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 Table of Contents  
ORIGINAL ARTICLE
Year : 2018  |  Volume : 16  |  Issue : 4  |  Page : 414-419

Outcomes of pars plana vitrectomy for the treatment of persistent diffuse diabetic macular edema


1 Department of Ophthalmology, Faculty of Medicine, Al-Azhar University Hospital, Assiut, Egypt
2 Faculty of Medicine, Al-Azhar University, Cairo, Egypt

Date of Submission26-Nov-2018
Date of Acceptance03-Mar-2019
Date of Web Publication23-Apr-2019

Correspondence Address:
Ashraf M Gad Elkareem
Department of Ophthalmology, Faculty of Medicine, Al-Azhar University Hospital, Assiut, 71524
Egypt
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/AZMJ.AZMJ_130_18

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  Abstract 


Aim The aim of this study was to evaluate surgical outcome of pars plana vitrectomy on patients with persistent diffuse diabetic macular edema (dDME) in the presence or absence of complete posterior vitreous detachment (PVD).
Patients and methods Pars plana vitrectomy was performed on 37 eyes of 37 patients with dDME. They were divided into two groups: group I consisted of 21 eyes of 21 patients with dDME and attached posterior vitreous face. Group II consisted of 16 eyes of 16 patients with dDME and detached posterior vitreous face. Both visual acuity (VA) as logMAR values and central macular thickness using optical coherence tomography were measured before,1, 3, and 6 months postvitrectomy.
Results The baseline VA was 0.8±0.17 and 0.7±0.39 logMAR in groups I and II, respectively. One month after vitrectomy, VA significantly improved to 0.5±0.23 (P=0.002) and to 0.5±0.24 (P=0.015) in groups I and II, respectively. The VA was 0.4±0.13 (P=0.001), 0.5±0.19 (P=0.003) 3 months postvitrectomy and was 0.4±0.25 (P=0.005) and 0.5± 0.22 (P=0.014) after 6 months in groups I and II, respectively. The mean foveal thickness before surgery was 598.6±105.4 and 520.87±103.15 µm in groups I and II, respectively. After 3 months it significantly improved to 235.25±110.2 µm (P=0.0001) and 280.23±112.3 µm (P=0.002), whereas after 6 months it was 220.13±98.15 and 270.62±85.15 µm in groups I and II, respectively.
Conclusion Vitrectomy with removal of the posterior hyaloid face and the premacular vitreous pocket may achieve resolution of dDME and improve vision in some patients who failed to respond to conventional treatment. The visual and anatomical outcomes seem to be better in eyes with early stages of diabetic macular edema and good preoperative VA.

Keywords: central macular thickness, diabetic macular edema, pars plana vitrectomy, posterior vitreous detachment


How to cite this article:
Gad Elkareem AM, Rashed MA. Outcomes of pars plana vitrectomy for the treatment of persistent diffuse diabetic macular edema. Al-Azhar Assiut Med J 2018;16:414-9

How to cite this URL:
Gad Elkareem AM, Rashed MA. Outcomes of pars plana vitrectomy for the treatment of persistent diffuse diabetic macular edema. Al-Azhar Assiut Med J [serial online] 2018 [cited 2019 Aug 20];16:414-9. Available from: http://www.azmj.eg.net/text.asp?2018/16/4/414/256748




  Introduction Top


Diabetic macular edema (DME) is one of the leading causes of blindness in the working age population and is caused by disrupted blood–retinal barriers with increased vascular permeability, resulting in leakage of blood constituents into the retinal tissues leading to its thickening [1].

More than 50% of patients with macular edema will have a loss of two or more lines of their best-corrected visual acuity (VA) after 2 years of follow-up [2].

Laser photocoagulation is the standard treatment of macular edema [3]. However, the Early Treatment Diabetic Retinopathy Study [4] reported that focal laser photocoagulation in eyes having DME decreased the incidence of moderate visual loss by 50% or more. Also, 15% of eyes still suffer visual loss after 3 years of follow-up in spite of good focal laser photocoagulation. Furthermore, only 3% of laser-treated eyes had a VA improvement of three lines.

