An electrophysiological study of retinal function in the diabetic female rat

PURPOSE

To examine retinal function in female Long-Evans rats with streptozotocin (STZ)-induced diabetes.

METHODS

Hyperglycemia was induced by IV injection of STZ, and ERG responses were recorded at 4-week intervals over 12 weeks. Oscillatory potentials (OPs) and responses to intermittent stimulation were analyzed with a custom computer program. The GABA-induced responses of individual rod bipolar cells were obtained from patch-clamp recordings, and immunohistochemistry was used to illustrate the retinal distribution of GABA (gamma-aminobutyric acid) and GABA(C) receptors.

RESULTS

Hyperglycemia developed in rats 2 to 3 days after injection of STZ. Compared with previous reports of the effects of diabetes in male rats, visual function abnormalities appeared to be milder in STZ-treated female rats. No significant differences were observed in the sensitivity or amplitude of the a- or b-wave components of the ERG between diabetic and control animals, and both animal groups exhibited a similar time course of neuronal dark adaptation. In contrast, diabetic animals showed significant differences in the pattern of OPs and in the amplitudes of their responses to flicker. The accumulation of GABA in the inner retina of diabetic rats, combined with the results of patch-clamp recordings from individual bipolar cells, revealed that the circuitry underlying the GABA signal of the proximal retina is affected by hyperglycemia.

CONCLUSIONS

The results suggest that changes in the GABA-signaling pathway may be the underlying cellular mechanism for altered ERG responses in STZ-induced diabetes in rats. Recognition of these early neurosensory defects would enable a better understanding of the pathophysiological basis of diabetic retinopathy.

Hypoxia and Dark Adaptation in Diabetic Retinopathy: Interactions, Consequences, and Therapy

In diabetes, retinal blood flow is compromised, and retinal hypoxia is likely to be further intensified during periods of darkness. During dark adaptation, rod photoreceptors in the outer retina are maximally depolarized and continuously release large amounts of the neurotransmitter glutamate-an energetically demanding process that requires the highest oxygen consumption per unit volume of any tissue of the body. In complete darkness, even more oxygen is consumed by the outer retina, producing a steep fall in the retinal oxygen tension curve which reaches a nadir at the depth of the mitochondrial-rich rod inner segments. In contrast to the normal retina, the diabetic retina cannot meet the added metabolic load imposed by the dark-adapted rod photoreceptors; this exacerbates retinal hypoxia and stimulates the overproduction of vascular endothelial growth factor (VEGF). The use of nocturnal illumination to prevent dark adaptation, specifically reducing the rod photoreceptor dark current, should ameliorate diabetic retinopathy.

Streptozotocin-induced diabetes modulates GABA receptor activity of rat retinal neurons

Neural deficits suggestive of involvement of the GABA signaling pathway can often be detected early in the course of diabetic retinopathy, a leading cause of blindness in the United States. To examine in greater detail the nature of the neuronal changes associated with hyperglycemia, we investigated GABA receptor activity on retinal bipolar cells in streptozotocin-induced diabetic rats; cells from age-matched normal rats served as controls. Patch-clamp recordings from isolated rod-bipolar cells revealed that diabetes enhanced the whole cell currents elicited by GABA. Responses of the GABA(C) receptor, the predominant GABA receptor on rat rod bipolar cells, exhibited a greater sensitivity to GABA, larger maximum current responses, slower response kinetics, and a smaller single channel conductance among diabetic cells relative to those recorded from normal controls. Compared with the properties of homomeric rho1 and heteromeric rho1rho2 receptors formed in a heterologous expression system, these results suggested that there was a greater contribution from the rho1 subunit in the GABA(C) receptor-mediated response of diabetic cells. The levels of mRNA, measured with real-time RT-PCR, were consistent with this finding. There was a significant enhancement in the ratio of rho1/rho2 subunit expression in the retina of diabetic animals, although the levels of GABA rho1 subunit expression were comparable in diabetic and normal retinas. Taken together, the results suggest that diabetes modifies the subunit composition of the GABA(C) receptor on retinal neurons, most likely through its effect on the efficacy of gene transcription.

Automated image alignment and segmentation to follow progression of geographic atrophy in age-related macular degeneration

PURPOSE

To develop a computer-based image segmentation method for standardizing the quantification of geographic atrophy (GA).

