Loss of melanopsin-containing retinal ganglion cells in a rat glaucoma model:

The structure-function relationship between multifocal pupil perimetry and retinal nerve fibre layer in glaucoma

BACKGROUND

Multifocal pupillographic objective perimetry (mfPOP) is a novel method for assessing functional change in diseases like glaucoma. Previous research has suggested that, in contrast to the pretectally-mediated melanopsin response of intrinsically photosensitive retinal ganglion cells, mfPOP responses to transient onset stimuli involve the extrastriate cortex, and thus the main visual pathway. We therefore investigate the correlation between peripapillary retinal nerve fibre layer (pRNFL) thickness and glaucomatous visual field changes detected using mfPOP. Parallel analyses are undertaken using white on white standard automated perimetry (SAP) for comparison.

METHODS

Twenty-five glaucoma patients and 24 normal subjects were tested using SAP, 3 mfPOP variants, and optical coherence tomography (OCT). Arcuate clusters of the SAP and mfPOP deviations were weighted according to their contribution to published arcuate divisions of the retinal nerve fibre layer. Structure-function correlation coefficients (r) were computed between pRNFL clock-hour sector thickness measurements, and the local visual field sensitivities from both SAP and mfPOP.

RESULTS

The strongest correlation was observed in the superior-superotemporal disc sector in patients with worst eye SAP MD < -12 dB: r = 0.93 for the mfPOP LumBal test (p < 0.001). Correlations across all disc-sectors were strongest in these same patients in both SAP and mfPOP: SAP r = 0.54, mfPOP LumBal r = 0.55 (p < 0.001). In patients with SAP MD ≥ -6 dB in both eyes, SAP correlations across all sectors were higher than mfPOP; mfPOP correlations however, were higher than SAP in more advanced disease, and in normal subjects.

CONCLUSIONS

For both methods the largest correlations with pRNFL thickness corresponded to the inferior nasal field of more severely damaged eyes. Head-to-head comparison of mfPOP and SAP showed similar structure-function relationships. This agrees with our recent reports that mfPOP primarily stimulates the cortical drive to the pupils.

Pupillary response to chromatic light stimuli as a possible biomarker at the early stage of glaucoma: a review

Glaucoma is a multifactorial neurodegenerative disease of the optic nerve currently considered a severe health problem because of its high prevalence, being the primary cause of irreversible blindness worldwide. The most common type corresponds to Primary Open-Angle Glaucoma. Glaucoma produces, among other alterations, a progressive loss of retinal ganglion cells (RGC) and its axons which are the key contributors to generate action potentials that reach the visual cortex to create the visual image. Glaucoma is characterized by Visual Field loss whose main feature is to be painless and therefore makes early detection difficult, causing a late diagnosis and a delayed treatment indication that slows down its progression. Intrinsically photosensitive retinal ganglion cells, which represent a subgroup of RGCs are characterized by their response to short-wave light stimulation close to 480 nm, their non-visual function, and their role in the generation of the pupillary reflex. Currently, the sensitivity of clinical examinations correlates to RGC damage; however, the need for an early damage biomarker is still relevant. It is an urgent task to create new diagnostic approaches to detect an early stage of glaucoma in a prompt, quick, and economical manner. We summarize the pathology of glaucoma and its current clinical detection methods, and we suggest evaluating the pupillary response to chromatic light as a potential biomarker of disease, due to its diagnostic benefit and its cost-effectiveness in clinical practice in order to reduce irreversible damage caused by glaucoma.

