Structure, function, and age-related changes of the human vitreous

In Vivo Ocular Pharmacokinetics and Toxicity of Siponimod in Albino Rabbits

Siponimod is a promising agent for the inhibition of ocular neovascularization in diabetic retinopathy and age-related macular degeneration. Siponimod's development for ophthalmological application is hindered by the limited information available on the drug's solubility, stability, ocular pharmacokinetics (PK), and toxicity in vivo. In this study, we investigated the aqueous stability of siponimod under stress conditions (up to 60 °C) and its degradation behavior in solution. Additionally, siponimod's ocular PK and toxicity were investigated using intravitreal injection of two different doses (either 1300 or 6500 ng) in an albino rabbit model. Siponimod concentration was quantified in the extracted vitreous, and the PK parameters were calculated. The drug half-life after administration of the low and high doses was 2.8 and 3.9 h, respectively. The data obtained in vivo was used to test the ability of published in silico models to predict siponimod's PK accurately. Two models that correlated siponimod's molecular descriptors with its elimination from the vitreous closely predicted the half-life. Furthermore, 24 h and 7 days after intravitreal injections, the retinas showed no signs of toxicity. This study provides important information necessary for the formulation and development of siponimod for ophthalmologic applications. The short half-life of siponimod necessitates the development of a sustained drug delivery system to maintain therapeutic concentrations over an extended period, while the lack of short-term ocular toxicity observed in the retinas of siponimod-treated rabbits supports possible clinical use.

Non-invasive molecular tracking method that measures ocular drug distribution in non-human primates

Intravitreal (IVT) injection has become the standard route for drug administration in retinal diseases. However, the ability to measure biodistribution of ocular therapeutics in large species remains limited, due to the invasive nature of some techniques or their lack of spatial information. The aim of this study was to develop in cynomolgus monkeys a non-invasive fluorescence imaging technology that enables tracking of IVT-dosed drugs and could be easily translated into humans. Here, we show a proof-of-concept for labeled ranibizumab with observed half-lives of 3.34 and 4.52 days at the retina and in the vitreous, respectively. We further investigate a long acting anti-VEGF antibody, which remains as an agglomerate with some material leaking out until the end of the study at Day 35. Overall, we were able to visualize and measure differences in the in vivo behavior between short and long-acting antibodies, demonstrating the power of the technology for ocular pharmacokinetics.

Guillaume Normand et al. present a non-invasive fluorescence imaging technology that enables a longitudinal tracking of drugs delivered into the eyes. This method allows direct monitoring of any drugs delivered into the eyes, which could potentially inform clinicians of optimal dosing frequency for each patient.

Age-dependent Deformation of the Optic Nerve Head and Peripapillary Retina by Horizontal Duction

PURPOSE

To study effects of age and horizontal duction on deformation of the optic nerve head (ONH) and peripapillary retina (PPR), as reflected by displacement of vascular landmarks, to explore the influence of adduction tethering.

DESIGN

Cross-sectional study.

METHODS

Setting: University.

STUDY POPULATION

Single eyes of 20 healthy young adults (average age 23.9 ± 3.9 [SD] years) were compared to 20 older subjects (average age 61.4 ± 9.3 years). Observational Procedure: The disc and PPR were imaged by scanning laser ophthalmoscopy in central gaze and at 35 degrees abduction and adduction.

MAIN OUTCOME MEASURE

Deformations of the disc and adjacent PPR were measured by comparing positions of epipapillary and epiretinal blood vessels.

RESULTS

Vessels within the ONH of younger subjects shifted temporally during adduction and nasally during abduction. Displacement of the nasal hemi-disc in adduction was greater at 38.5 ± 1.7 μm (standard error of mean) than the temporal half at 4.1 ± 2.1 μm (P < .001). PPR within 1 radius of the disc margin underwent 7.6 ± 1.6 μm average temporal displacement in adduction in young subjects. In abduction, the young temporal hemi-disc shifted 4.4 ± 0.6 μm nasally without significant displacement in the nasal half. Older subjects' ONH showed less temporal shift and less displacement in the PPR within 1 disc radius (P < .0001) in adduction; the nasal hemi-disc shifted 24.5 ± 1.3 μm compared with 4.4 ± 2.1 μm in the temporal half. There were no significant deformations of the disc during abduction by older subjects.

CONCLUSION

Large horizontal duction, particularly adduction, deforms the disc and peripapillary vasculature. This deformation, which is larger in younger than older subjects, may be due to optic nerve tethering in adduction.

Vitreous Antioxidants, Degeneration, and Vitreo-Retinopathy: Exploring the Links

The transparent vitreous body, which occupies about 80% of the eye’s volume, is laden with numerous enzymatic and non-enzymatic antioxidants that could protect the eye from oxidative stress and disease. Aging is associated with degeneration of vitreous structure as well as a reduction in its antioxidant capacity. A growing body of evidence suggests these age-related changes may be the precursor of numerous oxidative stress-induced vitreo-retinopathies, including vision degrading myodesopsia, the clinically significant entoptic phenomena that can result from advanced vitreous degeneration. Adequate intravitreal antioxidant levels may be protective against vitreous degeneration, possibly preventing and even improving vision degrading myodesopsia as well as mitigating various other vitreo-retinopathies. The present article is, therefore, a review of the different antioxidant molecules within vitreous and the inter-relationships between vitreous antioxidant capacity and degeneration.

Posterior vitreous detachment following panretinal laser photocoagulation

A total of 30 eyes of 19 patients with type I diabetes, varying severity of retinopathy, and no posterior vitreous detachment (PVD) were studied clinically, and vitreous examination was performed by preset lens biomicroscopy. Follow-up was 4.0-7.5 years. A total of 15 eyes underwent panretinal laser photocoagulation (PRP) and 15 eyes were left untreated. The incidence of PVD was 8 of 15 353%) after PRP and 1 of 15 (7%) in untreated eyes (P less than 0.02). Minimal vitreous hemorrhage occurred in 4 of 7 treated eyes (57%) that did not develop PVD and in only 2 of 8 (25%) that did. In treated eyes with no history of vitreous hemorrhage, the incidence of PVD was 6/9 (67%); in treated eyes with minimal vitreous hemorrhage at any time, it was 2/6 (33%). In treated eyes, the presence of Diabetic Retinopathy Study (DRS) high-risk characteristics was equally frequent in eyes that developed PVD as in those that did not. These data suggest that PVD occurs following PRP, independent of the severity of diabetic retinopathy or prior vitreous hemorrhage.