Proteins in the Subretinal Fluid

Does Subretinal Fluid Optical Density Ratio Differ Among the Eyes with Acute Central Serous Chorioretinopathy,Vogt Koyanagi Harada Disease and Choroidal Hemangioma: A Cross-sectional Study

PURPOSE

To investigate the diagnostic value of optical density ratio (ODR) in various diseases with subretinal fluid (SRF) due to different pathophysiologies.

METHODS

Patients with acute central serous chorioretinopathy; CSCR (n=49), Vogt Koyanagi Harada disease; VKH (n=34), and choroidal hemangioma (n=17) characterized with SRF were included. Spectral-domain optical coherence tomography (SD-OCT) images were analyzed using ImageJ by three independent readers. The ODRs were calculated using "region of interest (ROI)" and "entire region (TOTAL)" selection methods from the SRF to the vitreous, retinal nerve fiber layer (RNFL), and retinal pigment epithelium (RPE) reflectivity ratios. A correlation analysis between age, central macular thickness (CMT), SRF height, SRF width, and ODRs were obtained.

RESULTS

Optical density (OD) measurement was highly reproducible (intraclass correlation coefficient> 0.9). Optical density of the SRF, vitreous, RNFL, and signal strength were comparable (p=0.360, p=0.247, p=0.105, and 0.628, respectively). There was no difference in SRF OD measurements between the two methods (p=0.401), while there was a significant difference in vitreous OD measurements (p=0.016). ANOVA test of ODR_(ROI), ODR_(TOTAL), ODR-RPE _(ROI) and ODR-RNFL _(ROI) revealed no significant difference among acute CSCR, VKH disease and choroidal hemangioma groups (p>0.05 for all). Correlation analysis revealed a significant negative correlation between SRF height (p < 0.05) and CMT (p < 0.01) with SRF ODR_(ROI).

CONCLUSION

ODR measurement appears to be a highly repeatable SD-OCT parameter for diseases characterized with SRF collection. Despite variations in their pathophysiology, the ODR was not statistically different in acute CSCR, VKH disease, and choroidal hemangioma.

PREDISPOSING CHARACTERISTICS OF OPTICAL COHERENCE TOMOGRAPHY FOR PATIENTS WITH PERSISTENT SUBRETINAL FLUID AFTER SUCCESSFUL REPAIR OF RHEGMATOGENOUS RETINAL DETACHMENT

PURPOSE

To investigate the predisposing clinical parameters and characteristics of fundus imaging of patients with persistent subretinal fluid (PSF) after successful repair of rhegmatogenous retinal detachment.

METHODS

A retrospective study recruiting 57 patients was conducted. All patients underwent pars plana vitrectomy with silicone oil tamponade. Patients were divided into two groups: patients presenting PSF by the time of silicone oil removal as PSF group and patients presenting no PSF by the time of silicone oil removal as control group. All patients were followed up for 3 months or longer after primary surgery. Ophthalmic examinations, including fundus photography and optical coherence tomography, were performed.

RESULTS

There were significant differences between the two groups in average age, durations of preoperative symptoms, and type of retinal breaks ( P < 0.05). These clinical parameters showed statistical correlations with PSF ( P < 0.05). The proportions of patients presenting distinctive boundaries of the detached retina on fundus photograph and patients showing a hyperreflective line underlying the detached retina on optical coherence tomography in the PSF group were both significantly higher than the control group ( P < 0.05). The macular detachment heights on optical coherence tomography in the PSF group were significantly lower than the control group ( P < 0.05). These imaging characteristics also showed strong correlations with PSF ( P < 0.05).

CONCLUSION

This study suggests that patients with PSF have younger age, longer symptom duration, and higher incidence of retinal holes. The distinctive detachment boundary on fundus photograph, lower macular detachment height, and hyperreflective line underlying the detached retina on optical coherence tomography may be the predisposing characteristics of PSF.

Transthyretin proteoforms of intraocular origin in human subretinal fluid

Understanding the molecular composition of ocular tissues and fluids could inform new approaches to prevalent causes of blindness. Subretinal fluid accumulating between the photoreceptor outer segments and retinal pigment epithelium (RPE) is potentially a rich source of proteins and lipids normally cycling among outer retinal cells and choroid. Herein, intact post-translationally modified proteins (proteoforms) were extracted from subretinal fluids of five patients with rhegmatogenous retinal detachment (RRD), analyzed by tandem mass spectrometry, and compared to published data on these same proteins as synthesized by other organs. Single-nuclei transcriptomic data from non-diseased human retina/RPE were used to identify whether proteins in subretinal fluid were of potential ocular origin. Two human donor eyes with normal maculas were immunoprobed for transthyretin (TTR) with appropriate controls. The three most abundant proteins detected in subretinal fluid were albumin, TTR, and apolipoprotein A-I. Remarkably, TTR relative to the other proteins was more abundant than its serum counterpart, suggestive of TTR being synthesized predominantly locally. Six post-translationally modified protein forms (proteoforms) of TTR were detected, with the relative amount of glutathionylated TTR being much higher in the subretinal fluid (12-43%) than values reported for serum (<5%) and cerebrospinal fluid (0.4-13%). Moreover, a putative glycosylated TTR dimer of 32,428 Da was detected as the fourth most abundant protein. The high abundance of TTR and putative TTR dimer in subretinal fluid was supported by analysis of available single-nuclei transcriptomic data, which showed strong and specific signal for TTR in RPE. Immunohistochemistry further showed strong diffuse TTR immunoreactivity in choroidal stroma that contrasted with vertically aligned signal in the outer segment zone of the subretinal space and negligible signal in RPE cell bodies. These results suggest that TTR in the retina is synthesized intraocularly, and glutathionylation is crucial for its normal function. Further studies on the composition, function, and quantities of TTR and other proteoforms in subretinal fluid could inform mechanisms, diagnostic methods, and treatment strategies for age-related macular degeneration, familial amyloidosis, and other retinal diseases involving dysregulation of physiologic lipid transfer and oxidative stress.

