To see the invisible: the quest of imaging vitreous

Hyalocyte origin, structure, and imaging

Introduction

Hyalocytes have been recognized as resident tissue macrophages of the vitreous body since the mid-19th century. Despite this, knowledge about their origin, turnover, and dynamics is limited.

Areas covered

Historically, initial studies on the origin of hyalocytes used light and electron microscopy. Modern investigations across species including rodents and humans will be described. Novel imaging is now available to study human hyalocytes in vivo. The shared ontogeny with retinal microglia and their eventual interdependence as well as differences will be discussed.

Expert opinion

Owing to a common origin as myeloid cells, hyalocytes and retinal microglia have similarities, but hyalocytes appear to be distinct as resident macrophages of the vitreous body.

Effect of posterior vitreous detachment on treat-and-extend versus monthly ranibizumab for neovascular age-related macular degeneration

AIMS

To investigate the impact of posterior vitreous detachment (PVD) on the efficacy of treat-and-extend (T&E) ranibizumab in neovascular age-related macular degeneration.

METHODS

In a post hoc analysis of a randomised controlled clinical trial, spectral-domain optical coherence tomography images of treatment-naïve patients randomised to receive T&E (n=265) or monthly (n=264) ranibizumab for 12 months were included. Certified, masked graders diagnosed the presence or the absence of complete PVD. The main outcome measures were the mean change in best-corrected visual acuity (BCVA) and central retinal thickness (CRT) at month 12, the number of administered ranibizumab injections and the proportion of patients extended to more than 8 weeks.

RESULTS

At baseline, complete PVD was present in 51% and 56% of patients in the monthly and T&E arms, respectively. Mean change in BCVA at month 12 was +9.0 (PVD) vs +9.5 letters (no PVD, p=0.78) in monthly treated eyes, and +6.0 (PVD) vs +7.5 letters (no PVD, p=0.42) in T&E treated eyes. Conversely, mean change in CRT at month 12 was -174 (PVD) vs -173 µm (no PVD, p=0.98) in the monthly arm, and -175 (PVD) vs -164 µm (no PVD, p=0.58) in the T&E arm. In T&E treated patients, the median number of injections was eight vs nine (p=0.035). 71% of PVD eyes were extended successfully, compared with 55% of eyes without PVD (p=0.005).

CONCLUSION

PVD was not found to impact functional and anatomical outcomes of T&E ranibizumab therapy. However, patients without a complete PVD required more retreatments and were significantly less likely to be successfully extended.

TRIAL REGISTRATION NUMBER

NCT01948830.

Diabetes-induced oxidative stress in the vitreous humor

Purpose

Diabetes is accompanied by fundamental rearrangements in redox homeostasis. Hyperglycemia triggers the production of reactive oxygen and nitrogen species which contributes to tissue damage in various target organs. Proliferative diabetic retinopathy (PDR) is a common manifestation of diabetic complications but information on the possible role of reactive intermediates in this condition with special regard to the involvement of the vitreous in PDR-associated redox alterations is scarce.

The aim of the study was to determine key parameters of redox homeostasis [advanced glycation endproducts (AGE); protein carbonyl and glutathione (GSH)] content in the vitreous in PDR patients.

Methods

The study population involved 10 diabetic patients undergoing surgery for complications of proliferative diabetic retinopathy and 8 control (non-diabetic) patients who were undergoing surgery for epiretinal membranes. Vitreal fluids were assayed for the above biochemical parameters.

Results

We found elevated levels of AGE in the vitreous of PDR patients (812.10 vs 491.69 ng AGE/mg protein). Extent of protein carbonylation was also higher in the samples of diabetic patients (2.08 vs 0.67 A/100 μg protein). The GSH content also increased in the vitreous of PDR patients as compared to the control group (4.54 vs 2.35 μmol/μg protein), respectively.

Conclusion

The study demonstrates that diabetes-associated redox alterations also reach the vitreous with the most prominent changes being increased protein carbonylation and increased antioxidant levels.

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Vitreal AGE levels are elevated in PDR patients.

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Extent of protein carbonylation is higher in the vitreal samples of PDR patients.

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The glutathione content is increased in the vitreous of PDR patients.

