Medical therapy for glaucoma: A review Casson, Robert J.
Clinical & experimental ophthalmology,
March 2022, 2022-03-00, 20220301, Letnik:
50, Številka:
2
Journal Article
Recenzirano
A number of pharmacological targets are exploited to modify the parameters in the Goldmann equation and reduce the intraocular pressure (IOP). This strategy constitutes the foundation for the medical ...management of glaucoma, the evolution of which, until only recently, has been in relative stagnation. A burst of innovation has produced new ocular hypotensive drugs and long‐acting delivery methods, including intracameral delivery, which are expanding the clinician's medical armamentarium. A number of IOP‐independent neuroprotection strategies have shown strong potential in animal models of glaucoma, but translational attempts have been surprisingly limited. However, while pharmacological options are expanding, the traditional role of topical medical therapy is being challenged by selective laser trabeculoplasty, micro‐invasive glaucoma surgery, and sustained delivery methods. A scientifically rigorous assessment of new treatments will be critical to empower clinicians with evidence‐based information to optimise vision preservation and quality of life outcomes for their patients.
The vascular hypothesis of glaucoma proposes that retinal ganglion cell axons traversing the optic nerve head (ONH) undergo oxygen and nutrient insufficiency as a result of compromised local blood ...flow, ultimately leading to their degeneration. To date, evidence for the hypothesis is largely circumstantial. Herein, we made use of an induced rat model of glaucoma that features reproducible and widespread axonal transport disruption at the ONH following chronic elevation of intraocular pressure. If vascular insufficiency plays a role in the observed axonal transport failure, there should exist a physical signature at this time point. Using a range of immunohistochemical and molecular tools, we looked for cellular events indicative of vascular insufficiency, including the presence of hypoxia, upregulation of hypoxia-inducible, or antioxidant-response genes, alterations to antioxidant enzymes, increased formation of superoxide, and the presence of oxidative stress. Our data show that ocular hypertension caused selective hypoxia within the laminar ONH in 11/13 eyes graded as either medium or high for axonal transport disruption. Hypoxia was always present in areas featuring injured axons, and, the greater the abundance of axonal transport disruption, the greater the likelihood of a larger hypoxic region. Nevertheless, hypoxic regions were typically focal and were not necessarily evident in sections taken deeper within the same ONH, while disrupted axonal transport was frequently encountered without any discernible hypoxia. Ocular hypertension caused upregulation of heme oxygenase-1-an hypoxia-inducible and redox-sensitive enzyme-in ONH astrocytes. The distribution and abundance of heme oxygenase-1 closely matched that of axonal transport disruption, and encompassed hypoxic regions and their immediate penumbra. Ocular hypertension also caused upregulations in the iron-regulating protein ceruloplasmin, the anaerobic glycolytic enzyme lactate dehydrogenase, and the transcription factors cFos and p-cJun. Moreover, ocular hypertension increased the generation of superoxide radicals in the retina and ONH, as well as upregulating the active subunit of the superoxide-generating enzyme NADPH oxidase, and invoking modest alterations to antioxidant-response enzymes. The results of this study provide further indirect support for the hypothesis that reduced blood flow to the ONH contributes to axonal injury in glaucoma.
Retinitis pigmentosa (RP) is an inherited condition that features degeneration of rod and cone photoreceptors. In all forms of RP, the genetic mutation is expressed exclusively in rods; however, ...cones die too. The secondary death of cones in RP remains somewhat mysterious. A better understanding of the mechanisms that cause cone degeneration in RP could lead to novel treatments that preserve cones. There are a number of prevailing theories that attempt to explain cone degeneration in RP. One concept is that cone survival is dependent on trophic factors produced by rods. Another hypothesis is that cones suffer from a nutrient shortage after rods have been lost. Additionally, oxidative stress and pro‐inflammatory microglial activation have also been suggested to play a role in cone death. The present review evaluates the evidence supporting these theories and provides an update on the mechanisms of cone degeneration in RP.
