Assessment of bilateral pupillary centroid characteristics at varying illuminations and post-photopic flash response using an automated pupillometer

2016 ◽  
Vol 99 (6) ◽  
pp. 535-543 ◽  
Author(s):  
Gaurav Prakash ◽  
Dhruv Srivastava ◽  
Muhammad Suhail ◽  
Ruthchel Bacero
Keyword(s):  
Flash Response

scholarly journals Does ganciclovir exert retinal toxicity after multiple continuous intravitreal injections?

2021 ◽  
Vol 21 (1) ◽  
Author(s):  
Feng Hu ◽  
Ya Ma ◽  
Xiaoyan Peng
Keyword(s):  
Visual Acuity ◽  
Capillary Density ◽  
Acute Retinal Necrosis ◽  
Case Presentation ◽  
Visual Damage ◽  
Retinal Capillary ◽  
Single Flash ◽  
Interdigitation Zone ◽  
Anatomical Outcomes ◽  
Flash Response

Abstract Background The objective of this study is to report a case of acute retinal necrosis in which abnormalities in visual function did not correspond to retinal anatomical outcomes. Case presentation A 39-year-old female diagnosed with acute retinal necrosis underwent repeated (nine rounds) intravitreal ganciclovir injection (3 mg/0.1 ml) into the left eye, one injection every 2 weeks. During the therapy, the patient noticed her visual acuity declining gradually. The best corrected visual acuity in the left eye was 20/33. The visual field showed massive visual damage. There was no posterior necrotizing involvement, no macular edema or exudation, and only slight abnormity of the interdigitation zone in the fovea area was visible on OCT. Angio-OCT revealed normal capillary density of three retinal capillary and choriocapillaris layers. The visually evoked potential was normal. The photopic single-flash response showed a declined amplitude of a-wave and b-wave. The amplitudes of photopic 30 Hz flicker were decreased. Multifocal electroretinography revealed macular dysfunction. Conclusion Ganciclovir-associated photoreceptor damage may induce abnormalities in retinal function in response to multiple continuous intravitreal ganciclovir injections at a relatively high dosage (3 mg/0.1 ml).

scholarly journals Kinetics of Recovery of the Dark-adapted Salamander Rod Photoresponse

1998 ◽  
Vol 111 (1) ◽  
pp. 7-37 ◽  
Author(s):  
S. Nikonov ◽  
N. Engheta ◽  
E.N. Pugh
Keyword(s):  
Theoretical Analysis ◽  
Time Constant ◽  
Translation Invariance ◽  
Flash Intensity ◽  
Translation Invariant ◽  
Calcium Dependent ◽  
The Difference ◽  
Analytical Expressions ◽  
Kinetics Of ◽  
Flash Response

The kinetics of the dark-adapted salamander rod photocurrent response to flashes producing from 10 to 105 photoisomerizations (Φ) were investigated in normal Ringer's solution, and in a choline solution that clamps calcium near its resting level. For saturating intensities ranging from ∼102 to 104 Φ, the recovery phases of the responses in choline were nearly invariant in form. Responses in Ringer's were similarly invariant for saturating intensities from ∼103 to 104 Φ. In both solutions, recoveries to flashes in these intensity ranges translated on the time axis a constant amount (τc) per e-fold increment in flash intensity, and exhibited exponentially decaying “tail phases” with time constant τc. The difference in recovery half-times for responses in choline and Ringer's to the same saturating flash was 5–7 s. Above ∼104 Φ, recoveries in both solutions were systematically slower, and translation invariance broke down. Theoretical analysis of the translation-invariant responses established that τc must represent the time constant of inactivation of the disc-associated cascade intermediate (R*, G*, or PDE*) having the longest lifetime, and that the cGMP hydrolysis and cGMP-channel activation reactions are such as to conserve this time constant. Theoretical analysis also demonstrated that the 5–7-s shift in recovery half-times between responses in Ringer's and in choline is largely (4–6 s) accounted for by the calcium-dependent activation of guanylyl cyclase, with the residual (1–2 s) likely caused by an effect of calcium on an intermediate with a nondominant time constant. Analytical expressions for the dim-flash response in calcium clamp and Ringer's are derived, and it is shown that the difference in the responses under the two conditions can be accounted for quantitatively by cyclase activation. Application of these expressions yields an estimate of the calcium buffering capacity of the rod at rest of ∼20, much lower than previous estimates.