Vision-Related Quality of Life and Seasonal Affective Disorder in Patients with Glaucoma and Macular Degeneration

Seasonal affective disorder (SAD) is characterized by depressive episodes related to changes in the seasons. Patients with severe vision loss are at an increased risk of SAD. This study seeks to determine the extent to which patients with moderate vision loss report symptoms of SAD. In this cross-sectional, comparative case series, the Seasonal Pattern Assessment Questionnaire (SPAQ) and the National Eye Institute Visual Function Questionnaire (VFQ-39) were used to screen 111 patients with age-related macular degeneration (AMD) and/or primary open-angle glaucoma (POAG). A multiple regression analysis was performed to create a predictive model for SAD based on the Global Seasonality Score (GSS) using the VFQ-39. Subjects who reported symptoms of SAD (GSS > 8) had lower vision-related quality of life (composite score: 57.2 versus 73.2, p < 0.001). Exploratory factor analysis revealed that the items on the VFQ-39 split into two distinct dimensions that together accounted for 63.2% of the total variance in the GSS. One group of questions addressed vision-related problems; the other group comprised questions related to the quality of life. Whereas this model successfully identified patients with vision loss at risk of SAD, a model restricted to the questions available on the shorter, widely used VFQ-25 instrument did not reliably identify patients at risk of SAD.

Handheld chromatic pupillometry can accurately and rapidly reveal functional loss in glaucoma

BACKGROUND/AIMS

Early detection and treatment of glaucoma can delay vision loss. In this study, we evaluate the performance of handheld chromatic pupillometry (HCP) for the objective and rapid detection of functional loss in glaucoma.

METHODS

In this clinic-based, prospective study, we enrolled 149 patients (median (IQR) years: 68.5 (13.6) years) with confirmed glaucoma and 173 healthy controls (55.2 (26.7) years). Changes in pupil size in response to 9 s of exponentially increasing blue (469 nm) and red (640 nm) light-stimuli were assessed monocularly using a custom-built handheld pupillometer. Pupillometric features were extracted from individual traces and compared between groups. Features with the highest classification potential, selected using a gradient boosting machine technique, were incorporated into a generalised linear model for glaucoma classification. Receiver operating characteristic curve analyses (ROC) were used to compare the performance of HCP, optical coherence tomography (OCT) and Humphrey Visual Field (HVF).

RESULTS

Pupillary light responses were altered in glaucoma compared with controls. For glaucoma classification, HCP yielded an area under the ROC curve (AUC) of 0.94 (95% CI 0.91 to 0.96), a sensitivity of 87.9% and specificity of 88.4%. The classification performance of HCP in early-moderate glaucoma (visual field mean deviation (VFMD) > -12 dB; AUC=0.91 (95% CI 0.87 to 0.95)) was similar to HVF (AUC=0.91) and reduced compared with OCT (AUC=0.97; p=0.01). For severe glaucoma (VFMD ≤ -12 dB), HCP had an excellent classification performance (AUC=0.98, 95% CI 0.97 to 1) that was similar to HVF and OCT.

CONCLUSION

HCP allows for an accurate, objective and rapid detection of functional loss in glaucomatous eyes of different severities.

Glare and Mobility Performance in Glaucoma: A Pilot Study

PRCIS

Glare disability affects patients with moderate and severe glaucoma. Under glare conditions, mobility performances of glaucoma patients are reduced.

PURPOSE

The aim of this study was to evaluate glare disability and its impact on mobility and orientation in glaucoma patients.

METHODS

Twenty-two glaucoma patients and 12 age-matched control subjects were included. All patients underwent a clinical evaluation of visual function and halo size measurements to determine glare disability with a glare score (GS) of the best eye and worse eye. Mobility was evaluated by 4 mobility courses on an artificial street (StreetLab) under photopic conditions (P) and mesopic conditions with an additional light source in front of the patient to mimic dazzling conditions (M+G). Mobility time, mobility incidents, trajectory segmentation, distance traveled, preferred walking speed on trial (WS) and percentage of preferred walking speed (PPWS) were recorded, and the Nasa task load index (Nasa-TLX) was evaluated.

