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Birch EE, Duffy KR. Leveraging neural plasticity for the treatment of amblyopia. Surv Ophthalmol 2024:S0039-6257(24)00046-8. [PMID: 38763223 DOI: 10.1016/j.survophthal.2024.04.006] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/25/2023] [Revised: 04/27/2024] [Accepted: 04/29/2024] [Indexed: 05/21/2024]
Abstract
Amblyopia is a form of visual cortical impairment that arises from abnormal visual experience early in life. Most often, amblyopia is a unilateral visual impairment that can develop as a result of strabismus, anisometropia, or a combination of these conditions that result in discordant binocular experience. Characterized by reduced visual acuity and impaired binocular function, amblyopia places a substantial burden on the developing child. Although frontline treatment with glasses and patching can improve visual acuity, residual amblyopia remains for most children. Newer binocular-based therapies can elicit rapid recovery of visual acuity and may also improve stereoacuity in some children. Nevertheless, for both treatment modalities full recovery is elusive, recurrence of amblyopia is common, and improvements are negligible when treatment is administered at older ages. Insights derived from animal models about the factors that govern neural plasticity have been leveraged to develop innovative treatments for amblyopia. These novel therapies exhibit efficacy to promote recovery, and some are effective even at ages when conventional treatments fail to yield benefit. Approaches for enhancing visual system plasticity and promoting recovery from amblyopia include altering the balance between excitatory and inhibitory mechanisms, reversing the accumulation of proteins that inhibit plasticity, and harnessing the principles of metaplasticity. Although these therapies have exhibited promising results in animal models, their safety and ability to remediate amblyopia need to be evaluated in humans.
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Affiliation(s)
- Eileen E Birch
- Crystal Charity Ball Pediatric Vision Laboratory, Retina Foundation, Dallas, TX, USA; University of Texas Southwestern Medical Center, Dallas, TX, USA.
| | - Kevin R Duffy
- Department of Psychology and Neuroscience, Dalhousie University, Halifax, NS, Canada
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2
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Sharp T, Collins H. Mechanisms of SSRI Therapy and Discontinuation. Curr Top Behav Neurosci 2023. [PMID: 37955823 DOI: 10.1007/7854_2023_452] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2023]
Abstract
SSRIs are one of the most widely used drug therapies in primary care and psychiatry, and central to the management of the most common mental health problems in today's society. Despite this, SSRIs suffer from a slow onset of therapeutic effect and relatively poor efficacy as well as adverse effects, with recent concerns being focused on a disabling SSRI discontinuation syndrome. The mechanism underpinning their therapeutic effect has long shifted away from thinking that SSRIs act simply by increasing 5-HT in the synapse. Rather, a current popular view is that increased 5-HT is just the beginning of a series of complex downstream signalling events, which trigger changes in neural plasticity at the functional and structural level. These changes in plasticity are then thought to interact with neuropsychological processes to enhance re-learning of emotional experiences that ultimately brings about changes in mood. This compelling view of SSRI action is underpinning attempts to understand fast-acting antidepressants, such as ketamine and psychedelic drugs, and aid the development of future therapies. An important gap in the theory is evidence that changes in plasticity are causally linked to relevant behavioural effects. Also, predictions that the SSRI-induced neural plasticity might have applicability in other areas of medicine have not yet been borne out. In contrast to the sophisticated view of the antidepressant action of SSRIs, the mechanism underpinning SSRI discontinuation is little explored. Nevertheless, evidence of rebound increases in 5-HT neuron excitability immediately on cessation of SSRI treatment provide a starting point for future investigation. Indeed, this evidence allows formulation of a mechanistic explanation of SSRI discontinuation which draws on parallels with the withdrawal states of other psychotropic drugs.
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Affiliation(s)
- Trevor Sharp
- Department of Pharmacology, University of Oxford, Oxford, UK.
