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1. A new polygenic score for refractive error improves detection of children at risk of high myopia but not the prediction of those at risk of myopic macular degeneration

Author

Rosie Clark, Samantha Sze-Yee Lee, Ran Du, Yining Wang, Sander C.M. Kneepkens, Jason Charng, Yu Huang, Michael L. Hunter, Chen Jiang, J.Willem L. Tideman, Ronald B. Melles, Caroline C.W. Klaver, David A. Mackey, Cathy Williams, Hélène Choquet, Kyoko Ohno-Matsui, Jeremy A. Guggenheim, Joan E. Bailey-Wilson, Paul N. Baird, Veluchamy A. Barathi, Ginevra Biino, Kathryn P. Burdon, Harry Campbell, Li Jia Chen, Ching-Yu Cheng, Emily Y. Chew, Jamie E. Craig, Margaret M. Deangelis, Cécile Delcourt, Xiaohu Ding, Qiao Fan, Maurizio Fossarello, Paul J. Foster, Puya Gharahkhani, Xiaobo Guo, Annechien E.G. Haarman, Toomas Haller, Christopher J. Hammond, Xikun Han, Caroline Hayward, Mingguang He, Alex W. Hewitt, Quan Hoang, Pirro G. Hysi, Adriana I. Iglesias, Robert P. Igo, Sudha K. Iyengar, Jost B. Jonas, Mika Kähönen, Jaakko Kaprio, Anthony P. Khawaja, Barbara E. Klein, Jonathan H. Lass, Kris Lee, Terho Lehtimäki, Deyana Lewis, Qing Li, Shi-Ming Li, Leo-Pekka Lyytikäinen, Stuart MacGregor, Nicholas G. Martin, Akira Meguro, Andres Metspalu, Candace Middlebrooks, Masahiro Miyake, Nobuhisa Mizuki, Anthony Musolf, Stefan Nickels, Konrad Oexle, Chi Pui Pang, Olavi Pärssinen, Andrew D. Paterson, Norbert Pfeiffer, Ozren Polasek, Jugnoo S. Rahi, Olli Raitakari, Igor Rudan, Srujana Sahebjada, Seang-Mei Saw, Claire L. Simpson, Dwight Stambolian, E-Shyong Tai, Milly S. Tedja, J. Willem L. Tideman, Akitaka Tsujikawa, Cornelia M. van Duijn, Virginie J.M. Verhoeven, Veronique Vitart, Ningli Wang, Ya Xing Wang, Juho Wedenoja, Wen Bin Wei, Katie M. Williams, James F. Wilson, Robert Wojciechowski, Jason C.S. Yam, Kenji Yamashiro, Maurice K.H. Yap, Seyhan Yazar, Shea Ping Yip, Terri L. Young, Xiangtian Zhou, Naomi Allen, Tariq Aslam, Denize Atan, Sarah Barman, Jenny Barrett, Paul Bishop, Graeme Black, Catey Bunce, Roxana Carare, Usha Chakravarthy, Michelle Chan, Sharon Chua, Valentina Cipriani, Alexander Day, Parul Desai, Bal Dhillon, Andrew Dick, Alexander Doney, Cathy Egan, Sarah Ennis, Paul Foster, Marcus Fruttiger, John Gallacher, David Garway-Heath, Jane Gibson, Dan Gore, Jeremy Guggenheim, Chris Hammond, Alison Hardcastle, Simon Harding, Ruth Hogg, Pirro Hysi, Pearse A. Keane, Peng Tee Khaw, Anthony Khawaja, Gerassimos Lascaratos, Thomas Littlejohns, Andrew Lotery, Phil Luthert, Tom MacGillivray, Sarah Mackie, Bernadette McGuinness, Gareth McKay, Martin McKibbin, Danny Mitry, Tony Moore, James Morgan, Zaynah Muthy, Eoin O'Sullivan, Chris Owen, Praveen Patel, Euan Paterson, Tunde Peto, Axel Petzold, Nikolas Pontikos, Jugnoo Rahi, Alicja Rudnicka, Jay Self, Panagiotis Sergouniotis, Sobha Sivaprasad, David Steel, Irene Stratton, Nicholas Strouthidis, Cathie Sudlow, Robyn Tapp, Caroline Thaung, Dhanes Thomas, Emanuele Trucco, Adnan Tufail, Stephen Vernon, Ananth Viswanathan, Katie Williams, Jayne Woodside, Max Yates, Jennifer Yip, Yalin Zheng, Neurology, Ophthalmology, APH - Mental Health, APH - Methodology, Amsterdam Neuroscience - Neuroinfection & -inflammation, Epidemiology, Clinical Genetics, and Erasmus MC other