RESULTS

GS of the worse eye and GS of the best eye were significantly higher in glaucoma patients than in the control group (P=0.001 and 0.003). It was significantly different between moderate glaucoma patients and controls (P=0.001 and 0.010, respectively) and between severe glaucoma patients and controls (P=0.049 and 0.016). In locomotion tasks, comparing performance under M+G and P conditions, mobility performance was significantly different concerning mobility time (P=0.010), distance traveled (P=0.008), WS (P=0.007), PPWS (P=0.006), and Nasa-TLX (P=0.017) in the glaucoma group. Under M+G lighting conditions, mobility performance for glaucoma patients was significantly worse than controls with regard to WS (P=0.038), PPWS (P=0.0498), mobility time (P=0.046), and Nasa-TLX (P=0.006).

CONCLUSION

Glare disability was observed in patients with moderate and severe glaucoma and had an impact on their mobility performance.

Chronotyping glaucoma patients with the Munich ChronoType Questionnaire: A case-control study

Purpose

The circadian clock is entrained to light by the intrinsically photosensitive retinal ganglion cells. Loss of these cells in glaucoma, an eye disease with loss of retinal ganglion cells as its key feature, might thus result in a change in chronotype. We aimed to compare the chronotype between glaucoma patients and healthy subjects.

Methods

We sent the Munich ChronoType Questionnaire to 221 glaucoma patients (response rate 81%); controls (primary control group) were primarily their spouses. After exclusion of shift workers and participants who woke-up due to an alarm clock on days off, 159 glaucoma patients (88 early, 21 moderate, 23 severe) and 163 controls remained. We calculated chronotype as the mid-sleep on days off, corrected for workweek accumulated sleep debt (MSF_sc). We compared means and variances between groups using Welch’s tests and F-tests, respectively. A secondary control group was recruited from participants in a citizen-science project (n = 17073) who completed an online questionnaire. A resampling method was applied to enable an age- and gender- matched comparison with the glaucoma patients.

Results

Compared to the primary control group, glaucoma did not affect the mean MSF_sc (controls 3:47; early, moderate, and severe glaucoma 3:40, 3:45, and 3:33, respectively [P = 0.62]). Chronotype variability seemed to increase with increasing disease severity (severe glaucoma versus controls: P = 0.023). The mean MSF_sc of the secondary control group was 3:50 (95% confidence interval 3:48 to 3:52); significantly later than that of the glaucoma patients (3:40; P = 0.024). Mean MSF_sc did not differ significantly between the control groups (P = 0.42).

Conclusions

No clear changes were found in the chronotype as determined by sleep phase in patients with glaucoma, especially not in early and moderate glaucoma. In severe glaucoma, chronotype variability seems to increase, possibly alongside a small advancement.

Regulation of Reentrainment Function Is Dependent on a Certain Minimal Number of Intact Functional ipRGCs in rd Mice

Purpose

To investigate the effect of partial ablation of melanopsin-containing retinal ganglion cells (mcRGCs) on nonimage-forming (NIF) visual functions in rd mice lacking rods.

Methods

The rd mice were intravitreally injected with different doses (100 ng/μl, 200 ng/μl, and 400 ng/μl) of immunotoxin melanopsin-SAP. And then, the density of ipRGCs was examined. After establishing the animal models with different degrees of ipRGC damage, a wheel-running system was used to evaluate their reentrainment response.

Results

Intravitreal injection of melanopsin-SAP led to partial ablation of ipRGCs in a dose-dependent manner. The survival rates of ipRGCs in the 100 ng/μl, 200 ng/μl, and 400 ng/μl groups were 74.14% ± 4.15%, 39.25% ± 2.29%, and 38.38% ± 3.74%, respectively. The wheel-running experiments showed that more severe ipRGC loss was associated with a longer time needed for reentrainment. When the light/dark cycle was delayed by 8 h, the rd mice in the PBS control group took 4.67 ± 0.79 days to complete the synchronization with the shifted cycle, while those in the 100 ng/μl and 200 ng/μl groups required 7.90 ± 0.55 days and 11.00 ± 0.79 days to complete the synchronization with the new light/dark cycle, respectively.

