CHEMICAL COMPOSITION OF SUBRETINAL FLUID

Characteristics of subretinal particles detected after pars plana vitrectomy for rhegmatogenous retinal detachment

BACKGROUND

To determine the incidence and characteristics of the multiple subretinal particles (SRPs) present after pars plana vitrectomy (PPV) for rhegmatogenous retinal detachment (RRD).

METHODS

The medical records of 224 eyes of 224 patients that underwent PPV for RRD were reviewed. The presence of SRPs in the subretinal fluid blebs and the presence of subretinal deposits were determined by optical coherence tomography (OCT) and fundus autofluorescence (FAF). The characteristics of the FAF and infrared reflectance (IR) images of a scanning laser ophthalmoscope in eyes with SRPs (SRPs group) were compared to that of eyes without SRPs (control group).

RESULTS

SRPs were observed in 27 eyes (12%), and they were completely resolved in 20 eyes (74%) after 6 months. The incidence of macula-off RRD (85%) and preoperative precipitates (41%) were significantly higher in the SRPs group than that in the control group (64%, P = 0.046; 12%, P = 0.002). The axial length was significantly shorter in the SRPs group than that in the control group (25.04 ± 1.54 mm, 26.00 ± 1.78 mm, P = 0.012). The preoperative and postoperative best-corrected visual acuity were not significantly different between the two groups (P = 0.702, P = 0.337). The subretinal fluid bleb determined by OCT were hyperfluorescent in the FAF images in 24 eyes (89%), and the subretinal deposits were hypofluorescent with solid appearance by OCT other than fluid in 3 eyes (11%). The hypofluorescent subretinal deposits in the FAF images were bright in the IR images in 2 eyes.

CONCLUSIONS

The SRPs consist of lipofuscin-related hyperfluorescent subretinal fluid and the subretinal deposits containing bright IR melanin particles of proliferating retinal pigment epithelial cells.

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.

A mathematical determination of foveal attachment in primary rhegmatogenous retinal detachment when obscured by bullous retina

In primary rhegmatogenous retinal detachment (RRD), the foveal attachment is an important prognostic factors for post-operative vision. When the fovea is obscured by the RRD, its attachment status is considered uncertain. Using a model of the reduced emmetropic and − 10 dioptre myopic eye and the physical properties of the detached retina, we aimed to mathematically ascertain if it is clinically possible for the fovea to be attached while it is obscured by the primary RRD. With the patient upright, a primary RRD due to a 12 o’clock break directly above the fovea was considered. Mathematically, once the trough of the RRD touches the visual axis the edge of the RRD nearest to fovea is \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$2.77\,{\text{mm}}$$\end{document}2.77mm away from fovea in emmetropic eye and \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$2.89\;\,{\text{mm}}$$\end{document}2.89mm in myopic eye. When the RRD reaches the fovea, its trough is \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$2.20{\text{ mm}}$$\end{document}2.20mm below the visual axis in emmetropic eye and \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$2.29{\text{ mm}}$$\end{document}2.29mm in myopic eye. However, in vivo the RRD makes an acute angle with the retinal pigment epithelium and the corrugation of the retina in RRD shortens the retina. When these in vivo constraints are considered, in both of the above situations the fovea will be detached. If the fovea is obscured by an RRD, the fovea is very likely to be detached. In idiomatic terms, if the fovea cannot be seen, the fovea cannot see. This is an important clinical diagnosis for appropriate triage of the patient.

Can the Macula be Attached if View Is Obscured by a Bullous Retinal Detachment? A Mathematical Consideration

Purpose

The purpose of this study was to determine if it is possible for the macula to remain attached if a bullous retinal detachment blocks the examiner's view to the macula.

Methods

A mathematical analysis compared the arc length of the attached retina versus the length of a detached retina necessary to obscure the macula (hang over the visual axis). The shape (oblate ellipsoid) and dimensions of the retina were based on a published study. The complete path of the hanging retina was calculated as a static catenary so as to depict the lowest possible position (“worst case scenario”).