METHODS

The authors present an automated image segmentation method based on the fuzzy c-means clustering algorithm for the detection of GA lesions. The method is evaluated by comparing computerized segmentation against outlines of GA drawn by an expert grader for a longitudinal series of fundus autofluorescence images with paired 30° color fundus photographs for 10 patients.

RESULTS

The automated segmentation method showed excellent agreement with an expert grader for fundus autofluorescence images, achieving a performance level of 94 ± 5% sensitivity and 98 ± 2% specificity on a per-pixel basis for the detection of GA area, but performed less well on color fundus photographs with a sensitivity of 47 ± 26% and specificity of 98 ± 2%. The segmentation algorithm identified 75 ± 16% of the GA border correctly in fundus autofluorescence images compared with just 42 ± 25% for color fundus photographs.

CONCLUSION

The results of this study demonstrate a promising computerized segmentation method that may enhance the reproducibility of GA measurement and provide an objective strategy to assist an expert in the grading of images.

Genetic advances in ophthalmology: the role of melanopsin-expressing, intrinsically photosensitive retinal ganglion cells in the circadian organization of the visual system

Daily changes in the light-dark cycle are the principal environmental signal that enables organisms to synchronize their internal biology with the 24-hour day-night cycle. In humans, the visual system is integral to photoentrainment and is primarily driven by a specialized class of intrinsically photosensitive retinal ganglion cells (ipRGCs) that express the photopigment melanopsin (OPN4) in the inner retina. These cells project through the retinohypothalamic tract (RHT) to the suprachiasmatic nuclei (SCN) of the hypothalamus, which serves as the body's master biological clock. At the same time, the retina itself possesses intrinsic circadian oscillations, exemplified by diurnal fluctuations in visual sensitivity, neurotransmitter levels, and outer segment turnover rates. Recently, it has been noted that both central and peripheral oscillators share a molecular clock consisting of an endogenous, circadian-driven, transcription-translation feedback loop that cycles with a periodicity of approximately 24 hours. This review will cover the role that melanopsin and ipRGCs play in the circadian organization of the visual system.

Complications of subspecialty ophthalmic care: systemic complications from the intravitreal administration of agents that target the vascular endothelial growth factor pathway

The treatment of neovascular age-related macular degeneration (AMD) and other pathologic ocular conditions that overexpress the vascular endothelial growth factor (VEGF) has been revolutionized in the last decade by the introduction of intravitreal agents that target the VEGF pathway. Since treatment trials are designed primarily to assess the prevention of vision loss caused by ocular conditions, they are inadequate for detecting rare, but potentially serious, systemic side effects. The aim of this article is to present what the ophthalmologist needs to know about systemic complications from anti-VEGF therapy and review the likelihood that these side effects occur in the context of small, but often-repeated, intravitreal doses of these potent biological medications. Preferred practice patterns need to be developed that weigh the ability of these medications to mitigate potentially blinding conditions, while at the same time minimizing the risk of adverse outcomes in specific patient populations that possess multiple and often interrelated medical comorbidities.

Early Conversion to Aflibercept for Persistent Diabetic Macular Edema Results in Better Visual Outcomes and Lower Treatment Costs

PURPOSE

To evaluate the functional and anatomic outcomes, as well as cost-effectiveness, of the timing of conversion to intravitreal aflibercept (IVA) in patients with treatment-resistant diabetic macular edema (DME).

METHODS

Thirty consecutive eyes (25 patients) were identified that were treated with ≥3 intravitreal bevacizumab (IVB) and/or ranibizumab (IVR) injections prior to treatment with ≥3 IVA injections. Eyes that received ≤6 IVB and/or IVR injections (early-switch) were compared to those that received ≥7 injections (late-switch) prior to conversion to IVA. Treatment effectiveness was measured in quality-adjusted life years (QALYs). A micro-simulation model examined the impact of treatment duration on outcomes.

RESULTS

Early- (n=18) and late- (n=12) switch eyes had similar vision prior to conversion to IVA. Despite improvements in retinal thickness, only the early-switch eyes maintained vision gains after conversion to IVA through the end of follow-up (p=0.027). Early switch saved $22,884/eye and produced an additional 0.027 QALYs.