Conclusion

Our study indicates that the regulation of some NIF visual functions is dependent on a certain minimal number of intact functional ipRGCs.

Quadrant Field Pupillometry Detects Melanopsin Dysfunction in Glaucoma Suspects and Early Glaucoma

It is difficult to detect visual function deficits in patients at risk for glaucoma (glaucoma suspects) and at early disease stages with conventional ophthalmic tests such as perimetry. To this end, we introduce a novel quadrant field measure of the melanopsin retinal ganglion cell mediated pupil light response corresponding with typical glaucomatous arcuate visual field defects. The melanopsin-mediated post-illumination pupil response (PIPR) was measured in 46 patients with different stages of glaucoma including glaucoma suspects and compared to a healthy group of 21 participants with no disease. We demonstrate that the superonasal quadrant PIPR differentiated glaucoma suspects and early glaucoma patients from controls with fair (AUC = 0.74) and excellent (AUC = 0.94) diagnostic accuracy, respectively. The superonasal PIPR provides a linear functional correlate of structural retinal nerve fibre thinning in glaucoma suspects and early glaucoma patients. This first report that quadrant PIPR stimulation detects melanopsin dysfunction in patients with early glaucoma and at pre-perimetric stages may have future implications in treatment decisions of glaucoma suspects.

Pupillary Responses to High-Irradiance Blue Light Correlate with Glaucoma Severity

PURPOSE

To evaluate whether a chromatic pupillometry test can be used to detect impaired function of intrinsically photosensitive retinal ganglion cells (ipRGCs) in patients with primary open-angle glaucoma (POAG) and to determine if pupillary responses correlate with optic nerve damage and visual loss.

DESIGN

Cross-sectional study.

PARTICIPANTS

One hundred sixty-one healthy controls recruited from a community polyclinic (55 men; 151 ethnic Chinese) and 40 POAG patients recruited from a glaucoma clinic (22 men; 35 ethnic Chinese) 50 years of age or older.

METHODS

Subjects underwent monocular exposure to narrowband blue light (469 nm) or red light (631 nm) using a modified Ganzfeld dome. Each light stimulus was increased gradually over 2 minutes to activate sequentially the rods, cones, and ipRGCs that mediate the pupillary light reflex. Pupil diameter was recorded using an infrared pupillography system.

MAIN OUTCOME MEASURES

Pupillary responses to blue light and red light were compared between control subjects and those with POAG by constructing dose-response curves across a wide range of corneal irradiances (7-14 log photons/cm(2) per second). In patients with POAG, pupillary responses were evaluated relative to standard automated perimetry testing (Humphrey Visual Field [HVF]; Carl Zeiss Meditec, Dublin, CA) and scanning laser ophthalmoscopy parameters (Heidelberg Retinal Tomography [HRT]; Heidelberg Engineering, Heidelberg, Germany).

RESULTS

The pupillary light reflex was reduced in patients with POAG only at higher irradiance levels, corresponding to the range of activation of ipRGCs. Pupillary responses to high-irradiance blue light associated more strongly with disease severity compared with responses to red light, with a significant linear correlation observed between pupil diameter and HVF mean deviation (r = -0.44; P = 0.005) as well as HRT linear cup-to-disc ratio (r = 0.61; P < 0.001) and several other optic nerve head parameters.

CONCLUSIONS

In glaucomatous eyes, reduced pupillary responses to high-irradiance blue light were associated with greater visual field loss and optic disc cupping. In POAG, a short chromatic pupillometry test that evaluates the function of ipRGCs can be used to estimate the degree of damage to retinal ganglion cells that mediate image-forming vision. This approach could prove useful in detecting glaucoma.

