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Keywords:

  • macular hole;
  • macular pucker;
  • posterior vitreous cortex;
  • posterior vitreous detachment;
  • vitrectomy;
  • vitreoretinal interface

Abstract.

  1. Top of page
  2. Abstract.
  3. Introduction
  4. Methods
  5. Results
  6. Discussion
  7. Acknowledgements
  8. References

Purpose:  To find the most reliable and efficient noninvasive technique to clinically detect a posterior vitreous detachment.

Methods:  In a prospective study of 30 eyes in 30 patients with macular pucker or macular hole formation, the posterior vitreous cortex was examined 1 day prior to a scheduled vitrectomy. Three independent investigators classified the posterior vitreous cortex of each eye as ‘attached’ or ‘detached’ via slit-lamp biomicroscopy (BM), 10-MHz B-scan ultrasonography (I³ Innovative Imaging Inc.), and optical coherence tomography [OCT III Stratus® (Carl Zeiss Meditec Inc.) and RTVue-100 OCT (Optovue Corp.)]. These preoperative findings were then compared during a triamcinolone acetonide-assisted vitrectomy 1 day later.

Results:  Triamcinolone acetonide-assisted vitrectomy showed in 60% a posterior vitreous detachment and in 40% an attached posterior vitreous cortex. Preoperatively conducted B-scan ultrasonography and BM revealed the highest, correct evaluation of the posterior vitreous status. The prediction of the OCT was confirmed intraoperatively in 12.5%. In all other cases, the evaluation by OCT was not possible or was inadequate.

Conclusion:  The prognostic most reliable but investigator-dependent methods to clinically detect whether the posterior vitreous cortex is detached are B-scan ultrasonography and BM. The objective technique of the high-resolution, two-dimensional time-domain OCT allows only in a few cases a clear differentiation of preretinal structures.


Introduction

  1. Top of page
  2. Abstract.
  3. Introduction
  4. Methods
  5. Results
  6. Discussion
  7. Acknowledgements
  8. References

As the largest structure within the eye, but mostly invisible, the vitreous received little attention in the past. Consisting of water (98%) and macromolecules (2%) (Sebag 1989), its outer shell is called the posterior vitreous cortex, which displays an adherence to the internal limiting membrane (ILM) of the retina. During the ageing process, the vitreous loses its gel-like structure and the vitreoretinal adhesion weakens, successively resulting in a liquefaction of the vitreous. The process of the separation of the posterior vitreous cortex from the ILM is called a posterior vitreous detachment (PVD).

It is largely unknown, which factors induce a PVD, but recent studies have shown, that the interaction between the posterior vitreous cortex and the retina seems to play a crucial role for the pathogenesis of many posterior pole disorders (Krebs et al. 2007; Murakami et al. 2007; Schulze et al. 2008, 2010; Robison et al. 2009; Bertelmann et al. 2011; Mennel et al. 2011).

The purpose of this study was to evaluate the most efficient and reliable, clinical technique to determine whether the posterior vitreous cortex is attached or detached within the vitreoretinal interface at the macula.

Methods

  1. Top of page
  2. Abstract.
  3. Introduction
  4. Methods
  5. Results
  6. Discussion
  7. Acknowledgements
  8. References

In this prospective clinical practice study, the posterior vitreous cortex of 30 eyes in 30 patients was examined by three independent investigators. Patients were enrolled between January 2009 and August 2010 at the University Eye Hospital of Marburg. Twenty-one patients had macular pucker, six macular hole formation, two macular hole with macular pucker formation and one patient vitreomacular traction. All 30 patients were scheduled to receive a pars plana vitrectomy with chromodissection as a result of the above listed posterior pole disorders. Only patients assigned for surgery were included in this study. Excluded were patients younger than 55 years, with proliferative diabetic retinopathy, opaque media, vitreous haze or vitreous bleeding.

The posterior vitreous cortex of each eye was examined via biomicroscopy (BM), 10-MHz B-scan ultrasonography (I³ Innovative Imaging Inc., Business Park Drive Sacramento, CA, USA), OCT OCT III Stratus® (Carl Zeiss Meditec, Inc., Dublin, CA, USA) and RTVue-100-OCT (Optovue Corp., Fremont, CA, USA).

One day prior to vitrectomy an independent, experienced retinal specialist performed slit-lamp BM using an external lens of 78 dioptres (Volk®, Volk Optical Inc., Enterprise Drive Mentor, OH, USA). A PVD was identified by the presence of a Weiss ring and the visible posterior vitreous cortex.