scholarly journals Turning Cones Off: the Role of the 9-Methyl Group of Retinal in Red Cones

2006 ◽  
Vol 128 (6) ◽  
pp. 671-685 ◽  
Author(s):  
Maureen E. Estevez ◽  
Petri Ala-Laurila ◽  
Rosalie K. Crouch ◽  
M. Carter Cornwall
Keyword(s):  
Visual Pigment ◽  
Bright Light ◽  
Rapid Rate ◽  
Methyl Group ◽  
Cone Opsin ◽  
Rate Of Recovery ◽  
Kinetics Of ◽  
Flash Response

Our ability to see in bright light depends critically on the rapid rate at which cone photoreceptors detect and adapt to changes in illumination. This is achieved, in part, by their rapid response termination. In this study, we investigate the hypothesis that this rapid termination of the response in red cones is dependent on interactions between the 9-methyl group of retinal and red cone opsin, which are required for timely metarhodopsin (Meta) II decay. We used single-cell electrical recordings of flash responses to assess the kinetics of response termination and to calculate guanylyl cyclase (GC) rates in salamander red cones containing native visual pigment as well as visual pigment regenerated with 11-cis 9-demethyl retinal, an analogue of retinal in which the 9-methyl group is missing. After exposure to bright light that photoactivated more than ∼0.2% of the pigment, red cones containing the analogue pigment had a slower recovery of both flash response amplitudes and GC rates (up to 10 times slower at high bleaches) than red cones containing 11-cis retinal. This finding is consistent with previously published biochemical data demonstrating that red cone opsin regenerated in vitro with 11-cis 9-demethyl retinal exhibited prolonged activation as a result of slowed Meta II decay. Our results suggest that two different mechanisms regulate the recovery of responsiveness in red cones after exposure to light. We propose a model in which the response recovery in red cones can be regulated (particularly at high light intensities) by the Meta II decay rate if that rate has been inhibited. In red cones, the interaction of the 9-methyl group of retinal with opsin promotes efficient Meta II decay and, thus, the rapid rate of recovery.

scholarly journals Light adaptation in retinal rods of the rabbit and two other nonprimate mammals.

1991 ◽  
Vol 97 (3) ◽  
pp. 413-435 ◽  
Author(s):  
K Nakatani ◽  
T Tamura ◽  
K W Yau
Keyword(s):  
Light Adaptation ◽  
Evoked Responses ◽  
Flash Intensity ◽  
Exponential Form ◽  
Time To Peak ◽  
Outward Currents ◽  
Retinal Rods ◽  
Response Peak ◽  
Flash Response ◽  
Plateau Level

The responses of rabbit rods to light were studied by drawing a single rod outer segment projecting from a small piece of retina into a glass pipette to record membrane current. The bath solution around the cells was maintained at near 40 degrees C. Light flashes evoked transient outward currents that saturated at up to approximately 20 pA. One absorbed photon produced a response of approximately 0.8 pA at peak. At the rising phase of the flash response, the relation between response amplitude and flash intensity (IF) had the exponential form 1-e-kappa FIF (where kappa F is a constant denoting sensitivity) expected from the absence of light adaptation. At the response peak, however, the amplitude-intensity relation fell slightly below the exponential form. At times after the response peak, the deviation was progressively more substantial. Light steps evoked responses that rose to a transient peak and rapidly relaxed to a lower plateau level. The response-intensity relation again indicated that light adaptation was insignificant at the early rising phase of the response, but became progressively more prominent at the transient peak and the steady plateau of the response. Incremental flashes superposed on a steady light of increasing intensity evoked responses that had a progressively shorter time-to-peak and faster relaxation, another sign of light adaptation. The flash sensitivity changed according to the Weber-Fechner relation (i.e., inversely) with background light intensity. We conclude that rabbit rods adapt to light in a manner similar to rods in cold-blooded vertebrates. Similar observations were made on cattle and rat rods.