Blood components and OCT reflectivity evaluated in animal model

BACKGROUND/PURPOSE

To see the relationship between blood components and optical coherence tomography (OCT) reflectivity using an animal model in which the aqueous humor was substituted by different experimental solutions without changing the integrity of the retina.

MATERIALS AND METHODS

The aqueous humor of an enucleated swine eye was replaced with plasma obtained from healthy volunteers. The OCT reflectivity of the anterior chamber filled with each plasma was calculated from individual OCT images, and was expressed by an arbitrary unit (AU). The concentration of blood components such as cholesterol, hemoglobin (Hb) and bilirubin of each individual was measured, and the correlation between each of them and the OCT reflectivity of aqueous humor in an enucleated swine eye was analyzed. Using the same model, the effects of the single plasma component on OCT reflectivity were examined.

RESULTS

Blood samples were obtained from 24 individuals. OCT reflectivity was 30.68 ± 14.8 AU (average ± SD), ranging from 11.11 to 60.31 AU. OCT reflectivity correlated significantly with the concentration of triglycerides (R = 0.634, p = 0.001) and total cholesterol (R = 0.488, p = 0.015) using Spearman's rank correlation coefficient. While a partial correlation analysis showed that it correlated significantly with triglyceride (R = 0.60, p = 0.003), but not total cholesterol. OCT reflectivity was highest in a balanced salt solution (BSS) with Hb (average 42.05 AU), followed by fibrinogen (8.08 AU), bilirubin (6.12 AU) and γ-globulin (2.85 AU). Albumin did not increase the reflectivity of the BSS with a normal concentration (1.11 AU) compared to the control BSS alone (0.73 AU).

CONCLUSIONS

OCT reflectivity was most strongly affected by the presence of triglycerides among the blood components. Some molecules such as Hb and fibrinogen significantly increase the OCT reflectivity. This information should be helpful for interpreting the OCT findings correctly.

Concentration of neuron-specific enolase and S100 protein in the subretinal fluid of rhegmatogenous retinal detachment

BACKGROUND

Neuron-specific enolase and S100 protein are markers of neuronal lysis. To assess the neuronal suffering in rhegmatogenous retinal detachment we quantified neuron-specific enolase and S100 protein in the subretinal fluid.

METHODS

The puncture was performed in the sclera with a Merseture 5/0 round needle, and the fluid was collected with a glass capillary tube. Twelve subretinal fluid samples were obtained from 12 eyes with rhegmatogenous retinal detachment undergoing retinal detachment surgery. Vitreous from ten eyes with macular hole or epimacular membrane served as negative control group, and vitreous collected during cornea procurement from ten deceased patients served as positive control group.

RESULTS

The mean concentration of neuron-specific enolase (in nanogrammes per millilitre) was 602 in the subretinal fluid of rhegmatogenous retinal detachment, 10.2 in the serum of these patients, 2.9 in the vitreous of the negative control group, and 364 in the positive control group. The mean concentration of S100 protein (in nanogrammes per millilitre) was 104 in the subretinal fluid of rhegmatogenous retinal detachment, <0.1 in the serum of these patients and in the vitreous of the control negative group, and 11.18 in the positive control group.

CONCLUSION

Neuron-specific enolase (NSE) and S100 are known to be good markers of brain stress and, thus, are good markers of retinal stress.

Subretinal fluid in primary rhegmatogenous retinal detachment: physiopathology and composition

During retinal detachment, subretinal fluid is present, whose composition and physiopathology are still little known. Under normal conditions, osmotic and oncotic pressures help keep the retina in place, but the main retinal attachment force is provided by active transport in the pigment epithelium. Subretinal fluid composition varies according to detachment duration; total protein concentration in subretinal fluid increases with time. In addition, all proteins are qualitatively modified. The detached retina loses its oxygen supply, and it then uses the anaerobic pathway to degrade glucose. Thus, long-duration retinal detachments feature increased lactic acid and dextrose concentrations. Phospholipids are also increased in subretinal fluid, reflecting retinal degradation. This review presents data on the physiopathology and composition of the subretinal fluid in retinal detachments.

Von Willebrand factor in subretinal fluid

PURPOSE

To measure the vWF antigen concentration (vWF Ag) in subretinal fluid (SRF) and blood plasma.

METHODS

Prospective study of 30 patients, aged from 15 to 78 years (mean 52.7 years), undergoing retinal detachment surgery. Excluded were patients with venous or arterial disease or any other factors that could affect the parameters evaluated. Subretinal samples were obtained at the time of routine drainage during retinal detachment surgery. Venous blood samples were taken from the cubital vein into sodium citrate solution (9:1) immediately after induction of anesthesia but before surgery. VWF in plasma and in SRF and its relation to patients' age, sex, the duration and extent of retinal detachment, number of retinal tears, and cryopexy application were evaluated.

RESULTS

The median level of vWFAg in 30 samples of SRF was 6.3%. The median level of vWF Ag in blood plasma was 70.34%. The levels of vWF Ag in SRF were significantly lower than in blood plasma (p<0.00001). We found no correlation between the vWF Ag concentration in plasma or in SRF and sex, the degree of myopia, the duration and extent of retinal detachment, number of retinal tears and the use of cryopexy.

CONCLUSIONS

Determination of vWF Ag showed that this factor in SRF is unrelated to patients', sex, the degree of myopia, the duration and extent of retinal detachment, number of retinal tears and use of cryopexy.