Subjects
All institutes and research themes of the Radboud University Medical Center, General Medicine, General Biochemistry, Genetics and Molecular Biology, Sensory disorders Donders Center for Medical Neuroscience [Radboudumc 12]
Abstract

Contains fulltext : 292919.pdf (Publisher’s version ) (Open Access) BACKGROUND: High myopia (HM), defined as a spherical equivalent refractive error (SER) ≤ -6.00 diopters (D), is a leading cause of sight impairment, through myopic macular degeneration (MMD). We aimed to derive an improved polygenic score (PGS) for predicting children at risk of HM and to test if a PGS is predictive of MMD after accounting for SER. METHODS: The PGS was derived from genome-wide association studies in participants of UK Biobank, CREAM Consortium, and Genetic Epidemiology Research on Adult Health and Aging. MMD severity was quantified by a deep learning algorithm. Prediction of HM was quantified as the area under the receiver operating curve (AUROC). Prediction of severe MMD was assessed by logistic regression. FINDINGS: In independent samples of European, African, South Asian and East Asian ancestry, the PGS explained 19% (95% confidence interval 17-21%), 2% (1-3%), 8% (7-10%) and 6% (3-9%) of the variation in SER, respectively. The AUROC for HM in these samples was 0.78 (0.75-0.81), 0.58 (0.53-0.64), 0.71 (0.69-0.74) and 0.67 (0.62-0.72), respectively. The PGS was not associated with the risk of MMD after accounting for SER: OR = 1.07 (0.92-1.24). INTERPRETATION: Performance of the PGS approached the level required for clinical utility in Europeans but not in other ancestries. A PGS for refractive error was not predictive of MMD risk once SER was accounted for. FUNDING: Supported by the Welsh Government and Fight for Sight (24WG201).