Results

The measured and calculated angle between the fovea and ora serrata was 105 degrees. When considering a catenary shape of the hanging retina, the macula could, mathematically, still be attached despite the retina hanging down 1.03 mm below the visual axis for an emmetropic eye. The maximal distance calculated was 1.095 mm for a −12 diopter (D) myopic eye.

Conclusions

If the macular center cannot be viewed due to a bullous superior retinal detachment hanging into the examiner's view, it is unlikely but possible that the macula remains attached. If the view is obscured by at least 1 mm below the fovea, it is not mathematically possible for the fovea to be attached.

Translational Relevance

The status of the macula being detached is subject to mathematical constraints, which, explored herein, offer a higher certainty of clinical decision making that could inform management for better clinical results.

Minocycline prevents the inflammatory response after retinal detachment, where microglia phenotypes being regulated through A20

Retinal detachment (RD) is a severe sight-threatening complication that can be caused by a multitude of retinal diseases. It has been evidenced that minocycline exerts neuroprotective effects by targeting microglia in the pathogenesis of massive ocular lesions including RD, but mechanisms remain elusive. We carried out this research to elucidate the potential mediators that link RD-induced vision loss with microglia reactivity by discussing effects of minocycline on cytokine levels and A20, a negative regulator of inflammation. Minocycline or vehicle was intraperitoneally administrated immediately after RD and continued daily before animals being euthanized. The oxygen glucose deprivation assay was undertaken on the co-cultured BV-2 and 661W cells to mimic the condition of RD in vitro, where A20 siRNA was adopted to knock down the A20 expression in BV-2 cells. Photoreceptor cells apoptosis, inflammatory response and microglia activity following RD with or without minocycline were evaluated. Photoreceptor cells apoptosis and inflammatory response were induced after RD, which could be largely counteracted by minocycline. Minocycline postponed the migration and proliferation of microglia and facilitated their transition to the M2 subtype following RD. Blocking A20 expression in BV-2 cells with siRNA crippled the effect of minocycline. Collectively, minocycline yields a promoting effect on photoreceptor cells survival post-RD by modulating the transformation of microglia phenotypes, in which process A20 may play a "bridge" role.

Multiple subretinal fluid blebs after pars plana vitrectomy for rhegmatogenous retinal detachment repair

PURPOSE

To investigate the incidence of and clinical risk factors for multiple subretinal fluid (SRF) blebs after pars plana vitrectomy (PPV).

METHODS

This study examined patients who underwent PPV (25- or 27-gauge) to repair a primary rhegmatogenous retinal detachment (RRD). Clinical characteristics, including age, sex, axial length, symptom duration, and postoperative best-corrected visual acuity (BCVA), were compared between eyes with and without multiple SRF blebs. Intentional drainage retinotomy and cryotherapy use were also performed. Main outcome measures were the effect of these parameters on multiple SRF bleb incidence 1 month after surgery.

RESULTS

A total of 108 eyes of 106 patients (76 men and 32 women; mean age = 58.9 ± 9.0 years) were included. Multiple SRF blebs were observed in 8 eyes (7.4%). Logistic regression analysis showed that creation of intentional drainage retinotomy and 27-gauge PPV are risk factors for the development of multiple SRF blebs. The number and size of blebs spontaneously decreased over time, and SRF had completely resolved in 5 eyes (62.5%) 1 year after surgery.

CONCLUSION

Multiple SRF blebs developed even after small gauge vitrectomy. The SRF did not affect postoperative BCVA and gradually absorbed without treatment.

Microglia inhibit photoreceptor cell death and regulate immune cell infiltration in response to retinal detachment

Photoreceptor cell death resulting from retinal detachment (RD) causes significant visual loss. While the immune system is activated during RD, its role is still unclear. Microglia are resident immune cells in the retina and are thought to be either protective or deleterious in response to neuronal injury, suggesting context-dependent effects. Here, we demonstrate that microglia limit retinal damage during acute injury, since microglial ablation led to increased photoreceptor death. Microglial morphological–activation changes triggered their migration into injured tissue where they formed intimate connections with infiltrating immune cells and phagocytized injured photoreceptors. These findings provide insight into the microglial response and function during RD, indicating microglia promote photoreceptor survival during acute phase injury by removing potentially damaging cell debris.