Retinal neurodegeneration in experimental glaucoma

In rats and mice, limbar tissues of the left eye were laser-photocoagulated (LP) and ocular hypertension (OHT) effects were investigated 1 week to 6 months later. To investigate the innermost layers, retinas were examined in wholemounts using tracing from the superior colliculi to identify retinal ganglion cells (RGCs) with intact retrograde axonal transport, melanopsin immunodetection to identify intrinsically photosensitive RGCs (m(+)RGC), Brn3a immunodetection to identify most RGCs but not m(+)RGCs, RECA1 immunodetection to examine the inner retinal vessels, and DAPI staining to detect all nuclei in the GC layer. The outer retinal layers (ORLs) were examined in cross sections analyzed morphometrically or in wholemounts to study S- and L-cones. Innervation of the superior colliculi was examined 10 days to 14 weeks after LP with orthogradely transported cholera toxin subunit B. By 2 weeks, OHT resulted in pie-shaped sectors devoid of FG(+)RGCs or Brn3a(+)RGCs but with large numbers of DAPI(+)nuclei. Brn3a(+)RGCs were significantly greater than FG(+)RGCs, indicating the survival of large numbers of RGCs with their axonal transport impaired. The inner retinal vasculature showed no abnormalities that could account for the sectorial loss of RGCs. m(+)RGCs decreased to approximately 50-51% in a diffuse loss across the retina. Cross sections showed focal areas of degeneration in the ORLs. RGC loss at 1m diminished to 20-25% and did not progress further with time, whereas the S- and L-cone populations diminished progressively up to 6m. The retinotectal projection was reduced by 10 days and did not progress further. LP-induced OHT results in retrograde degeneration of RGCs and m(+)RGCs, severe damage to the ORL, and loss of retinotectal terminals.

Effects of ocular hypertension in the visual system of pigmented mice

To study the effects of ocular hypertension (OHT) on the visual system of C57BL/6 pigmented mice, the limbal and episcleral veins of the left eye were laser photocoagulated (LP). LP increased the intraocular pressure during the first five days (d), reaching basal values at 7d. To investigate the effect of OHT on the retinal ganglion cell (RGC) retrograde axonal transport, hydroxistilbamidine methanesulfonate (OHSt) was applied to both superior colliculi (SCi) and the retinas were dissected 2 or 4 weeks after LP. To determine RGC survival, these same retinas were immunoreacted against Brn3a (general RGC population) and melanopsin (intrinsically photosensitive RGCs, m⁺RGCs). To study whether OHT affected non-RGC neurons in the ganglion cell layer (GCL), RGCs were immunodetected with Brn3a and all GCL nuclei counterstained with DAPI in a group of animals examined 4 weeks post-LP. Innervation of the SCi was examined at 10 days, 8 or 14 weeks after LP with the orthogradely transported cholera toxin subunit-B. OHT resulted in diffuse and sectorial loss of OHSt+RGCs (50% at 2 weeks and 62% at 4 weeks) and in a comparable loss of Brn3a+RGCs at the same time intervals. m+RGCs decreased to 59% at 2 weeks and to 46% at 4 weeks, such loss was diffuse, did not parallel the sectorial loss of the general RGC population and was more severe in the superior-temporal retina. In the GCL, cell loss is selective for RGCs and does not affect other non-RGC neurons. The retinotectal innervation appeared significantly reduced at 10 days (55.7%) and did not progress further up to 14 weeks (46.6%). Thus, LP-induced OHT results in retrograde degeneration of RGCs and m+RGCs, as well as in the loss of CTB-labelled retinotectal terminals.