| | - Helen Collins
- Department of Pharmacology, University of Oxford, Oxford, UK
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3
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Duffy KR, Bear MF, Patel NB, Das VE, Tychsen L. Human deprivation amblyopia: treatment insights from animal models. Front Neurosci 2023; 17:1249466. [PMID: 37795183 PMCID: PMC10545969 DOI: 10.3389/fnins.2023.1249466] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/28/2023] [Accepted: 09/04/2023] [Indexed: 10/06/2023] Open
Abstract
Amblyopia is a common visual impairment that develops during the early years of postnatal life. It emerges as a sequela to eye misalignment, an imbalanced refractive state, or obstruction to form vision. All of these conditions prevent normal vision and derail the typical development of neural connections within the visual system. Among the subtypes of amblyopia, the most debilitating and recalcitrant to treatment is deprivation amblyopia. Nevertheless, human studies focused on advancing the standard of care for amblyopia have largely avoided recruitment of patients with this rare but severe impairment subtype. In this review, we delineate characteristics of deprivation amblyopia and underscore the critical need for new and more effective therapy. Animal models offer a unique opportunity to address this unmet need by enabling the development of unconventional and potent amblyopia therapies that cannot be pioneered in humans. Insights derived from studies using animal models are discussed as potential therapeutic innovations for the remediation of deprivation amblyopia. Retinal inactivation is highlighted as an emerging therapy that exhibits efficacy against the effects of monocular deprivation at ages when conventional therapy is ineffective, and recovery occurs without apparent detriment to the treated eye.
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Affiliation(s)
- Kevin R. Duffy
- Department of Psychology and Neuroscience, Dalhousie University, Halifax, NS, Canada
| | - Mark F. Bear
- Picower Institute for Learning and Memory, Department of Brain and Cognitive Sciences, Massachusetts Institute of Technology, Cambridge, MA, United States
| | - Nimesh B. Patel
- College of Optometry, University of Houston, Houston, TX, United States
| | - Vallabh E. Das
- College of Optometry, University of Houston, Houston, TX, United States
| | - Lawrence Tychsen
- Department of Ophthalmology and Visual Sciences, Washington University School of Medicine, St. Louis, MO, United States
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Wu C, Gaier ED, Nihalani BR, Whitecross S, Hensch TK, Hunter DG. Durable recovery from amblyopia with donepezil. Sci Rep 2023; 13:10161. [PMID: 37349338 PMCID: PMC10287641 DOI: 10.1038/s41598-023-34891-5] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/24/2022] [Accepted: 05/09/2023] [Indexed: 06/24/2023] Open
Abstract
An elevated threshold for neuroplasticity limits visual gains with treatment of residual amblyopia in older children and adults. Acetylcholinesterase inhibitors (AChEI) can enable visual neuroplasticity and promote recovery from amblyopia in adult mice. Motivated by these promising findings, we sought to determine whether donepezil, a commercially available AChEI, can enable recovery in older children and adults with residual amblyopia. In this open-label pilot efficacy study, 16 participants (mean age 16 years; range 9-37 years) with residual anisometropic and/or strabismic amblyopia were treated with daily oral donepezil for 12 weeks. Donepezil dosage was started at 2.5 or 5.0 mg based on age and increased by 2.5 mg if the amblyopic eye visual acuity did not improve by 1 line from the visit 4 weeks prior for a maximum dosage of 7.5 or 10 mg. Participants < 18 years of age further patched the dominant eye. The primary outcome was visual acuity in the amblyopic eye at 22 weeks, 10 weeks after treatment was discontinued. Mean amblyopic eye visual acuity improved 1.2 lines (range 0.0-3.0), and 4/16 (25%) improved by ≥ 2 lines after 12 weeks of treatment. Gains were maintained 10 weeks after cessation of donepezil and were similar for children and adults. Adverse events were mild and self-limited. Residual amblyopia improves in older children and adults treated with donepezil, supporting the concept that the critical window of visual cortical plasticity can be pharmacologically manipulated to treat amblyopia. Placebo-controlled studies are needed.
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Affiliation(s)
- Carolyn Wu
- Department of Ophthalmology, Boston Children's Hospital, Boston, MA, USA.
- Department of Ophthalmology, Harvard Medical School, Boston, MA, USA.
