Melanopsin: The Tale of the Tail

In this issue of Neuron, Mure et al. (2016) demonstrate that two mechanisms-phosphorylation of a C-terminal intracellular region, and mechanism involving the whole of the C terminus-oppositely shape the kinetics and sensitivity of the nonvisual photoreceptor melanopsin.

Multimodal Imaging in Wagner Syndrome

Wagner syndrome is a rare vitreoretinopathy described in a limited number of families. Here the authors describe four cases of suspected Wagner syndrome. All four cases had depressed rod and cone function on electroretinography, outer retinal disruption on spectral-domain optical coherence tomography, and constricted central visual fields with smaller isopter testing. Fundus autofluorescence performed in one patient highlighted a perivascular pattern to chorioretinal atrophy. Two patients had a history of uveitis with active cystoid macular edema. The diagnosis of Wagner syndrome was supported in three cases with genetic testing for VCAN mutations, whereas the other case harbored a variation of unknown significance in VCAN that may have been nonpathogenic. [Ophthalmic Surg Lasers Imaging Retina. 2016;47:574-579.].

In Vivo Bioluminescence Imaging for Longitudinal Monitoring of Inflammation in Animal Models of Uveitis

Purpose

We develop a quantitative bioluminescence assay for in vivo longitudinal monitoring of inflammation in animal models of uveitis.

Methods

Three models of experimental uveitis were induced in C57BL/6 albino mice: primed mycobacterial uveitis (PMU), endotoxin-induced uveitis (EIU), and experimental autoimmune uveitis (EAU). Intraperitoneal injection of luminol sodium salt, which emits light when oxidized, provided the bioluminescence substrate. Bioluminescence images were captured by a PerkinElmer In Vivo Imaging System (IVIS) Spectrum and total bioluminescence was analyzed using Living Image software. Bioluminescence on day zero was compared to bioluminescence on the day of peak inflammation for each model. Longitudinal bioluminescence imaging was performed in EIU and EAU.

Results

In the presence of luminol, intraocular inflammation generates detectable bioluminescence in three mouse models of uveitis. Peak bioluminescence in inflamed PMU eyes (1.46 × 10⁵ photons/second [p/s]) was significantly increased over baseline (1.47 × 10⁴ p/s, P = 0.01). Peak bioluminescence in inflamed EIU eyes (3.18 × 10⁴ p/s) also was significantly increased over baseline (1.09 × 10⁴ p/s, P = 0.04), and returned to near baseline levels by 48 hours. In EAU, there was a nonsignificant increase in bioluminescence at peak inflammation.

Conclusions

In vivo bioluminescence may be used as a noninvasive, quantitative measure of intraocular inflammation in animal models of uveitis. Primed mycobacterial uveitis and EIU are both acute models with robust anterior inflammation and demonstrated significant changes in bioluminescence corresponding with peak inflammation. Experimental autoimmune uveitis is a more indolent posterior uveitis and generated a more modest bioluminescent signal. In vivo imaging system bioluminescence is a nonlethal, quantifiable assay that can be used for monitoring inflammation in animal models of uveitis.

Global rise of potential health hazards caused by blue light-induced circadian disruption in modern aging societies

Mammals receive light information through the eyes, which perform two major functions: image forming vision to see objects and non-image forming adaptation of physiology and behavior to light. Cone and rod photoreceptors form images and send the information via retinal ganglion cells to the brain for image reconstruction. In contrast, nonimage-forming photoresponses vary widely from adjustment of pupil diameter to adaptation of the circadian clock. nonimage-forming responses are mediated by retinal ganglion cells expressing the photopigment melanopsin. Melanopsin-expressing cells constitute 1–2% of retinal ganglion cells in the adult mammalian retina, are intrinsically photosensitive, and integrate photic information from rods and cones to control nonimage-forming adaptation. Action spectra of ipRGCs and of melanopsin photopigment peak around 480 nm blue light. Understanding melanopsin function lets us recognize considerable physiological effects of blue light, which is increasingly important in our modern society that uses light-emitting diode. Misalignment of circadian rhythmicity is observed in numerous conditions, including aging, and is thought to be involved in the development of age-related disorders, such as depression, diabetes, hypertension, obesity, and cancer. The appropriate regulation of circadian rhythmicity by proper lighting is therefore essential. This perspective introduces the potential risks of excessive blue light for human health through circadian rhythm disruption and sleep deprivation. Knowing the positive and negative aspects, this study claims the importance of being exposed to light at optimal times and intensities during the day, based on the concept of the circadian clock, ultimately to improve quality of life to have a healthy and longer life.

Quantitative Assessment of Anterior Segment Inflammation in a Rat Model of Uveitis Using Spectral-Domain Optical Coherence Tomography

Purpose

To develop anterior segment spectral-domain optical coherence tomography (SD-OCT) and quantitative image analysis for use in experimental uveitis in rats.

Methods

Acute anterior uveitis was generated in Lewis rats. A spectral domain anterior segment OCT system was used to image the anterior chamber (AC) and ciliary body at baseline and during peak inflammation 2 days later. Customized MatLab image analysis algorithms were developed to segment the AC, count AC cells, calculate central corneal thickness (CCT), segment the ciliary body and zonules, and quantify the level of ciliary body inflammation with the ciliary body index (CBI). Images obtained at baseline and during peak inflammation were compared. Finally, longitudinal imaging and image analysis was performed over the 2-week course of inflammation.