Vitreous floaters: Etiology, diagnostics, and management

Vitreous is a hydrated extracellular matrix comprised primarily of water, collagens, and hyaluronan organized into a homogeneously transparent gel. Gel liquefaction results from molecular alterations with dissociation of collagen from hyaluronan and aggregation of collagen fibrils forming fibers that cause light scattering and hence symptomatic floaters, especially in myopia. With aging, gel liquefaction and weakened vitreoretinal adhesion result in posterior vitreous detachment, the most common cause of primary symptomatic floaters arising from the dense collagen matrix of the posterior vitreous cortex. Recent studies indicate that symptomatic floaters are not only more prevalent, but also have a negative impact on the quality of life that is greater than previously appreciated. We review the literature concerning management of symptomatic vitreous floaters, currently either with observation, vitrectomy, or Nd:YAG laser. Published evidence is consistent with a low-risk profile and excellent success rate for floater vitrectomy, particularly with sutureless small gauge instruments and a limited core vitrectomy without PVD induction. Nd:YAG laser treatment of floaters, reported less commonly, claims resolution of floaters ranging between 0% and 100%; however, both peer-reviewed literature and assertions on web-based nonpeer-reviewed laser vitreolysis sites remain to be substantiated, and at present only vitrectomy has proven value. Prospective studies using objective, quantitative outcome measures are required to assess the relative efficacy and safety of these two procedures as well as new therapies such as pharmacologic vitreolysis.

Evaluation of a posterior vitreous detachment: a comparison of biomicroscopy, B-scan ultrasonography and optical coherence tomography to surgical findings with chromodissection

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.

[The myopic vitreous. Why is its examination so difficult?]

The examination of a high myopic vitreous is difficult for several reasons, including optic phenomena and vitreous liquefaction. The diagnosis of a posterior vitreous detachment may be problematic and confused with the observation of a large lacuna posterior margin.

Vitreous deformation during eye movement

Retinal detachment results in visual loss and requires surgical treatment. The risk of retinal detachment depends, among other factors, on the vitreous rheology, which varies with age. To date, the viscoelasticity of the vitreous body has only been measured in cadaver eyes. However, the ex vivo and in vivo viscoelasticity may differ as a result of the effect of intravitreal membranes. Therefore, an MRI method and appropriate postprocessing tools were developed to determine the vitreous deformation and viscoelastic properties in the eyes of living humans. Nineteen subjects (eight women and 11 men; mean age, 33 years; age range, 14-62 years) gazed at a horizontal sinusoidal moving target during the segmented acquisition of complementary spatial modulation of magnetization images. The center of the lens and the scleral insertion of the optic nerve defined the imaging plane. The vitreous deformation was tracked with a dedicated algorithm and fitted with the commonly used viscoelastic model to determine the model parameters: the modified Womersley number a and the phase angle b. The vitreous deformation was successfully quantified in all 17 volunteers having a monophasic vitreous. The mean and standard deviation of the model parameters were determined to be 5.5 ± 1.3 for a and -2.3 ± 0.2 for b. The correlation coefficient (-0.76) between a and b was significant. At the eye movement frequency used, the mean storage and loss moduli of the vitreous were around 3 ± 1 hPa. For two subjects, the vitreous deformation was clearly polyphasic: some compartments of the vitreous were gel-like and others were liquefied. The borders of these compartments corresponded to reported intravitreal membrane patterns. Thus, the deformation of the vitreous can now be determined in situ, leaving the structure of the intravitreal membranes intact. Their effect on vitreous dynamics challenges actual vitreous viscoelastic models. The determination of the vitreous deformation will aid in the quantification of local vitreous stresses and their correlation with retinal detachment.

Diffusion changes in the vitreous humor of the eye during aging

BACKGROUND AND PURPOSE

The inability to image the vitreous humor of the eye adequately hinders a complete understanding of its normal structure and the changes occurring in aging and disease. The purpose of the present study was to reveal normative data and age-related changes of the vitreous humor by using DWI.

MATERIALS AND METHODS

A total of 160 patients were enrolled in the present study. Patients were divided into 8 groups according to decade of age, and each group was of equal size with 20 patients. The ADCs were determined for each vitreous humor. Each determination was obtained by using average regions of interest of 50 ± 2 mm(2). ADC values were then plotted against age.

RESULTS

The ADC values obtained from group 0 (0-10 years of age) were statistically different from those of all other groups (P < .05). Group 1 (11-20 years of age) was statistically different from groups 3, 5, 6, and 7 (P < .05). A trend toward increased ADC values with increasing age was not statistically significant.

CONCLUSIONS

Besides the statistically significant difference between pediatric and adult patients, a statistically insignificant trend of increased ADC values among aging adults has been demonstrated. These normative data contribute to our understanding of how DWI can aid in the diagnosis of age-related changes in eye health and function.