Published
2023

2. The association between serum lipids and intraocular pressure in 2 large United Kingdom cohorts

Author

Kian M. Madjedi, Kelsey V. Stuart, Sharon Y.L. Chua, Robert N. Luben, Alasdair Warwick, Louis R. Pasquale, Jae H. Kang, Janey L. Wiggs, Marleen A.H. Lentjes, Hugues Aschard, Naveed Sattar, Paul J. Foster, Anthony P. Khawaja, Mark Chia, Ron Do, Alan Kastner, Jihye Kim, Giovanni Montesano, Denize Atan, Tariq Aslam, Sarah A. Barman, Jenny H. Barrett, Paul Bishop, Peter Blows, Catey Bunce, Roxana O. Carare, Usha Chakravarthy, Michelle Chan, David P. Crabb, Philippa M. Cumberland, Alexander Day, Parul Desai, Bal Dhillon, Andrew D. Dick, Cathy Egan, Sarah Ennis, Paul Foster, Marcus Fruttiger, John E.J. Gallacher, David F. Garway-Heath, Jane Gibson, Dan Gore, Jeremy A. Guggenheim, Chris J. Hammond, Alison Hardcastle, Simon P. Harding, Ruth E. Hogg, Pirro Hysi, Pearse A. Keane, Sir Peng T. Khaw, Gerassimos Lascaratos, Andrew J. Lotery, Tom Macgillivray, Sarah Mackie, Keith Martin, Michelle McGaughey, Bernadette McGuinness, Gareth J. McKay, Martin McKibbin, Danny Mitry, Tony Moore, James E. Morgan, Zaynah A. Muthy, Eoin O’Sullivan, Chris G. Owen, Praveen Patel, Euan Paterson, Tunde Peto, Axel Petzold, Jugnoo S. Rahi, Alicja R. Rudnikca, Jay Self, Sobha Sivaprasad, David Steel, Irene Stratton, Nicholas Strouthidis, Cathie Sudlow, Dhanes Thomas, Emanuele Trucco, Adnan Tufail, Veronique Vitart, Stephen A. Vernon, Ananth C. Viswanathan, Cathy Williams, Katie Williams, Jayne V. Woodside, MaxM. Yates, Jennifer Yip, Yalin Zheng, NIHR Biomedical Research Centre [London], Guy's and St Thomas' NHS Foundation Trust-King‘s College London, University of Calgary, University of Cambridge [UK] (CAM), University College of London [London] (UCL), Icahn School of Medicine at Mount Sinai [New York] (MSSM), Harvard Medical School [Boston] (HMS), Örebro University, Institut Pasteur [Paris] (IP), University of Glasgow, Supported by UCL Overseas Research Scholarship (K.V.S.), Fight for Sight, London, United Kingdom (grant no.: 1956A [K.V.S.]), The Desmond Foundation (K.V.S.), the Wellcome Trust (grant no.: 220558/Z/20/Z [A.W.]), Alcon (P.J.F.), United Kingdom Research and Innovation Future Leaders Fellowship (A.P.K.), Moorfields Eye Charity (Springboard Award [R.N.L.] and Career Development Fellowship [A.P.K.]), the National Eye Institute, National Institutes of Health, Bethesda, Maryland (grant nos.: EY015473 [L.R.P.], EY032559 [L.R.P.], [J.L.W.]), Research to Prevent Blindness, Inc., New York, New York (Challenge Grant [L.R.P., J.L.W.]), The Glaucoma Foundation, New York, New York (L.R.P.), Astra Zeneca (N.S.), Boehringer Ingelheim (N.S.), Novartis (N.S.), Roche Diagnostics (N.S.), Association for Research in Vision and Ophthalmology Foundation (David Epstein Award [J.L.W.]), and UK Research and Innovation Future Leaders Fellowship (Medical Research Council grant no.: MR/T040912/1 [A.P.K.]). The authors acknowledge a proportion of their financial support from the United Kingdom Department of Health through an award made by the National Institute for Health Research to Moorfields Eye Hospital NHS Foundation Trust and UCL Institute of Ophthalmology for a Biomedical Research Centre for Ophthalmology. This research used data from the UK Biobank Resource under data access request nos. 2112 and 36741. The UK Biobank Eye and Vision Consortium is supported by grants from Moorfields Eye Charity, The NIHR Biomedical Research Centre at Moorfields Eye Hospital NHS Foundation Trust and UCL Institute of Ophthalmology, the Alcon Research Institute, and the International Glaucoma Association (United Kingdom). The EPIC-Norfolk study was supported by the Medical Research Council, United Kingdom (grant nos.: SP2024/0201 and MR/N003284/1), and Cancer Research United Kingdom (grant nos.: G9502233 and C864/A8257)., Neurology, Ophthalmology, APH - Mental Health, APH - Methodology, and Amsterdam Neuroscience - Neuroinfection & -inflammation

Subjects
Intraocular pressure, Cholesterol, HDL, Glaucoma, Cholesterol, LDL, Middle Aged, Lipids, United Kingdom, Ophthalmology, Cross-Sectional Studies, Cholesterol, SDG 3 - Good Health and Well-being, RA0421, Risk Factors, Humans, RE, [SDV.SPEE]Life Sciences [q-bio]/Santé publique et épidémiologie, Prospective Studies, Triglycerides, Aged
Abstract

Purpose: Serum lipids are modifiable, routinely collected blood test features associated with cardiovascular health. We examined the association of commonly collected serum lipid measures (total cholesterol [TC], high-density lipoprotein cholesterol [HDL-C], low-density lipoprotein cholesterol [LDL-C], and triglycerides) with intraocular pressure (IOP). Design: Cross-sectional study in the UK Biobank and European Prospective Investigation into Cancer and Nutrition (EPIC)-Norfolk cohorts. Participants: We included 94 323 participants from the UK Biobank (mean age, 57 years) and 6230 participants from the EPIC-Norfolk (mean age, 68 years) cohorts with data on TC, HDL-C, LDL-C, and triglycerides collected between 2006 and 2009. Methods: Multivariate linear regression adjusting for demographic, lifestyle, anthropometric, medical, and ophthalmic covariables was used to examine the associations of serum lipids with corneal-compensated IOP (IOPcc). Main Outcome Measures: Corneal-compensated IOP. Results: Higher levels of TC, HDL-C, and LDL-C were associated independently with higher IOPcc in both cohorts after adjustment for key demographic, medical, and lifestyle factors. For each 1-standard deviation increase in TC, HDL-C, and LDL-C, IOPcc was higher by 0.09 mmHg (95% confidence interval [CI], 0.06–0.11 mmHg; P < 0.001), 0.11 mmHg (95% CI, 0.08–0.13 mmHg; P < 0.001), and 0.07 mmHg (95% CI, 0.05–0.09 mmHg; P < 0.001), respectively, in the UK Biobank cohort. In the EPIC-Norfolk cohort, each 1-standard deviation increase in TC, HDL-C, and LDL-C was associated with a higher IOPcc by 0.19 mmHg (95% CI, 0.07–0.31 mmHg; P = 0.001), 0.14 mmHg (95% CI, 0.03–0.25 mmHg; P = 0.016), and 0.17 mmHg (95% CI, 0.06–0.29 mmHg; P = 0.003). An inverse association between triglyceride levels and IOP in the UK Biobank (–0.05 mmHg; 95% CI, –0.08 to –0.03; P < 0.001) was not replicated in the EPIC-Norfolk cohort (P = 0.30). Conclusions: Our findings suggest that serum TC, HDL-C, and LDL-C are associated positively with IOP in 2 United Kingdom cohorts and that triglyceride levels may be associated negatively. Future research is required to assess whether these associations are causal in nature.