| | - Eric D Gaier
- Department of Ophthalmology, Boston Children's Hospital, Boston, MA, USA
- Department of Ophthalmology, Harvard Medical School, Boston, MA, USA
- Picower Institute for Learning and Memory, Massachusetts Institute of Technology, Cambridge, MA, USA
| | - Bharti R Nihalani
- Department of Ophthalmology, Boston Children's Hospital, Boston, MA, USA
- Department of Ophthalmology, Harvard Medical School, Boston, MA, USA
| | - Sarah Whitecross
- Department of Ophthalmology, Boston Children's Hospital, Boston, MA, USA
| | - Takao K Hensch
- Center for Brain Science, Department of Molecular Cellular Biology, Harvard University, Cambridge, MA, USA
- International Research Center for Neurointelligence, University of Tokyo Institutes for Advanced Study, Tokyo, Japan
- FM Kirby Neurobiology Center, Boston Children's Hospital, Harvard Medical School, Boston, MA, USA
| | - David G Hunter
- Department of Ophthalmology, Boston Children's Hospital, Boston, MA, USA
- Department of Ophthalmology, Harvard Medical School, Boston, MA, USA
- International Research Center for Neurointelligence, University of Tokyo Institutes for Advanced Study, Tokyo, Japan
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Birch EE, Kelly KR, Wang J. Recent Advances in Screening and Treatment for Amblyopia. Ophthalmol Ther 2021; 10:815-830. [PMID: 34499336 PMCID: PMC8589941 DOI: 10.1007/s40123-021-00394-7] [Citation(s) in RCA: 14] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/23/2021] [Accepted: 08/26/2021] [Indexed: 11/30/2022] Open
Abstract
Amblyopia is the most common cause of monocular visual impairment in children, with a prevalence of 2-3%. Not only is visual acuity reduced in one eye but binocular vision is affected, fellow eye deficits may be present, eye-hand coordination and reading can be affected, and self-perception may be diminished. New technologies for preschool vision screening hold promise for accessible, early, and accurate detection of amblyopia. Together with recent advances in our theoretical understanding of amblyopia and technological advances in amblyopia treatment, we anticipate improved visual outcomes for children affected by this very common eye condition. This article is based on previously conducted studies and does not contain any new studies with human participants or animals performed by any of the authors.
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Affiliation(s)
- Eileen E Birch
- Retina Foundation of the Southwest, 9600 N. Central Expressway, Suite 200, Dallas, TX, 75231, USA.
- Department of Ophthalmology, University of Texas Southwestern Medical Center, Dallas, TX, USA.
| | - Krista R Kelly
- Retina Foundation of the Southwest, 9600 N. Central Expressway, Suite 200, Dallas, TX, 75231, USA
- Department of Ophthalmology, University of Texas Southwestern Medical Center, Dallas, TX, USA
| | - Jingyun Wang
- SUNY College of Optometry, State University of New York, New York, NY, USA
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Fong MF, Duffy KR, Leet MP, Candler CT, Bear MF. Correction of amblyopia in cats and mice after the critical period. eLife 2021; 10:70023. [PMID: 34464258 PMCID: PMC8456712 DOI: 10.7554/elife.70023] [Citation(s) in RCA: 7] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/04/2021] [Accepted: 08/20/2021] [Indexed: 11/25/2022] Open
Abstract
Monocular deprivation early in development causes amblyopia, a severe visual impairment. Prognosis is poor if therapy is initiated after an early critical period. However, clinical observations have shown that recovery from amblyopia can occur later in life when the non-deprived (fellow) eye is removed. The traditional interpretation of this finding is that vision is improved simply by the elimination of interocular suppression in primary visual cortex, revealing responses to previously subthreshold input. However, an alternative explanation is that silencing activity in the fellow eye establishes conditions in visual cortex that enable the weak connections from the amblyopic eye to gain strength, in which case the recovery would persist even if vision is restored in the fellow eye. Consistent with this idea, we show here in cats and mice that temporary inactivation of the fellow eye is sufficient to promote a full and enduring recovery from amblyopia at ages when conventional treatments fail. Thus, connections serving the amblyopic eye are capable of substantial plasticity beyond the critical period, and this potential is unleashed by reversibly silencing the fellow eye.
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Affiliation(s)
- Ming-Fai Fong
- The Picower Institute for Learning and Memory, Department of Brain and Cognitive Sciences, Massachusetts Institute of Technology, Cambridge, United States
| | - Kevin R Duffy
- Department of Psychology and Neuroscience, Dalhousie University, Halifax, Canada
| | - Madison P Leet
- The Picower Institute for Learning and Memory, Department of Brain and Cognitive Sciences, Massachusetts Institute of Technology, Cambridge, United States
| | - Christian T Candler
- The Picower Institute for Learning and Memory, Department of Brain and Cognitive Sciences, Massachusetts Institute of Technology, Cambridge, United States
| | - Mark F Bear
- The Picower Institute for Learning and Memory, Department of Brain and Cognitive Sciences, Massachusetts Institute of Technology, Cambridge, United States
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Pak A, Chubykin AA. Cortical Tuning is Impaired After Perceptual Experience in Primary Visual Cortex of Serotonin Transporter-Deficient Mice. Cereb Cortex Commun 2020; 1:tgaa066. [PMID: 33134928 PMCID: PMC7575641 DOI: 10.1093/texcom/tgaa066] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/27/2020] [Revised: 08/27/2020] [Accepted: 09/06/2020] [Indexed: 11/16/2022] Open
Abstract
Serotonin (5-hydroxytryptamine) is crucial for the proper development of neuronal circuits early in life and their refinement throughout adulthood. Its signaling is tightly regulated by the serotonin transporter (SERT), alterations of which were implicated in various neurological and psychiatric disorders. Animal models lacking a functional SERT variant display diverse phenotypes, including increased anxiety, social communication deficits, and altered cortical development. However, it remains unclear how SERT disruption affects sensory processing and experience-dependent learning in adulthood. It has been previously shown that perceptual experience leads to the development of visual familiarity-evoked theta oscillations in mouse V1. Here, we discovered that familiarity-evoked theta oscillations were longer and less stimulus specific in SERT knockout (KO) compared with wild-type (WT) mice. Interestingly, while the overall visual response properties were similar in naive mice, orientation and spatial frequency processing were significantly impaired in SERT KO compared with WT or SERT heterozygous mice following perceptual experience. Our findings shed more light on the mechanism of familiarity-evoked oscillations and highlight the importance of serotonin signaling in perceptual learning.