Vitreous substitutes: a comprehensive review

Vitreoretinal disorders constitute a significant portion of treatable ocular disease. Advances in vitreoretinal surgery have included the development and characterization of suitable substitutes for the vitreous. Air, balanced salt solutions, perfluorocarbons, expansile gases, and silicone oil serve integral roles in modern vitreoretinal surgery. Vitreous substitutes vary widely in their properties, serve different clinical functions, and present different shortcomings. Permanent vitreous replacement has been attempted with collagen, hyaluronic acid, hydroxypropylmethylcellulose, and natural hydrogel polymers. None, however, have proven to be clinically viable. A long-term vitreous substitute remains to be found, and recent research suggests promise in the area of synthetic polymers. Here we review the currently available vitreous substitutes, as well those in the experimental phase. We classify these compounds based on their functionality, composition, and properties. We also discuss the clinical use, advantages, and shortcomings of the various substitutes. In addition we define the ideal vitreous substitute and highlight the need for a permanent substitute with long-term viability and compatibility. Finally, we attempt to define the future role of biomaterials research and the various functions they may serve in the area of vitreous substitutes.

Observations by spectral-domain optical coherence tomography combined with simultaneous scanning laser ophthalmoscopy: imaging of the vitreous

PURPOSE

To determine the ability to detect normal vitreous structure, evolving posterior vitreous detachment (PVD), and related vitreoretinal changes with combined spectral-domain optical coherence tomography (SD-OCT) and scanning laser ophthalmoscopy (SLO).

DESIGN

Observational cross-sectional study.

METHODS

Simultaneous SD-OCT and SLO imaging instruments (SD-OCT/SLO) were used to image both eyes of patients with symptoms of PVD. The vitreous cortex, preretinal lacunae, hyaloid, and its relations to the retinal surface were analyzed. In addition, ultrasound was performed in a subset of patients to determine the stage of PVD.

RESULTS

Two-hundred two eyes of 113 subjects were scanned. There was a high correlation between diagnosis of complete PVD by clinical examination and OCT (95 vs 93 eyes, respectively; kappa, 0.82). A partial PVD was detected more frequently by SD-OCT/SLO than by biomicroscopy examination (45 vs 7 eyes; P < .0001). Ultrasound was performed in a subset of 30 eyes. A high agreement was found between ultrasound and SD-OCT/SLO results for both complete PVD (kappa, 0.933) and incomplete PVD (kappa, 0.91). Vitreous cortex was detected in 181 eyes, and posterior precortical vitreous pocket was detected in 85 eyes. The effects of PVD, including vitreoretinal traction, paravascular lamellar holes, and fine changes at the fovea, could be visualized reliably in detail only with SD-OCT/SLO. In all these eyes, SD-OCT/SLO allowed improved visualization of the vitreoretinal relationship.

CONCLUSIONS

SD-OCT/SLO provides unprecedented in vivo information about the physiologic and pathologic vitreous structure; it allows an extremely detailed analysis of the vitreoretinal interface, and it is particularly useful for defining focal changes and PVD.

Spectral-domain optical coherence tomography: a comparison of modern high-resolution retinal imaging systems

PURPOSE

To provide a review of commercially available spectral-domain optical coherence tomography (SD OCT) systems in clinical ophthalmology.

DESIGN

Perspective.

METHODS

Review of current manufacturer information, selected articles from the literature, and the authors' clinical experience.

RESULTS

Because the premise of SD OCT technology is the nonproprietary mathematical formula of Fourier transformation, 9 different SD OCT systems currently are or soon will be commercially available. Also demonstrated are Cirrus en face C-scan visualization of photoreceptor attenuation resulting from acute zonal occult outer retinopathy and Spectral OCT/scanning laser ophthalmoscopy microperimetric analysis of a macular caldera lesion resulting from North Carolina macular dystrophy.

CONCLUSIONS

Advances in high-resolution imaging of the anterior and posterior segment have revealed new in vivo details of anatomic, physiologic, and pathologic data for the practice of ophthalmology. Compared with time-domain OCT, SD OCT tends to derive increased retinal thickness and decreased nerve fiber layer thickness measurements. This is likely because of increased depth of resolution and greater volume of data acquired with each scan. Interdevice comparison is not practical because of differences in individual segment boundary algorithms. Improvements in photoreceptor inner segment-outer segment layer visualization should aid our understanding of visual dysfunction in a variety of retinal pathologic features. As the technology develops, SD OCT will continue to provide new insights about ocular structure and disease.