Published
2022

3. Comparison of Associations with Different Macular Inner Retinal Thickness Parameters in a Large Cohort

Author

Anthony P. Khawaja, Sharon Chua, Pirro G. Hysi, Stelios Georgoulas, Hannah Currant, Tomas W. Fitzgerald, Ewan Birney, Fang Ko, Qi Yang, Charles Reisman, David F. Garway-Heath, Chris J. Hammond, Peng T. Khaw, Paul J. Foster, Praveen J. Patel, Nicholas Strouthidis, Denize Atan, Tariq Aslam, Sarah A. Barman, Jenny H. Barrett, Paul Bishop, Peter Blows, Catey Bunce, Roxana O. Carare, Usha Chakravarthy, Michelle Chan, Sharon Y.L. Chua, David P. Crabb, Philippa M. Cumberland, Alexander Day, Parul Desai, Bal Dhillon, Andrew D. Dick, Cathy Egan, Sarah Ennis, Paul Foster, Marcus Fruttiger, John E.J. Gallacher, Jane Gibson, Dan Gore, Jeremy A. Guggenheim, Alison Hardcastle, Simon P. Harding, Ruth E. Hogg, Pirro Hysi, Pearse A. Keane, Sir Peng T. Khaw, Gerassimos Lascaratos, Andrew J. Lotery, Tom Macgillivray, Sarah Mackie, Keith Martin, Michelle McGaughey, Bernadette McGuinness, Gareth J. McKay, Martin McKibbin, Danny Mitry, Tony Moore, James E. Morgan, Zaynah A. Muthy, Eoin O’Sullivan, Chris G. Owen, Praveen Patel, Euan Paterson, Tunde Peto, Axel Petzold, Jugnoo S. Rahi, Alicja R. Rudnikca, Jay Self, Sobha Sivaprasad, David Steel, Irene Stratton, Cathie Sudlow, Dhanes Thomas, Emanuele Trucco, Adnan Tufail, Veronique Vitart, Stephen A. Vernon, Ananth C. Viswanathan, Cathy Williams, Katie Williams, Jayne V. Woodside, Max M. Yates, Jennifer Yip, and Yalin Zheng

Subjects
0303 health sciences, Intraocular pressure, medicine.medical_specialty, Cross-sectional study, business.industry, Glaucoma, Retinal, medicine.disease, Confidence interval, 03 medical and health sciences, Ophthalmology, chemistry.chemical_compound, 0302 clinical medicine, Quartile, chemistry, 030221 ophthalmology & optometry, medicine, sense organs, business, Body mass index, 030304 developmental biology, Cohort study
Abstract