Energy metabolism refers to the processes by which life transfers energy to do cellular work. The retina's relatively large energy demands make it vulnerable to energy insufficiency. In addition, ...evolutionary pressures to optimize human vision have been traded against retinal ganglion cell bioenergetic fragility. Details of the metabolic profiles of the different retinal cells remain poorly understood and are challenging to resolve. Detailed immunohistochemical mapping of the energy pathway enzymes and substrate transporters has provided some insights and highlighted interspecies differences. The different spatial metabolic patterns between the vascular and avascular retinas can account for some inconsistent data in the literature. There is a consilience of evidence that at least some individuals with glaucoma have impaired RGC energy metabolism, either due to impaired nutrient supply or intrinsic metabolic perturbations. Bioenergetic-based therapy for glaucoma has a compelling pathophysiological foundation and is supported by recent successes in animal models. Recent demonstrations of visual and electrophysiological neurorecovery in humans with glaucoma is highly encouraging and motivates longer duration trials investigating bioenergetic neuroprotection.
Like cancer cells, photoreceptor cells produce lactate aerobically, requiring lactate dehydrogenase A (LDH-A). Cancer cells also use glycolytic intermediates for biosynthesis. The molecular switch ...controlling glycolytic flow is thought to be an isoenzyme of pyruvate kinase (PKM2). Here, we determined the expression and localization of PKM2 and LDH-A in mammalian retina and make comparisons with the brain.
Single- and double-labeling immunohistochemistry for PKM2, pyruvate kinase M1 (PKM1), and LDH-A were performed using retinal sections from C57BL/6 mice, Sprague-Dawley rats, rabbits, marmosets, and humans. Pyruvate kinase M1 and PKM2 mRNA and protein expression levels were quantified in rodent retina and brain by using qPCR and immunoblotting. The quaternary forms of PKM2 in rat retina were also determined.
Pyruvate kinase M2 was present in some glial cells and rod and cone photoreceptors in the retina of all species but was exclusively localized to glia in the brain. Pyruvate kinase M1 was confined to neurons in the retina and brain. Lactate dehydrogenase A was principally found in photoreceptors and inner portion of the avascular rabbit retina. Western blotting and qPCR confirmed high levels of PKM2 and LDH-A in the retina. There was a 6- to 9-fold greater expression of PKM2 mRNA in the rodent retina than in the brain. Both the dimeric (inactive, biosynthesis-driving form) and the active tetrameric (glycolytic-driving) forms of PKM2 were present in retina but not in brain.
Mammalian photoreceptors contain dimeric and tetrameric PKM2 and LDH-A. This is consistent with the ability to switch between energy production and biosynthesis like a proliferating tissue, possibly due to demands of opsin synthesis.
Retinal detachment is a sight-threatening disorder, which occurs when the photoreceptors are separated from their vascular supply. The aim of the present study was to shed light on photoreceptor ...energy metabolism during experimental detachment in rats. Retinal detachment was induced in the eyes of rats
via
subretinal injection of sodium hyaluronate. Initially, we investigated whether detachment caused hypoxia within photoreceptors, as evaluated by the exogenous and endogenous biomarkers pimonidazole and HIF-1α, as well as by qPCR analysis of HIF target genes. The results showed no unequivocal staining for pimonidazole or HIF-1α within any detached retina, nor upregulation of HIF target genes, suggesting that any reduction in pO
2
is of insufficient magnitude to produce hypoxia-induced covalent protein adducts or HIF-1α stabilisation. Subsequently, we analysed expression of cellular bioenergetic enzymes in photoreceptors during detachment. We documented loss of mitochondrial, and downregulation of glycolytic enzymes during detachment, indicating that photoreceptors have reduced energetic requirements and/or capacity. Given that detachment did not cause widespread hypoxia, but did result in downregulated expression of bioenergetic enzymes, we hypothesised that substrate insufficiency may be critical in terms of pathogenesis, and that boosting metabolic inputs may preserve photoreceptor bioenergetic production and, protect against their degeneration. Thus, we tested whether supplementation with the bioavailable energy substrate pyruvate mitigated rod and cone injury and degeneration. Despite protecting photoreceptors in culture from nutrient deprivation, pyruvate failed to protect against apoptotic death of rods, loss of cone opsins, and loss of inner segment mitochondria,
in situ
, when evaluated at 3 days after detachment. The regimen was also ineffective against cumulative photoreceptor deconstruction and degeneration when evaluated after 4 weeks. Retinal metabolism, particularly the bioenergetic profiles and pathological responses of the various cellular subtypes still presents a considerable knowledge gap that has important clinical consequences. While our data do not support the use of pyruvate supplementation as a means of protecting detached photoreceptors, they do provide a foundation and motivation for future research in this area.
