Macular Appearance After Diabetic Vitrectomy
Condition: Proliferative Diabetic Retinopathy; Vitrectomy
MeSH terms: Diabetic Retinopathy
Study type: Observational

Summary: 
      Vitrectomy is one of the major treatment methods for complications of diabetic retinopathy.
      As surgical techniques and instruments improve, high anatomical success may be achieved;
      however, functional results are less favorable. Despite attached retina, postoperative visual
      function may be affected by various macular and disc abnormalities. Major changes include
      optic atrophy, atrophic retina, poor macular perfusion, and structural alternations of the
      macula. Funduscopy, fluorescein angiography, and, more recently, optical coherence tomography
      (OCT) can be used to detect and document these alterations. Although fluorescein angiography
      is valuable in the assessment of various macular lesions as well as retinal vascular
      abnormalities, its usefulness in evaluating macular changes is limited in eyes that have
      undergone diabetic vitrectomy. The quality of the images may be compromised by mild diffuse
      hyperfluorescence in the posterior pole in middle and late phase angiography, which obscures
      capillary detail and subtle macular changes. Furthermore, quantification of changes may not
      be possible. Recently, optical coherence tomography has become very useful for the detection
      of vitreomacular abnormalities. The examination is noninvasive, can qualify the changes and
      detect subtle abnormalities not evident with other imaging studies.

      In this study, OCT was applied to investigate how common macular structure abnormalities are
      present after surgery for complications of diabetic retinopathy, and how they may affect
      visual prognosis.
    

Detailed description: 
      From June 2008 to December 2008 consecutive patients undergo pars plana vitrectomy for
      diabetic fibrovascular proliferation were included in the study.

      All cases have fibrovascular proliferation with vitreo-retinal adhesions in 3 or more sites
      but not extending beyond equator in more than one quadrant. Complete removal of the visible
      posterior preretinal membrane was done during surgery in every case. All cases included in
      the study had attached retina postoperatively. Cases with rhegmatogenous detachment, silicone
      oil infusion, or post-operative moderate to dense cataract were not included. Surgical
      indications included progressive fibrovascular proliferation (FVP), and traction retinal
      detachment. Postoperative standard 6 mm 6-line OCT (Stratus OCTTM optical coherence
      tomography, Carl Zeiss Meditec, Inc., Dublin, CA) study centered on the macula and fundus
      photography were carried out between 7 months to 15 months after surgery. All cases were
      enrolled from the Department of Ophthalmology, National Taiwan University Hospital, Taipei,
      Taiwan.

      Data on patients' age, gender, systemic diseases, study eye, types and duration of diabetes
      mellitus, intraoperative diagnosis, and additional surgical procedures such as cryotherapy,
      scleral buckling [segmental sponge or 360º encircling buckle (Gore-Tex®,
      polytetrafluoroethylene, W. L. Gore & Associates, Inc., Flagstaff, AZ)], or internal gas
      (C3F8 or SF6) are recorded. Further data about OCT findings, best-corrected visual acuity at
      the time of OCT images, and the duration of post-operative follow-up also are compiled.
      Different morphological appearances of the macula detected by OCT are categorized. These
      changes are compared between the two surgical subgroups. Correlations of the morphological
      changes with postoperative visual outcome are conducted.

      For the purpose of OCT categorization, measured thickness of more than 300um in the central
      foveal area and more than 400um in the surrounding macular area in at least 3 examination
      lines with or without intraretinal cystic spaces or epiretinal membrane is defined as
      increase of macular thickness. Visible cystic spaces in and immediate adjacent to the fovea
      is categorized as foveal cysts. The presence of clear optical empty space between pigment
      epithelium and neurosensory retina are defined foveal detachment.

      Statistical analysis In the first step of the statistical analyses, Chi-square test (or
      Fisher exact test, if n<5) and Kruskal-Wallis test, followed by the Mann-Whitney U test were
      used to analyze each variant individually for univariate analysis. In the second step,
      multivariate regression models were used for elucidating the independent influence of each
      morphological change on postoperative visual outcome. Levels of statistical significance were
      set at P<0.05.
    

Observational model: Cohort
Time perspective: Retrospective
Sampling method: Non-Probability Sample
Study population: 
        Proliferative diabetic retinopathy
      
Keywords: Diabetic vitrectomy; Epiretinal membrane (ERM); Macular appearance; Optical coherence tomography (OCT); Visual function