However, Lee and Olk [5] showed that grid-pattern laser photocoagulation resolved diffuse diabetic macular edema (dDME) in 68–94% of cases and stabilized VA in 61%. In contrast, they found that VA decreased by three or more lines in 24.6% of the eyes in their series, despite treatment.

The higher incidence of DME in diabetics with lack of an ideal treatment modality has resulted in a search for alternative therapies.

Several studies have reported the role of vitreous in the pathogenesis of DME [6],[7],[8]; hence surgical induction of posterior vitreous detachment (PVD) may prevent or result in spontaneous resolution of DME [9].

The question is whether vitrectomy will be similarly beneficial in reducing dDME in the presence or absence of attached posterior hayloid face?

Since the publication of Lewis et al. [10], which studied a number of patients having tractional DME with thickened posterior hyaloid, an interest was developed in vitrectomy as an alternative line of treatment for refractory DME. Several authors have stated that vitrectomy is effective for dDME, especially for eyes with thickened, taut posterior hyaloid. The encouraging results obtained in such cases after vitrectomy with PVD induction [11],[12],[13] suggest that tangential vitreomacular traction has a role in the development of DME. Furthermore, several studies have shown that vitrectomy may be effective in resolving DME with apparently normal posterior hyaloid and no PVD [14],[15],[16],[17].

The aim of this study is to evaluate the role of vitrectomy in resolving persistent dDME in the presence or absence of attached posterior hyaloid face.


  Patients and methods Top


This is a prospective study carried out on 37 eyes of 37 patients with persistent dDME with and without a PVD. This study was approved by the Ethical Committee of the Al-Azhar University. Pars plana vitrectomy (PPV) was performed between October 2016 and May 2017 for the treatment of dDME.

The clinical data of the 37 patients are described in [Table 1]. They are divided into two groups according to the state of the posterior vitreous face (PVF) which is either attached or detached (PVD) from the macular area. Twenty-one patients having attached PVF were enrolled in group I and 16 patients having PVD were enrolled in group II. All included eyes had received macular laser treatment of about two settings with the last one being 3 months before surgery and had received three to four intravitreal injections of anti-vascular endothelial growth factor 3 months before entry into this study. The duration of macular edema is not longer than 1 year. All included eyes are phakic. Excluded from the study are pseudophakic and aphakic eyes to rule out other factors contributing to macular edema than diabetes. Eyes receiving intravitreal injections or argon laser photocoagulation 1–2 months before surgery are excluded from the study. A written informed consent was obtained from all patients before enrollment in the study.
Table 1 Demographic data of the patients enrolled in this study

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The posterior segment and state of the PVF at the macula was assessed by indirect ophthalmoscopy and biomicroscopy using +78 D lens with a slit lamp to visualize the Weiz ring as well as by B-scan ultrasound. The retinal thickness in the foveal region and the state of the vitreous of all patients were assessed preoperatively, 3 and 6 months postoperatively by optical coherence tomography (OCT). We defined the retinal thickness as the distance between the inner retinal surface and the retinal pigment epithelium. VA was measured preoperatively, 1, 3, and 6 months after vitrectomy using Snellen’s chart and was converted into logMAR units. The surgical procedure was a standard three-port vitrectomy under local anesthesia combined with induction of PVD when the PVF was attached to the retina. The internal limiting membrane was stained with 0.1 ml of a 0.06% brilliant blue solution and then peeled with a forceps. Tamponade was achieved at the end of the operation using nonexpansile concentration of sulfur hexafluoride 20%.

The state of the PVF was re-evaluated as attached or detached to the macular area during surgery as well.

Postoperatively, topical antibiotic and anti-inflammatory therapy was administered three times daily.

Wilcoxon signed-rank test was used for comparison between preoperative and postoperative foveal thickness and visual acuities. Kruskal–Wallis test was used for comparison of the improvement of visual acuities and the decrease of foveal thickness.