Retinal detachment (RD) is a sight-threatening complication common in many highly prevalent retinal disorders. RD rapidly leads to photoreceptor cell death beginning within 12 h following detachment. In patients with sustained RD, progressive visual decline due to photoreceptor cell death is common, leading to significant and permanent loss of vision. Microglia are the resident immune cells of the central nervous system, including the retina, and function in the homeostatic maintenance of the neuro-retinal microenvironment. It is known that microglia become activated and change their morphology in retinal diseases. However, the function of activated microglia in RD is incompletely understood, in part because of the lack of microglia-specific markers. Here, using the newly identified microglia marker P2ry12 and microglial depletion strategies, we demonstrate that retinal microglia are rapidly activated in response to RD and migrate into the injured area within 24 h post-RD, where they closely associate with infiltrating macrophages, a population distinct from microglia. Once in the injured photoreceptor layer, activated microglia can be observed to contain autofluorescence within their cell bodies, suggesting they function to phagocytose injured or dying photoreceptors. Depletion of retinal microglia results in increased disease severity and inhibition of macrophage infiltration, suggesting that microglia are involved in regulating neuroinflammation in the retina. Our work identifies that microglia mediate photoreceptor survival in RD and suggests that this effect may be due to microglial regulation of immune cells and photoreceptor phagocytosis.

Proteins in the Subretinal Fluid

This study was designed to improve the understanding of the mechanisms that govern the origin of retinal detachment (RD) by examining the quantitative composition of proteins in the subretinal fluid (SRF). Inflammation proteins and immunoglobulins (Ig) were titrated from SRF and sera in 25 patients with RD The following concentrations were found in SRF: total proteins 16 g/l; albumin 12.6 g/l; pre-albumin 0.37 g/l; transferin 1.8 g/l in 68% of cases; haptoglobin and alpha 2 macroglobin were present in only one SRF: alpha 1 antitrypsin 0.86 g/l in 48%; orosomucoid 0.57 g/l in 32%; IgG 2 g/l in 52%; Ig A 0.17 g/l in 88% and IgM 15.9 mg/l in 56%. Correlations were found between the duration of detachment and the concentration of total proteins (p < 0.01). The extent of RD was correlated with the concentration of IgG or IgA in the SRF (p < 0.01). These findings suggest that the correlation between the Ig concentration and the extent of RD is an argument for the participation of choriocapillaris in the genesis of SRF

Macrophage- and RIP3-dependent inflammasome activation exacerbates retinal detachment-induced photoreceptor cell death

Detachment of photoreceptors from the retinal pigment epithelium is seen in various retinal disorders, resulting in photoreceptor death and subsequent vision loss. Cell death results in the release of endogenous molecules that activate molecular platforms containing caspase-1, termed inflammasomes. Inflammasome activation in retinal diseases has been reported in some cases to be protective and in others to be detrimental, causing neuronal cell death. Moreover, the cellular source of inflammasomes in retinal disorders is not clear. Here, we demonstrate that patients with photoreceptor injury by retinal detachment (RD) have increased levels of cleaved IL-1β, an end product of inflammasome activation. In an animal model of RD, photoreceptor cell death led to activation of endogenous inflammasomes, and this activation was diminished by Rip3 deletion. The major source of Il1b expression was found to be infiltrating macrophages in the subretinal space, rather than dying photoreceptors. Inflammasome inhibition attenuated photoreceptor death after RD. Our data implicate the infiltrating macrophages as a source of damaging inflammasomes after photoreceptor detachment in a RIP3-dependent manner and suggest a novel therapeutic target for treatment of retinal diseases.