The second independent investigator examined the posterior vitreous cortex of all eyes by a high-gain ultrasonography device (10-MHz). This technique was performed open-eyed via transversal and longitudinal scans in the 3, 6, 9 and 12 o’clock position. The ultrasonography was performed in a supine position.

A third independent investigator performed optical coherence tomography (OCT) to assess the status of the posterior vitreous cortex. Two OCT instruments were used in each eye. OCT III Stratus® and RTVue-100-OCT were used in each eye, respectively, and all measurements were performed under identical mydriatic conditions. All images were assessed independently with reference to the vitreoretinal interface, particularly the discrete linear signals in the posterior vitreous, believed to be the posterior vitreous cortex separated from the retina. Six radial scans were performed through the centre of the fovea with additional lines through the upper and lower arcades. The results were statistically analysed using the statistical software spss 14.0 for Windows (SPSS Inc., Chicago, IL, USA). We used Fisher’s exact t-test for the statistical analysis. Significant results were assumed if p < 0.05.

These preoperative results were compared with findings on the following day during a scheduled triamcinolone acetonide-assisted vitrectomy. Positioning of the head, especially during surgery, causes a movement of the vitreous to the macula. Therefore, after injecting triamcinolone acetonide, the posterior vitreous cortex was evaluated during vitrectomy. A mobile vitreous was defined as PVD. Only when a firm attachment had to be removed by vitreous cutter suction, an attached vitreous was stated.

Results

  1. Top of page
  2. Abstract.
  3. Introduction
  4. Methods
  5. Results
  6. Discussion
  7. Acknowledgements
  8. References

A total of 30 eyes in 30 patients were examined in this study. The mean age was 67 years (range: 56–85 years). In the entire study population, 14 patients (46.6%) were men and 16 (53.3%) patients were women. Five patients (16.6%) were between 55 and 64 years old, two (6.6%) between 65 and 69 years, 22 (73.3%) between 70 and 79 years and one patient (3.3%) between 80 and 89 years. There were 21 patients (70%) with macular pucker, six (20%) with macular hole formation, two (6.6%) with macular hole combined with macular pucker formation and one patient (3.3%) with vitreomacular traction. Seven patients (23.3%) were pseudophac and 23 (76.6%) displayed a cataract formation. During triamcinolone acetonide-assisted vitrectomy, 12 eyes (40%) displayed an attached and 18 eyes (60%) a detached posterior vitreous cortex at the macula. Figure 1 shows the age distribution of the patients in correlation of the status of the vitreous cortex.

image

Figure 1.  Age pattern and distribution of status of the posterior vitreous cortex.

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In 83%, the preoperative evaluation of the expert using B-scan ultrasonography was correct. In our study, B-scan ultrasonography proved to be the method with the highest, informative value of all three tested techniques to assess the status of the posterior vitreous cortex preoperatively.

In 76%, the prediction by BM matched the intraoperative results. Biomicroscopy proved to be the second best method to clinically detect a PVD preoperatively.

In 70%, the OCT examiner was not able to make a clear judgment whether the posterior vitreous cortex was attached or detached. Neither Stratus® OCT (Carl Zeiss Meditec, Jena, Germany) nor RTVue OCT (Optovue, Heidelberg, Germany) displayed a clear preretinal structure. Therefore, an evaluation of the posterior vitreous cortex could not be made. In the remaining eight cases (30%), a fine preretinal, reflective structure above the macula was seen on both OCTs and evaluated by the OCT expert to be a PVD. Only in one case (12.5%), vitrectomy proved this reflective structure to be a PVD (Fig. 2).

image

Figure 2.  Recall ratio of validity of B-scan ultrasound (83%), biomicroscopy (76%), optical coherence tomography (OCT) (12.5%, Stratus®-OCT and RTVue-100) on the status of the posterior vitreous cortex.

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In the remaining seven cases, vitrectomy showed, despite a clear preretinal structure observed within both OCTs, a firm attached posterior vitreous cortex, which had to be mechanically pulled away from the posterior pole. No discrepancy between the findings of both OCT devices was observed. OCT proved to be the most inadequate technique of all three tested methods to assess the posterior vitreous cortex preoperatively (Table 1).

Table 1.   Testing of diagnostic finding’s dependence on diagnostic procedure. Diagnostic findings being the right/wrong/no assessment of the posterior vitreous cortex, diagnostic procedure being biomicroscopy (BM), ultrasonography and optical coherence tomography (OCT).
Posterior vitreous statusUltrasonographyBMOCT (Stratus/RTVue)
  1. p < 0.001, diagnostic finding is dependent on diagnostic procedure.