Glaucoma is a term describing a group of ocular disorders with multi‐factorial etiology united by a clinically characteristic intraocular pressure‐associated optic neuropathy. It is not a single ...entity and is sometimes referred to in the plural as the glaucomas. All forms are potentially progressive and can lead to blindness. The diverse conditions that comprise glaucoma are united by a clinically characteristic optic neuropathy: glaucomatous optic neuropathy (GON). Evidence suggests that the primary site of neurological injury is at the optic nerve head. This fact enables the conditions to be grouped, irrespective of the causal mechanism(s). The term experimental glaucoma implies model resemblance to the human condition. We propose that ‘experimental glaucoma’ be restricted to animal models with demonstrable features of GON and/or evidence of a primary axonopathy at the optic nerve head. A fundamental inadequacy in this framework is any reference to the pathogenesis of GON, which remains unclear.
Macular holes (MH) are full-thickness retinal defects affecting central vision. While vitrectomy with inner limiting membrane (ILM) peel is the conventional MH treatment, non-surgical alternatives ...are gaining interest to mitigate surgical risks. This study conducted a comprehensive literature review and analysis of nonsurgical MH management. A systematic literature search was conducted on PubMed, Embase, Scopus, and the Cochrane Library from January 1, 1973, to September 13, 2023. Treatments included laser therapy, carbonic anhydrase inhibitors (CAIs), nonsteroidal antiinflammatory drugs (NSAIDs), steroids (topical, subtenons, peribulbar, intravitreal), intravitreal gas, anti-vascular endothelial growth factors and ocriplasmin injections. Data extraction covered study details, patient characteristics, MH features, treatment outcomes, and recurrence rates. The initial search yielded 3352 articles, refined to 83 articles that met inclusion criteria following screening. Overall reported anatomical closure rates were 36% with laser photocoagulation, 37% with intravitreal ocriplasmin, 55% with intravitreal gas. Closures were more frequently observed with topical NSAIDs (79%), steroids (84%) and CAIs (73%). Closures were more often observed in patients with smaller MH and in the presence of cystic macular oedema. Although non-surgical MH management approaches show potential for conservative therapy, evidence is limited to support routine use. Stage 1 and traumatic MH may benefit from a short period of observation, but the gold standard approach for full-thickness MH remains to be vitrectomy with ILM peel.
•Idiopathic macular holes are thought to develop due to vitreomacular traction and retinal hydration.•Macular holes have conventionally required surgical intervention but closures using topical anti-inflammatories, carbonic anhydrase inhibitors, steroids, ocular injections as laser therapy have been reported.•There is lack of evidence to support the use of non-surgical therapy in the management of macular holes.•Development of conservative treatment options may allow patients to avoid the risk profiles associated with surgery.
Purpose
To determine whether Twitter improves dissemination of ophthalmology scientific publications
Methods
Data were collected on articles published on PubMed between the years 2016 and 2021 ...(inclusive) and identified with the word “ophthalmology”. Twitter performance metrics, including the number of tweets, number of likes, and number of retweets were collected from Twitter using the publicly available scientific API. Machine learning and descriptive statistics were used to outline Twitter performance metrics.
Results
The number of included articles was 433710. The percentage of articles that were in the top quartile for citation count, which had ≥1 tweet was 34.4% (number 437/1270). Conversely, the percentage of articles that were in the top quartile for citation count, which had 0 tweets was 27.8% (number 12023/43244). When machine learning was used to predict Twitter performance metrics an AUROC of 0.78 was returned. This was associated with an accuracy of 0.97
Conclusion
This study has shown preliminary evidence to support that Twitter may improve the dissemination of scientific ophthalmology publications.
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