  Results Top


A total of 37 patients were included in this study. Their ages ranged from 45 to 65 years (56.9±7.2 years), 59.46% (22 of 37) were men and 40.54% (15 of 37) were women. Both groups had a similar mean age and gender with no significant difference between them. The baseline VA varied from 0.9 to 0.5 with an average of 0.8±0.17 logMAR in group I, whereas in group II it ranged between 0.9 and 0.4with a mean of 0.7±0.39 logMAR.

One month after vitrectomy the mean VA significantly improved to 0.5±0.23 (P=0.002) and to 0.5±0.24 (P=0.015) in groups I and II, respectively.

After 3 months from surgery the VA in group I was 0.4±0.13 (P=0.001) and it was 0.5±0.19 (P=0.003) in group II ([Table 2]).
Table 2 Changes in visual acuity as logMAR in groups I and II before and after surgery

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By the end of 6 months postvitrectomy the VA in group I was 0.4±0.25 (P=0.005) and it improved by two or more lines in 11 (52.38%) of 21 eyes, remained unchanged in seven (33.33%) of 21 eyes, and worsened in three (14.28%) of 21 eyes because of a residual cystoid macular edema in two eyes and cataract formation in one eye ([Table 3]).
Table 3 Percentage and number of eyes that improved, unchanged, worsened their visual acuity after surgery in both groups

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Although in group II the final VA 6 months after surgery was 0.5±0.22(P=0.014) and it improved by two or more lines in nine (56.25%) of 16 eyes and remained unchanged in five (31.25%) of 16 eyes. In two (12.5%) eyes, there was a decrease in VA because of cataract formation in one eye and recurrence of macular edema in the other eye.

Comparison of the two groups showed that there was a significant difference in the change in VA in group I than in group II at the end of the follow-up period (P=0.02).

As regards the changes in foveal thickness, the postoperative mean foveal thickness (235.25±110.2 µm) was significantly less than the preoperative mean foveal thickness (598.6±105.4 µm; P=0.0001) in group I. However, in group II the postoperative mean foveal thickness (280.23±112.3 µm) also significantly improved than the baseline mean foveal thickness (520.87±103.15 µm; P=0.002) ([Figure 1] and [Figure 2]).
Figure 1 Optical coherence tomography images showing nontractional (with posterior vitreous detachment) diabetic macular edema (a, c) and optical coherence tomography images 6 months after vitrectomy showing resolved edema (b, d).

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Figure 2 Optical coherence tomography images showing tractional (no posterior vitreous detachment) diabetic macular edema (a, c) and optical coherence tomography images 6 months after vitrectomy showing resolved edema with removal of vitreomacular traction (b, d).

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At the end of the follow-up period, the foveal thickness was 220.13±98.15 µm and reduced by more than 40% of the baseline foveal thickness in 12 (57%) of 21 eyes and unchanged in six (28.6%) of 21 eyes and worsened in three (14.28%) of 21 eyes in group I. Although in group II at the end of 6 months, the foveal thickness was 270.62±85.15 µm and decreased by more than 32% of the baseline measurement in six (37.5%) of 16 eyes and remained unchanged in eight (50%) of 16 eyes and worsened in two (12.5%) of 16 eyes ([Table 4]).
Table 4 Changes in foveal thickness before and after surgery in both groups

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When we compare the two groups, there was no significant difference fund between the two groups in the reduction of the mean postoperative foveal thickness at the end of the follow-up period.

None of the eyes with worsened macular edema showed an increase of foveal thickness of more than 15% of the preoperative foveal thickness in the two groups.

Neither retinal nor lens complications developed during the course of the surgery, whereas postoperative complications were detected in three eyes. A posterior subcapsular cataract developed in two (5.4%) eyes and glaucoma in one eye 6 months after surgery.


  Discussion Top


Since the 1990s many studies have demonstrated that PPV is effective for treatment of dDME combined with a thickened taut posterior hyaloid [9],[10],[11],[12]. Others have also reported that PPV may achieve good results, even in the presence of PVD [15],[16],[17].