Effect of retinal ischemia on the non-image forming visual system

Retinal ischemic injury is an important cause of visual impairment. The loss of retinal ganglion cells (RGCs) is a key sign of retinal ischemic damage. A subset of RGCs expressing the photopigment melanopsin (mRGCs) regulates non-image-forming visual functions such as the pupillary light reflex (PLR), and circadian rhythms. We studied the effect of retinal ischemia on mRGCs and the non-image-forming visual system function. For this purpose, transient ischemia was induced by raising intraocular pressure to 120 mm Hg for 40 min followed by retinal reperfusion by restoring normal pressure. At 4 weeks post-treatment, animals were subjected to electroretinography and histological analysis. Ischemia induced a significant retinal dysfunction and histological alterations. At this time point, a significant decrease in the number of Brn3a(+) RGCs and in the anterograde transport from the retina to the superior colliculus and lateral geniculate nucleus was observed, whereas no differences in the number of mRGCs, melanopsin levels, and retinal projections to the suprachiasmatic nuclei and the olivary pretectal nucleus were detected. At low light intensity, a decrease in pupil constriction was observed in intact eyes contralateral to ischemic eyes, whereas at high light intensity, retinal ischemia did not affect the consensual PLR. Animals with ischemia in both eyes showed a conserved locomotor activity rhythm and a photoentrainment rate which did not differ from control animals. These results suggest that the non-image forming visual system was protected against retinal ischemic damage.

Clock genes and behavioral responses to light are altered in a mouse model of diabetic retinopathy

There is increasing evidence that melanopsin-expressing ganglion cells (ipRGCs) are altered in retinal pathologies. Using a streptozotocin-induced (STZ) model of diabetes, we investigated the impact of diabetic retinopathy on non-visual functions by analyzing ipRGCs morphology and light-induced c-Fos and Period 1–2 clock genes in the central clock (SCN). The ability of STZ-diabetic mice to entrain to light was challenged by exposure animals to 1) successive light/dark (LD) cycle of decreasing or increasing light intensities during the light phase and 2) 6-h advance of the LD cycle. Our results show that diabetes induces morphological changes of ipRGCs, including soma swelling and dendritic varicosities, with no reduction in their total number, associated with decreased c-Fos and clock genes induction by light in the SCN at 12 weeks post-onset of diabetes. In addition, STZ-diabetic mice exhibited a reduction of overall locomotor activity, a decrease of circadian sensitivity to light at low intensities, and a delay in the time to re-entrain after a phase advance of the LD cycle. These novel findings demonstrate that diabetes alters clock genes and behavioral responses of the circadian timing system to light and suggest that diabetic patients may show an increased propensity for circadian disturbances, in particular when they are exposed to chronobiological challenges.

Evaluation of pupillary response to light in patients with glaucoma: a study using computerized pupillometry

The aim of this study was to evaluate pupillary response to light stimulation in patients with different stages of glaucoma using computerized pupillometry. We conducted a retrospective study on a group of 44 glaucoma patients who had undergone complete ophthalmological examination, visual field test (Humphrey SITA Standard 24-2) and monocular dynamic pupillometry (MonCV3 Metrovision). Eyes were classified into stages of glaucoma according to visual field damage using the Glaucoma Staging System 2. A group of 18 healthy subjects, homogeneous for age and sex with glaucoma patients, was used as a control. The following parameters were considered-latency and duration of contraction and dilatation; initial, minimum, maximum, and mean pupil diameter; amplitude of contraction; contraction and dilatation speed; and percent pupil contraction (PPC). PPC and pupil contraction speed and minimum diameter showed covariate correlation with the stages of glaucoma. The control group significantly differed from the stage 3 group in terms of PPC and from the stage 4 group in terms of minimum diameter. There were significant differences between the stage 5 group and stage 1, 2, 3 and control groups. Ordinal logistic regression showed a correlation between pupil contraction speed, minimum diameter, PPC, initial diameter and the stage of glaucoma. The study showed that glaucoma damage is associated with altered values of pupillary response to light. This event may be the consequence of the progressive loss of retinal ganglion cells and their axons induced by glaucoma.

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.