Correct assignment25231
Wrong assignment577
No assignment possible0022

Furthermore, we compared our OCT findings and the results of the pars plana vitrectomy with the results of our BM and ultrasonography experts. A subdivision of all eight cases that displayed a preretinal structure in both OCTs was made. One subdivision comprised all cases with preretinal structures with no contact to the fovea. The other subdivision consisted of all cases with preretinal structures with contact to the fovea. In seven cases, there was no contact of the preretinal structure to the neuroretina. In six of these seven cases, the expert of BM and ultrasonography assumed the vitreous to be attached. Only in one case, the experts disagreed. The expert of BM assumed to see an attached, and the expert of ultrasonography assumed to see a detached posterior vitreous cortex. The second group comprised one case with a fine preretinal structure that disclosed an adhesion at the fovea but had no neuroretinal contact at the extrafoveal region. The BM and ultrasonography experts assumed, in this case, the vitreous to be detached. In this case, the fine preretinal structure seen in the OCT was evaluated to present a partial PVD. In summary, the positive predictive value (PPV), the proportion of subjects with positive test results who are correctly diagnosed, was for BM and ultrasound (US) even and almost one. The negative predictive value, defined as the proportion of subjects with a negative test result who are correctly diagnosed, was also one for BM and ultrasound. Because of the restricted amount of useful data, OCT had to be excluded from this summary statistic. The combination of BM with (u) or versus ultrasound (v) displayed a high predictive value accuracy if there was PVD or not (Table 2).

Table 2.   Positive predictive value (PPV) and negative predictive value (NPV) for biomicroscopy (BM) and ultrasound (US) each and in combination of BM with (n) or versus ultrasound (v).
Predictive valueResult
PPV (BM v US)0.72222222
PPV (BM n US)0.83333333
PPV (BM)0.88888889
PPV (US)0.66666667
NPV (BM v US)0.83333333
NPV (BM n US)0.83333333
NPV (BM)0.75
NPV (US)0.91666667

Discussion

  1. Top of page
  2. Abstract.
  3. Introduction
  4. Methods
  5. Results
  6. Discussion
  7. Acknowledgements
  8. References

Recently, the evaluation of the status of the posterior vitreous cortex has become of great interest. Studies have shown that posterior pole pathologies are irrevocably involved with the structure of the posterior vitreous cortex (Krebs et al. 2007). To differentiate vitreomacular adhesion and PVD by a noninvasive technique is inevitable and decisive for further treatment.

In this prospective study, ultrasonography and BM served as the most reliable noninvasive techniques to assess the posterior vitreous cortex prior to vitrectomy. Triamcinolone acetonide was used for chromodissection to visualize the posterior vitreous cortex with little or no risk of retinal toxicity (Bababeygy & Sebag 2009). Ultrasonography and BM had the highest frequency of correct preoperative assessments, with 83% and 76%, respectively. Both techniques depend on the skills of the investigator and only serve as a reliable tool as long as the media are clear. It is common knowledge that two-dimensional OCT often shows a discrete linear signal above the neuroretina, devoid of any retinal contact. This is believed to be the posterior vitreous cortex separated from the retina, therefore displaying a PVD. In our study, no such preretinal, hyper-reflective structure could be observed in the OCT in the total of 22 cases. An evaluation whether the posterior vitreous cortex was attached or detached could not be made. In the remaining eight cases, this fine linear signal was observed in both OCTs. Triamcinolone acetonide-assisted vitrectomy proved only in one (12.5%) of eight cases this fine preretinal structure to be a PVD. In the remaining seven cases, the vitreous had to be detached mechanically from the retina. OCT revealed the lowest reliability index (12.5%) of correct assignments of all three tested methods with only one right assignment of eight cases. The remaining 22 cases could not be taken into consideration.