scholarly journals Origin and control of the dominant time constant of salamander cone photoreceptors

2012 ◽  
Vol 140 (2) ◽  
pp. 219-233 ◽  
Author(s):  
Jingjing Zang ◽  
Hugh R. Matthews
Keyword(s):  
Time Constant ◽  
External Solution ◽  
Light Response ◽  
Response Recovery ◽  
Bright Flash ◽  
Active Intermediates ◽  
And Control ◽  
Flash Response ◽  
Phototransduction Cascade ◽  
External Ph

Recovery of the light response in vertebrate photoreceptors requires the shutoff of both active intermediates in the phototransduction cascade: the visual pigment and the transducin–phosphodiesterase complex. Whichever intermediate quenches more slowly will dominate photoresponse recovery. In suction pipette recordings from isolated salamander ultraviolet- and blue-sensitive cones, response recovery was delayed, and the dominant time constant slowed when internal [Ca2+] was prevented from changing after a bright flash by exposure to 0Ca2+/0Na+ solution. Taken together with a similar prior observation in salamander red-sensitive cones, these observations indicate that the dominance of response recovery by a Ca2+-sensitive process is a general feature of amphibian cone phototransduction. Moreover, changes in the external pH also influenced the dominant time constant of red-sensitive cones even when changes in internal [Ca2+] were prevented. Because the cone photopigment is, uniquely, exposed to the external solution, this may represent a direct effect of protons on the equilibrium between its inactive Meta I and active Meta II forms, consistent with the notion that the process dominating recovery of the bright flash response represents quenching of the active Meta II form of the cone photopigment.

Remarkable differences in double-flash-response in rod-dominated and mixed retina

1971 ◽  
Vol 11 (10) ◽  
pp. 1221-1222 ◽  
Author(s):  
J. Schulze ◽  
F. Beddermann
Keyword(s):  
Flash Response ◽  
Double Flash

scholarly journals Novel Form of Adaptation in Mouse Retinal Rods Speeds Recovery of Phototransduction

2003 ◽  
Vol 122 (6) ◽  
pp. 703-712 ◽  
Author(s):  
Claudia M. Krispel ◽  
Ching-Kang Chen ◽  
Melvin I. Simon ◽  
Marie E. Burns
Keyword(s):  
Dark Current ◽  
Bright Light ◽  
Ambient Light ◽  
Rate Limiting Step ◽  
Limiting Step ◽  
Electrophysiological Recordings ◽  
Bright Flash ◽  
Retinal Rods ◽  
Rate Limiting ◽  
Flash Response

Photoreceptors of the retina adapt to ambient light in a manner that allows them to detect changes in illumination over an enormous range of intensities. We have discovered a novel form of adaptation in mouse rods that persists long after the light has been extinguished and the rod's circulating dark current has returned. Electrophysiological recordings from individual rods showed that the time that a bright flash response remained in saturation was significantly shorter if the rod had been previously exposed to bright light. This persistent adaptation did not decrease the rate of rise of the response and therefore cannot be attributed to a decrease in the gain of transduction. Instead, this adaptation was accompanied by a marked speeding of the recovery of the response, suggesting that the step that rate-limits recovery had been accelerated. Experiments on knockout rods in which the identity of the rate-limiting step is known suggest that this adaptive acceleration results from a speeding of G protein/effector deactivation.

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