This study evaluated the effectiveness and safety of PPV as a treatment strategy for dDME.

Macular edema is a multifactorial complicated pathology and the vitreoretinal interface has an important role in its pathogenesis [18].

Several risk factors contribute to the development of DME such as the long duration of diabetes, type I diabetes, poor glycemic control, hypertension, and renal impairment [19]. The important pathological change in diabetic retinopathy is the loss of pericytes in retinal capillaries causing an increased vasopermeability [1].

Furthermore, various inflammatory and chemical mediators, such as interleukin 6 and vascular endothelial growth factor, fill the vitreous as a result of breakdown of blood–retinal barrier and induce macular edema remain in close contact to the macula in case of vitreomacular adhesion [7]. These mediators provide a stimulus for cellular migration and contraction leading to tangential traction on the macula inducing or exacerbating macular edema [6].

In support of the vitreous role in DME, Sebag et al. [20] found that destabilization of the gel structure of the vitreous attached to the macula induced by increased level of enzyme-mediated collagen cross-linking and nonenzymatic glycation in the vitreous of human diabetic patients could induce traction on the macula and persistence of the edema.

The mechanism of macular edema reduction after vitrectomy is not well understood. However, Lewis et al. [10] postulated that removal of posterior vitreous macular traction with vitrectomy will reduce macular edema. However, in our study, vitrectomy decreased macular edema effectively in eyes that already had PVD before surgery.

In experimental models of branch retinal vein occlusion, Stefansson et al. [21] observed that preretinal oxygen tension was higher in eyes than nonvitrectomized eyes and assumed that after vitrectomy the oxygen will diffuse from the aqueous humor into the vitreous cavity in high concentrations providing higher oxygen tension.

This high oxygen tension in the preretinal vitreous induces retinal vasoconstriction, and hence reducing the vascular leakage and, subsequently, may reduce DME [22].

This study demonstrated the effectiveness of PPV for treatment for DME, and its results do not depend on the presence or absence of attached PVF to the macula. Also, it has been shown that PPV is effective in improving VA and decreasing foveal thickness as well as the stability of the results during the follow-up period. We also had the same results of the PPV in eyes having preoperative PVD. Therefore, PPV probably does not work only by releasing macular traction but also through improving retinal oxygenation and removing all chemical mediators contributing to the development and persistence of DME.Several studies have shown that vitrectomy with removal of the posterior hyaloid leads to visual improvement of two or more lines in 38–92% of the eyes and a functional improvement in about 50% of patients [10],[14],[15],[23],[24].

Otani et al. [25] stated that foveal thickness decreases even when the vitreous is still attached but without evident traction at OCT.

However, many authors noticed a mismatch between the anatomical and functional results after vitrectomy were the macular thickness improved but the VA does not improve [9],[26],[27]. It is well known that an earlier intervention with a good preoperative VA will improve the results of vitrectomy [28]. Again, the morphology of the macular edema with the OCT will help in guiding the choice of treatment and will affect the results of vitrectomy. Patients with long-standing macular edema with a lot of cystic changes and a poor preoperative VA will have a poor outcome after vitrectomy.

Our results are not in agreement with those of Massin et al. [29], who stated that vitrectomy is only beneficial for DME when it is combined with a taut posterior hyaloid and of no benefit in patients with detached PVF from the macula. In a trial to explain this discrepancy we found that they conducted their study in a small number of patients and also nowadays we have a better understanding about the pathogenesis of macular edema and how many factors, not only traction, are implicated in its development.


  Conclusion Top


Vitrectomy with removal of the posterior hyaloid face and the premacular vitreous pocket may achieve resolution of dDME and improve vision in some patients who failed to respond to conventional treatment. The visual and anatomical outcomes seem to be better in eyes with early stages of DME and good preoperative VA.

The treatment of DME is a big debate and further studies with a large number of patients and longer follow-up periods are needed to provide further data on the pathogenesis and the treatment strategies for DME and to confirm the results of this study.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.



 
  References Top

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