As a noninvasive tool with a reproducible depth into the vitreous cavity of approximately 1.000 μm, the OCT displays only a restricted view at the foveal depression and the vitreous above. In the absence of a fine preretinal structure in the OCT, a firm attached or even a more than 1.000 μm detached posterior vitreous cortex is possible. It is believed that if a PVD takes place within 1.000 μm above the fovea, a fine preretinal structure displays the posterior vitreous cortex in the OCT. Neither Stratus® OCT nor RTVue OCT clearly explain the origin of this hyper-reflective preretinal structure, seen approximately 100–200 μm above the fovea in the OCT. This fine structure is believed to be the posterior vitreous cortex, displaying a PVD. A PVD occurs after liquefied vitreous gets into the subhyaloidal space and separates the posterior vitreous cortex from the retina. Beside a complete PVD, a liquefaction of the vitreous gel without a vitreoretinal dehiscence may also occur. This is then called an anomalous PVD (Sebag 2008a,b). If during PVD the posterior vitreous cortex splits, it is called a vitreoschisis. Yamashita et al. (2008) observed during macular surgery a splitting of the posterior vitreous cortex into lamellae. A further hypothesis supports that epiretinal membranes are the results of anomalous PVD with vitreoschisis, leaving the outermost layer of posterior vitreous cortex attached to the macula. Several investigators (Wise 1975; Sidd et al. 1982; Kishi & Schimizu 1994; Appiah et al. 1998) reported in large clinical studies a partial or complete PVD that has been found in eyes with macular pucker in 80–95%. It is believed that macular pucker may be formed after hyalocytes proliferation contained within vitreous cortical remnants left on the retina surface after PVD. These remnants may then promote a fibrocellular proliferation (Sebag 2009; Gupta et al. 2011). Whether preretinal hyper-reflective lines in Stratus® OCT and RTVue OCT demonstrate a partial PVD or even an attached posterior vitreous cortex could not be drawn out. It remains unsolved whether the thin, hyper-reflective structure against the dark hypo-reflective vitreous cavity is indeed the posterior vitreous cortex or might be a rear panel of a bursa premacularis (Fig. 3).

image

Figure 3.  Optical coherence tomography (OCT III Stratus® above, RTVue-100 OCT below) images demonstrate a clear fine, hyper-reflective structure at an area above the neuroretina. Pars plana vitrectomy proved this fine structure only in 12.5% (one case) to be indeed a posterior vitreous detachment. In 87.5% (seven cases), the posterior vitreous cortex was attached despite a clear hyper-reflective structure seen on the OCT.

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Worst (1977) seeing vitreous cisterns after injecting India Ink intravitreally into autopsy eyes. They named the premacular structure bursa premacularis. Sebag (1989) observed in eyes with macular holes a round defect in the premacular vitreous cortex during vitrectomy. The premacular vitreous cortex was then sharply demarcated by a ring, the diameter two to four times of that of the Weiss ring. Doi et al. (2005) and Smiddy et al. (1988) described a premacular, liquefied space after the visualization of the vitreous with triamcinolone acetonide. This bursa premacularis is believed to form a subbursal space between the retina and the vitreous. Fine & Spaide observed (2006) a posterior precortical vitreous cortex during triamcinolone acetonide-assisted pars plana vitrectomy because of retinal detachment. Triamcinolone acetonide even filled the bursa and also its communicating channels. It might be possible that this discrete, hyper-reflective line seen on the OCT might be indeed a rear panel of a bursa premacularis.

In summary, our results show that BM and B-scan ultrasound are the most reliable clinical techniques, delivering a broad, general view of the posterior vitreous cortex interface, but still remaining dependent of the skills of the investigator. As a diagnostic tool, both deliver approximately equivalent results with 83% and 76% right assignments. The OCT displayed only in 30% a clear fine, hyper-reflective structure at an area within 1.000 μm above the neuroretina, demonstrating either the posterior vitreous cortex or the anterior wall of a thin posterior vitreous cortex adherent to the ILM. This structure was then correctly assigned in 12.5% (one case) via vitrectomy to be a PVD. In 70% (22 cases), the OCT could no give any assessment on the status of the posterior vitreous cortex at all and in 87.5% (seven cases) even gave an inadequate evaluation. Up to date, there is no definitive method to detect preoperatively whether the posterior vitreous cortex is attached or detached. The objective method of a high-resolution, two-dimensional OCT examination allows only in a few cases a differentiation of preretinal structures of the vitreous, leaving its interpretation restricted to a very small section of the retina and the vitreous.

Acknowledgements

  1. Top of page
  2. Abstract.
  3. Introduction
  4. Methods
  5. Results
  6. Discussion
  7. Acknowledgements
  8. References

There was no sponsor funding organization involved in this study. The author indicates no financial conflict of interest. The study and data accumulation were carried out with the approval of the appropriate Institutional Review Board. Informed consent from the research was obtained from the patients.

References

  1. Top of page
  2. Abstract.
  3. Introduction
  4. Methods
  5. Results
  6. Discussion
  7. Acknowledgements
  8. References