Changes in the circadian rhythm in patients with primary glaucoma

Purpose

The current study was undertaken to investigate whether glaucoma affects the sleep quality and whether there is any difference between patients with primary glaucoma (primary open angle glaucoma, POAG and primary angle-closure glaucoma, PACG) and healthy subjects, using a validated self-rated questionnaire, the Pittsburgh Sleep Quality Index (PSQI).

Methods

The sleep quality of patients with POAG and PACG was tested against normal controls. Subjects were divided into three sub-groups according to age. Differences in the frequency of sleep disturbances (PSQI score >7) were assessed. The differences of sleep quality within the three groups and within the POAG group depending on the patients’ intraocular pressure (IOP) and impairment of visual field (VF) were also studied.

Results

92 POAG patients, 48 PACG patients and 199 controls were included. Sleep quality declined with age in control and POAG group (tendency chi-square, P<0.05). The prevalence of sleep disturbances was higher in POAG and PACG group than in the control group, the differences were statistically significant. The prevalence of sleep disturbances was higher in patients with PACG, compared to POAG patients in the age interval of 61–80. In POAG group, the ratio of patients with sleep disorders increased with augmented impairment of VF, but the differences were not statistically significant (χ²-test, P>0.05). No significant differences were found in POAG group between patients with a highest IOP in daytime and at nighttime (χ²-test, P>0.05).

Conclusions

The prevalence of sleep disorders was higher in patients with POAG and PACG than in controls. PACG patients seemed to have a more serious problem of sleep disorders than POAG patients between 61 to 80 years old. No correlation was found between the prevalence of sleep disorders and impairment of VF or the time when POAG patients showed a highest IOP.

Quantitative analysis of pupillary light reflex by real-time autofluorescent imaging in a diabetic mouse model

Here we (i) introduce a novel laser-based quantitative method of measuring pupillary light reflex (PLR) and applied it for the in vivo PLR monitoring of early diabetic retinopathy (DR) in a mouse model, (ii) investigate if melanopsin-expressing retinal ganglion cells (mRGCs) are implicated in the early progression of DR and, if so, is there an impact on PLR and (iii) determine if changes in PLR precede the onset of retinal hypoperfusion. A base-line PLR measurement is captured from C57BL/6J wild type mice followed by a single intraperitoneal administration of 200 mg/kg streptozotocin (STZ) and citrate buffer (vehicle) for the "diabetic" (n=5) and "control" (n=5) mice respectively, the very next day. PLR measurements are repeated once a week for four weeks. The PLR data comprises retinal autofluorescence intensity (AFI) values sampled over a 5-min period under confocal excitation with 488 nm high intensity blue laser light. AFI is used here as an indirect measure of pupil size since the amount of excitation light entering and emission light leaving the eye is proportional to the pupil area. Immunohistochemistry (IHC) staining of mRGCs and RT-PCR of melanopsin mRNA are performed at the end-point. The vascular calibre of both control and STZ-treated diabetic mice is assessed via in vivo fluorescein angiography (FA) on day 0 (base-line), 1/2, 1 and 4 months post-STZ treatment. The PLR profile shows a more rapid pupil constriction and slower dilation in diabetic mice compared to the control. Changes in PLR coincide or even precede the onset of retinal hypoperfusion. Extensive dendritic network of the mRGCs in retinal whole-mounts and increased melanopsin mRNA from the whole eye are also observed in diabetic mice. These pathological changes to mRGCs during early DR may in turn contribute towards changes in PLR. We present here a quantitative method of measuring PLR which enables an early detection of DR with potential application in the clinical setting. In contrast to conventional measurements of PLR, we are able to calibrate the amount of light reaching the retina which is a crucial parameter in longitudinal studies.

