the eyes treated with IVT injection was proved after one and three months. In a pilot study performed by Chew et al, they proved less central subfield thickness after SBT but after longer follow up [2]. Song et al. found a better improvement in visual acuity 8 weeks after IVT with less macular thickness which was superior to intravitreal bevacizumab injection [3]. On the other hand Marey et al. stated that intravitreal bevacizumab alone was better and safer than both intravitreal TA and combined intravitreal bevacizumab-TA because of higher IOP [4]. Also Chung et al. proved the visual and foveal thickness improvement after SBT combined with laser macular therapy. It was comparable to IVT with lower IOP elevation [5]. Wang et al. proved that, intravitreal injection of bevacizumab combined with or without triamcinolone acetonide was effective in treatment of DME [6]. Choi et al. Cellini et al. and Qi et al. reported that IVTA and SBT had same effects on DME, but that IVTA elevated IOP. Ozdek et al. proved that 8.2% of the SBT cases showed a significant elevation in IOP (>21 mmHg), and 24.3% of cases in the IVT group had a significant elevation in IOP. Bakri and Kaiser reported minimal elevation in IOP at 3 months that was normalized at 6 months [7-9]. Ozdek et al. compared the IVT and SBT effects. They stated that both SBT and IVT significantly reduced the retinal edema, although the effects were more pronounced in the IVT group, SBT also seemed to be a safe and effective technique for treating DME. Bakri and Kaiser reported that SBT was safe and effective on DME are refractory to laser photocoagulation [7]. Jonas et al. found that 50% of IVT patients had increased IOP. The SBT is considered to be less invasive than the intravitreal one. IOP is not increased by the use of this approach with the exception of steroid responder patients. Cataract progression, central retinal vein occlusion, globe perforation and central retinal artery occlusion were found to be complication of SBT. Other complications described are blepharoptosis, orbital fat atrophy, strabismus and conjunctiva necrosis [9,10].

The subtenon route, although involving a limited number of cases, can be considered an easy, safe and valid alternative to the intravitreal route.

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The author does not have any financial competing interests. The author does not have any financial competing interests (political, personal, religious, ideological, academic, intellectual or commercial).