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Affiliation(s)
- Alexandr Pak
- Department of Biological Sciences, Purdue Institute for Integrative Neuroscience, Purdue University, West Lafayette, IN 47907, USA
| | - Alexander A Chubykin
- Department of Biological Sciences, Purdue Institute for Integrative Neuroscience, Purdue University, West Lafayette, IN 47907, USA
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Abstract
Recent work has transformed our ideas about the neural mechanisms, behavioral consequences and effective therapies for amblyopia. Since the 1700's, the clinical treatment for amblyopia has consisted of patching or penalizing the strong eye, to force the "lazy" amblyopic eye, to work. This treatment has generally been limited to infants and young children during a sensitive period of development. Over the last 20 years we have learned much about the nature and neural mechanisms underlying the loss of spatial and binocular vision in amblyopia, and that a degree of neural plasticity persists well beyond the sensitive period. Importantly, the last decade has seen a resurgence of research into new approaches to the treatment of amblyopia both in children and adults, which emphasize that monocular therapies may not be the most effective for the fundamentally binocular disorder that is amblyopia. These approaches include perceptual learning, video game play and binocular methods aimed at reducing inhibition of the amblyopic eye by the strong fellow eye, and enhancing binocular fusion and stereopsis. This review focuses on the what we've learned over the past 20 years or so, and will highlight both the successes of these new treatment approaches in labs around the world, and their failures in clinical trials. Reconciling these results raises important new questions that may help to focus future directions.
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Affiliation(s)
- Dennis M Levi
- University of California, Berkeley, School of Optometry & Helen Wills Neuroscience Institute, Berkeley, CA, USA.
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Searchfield GD, Spiegel DP, Poppe TNER, Durai M, Jensen M, Kobayashi K, Park J, Russell BR, Shekhawat GS, Sundram F, Thompson BB, Wise KJ. A proof-of-concept study comparing tinnitus and neural connectivity changes following multisensory perceptual training with and without a low-dose of fluoxetine. Int J Neurosci 2020; 131:433-444. [PMID: 32281466 DOI: 10.1080/00207454.2020.1746310] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/24/2022]
Abstract
Background. This proof-of-concept study investigated a method of multisensory perceptual training for tinnitus, and whether a short, low-dose administration of fluoxetine enhanced training effects and changed neural connectivity.Methods. A double-blind, randomized placebo controlled design with 20 participants (17 male, 3 female, mean age = 57.1 years) involved 30 min daily computer-based, multisensory training (matching visual, auditory and tactile stimuli to perception of tinnitus) for 20 days, and random allocation to take 20 mg fluoxetine or placebo daily. Behavioral measures of tinnitus and correlations between pairs of a priori regions of interest (ROIs), obtained using resting-state functional magnetic resonance imaging (rs-fMRI), were performed before and after the training.Results. Significant changes in ratings of tinnitus loudness, annoyance, and problem were observed with training. No statistically significant changes in Tinnitus Functional Index, Tinnitus Handicap Inventory or Depression Anxiety Stress Scales were found with training. Fluoxetine did not alter any of the behavioural outcomes of training compared to placebo. Significant changes in connectivity between ROIs were identified with training; sensory and attention neural network ROI changes correlated with significant tinnitus rating changes. Rs-fMRI results suggested that the direction of functional connectivity changes between auditory and non-auditory networks, with training and fluoxetine, were opposite to the direction of those changes with multisensory training and placebo.Conclusions. Improvements in tinnitus measures were correlated with changes in sensory and attention networks. The results provide preliminary evidence for changes in rs-fMRI accompanying a multisensory training method in persons with tinnitus.