CONCLUSION

Early conversion to IVA optimizes vision outcomes and results in lower overall treatment expenditures.

Long-term Outcome After Acute Peripheral Facial Palsy

PURPOSE

To analyze long-term outcomes in a large cohort of patients with acute peripheral facial palsy (APFP).

METHODS

Hospital-based, cross-sectional study. Data were abstracted from the electronic medical record. Time to recovery was assessed with Kaplan-Meier survival analyses. Binary logistic regression analysis was used to identify factors associated with outcome.

RESULTS

Three hundred seventy-two patients with APFP seen at a tertiary hospital between February 2015 and March 2021 were analyzed. Seasonal variation of APFP peaked in the early fall (September 29) and had a peak-to-low ratio of 1.36 (R 2 = 0.329, p < 0.001). Patients who tested positive for Lyme disease (10%) had an earlier peak (July 16) compared with those who were negative (October 15). Eighty-seven percent of patients had complete recovery (averaging 64 ± 61 days). Patients, with higher House-Brackmann (H-B) grades at presentation took longer to recover, were more likely to have aberrant regeneration and had lower final rates of recovery compared with those with lower H-B grades (χ 2 = 12.03, p < 0.001). Of the patients with residual palsies, 70% had evidence of aberrant regeneration, and nearly half of those had hemifacial spasm.

CONCLUSIONS

Most patients with APFP achieve complete recovery within 1 year, including those positive for Lyme. More severe palsy at presentation portends a worse outcome.

Dark Adaptation Survey as a Predictive Tool for Primary Open-Angle Glaucoma

PURPOSE

To study the extent to which patients with primary open-angle glaucoma (POAG) have subjective difficulties with dark (DA) adaptation and vision under low-luminance conditions and to correlate the reported difficulties with severity of disease, specifically visual field loss.

DESIGN

Prospective, comparative case series.

PARTICIPANTS

Two hundred twenty patients with and without POAG who sought treatment at an outpatient subspecialty glaucoma clinic between October 2016 and September 2018.

METHODS

A questionnaire designed to assess difficulties with DA and vision under low luminance (the DA survey) was developed and given to patients during routine clinical evaluation in a hospital-based eye clinic. Retrospective data related to ocular health and glaucoma severity were abstracted from the medical record. A multiple regression analysis was performed to create a predictive model for POAG.

MAIN OUTCOME MEASURES

Severity of glaucoma, specifically visual field loss, and classification of participants as glaucoma patients or control participants.

RESULTS

Eighty-five patients with POAG and 127 control participants completed the questionnaire. Exploratory factor analysis of the DA survey using a principal components analysis showed that the items split into 2 dimensions: tasks that involved difficulty with vision under low luminance and those that required DA. Cronbach's α showed a high degree of internal consistency reliability (α = 0.88). Increasing DA survey score correlated with binocular visual field loss among patients with mild, moderate, and advanced POAG (P < 0.001). A model used to differentiate patients with POAG from control participants that included average and intereye difference in cup-to-disc ratio, family history of glaucoma, and DA survey score showed an accuracy, sensitivity, and specificity of 96.7%, 92.9%, and 99.2%, respectively.

CONCLUSIONS

This pilot study revealed that problems with DA and vision under low luminance are commonly encountered by patients with POAG. These areas of visual disability are not assessed routinely in glaucoma care. A questionnaire assessing vision under low luminance and light-dark transitions may serve as a proxy for functional impairment in glaucoma. When paired with risk factors such as structural features of the optic nerve and family history, this survey instrument may be suitable to screen for patients with POAG.

Intraocular pressure decreases in eyes with glaucoma-related diagnoses after conversion to aflibercept for treatment-resistant age-related macular degeneration

OBJECTIVE

To understand intraocular pressure (IOP) response after switching from intravitreal bevacizumab (IVB) and/or ranibizumab (IVR) to intravitreal aflibercept (IVA) for treatment-resistant neovascular age-related macular degeneration (nAMD) in patients with and without coexisting glaucoma-related diagnoses.