Post-implantation impedance spectroscopy of subretinal micro-electrode arrays, OCT imaging and numerical simulation: towards a more precise neuroprosthesis monitoring tool

OBJECTIVE

Previous studies have shown that single-frequency impedance measurements could provide useful information about the distance between the neuroprosthesis and the retina. This work investigates the use of impedance spectroscopy in monitoring subretinal implantations of flexible micro-electrode arrays and focuses on determining what is governing impedance profiles.

APPROACH

In this study, we use impedance spectroscopy together with optical coherence tomography imaging and numerical simulation to quantitatively evaluate the constituent elements of measured impedance.

MAIN RESULTS

We show the existence of specific impedance spectrum profiles for retinal detection and retinal detachment that are in good agreement with numerical simulations. These simulations suggest that monopolar impedance is mainly influenced by the subretinal space. Numerical simulations also provide a quantitative prediction of the lateral spread of current density in the vicinity of the measuring contact as a function of retina-electrode distance.

SIGNIFICANCE

In general, our results point to the need for scanning a large frequency range for impedance measurements since capacitive and resistive regimes are strongly dependent on retina-electrode proximity. We believe that these results will contribute to a better understanding of electrical stimulation in neuroprostheses and ultimately improve their efficiency.

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.

Subretinal fluid ferning test in rhegmatogenous retinal detachment

PURPOSE

The ferning test involves a process of crystallization achieved simply by removing water and is feasible for all ocular fluids. The ferning test of subretinal fluid (SRF) from patients with rhegmatogenous retinal detachment (RRD) reveals three different patterns: type 1 showing thin crystals, type 2 with larger crystals and type 3 with small, curvilinear structures with no tree-like appearance. The present study was designed to determine whether the SRF ferning test is correlated with the clinical features and the surgical outcome of RRD.

METHODS

A series of 65 consecutive patients with RRD at the first onset were considered. Particular attention was paid to duration, extension, and surgical outcome of RRD. SRF samples were collected during scleral buckling surgery. The fluid was dropped onto the slide of a light microscope, left to dry, and examined under the microscope.

RESULTS

There was a significant difference between SRF ferning types 1 and 2 as regards, duration and extension (both p < 0.001). There was also a significant difference between SRF ferning types 2 and 3 as regards duration (p<0.001), extension (p<0.001), and surgical outcome (p<0.05).

CONCLUSIONS

The ferning test of SRF is quick and simple and can be regarded as a useful tool for obtaining information about clinical features, such as duration or extension of first, onset in uncomplicated cases of RRD especially for purposes of forensic medicine.

Management of persistent loculated subretinal fluid after pneumatic retinopexy

AIM

To report on the incidence and management of a unique and troublesome complication of pneumatic retinopexy-localised, delayed subretinal fluid absorption (DSRFA).

METHODS

A retrospective chart review was done for all patients who underwent pneumatic retinopexy for retinal detachment over a 5 year period to identify the patients with DSRFA.

RESULTS

Seven phakic patients (five females, two males, age range 26-87 years) were identified with the phenomenon of delayed resolution of subretinal fluid after pneumatic retinopexy and cryotherapy. In four patients the subretinal fluid involved the macula. Time taken to complete absorption of the subretinal fluid ranged from 10 to 26 months. In one patient there was still residual fluid inferiorly at 18 months of follow up. During the follow up period additional procedures were performed--scleral buckling (five eyes), pars plana vitrectomy (one eye), and mild laser scatter to extramacular areas of shallow subretinal fluid (four eyes). None of these procedures appeared to influence the rate of fluid absorption.

CONCLUSIONS

Loculated subretinal fluid following pneumatic retinopexy may persist for very long periods, extending up to more than 2 years. Additional surgical procedures or laser photocoagulation do not affect the rate of subretinal fluid absorption. Spontaneous reattachment eventually occurs in most eyes, and conservative management is indicated.

Antithrombin III activity in subretinal fluid

PURPOSE

To evaluate antithrombin III (AT III) activity in subretinal fluid (SRF) and blood plasma.