Purpose To describe and compare associations with macular retinal nerve fiber layer (mRNFL), ganglion cell complex (GCC), and ganglion cell–inner plexiform layer (GCIPL) thicknesses in a large cohort. Design Cross-sectional study. Participants We included 42 044 participants in the UK Biobank. The mean age was 56 years. Methods Spectral-domain OCT macular images were segmented and analyzed. Corneal-compensated intraocular pressure (IOPcc) was measured with the Ocular Response Analyzer (Reichert, Corp., Buffalo, NY). Multivariable linear regression was used to examine associations with mean mRNFL, GCC, and GCIPL thicknesses. Factors examined were age, sex, ethnicity, height, body mass index (BMI), smoking status, alcohol intake, Townsend deprivation index, education level, diabetes status, spherical equivalent, and IOPcc. Main Outcome Measures Thicknesses of mRNFL, GCC, and GCIPL. Results We identified several novel independent associations with thinner inner retinal thickness. Thinner inner retina was associated with alcohol intake (most significant for GCIPL: –0.46 μm for daily or almost daily intake compared with special occasion only or never [95% confidence interval (CI), 0.61–0.30]; P = 1.1×10–8), greater social deprivation (most significant for GCIPL: –0.28 μm for most deprived quartile compared with least deprived quartile [95% CI, –0.42 to –0.14]; P = 6.6×10–5), lower educational attainment (most significant for mRNFL: –0.36 μm for less than O level compared with degree level [95% CI, –0.45 to 0.26]; P = 2.3×10–14), and nonwhite ethnicity (most significant for mRNFL comparing blacks with whites: –1.65 μm [95% CI, –1.86 to –1.43]; P = 2.4×10–50). Corneal-compensated intraocular pressure was associated most significantly with GCIPL (–0.04 μm/mmHg [95% CI, –0.05 to –0.03]; P = 4.0×10–10) and was not associated significantly with mRNFL (0.00 μm/mmHg [95% CI, –0.01 to 0.01]; P = 0.77). The variables examined explained a greater proportion of the variance of GCIPL (11%) than GCC (6%) or mRNFL (7%). Conclusions The novel associations we identified may be important to consider when using inner retinal parameters as a diagnostic tool. Associations generally were strongest with GCIPL, particularly for IOP. This suggests that GCIPL may be the superior inner retinal biomarker for macular pathophysiologic processes and especially for glaucoma.

Published
2020

4. Optimization of Oxygen Dynamics, UV-A Delivery, and Drug Formulation for Accelerated Epi-On Corneal Crosslinking

Author

Jason H. Hill, Cailing Liu, Phillip Deardorff, Dan Gore, Behrouz Tavakol, William Eddington, Michael B. Raizman, Vance Thompson, and Desmond C. Adler

Subjects
Keratoconus, Stromal cell, Swine, Ultraviolet Rays, Corneal Stroma, Riboflavin, chemistry.chemical_element, Oxygen, 03 medical and health sciences, Cellular and Molecular Neuroscience, chemistry.chemical_compound, Benzalkonium chloride, 0302 clinical medicine, medicine, Animals, Photosensitizer, Photosensitizing Agents, Corneal Topography, medicine.disease, Sensory Systems, Ophthalmology, Disease Models, Animal, Cross-Linking Reagents, chemistry, Photochemotherapy, Sodium iodide, 030221 ophthalmology & optometry, Collagen, 030217 neurology & neurosurgery, Ex vivo, medicine.drug, Biomedical engineering
Abstract

Purpose: Corneal collagen crosslinking (CXL) through an intact epithelium (epi-on) at high irradiance could potentially improve patient comfort, visual recovery, and clinical workflow compared to conventional epi-off CXL. However, intact epithelium limits stromal delivery of the oxygen, photosensitizer, and ultraviolet-A (UV-A) radiation needed to drive CXL. This ex vivo study evaluated three different epi-on CXL protocols compared to positive and negative controls, specifically focusing on the impact of supplemental oxygen. Endpoints included stromal oxygen levels, stiffness of crosslinked tissue, and acute flattening of whole eyes.Materials & Methods: Ex vivo porcine eyes were held in a custom environmental chamber. Intrastromal oxygen levels were continuously measured before, during, and after UV illumination by a fiberoptic probe inserted into a laser-cut flap. Accelerated, high irradiance, epi-on CXL protocols using riboflavin formulated with benzalkonium chloride (BAC) were studied, with and without supplemental oxygen. These were compared to an alternate, low irradiance, epi-on protocol using riboflavin formulated with sodium iodide. Both negative (no CXL) and positive (epi-off modified Dresden protocol) controls were performed. Post-CXL elastic modulus was measured using extensiometry and anterior tangential curvature was measured using a Scheimpflug tomographer.Results: Protocols including supplemental oxygen resulted in an approximately 5-fold increase in stromal oxygen levels prior to CXL. During epi-on, high-irradiance UV-A delivery under hyperoxic conditions, an aerobic state was maintained. Conversely, under normoxic conditions, stromal oxygen rapidly depleted to 0-5% for all other protocols. The combination of supplemental oxygen, BAC formulation, and high-irradiance UV-A resulted in the largest biomechanical changes and most pronounced flattening effects of the three epi-on protocols.Conclusions: Ex vivo analysis of stromal oxygen levels, corneal stiffness, and acute anterior curvature change indicates that simultaneous optimization of the oxygen environment, riboflavin formulation, and UV-A protocol can significantly increase the effects of corneal collagen crosslinking.