METHODS

Retrospective, cross-sectional comparative case series of 62 eyes of 58 patients treated with intravitreal injection for nAMD from March 2010 to April 2018. Patients with glaucoma-related diagnoses, defined here as open-angle glaucoma or suspicion of open-angle glaucoma, ocular hypertension, and/or narrow-angle glaucoma, were compared to those without glaucoma. IOP data were collected at baseline, at the three visits where patients received loading doses of IVB/IVR, and at all of the visits following the switch to IVA through the end of follow-up.

RESULTS

19 eyes with pre-existing glaucoma-related diagnoses were compared to 43 eyes without such diagnoses. Baseline IOP was similar for glaucoma and non-glaucoma patients. The loading doses of IVB/IVR did not impact IOP; however, a small, sustained rise in IOP was noted among patients with glaucoma-related diagnoses by the final IVB/IVR injections before the switch to IVA (∆IOP 1.61 ± 0.52 mmHg, P < 0.002). After conversion to IVA, pre-injection IOP declined in eyes both with (-1.59 ± 0.54 mmHg, P < 0.001) and without (-0.99 ± 0.28 mmHg, P < 0.001) glaucoma-related diagnoses.

CONCLUSIONS

IOP in patients with glaucoma-related diagnoses appears to be more sensitive to intravitreal injections than it is in patients without glaucoma-related diagnoses. It rises with IVB/IVR and declines after the switch to IVA. Switching patients with nAMD to IVA may present an opportunity to lower IOP in patients with glaucoma.

Online ethics discussion forum facilitates medical center clinical ethics case reviews

Clinical ethics consultants are increasingly called upon to give counsel in the clinical arena on issues including but not limited to withdrawal or withholding of specific medical treatments, assisting minors and mentally impaired patients with care decisions, working with difficult patients and families, identifying appropriate surrogate decision makers, and executing advance directives and end-of-life decisions. Often, the consultant may need to convene the ethics committee members to review and provide feedback for a given case. This process may be difficult to schedule in a timely way because of member's clinical and other work-related obligations. To this end, the University of Illinois Medical Center in Chicago has set up a unique Web board to facilitate ongoing case discussions via a secured, password-protected ethics committee online forum. This allows for real-time review by all ethics committee members. We will explain our online process as well as discuss our clinical case experiences.

Telehealth Encourages Patients with Diabetes in Racial and Ethnic Minority Groups to Return for in-Person Ophthalmic Care During the COVID-19 Pandemic

PURPOSE

The COVID-19 pandemic had a disproportionate impact on patients from racial and/or ethnic minority groups, causing many to delay healthcare. This study evaluates the role telehealth visits played in helping patients with diabetes mellitus (DM) return for subsequent, in-person eye examinations after the outbreak of COVID-19.

METHODS

This retrospective, cross-sectional study analyzed 8147 patients with DM who had completed an outpatient ophthalmology and/or optometry visit in 2019 and who were due for return evaluation after the outbreak of COVID-19 in 2020. Factors associated with return for subsequent, in-person eye examination were assessed.

RESULTS

The mean age of patients was 68.8 (±13.0) years, and 42% were women. 7.4% of patients identified as Asian; 2.9% as Black; 3.4% as Hispanic or Latin American; 0.92%, as more than one race; 1.78%, as other races; and 80.7% as White. Patients from racial and/or ethnic minority groups completed fewer in-person eye examinations after the outbreak of COVID-19 compared with White patients (35.6% versus 44.5%, χ 2=36.172, P<0.001). However, both groups accessed telehealth services at a similar rate during this period (21.1% versus 21.9%, χ 2=0.417, P=0.518). Importantly, patients who received telehealth services returned for subsequent, in-person eye examinations at substantially higher rates, regardless of race (51.0% and 46.6%, respectively, χ 2=1.840, P=0.175). This offset the otherwise lower rate of return experienced by patients from racial and/or ethnic minority groups compared with White patients among the group of patients who did not receive any telehealth services (32.7% versus 42.7%, χ 2=36.582, P<0.001). The impact of telehealth on the likelihood of in-person return remained significant after taking into account age, gender, race, language, residence, severity of diabetic retinopathy (DR), and vision in a multivariate model.

CONCLUSION

Telehealth initiatives benefited patients from racial and/or ethnic minority groups by reducing disparities in access to eye care experienced during the COVID-19 pandemic.