METHODS

Prospective study of 32 patients, aged from 20 to 77 years (mean 53.8 years), undergoing retinal detachment surgery. Patients with vein or arterial disease or any other factors that could affect the parameters evaluated were excluded. 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. AT III activity in citrated plasma and in SRF and its relations to patients' age, sex, duration and extent of retinal detachment and degenerative changes of the retina, were evaluated.

RESULTS

The median level of AT III activity in 32 SRF samples was 16.5% (lower quartile 8.5% and upper quartile 23%). The mean level of AT III activity in plasma was 105% (SD 24%). AT III levels in SRF were significantly lower than in plasma (p < 0.0001). We found no correlation between AT III activity in SRF and plasma, and age, sex, the degree of myopia, the duration and extent of retinal detachment, or retinal degenerative changes.

CONCLUSIONS

In this study we detected AT III activity in all 32 SRF samples.

Fibrinolytic activity of subretinal fluid after cryopexy

PURPOSE

To measure the tissue plasminogen activator antigen (t-PA Ag) content and plasminogen activator inhibitor type 1 (PAI-1) activity of SRF and blood.

METHODS

22 patients aged from 20 to 77 years (median: 57.3 years), were studied, undergoing retinal detachment surgery. Excluded were patients with vein or arterial disease and any other factors that could change the parameters evaluated. Subretinal samples were obtained at the time of routine drainage during retinal detachment surgery, after cryopexy. Venous blood samples were taken from the cubital vein into sodium citrate solution (9:1) immediately after induction of anesthesia but before surgery. T-PA Ag concentration and PAI-1 activity in subretinal fluid and citrated plasma and their relation to patients' age and sex, the duration and extent of retinal detachment, and degenerative changes of the retina were assessed.

RESULTS

The median t-PA Ag concentration in 22 samples of SRF was 6.7 ng/ml (interquartile range 3.6 ng/ml) and PAI-1 activity 14.0 IU/ml (interquartile range 7.5 IU/ml). The median levels of t-PA Ag and PAI in plasma were respectively 10.7 ng/ml (interquartile range 8.6 ng/ml) and 15.7 IU/ml (interquartile range 12.2 IU/ml). There were no differences between the t-PA Ag concentration and PAI-1 activity in SRF and blood. We found no correlation between the levels of t-PA Ag and PAI-1 activity in SRF and age, sex, the degree of myopia, the duration and extent of retinal detachment, or retinal degenerative changes.

CONCLUSIONS

The parameters of the fibrinolytic cascade studied here indicated the presence of high levels of t-PA Ag and PAI-1 activity in SRF.

Immunoglobulins in paired specimens of vitreous and subretinal fluids from patients with rhegmatogenous retinal detachment

Evidence suggests that there is a net movement of fluid through the retinal break in eyes with rhegmatogenous retinal detachment, this net movement being directed from the vitreous humour into the subretinal space. However, it remains uncertain how much fluid exchange occurs in both directions across such breaks. The concentration ratios of IgG/IgM or IgA/IgM, derived from assay of immunoglobulins in vitreous humour, subretinal fluid, and serum from a group of 19 such patients, suggest a lack of free, two-directional, fluid movement across the retinal break. Furthermore the IgG/IgM ratios for the two intraocular fluids were significantly greater than that of serum, this suggesting that these intraocular fluids are formed, at least in part, by a selective transduction of serum.

Delayed subretinal fluid absorption after pneumatic retinopexy

Eight of 38 eyes consecutively treated with pneumatic retinopexy were found to have delayed subretinal fluid absorption (DSRFA). In six of eight eyes, a shallow pocket of loculated fluid developed with small subretinal pigment precipitates, possibly a unique feature associated with pneumatic retinopexy. Although loculated DSRFA may not affect the anatomic success, poor visual outcome can result if the macula is involved (4 eyes). Loculated submacular DSRFA may cause bothersome postoperative symptoms, because its resolution may be prolonged for months. Factors found significantly associated with DSRFA were subretinal precipitates and heavy cryotherapy. Demarcation lines, dependent subretinal fluid by the macula, long duration of detachment, and phakic status were factors more frequently found in eyes with than without DSRFA, although the correlations lacked statistical significance. A detailed description of loculated DSRFA after pneumatic retinopexy not found in the literature is presented.