Intrinsically photosensitive retinal ganglion cells

Intrinsically photosensitive retinal ganglion cells (ipRGCs) respond to light in the absence of all rod and cone photoreceptor input. The existence of these ganglion cell photoreceptors, although predicted from observations scattered over many decades, was not established until it was shown that a novel photopigment, melanopsin, was expressed in retinal ganglion cells of rodents and primates. Phototransduction in mammalian ipRGCs more closely resembles that of invertebrate than vertebrate photoreceptors and appears to be mediated by transient receptor potential channels. In the retina, ipRGCs provide excitatory drive to dopaminergic amacrine cells and ipRGCs are coupled to GABAergic amacrine cells via gap junctions. Several subtypes of ipRGC have been identified in rodents based on their morphology, physiology and expression of molecular markers. ipRGCs convey irradiance information centrally via the optic nerve to influence several functions including photoentrainment of the biological clock located in the hypothalamus, the pupillary light reflex, sleep and perhaps some aspects of vision. In addition, ipRGCs may also contribute irradiance signals that interface directly with the autonomic nervous system to regulate rhythmic gene activity in major organs of the body. Here we review the early work that provided the motivation for searching for a new mammalian photoreceptor, the ground-breaking discoveries, current progress that continues to reveal the unusual properties of these neuron photoreceptors, and directions for future investigation.

Intrinsically photosensitive retinal ganglion cells

Life on earth is subject to alternating cycles of day and night imposed by the rotation of the earth. Consequently, living things have evolved photodetective systems to synchronize their physiology and behavior with the external light-dark cycle. This form of photodetection is unlike the familiar "image vision," in that the basic information is light or darkness over time, independent of spatial patterns. "Nonimage" vision is probably far more ancient than image vision and is widespread in living species. For mammals, it has long been assumed that the photoreceptors for nonimage vision are also the textbook rods and cones. However, recent years have witnessed the discovery of a small population of retinal ganglion cells in the mammalian eye that express a unique visual pigment called melanopsin. These ganglion cells are intrinsically photosensitive and drive a variety of nonimage visual functions. In addition to being photoreceptors themselves, they also constitute the major conduit for rod and cone signals to the brain for nonimage visual functions such as circadian photoentrainment and the pupillary light reflex. Here we review what is known about these novel mammalian photoreceptors.

Evaluation of functional integrity of the retinohypothalamic tract in advanced glaucoma using multifocal electroretinography and light-induced melatonin suppression

The aim of the study was to investigate the survival of melanopsin-expressing retinal ganglion cells (mRGCs) and the functional integrity of the retinohypothalamic tract in patients with bilateral advanced glaucomatous optic neuropathy by measuring the neuroendocrine light response of the pineal gland. Nine patients with bilateral advanced primary open-angle glaucoma (glaucoma group) and nine normal control subjects (control group) were included in this pilot observational, prospective, case-control study. The best-corrected visual acuity logMAR, standard automated perimetry mean deviation, and the retinal nerve fiber layer thickness determined by optical coherence tomography and multifocal electroretinography were used to evaluate the changes. Melatonin was analyzed in the saliva by radioimmunoassay before and after exposure to bright light (600 lux) for 60 min at night. The advanced glaucoma group did not have any significant nocturnal melatonin suppression after exposure to bright light (14.28 ± 3.07 pg/ml pre-light melatonin concentration vs. 15.22 ± 3.56 pg/ml after light exposure; p = 0.798) unlike the marked melatonin suppression in the control group (22.43 ± 4.37 pg/ml pre-light melatonin concentration vs. 11.25 ± 1.89 pg/ml after light exposure; p < 0.002). Response density estimates by the scalar product amplitude measure for the interval 0-80 ms of the first-order kernel responses were similar in both groups, indicating that outer retinal function was significantly unchanged in the glaucoma group (5.95 ± 0.54 nV/dg^2) compared with the control group (6.20 ± 0.22 nV/dg^2) (p = 0.689). Our findings are consistent with the interpretation that the rhythmic secretion of melatonin was affected in advanced glaucoma, suggesting that attention should be paid to non-image-forming visual functions, such as control of circadian rhythm and the clinical impact in patients with glaucoma.