Published
2019

5. An Age of Infection Kernel, an R Formula, and Further Results for Arino–Brauer A, B Matrix Epidemic Models with Varying Populations, Waning Immunity, and Disease and Vaccination Fatalities

Author

Florin Avram, Rim Adenane, Lasko Basnarkov, Gianluca Bianchin, Dan Goreac, and Andrei Halanay

Subjects
epidemic models, varying population models, stability, next-generation matrix approach, basic replacement number, vaccination, Mathematics, QA1-939
Abstract

In this work, we first introduce a class of deterministic epidemic models with varying populations inspired by Arino et al. (2007), the parameterization of two matrices, demography, the waning of immunity, and vaccination parameters. Similar models have been focused on by Julien Arino, Fred Brauer, Odo Diekmann, and their coauthors, but mostly in the case of “closed populations” (models with varying populations have been studied in the past only in particular cases, due to the difficulty of this endeavor). Our Arino–Brauer models contain SIR–PH models of Riano (2020), which are characterized by the phase-type distribution (α→,A), modeling transitions in “disease/infectious compartments”. The A matrix is simply the Metzler/sub-generator matrix intervening in the linear system obtained by making all new infectious terms 0. The simplest way to define the probability row vector α→ is to restrict it to the case where there is only one susceptible class s, and when matrix B (given by the part of the new infection matrix, with respect to s) is of rank one, with B=bα→. For this case, the first result we obtained was an explicit formula (12) for the replacement number (not surprisingly, accounting for varying demography, waning immunity and vaccinations led to several nontrivial modifications of the Arino et al. (2007) formula). The analysis of (A,B) Arino–Brauer models is very challenging. As obtaining further general results seems very hard, we propose studying them at three levels: (A) the exact model, where only a few results are available—see Proposition 2; and (B) a “first approximation” (FA) of our model, which is related to the usually closed population model often studied in the literature. Notably, for this approximation, an associated renewal function is obtained in (7); this is related to the previous works of Breda, Diekmann, Graaf, Pugliese, Vermiglio, Champredon, Dushoff, and Earn. (C) Finally, we propose studying a second heuristic “intermediate approximation” (IA). Perhaps our main contribution is to draw attention to the importance of (A,B) Arino–Brauer models and that the FA approximation is not the only way to tackle them. As for the practical importance of our results, this is evident, once we observe that the (A,B) Arino–Brauer models include a large number of epidemic models (COVID, ILI, influenza, illnesses, etc.).

Published
2023
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6. Equity Cost Induced Dichotomy for Optimal Dividends with Capital Injections in the Cramér-Lundberg Model

Author

Florin Avram, Dan Goreac, Juan Li, and Xiaochi Wu

Subjects
optimal dividends, capital injections, Cramér-Lundberg model, buffered reflection, scale functions, absolutely continuous supersolutions, Mathematics, QA1-939
Abstract

We investigate a control problem leading to the optimal payment of dividends in a Cramér-Lundberg-type insurance model in which capital injections incur proportional cost, and may be used or not, the latter resulting in bankruptcy. For general claims, we provide verification results, using the absolute continuity of super-solutions of a convenient Hamilton-Jacobi variational inequality. As a by-product, for exponential claims, we prove the optimality of bounded buffer capital injections (−a,0,b) policies. These policies consist in stopping at the first time when the size of the overshoot below 0 exceeds a certain limit a, and only pay dividends when the reserve reaches an upper barrier b. An exhaustive and explicit characterization of optimal couples buffer/barrier is given via comprehensive structure equations. The optimal buffer is shown never to be of de Finetti (a=0) or Shreve-Lehoczy-Gaver (a=∞) type. The study results in a dichotomy between cheap and expensive equity, based on the cost-of-borrowing parameter, thus providing a non-trivial generalization of the Lokka-Zervos phase-transition Løkka-Zervos (2008). In the first case, companies start paying dividends at the barrier b*=0, while in the second they must wait for reserves to build up to some (fully determined) b*>0 before paying dividends.

Published
2021
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