Streaks (schlieren) as a sign of rhegmatogenous detachment in vitreous surgery

Schlieren or streaks can be observed as light passes through incompletely mixed fluids having different refractive indices. During vitreous surgery, the vitreous humor is replaced by an aqueous solution whose density and refractive index differ from those of subretinal fluid. The observation of schlieren during vitrectomy therefore suggests the presence of subretinal fluid and a retinal hole. After observing this sign, a careful search should be made for the retinal break if it has not been previously diagnosed.

Factors influencing absorption of subretinal fluid

In 200 cases of retinal detachment successfully treated without drainage of subretinal fluid complete reattachment of the retina was achieved in the first postoperative week in 76 per cent of cases. Delay in subretinal fluid absorption in the remaining 24 per cent of cases was directly related to the duration of the retinal detachment but was not influenced by the patient's age, refractive error, or the characteristics of the detachment.

Lysosomal enzymes in subretinal fluid

Samples of subretinal fluid (SRF) from patients with primary rhegmatogeneous retinal detachment of various duration were studied using standard enzymologic techniques. The protein content in SRF increased with the duration of detachment. The activities of lysosomal enzymes in SRF, which were acid phosphatase, beta-glucuronidase, and cathepsin D, also increased with the duration of detachment. Especially cathepsin D, which was not detected in serum, was present in SRF. The activity of a nonlysosomal enzyme, i. e., lactic dehydrogenase, which was used as a marker of cell disruption and of serum transudation was the same as that of serum. Because lysosomal enzymes are known to be able to degrade cells and tissues, the enzymologic analysis of SRF contributes to our understanding of the pathology of primary rhegmatogeneous retinal detachment.

Prognosis of primary rhegmatogenous retinal detachments. 1. Associations between clinical detachment characteristics, subretinal fluid butyrylcholinesterase and visual outcome following scleral buckling procedures

Thirty-five patients with primary rhegmatogenous retinal detachments were followed for at least 6 months after scleral buckling procedures with subretinal fluid (SRF) drainage, in order to define factors influencing anatomic and visual outcome. Thirty-two cases were surgically reattached; three were not. Among the reattached cases, final visual acuity was poorer in patients with: older age; longer standing, more extensive detachments; detachment of the macula (with or without the development of a visible macular lesion); macular lesions; and higher SRF butyrylcholinesterase activity. These factors were themselves interrelated. Follow-up duration was only weakly related to final acuity, probably because of the long post-surgical follow-up. Phakic/aphakic status bore little relationship to final acuity. The type or timing relative to drainage of inflammation producing treatment was not related to final acuity.

Biochemical investigation of the subretinal fluid

The level of total protein, protein fractions, sialic acids, and hexosamines was studied in the subretinal fluid (SRF) and blood of patients with retinal detachment. The level of these components in the SRF varied over a considerable range. A low level of total protein, sialic acids, and hexosamines was characteristic of patients with relatively recent clinical forms of retinal detachment, following the most favourable course, and with the best response to surgery. Higher indices were found in patients with marked changes in the fundus oculi, gross destruction of the vitreous body, considerable pathology of the crystalline lens, and correspondingly worse response to surgery. As the pathological changes develop in retinal detachment, there is a parallel increase in the protein levels in the SRF. However, exceptions to this rule indicate that the pathological process may vary. An inverse correlation is found between the level of total protein in the SRF and the electrical sensitivity of the retina. A comparison of the biochemical investigation with the clinical examination suggests that the occurrence of retinal tears and the increase of protein in the SRF are due to the same degenerative processes.

Clinical, biochemical, and immunoelectrophoretic study of subretinal fluid

Images