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Affiliation(s)
- G D Searchfield
- Eisdell Moore Centre & Audiology Section, The University of Auckland, Auckland, New Zealand.,Centre for Brain Research, The University of Auckland, Auckland, New Zealand.,Brain Research New Zealand, New Zealand
| | - D P Spiegel
- Essilor Research and Development, Singapore, Singapore
| | - T N E R Poppe
- Biomedical Engineering and Imaging Sciences, Kings College London, London, UK
| | - M Durai
- Eisdell Moore Centre & Audiology Section, The University of Auckland, Auckland, New Zealand.,Centre for Brain Research, The University of Auckland, Auckland, New Zealand
| | - M Jensen
- Bay of Plenty and School of Pharmacy, Pharmacy, Whakatane Hospital, University of Auckland, Auckland, New Zealand
| | - K Kobayashi
- Eisdell Moore Centre & Audiology Section, The University of Auckland, Auckland, New Zealand.,Acoustics Centre, Mechanical Engineering, The University of Auckland, Auckland, New Zealand
| | - J Park
- Eisdell Moore Centre & Audiology Section, The University of Auckland, Auckland, New Zealand
| | - B R Russell
- School of Pharmacy, Otago University, Dunedin, New Zealand
| | | | - F Sundram
- Department of Psychological Medicine, Faculty of Medical and Health Sciences, The University of Auckland, Auckland, New Zealand
| | - B B Thompson
- School of Optometry and Vision Science, University of Waterloo, Waterloo, Canada
| | - K J Wise
- Eisdell Moore Centre & Speech Science, The University of Auckland, Auckland, New Zealand
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Xin KZ, Prescott CR. Selective serotonin reuptake inhibitors may lead to improved cataract surgery outcomes in patients with amblyopia. Clin Ophthalmol 2019; 13:1517-1522. [PMID: 31496643 PMCID: PMC6691949 DOI: 10.2147/opth.s213289] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/27/2019] [Accepted: 07/02/2019] [Indexed: 11/23/2022] Open
Abstract
Purpose To evaluate the effects of selective serotonin reuptake inhibitor (SSRI)/serotonin norepinephrine reuptake inhibitor (SNRI) medications in combination with cataract surgery in treating amblyopia in adult patients. Patients and methods A retrospective chart review study was conducted on patients who had undergone cataract surgery at the Johns Hopkins Hospital Wilmer Eye Institute. Six inclusion criteria were used to assess patient eligibility: 1) >18 years of age, 2) diagnosis of amblyopia, 3) diagnosis of cataract and treatment with surgery, 4) electronic medical record contains pre-surgery and post-surgery visual acuity (VA) measurements, 5) electronic medical record contains information on whether the patient was ever prescribed a SSRI/SNRI and the treatment duration, and 6) interocular VA difference of two lines or more on Snellen chart prior to cataract surgery. From each record, preoperative VA, postoperative VA, date of surgery, date at which postoperative VA was measured, and age at surgery were collected. Results A total of 237 patients were included, with 38 of them being on SSRI/SNRI. The mean improvement in VA after surgery was not significantly greater in patients on SSRI/SNRI (SSRI/SNRI: −0.276 logMAR, control: −0.192 logMAR, p=0.15). Multivariable regression was subsequently performed and while holding all other variables constant, demonstrated a statistically significant improvement in VA in patients on SSRI/SNRI (95% CI: −0.194, −0.0116, p=0.03). The regression analysis further demonstrated that advanced age has an adverse effect on the change in post-op VA (CI: 3.34×10−3 logMAR, 9.77×10−3 logMAR, p<0.005). Worse baseline VA is associated with a greater improvement in post-op VA (95% CI: −0.659 logMAR, −0.463 logMAR, p<0.005) but adverse effect on the absolute post-op VA (95% CI: 0.341 logMAR, 0.544 logMAR, p<0.005). Conclusion This study suggests that patients with amblyopia undergoing cataract surgery may potentially have a greater visual improvement when treated with SSRI/SNRIs.
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Affiliation(s)
- Kevin Z Xin
- Department of Ophthalmology, Johns Hopkins Wilmer Eye Institute, Baltimore, MD, USA
| | - Christina R Prescott
- Department of Ophthalmology, Johns Hopkins Wilmer Eye Institute, Baltimore, MD, USA
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