Results

Spectral-domain optical coherence tomography identifies structural features of inflammation. Anterior chamber cell counts at peak inflammation obtained by automated image analysis and human grading were highly correlated (r = 0.961), and correlated well with the histologic score of inflammation (r = 0.895). Inflamed eyes showed a significant increase in average CCT (27 μm, P = 0.02) and an increase in average CBI (P < 0.0001). Longitudinal imaging and quantitative image analysis identified a significant change in AC cell and CBI on day 2 with spontaneous resolution of inflammation by day 14.

Conclusions

Spectral-domain optical coherence tomography provides high-resolution images of the structural changes associated with anterior uveitis in rats. Anterior chamber cell count and CBI determined by semi-automated image analysis strongly correlates with inflammation, and can be used to quantify inflammation longitudinally in single animals.

Photopharmacological control of bipolar cells restores visual function in blind mice

Photopharmacological control of neuronal activity using synthetic photochromic ligands, or photoswitches, is a promising approach for restoring visual function in patients suffering from degenerative retinal diseases. Azobenzene photoswitches, such as AAQ and DENAQ, have been shown to restore the responses of retinal ganglion cells to light in mouse models of retinal degeneration but do not recapitulate native retinal signal processing. Here, we describe diethylamino-azo-diethylamino (DAD), a third-generation photoswitch that is capable of restoring retinal ganglion cell light responses to blue or white light. In acute brain slices of murine layer 2/3 cortical neurons, we determined that the photoswitch quickly relaxes to its inactive form in the dark. DAD is not permanently charged, and the uncharged form enables the photoswitch to rapidly and effectively cross biological barriers and thereby access and photosensitize retinal neurons. Intravitreal injection of DAD restored retinal light responses and light-driven behavior to blind mice. Unlike DENAQ, DAD acts upstream of retinal ganglion cells, primarily conferring light sensitivity to bipolar cells. Moreover, DAD was capable of generating ON and OFF visual responses in the blind retina by utilizing intrinsic retinal circuitry, which may be advantageous for restoring visual function.

Paucibacterial Microbiome and Resident DNA Virome of the Healthy Conjunctiva

Purpose

To characterize the ocular surface microbiome of healthy volunteers using a combination of microbial culture and high-throughput DNA sequencing techniques.

Methods

Conjunctival swab samples from 107 healthy volunteers were analyzed by bacterial culture, 16S rDNA gene deep sequencing (n = 89), and biome representational in silico karyotyping (BRiSK; n = 80). Swab samples of the facial skin (n = 42), buccal mucosa (n = 50), and environmental controls (n = 27) were processed in parallel. 16S rDNA gene quantitative PCR was used to calculate the bacterial load in each site. Bacteria were characterized by site using principal coordinate analysis of metagenomics data. BRiSK data were analyzed for presence of fungi and viruses.

Results

Corynebacteria, Propionibacteria, and coagulase-negative Staphylococci were the predominant organisms identified by all three techniques. Quantitative 16S PCR demonstrated approximately 0.1 bacterial 16S rDNA/human actin copy on the ocular surface compared with greater than 10 16S rDNA/human actin copy for facial skin or the buccal mucosa. The conjunctival bacterial community structure is distinct compared with the facial skin (R = 0.474, analysis of similarities P = 0.0001), the buccal mucosa (R = 0.893, P = 0.0001), and environmental control samples (R = 0.536, P = 0.0001). 16S metagenomics revealed substantially more bacterial diversity on the ocular surface than other techniques, which appears to be artifactual. BRiSK revealed presence of torque teno virus (TTV) on the healthy ocular surface, which was confirmed by direct PCR to be present in 65% of all conjunctiva samples tested.

Conclusions

Relative to adjacent skin or other mucosa, healthy ocular surface microbiome is paucibacterial. Its flora are distinct from adjacent skin. Torque teno virus is a frequent constituent of the ocular surface microbiome. (ClinicalTrials.gov number, NCT02298881.)

Animal Cryptochromes: Divergent Roles in Light Perception, Circadian Timekeeping and Beyond

Cryptochromes are evolutionarily related to the light-dependent DNA repair enzyme photolyase, serving as major regulators of circadian rhythms in insects and vertebrate animals. There are two types of cryptochromes in the animal kingdom: Drosophila-like CRYs that act as nonvisual photopigments linking circadian rhythms to the environmental light/dark cycle, and vertebrate-like CRYs that do not appear to sense light directly, but control the generation of circadian rhythms by acting as transcriptional repressors. Some animals have both types of CRYs, while others possess only one. Cryptochromes have two domains, the photolyase homology region (PHR) and an extended, intrinsically disordered C-terminus. While all animal CRYs share a high degree of sequence and structural homology in their PHR domains, the C-termini are divergent in both length and sequence identity. Recently, cryptochrome function has been shown to extend beyond its pivotal role in circadian clocks, participating in regulation of the DNA damage response, cancer progression and glucocorticoid signaling, as well as being implicated as possible magnetoreceptors. In this review, we provide a historical perspective on the discovery of animal cryptochromes, examine similarities and differences of the two types of animal cryptochromes and explore some of the divergent roles for this class of proteins.

An LHX1-Regulated Transcriptional Network Controls Sleep/Wake Coupling and Thermal Resistance of the Central Circadian Clockworks

The suprachiasmatic nucleus (SCN) is the central circadian clock in mammals. It is entrained by light but resistant to temperature shifts that entrain peripheral clocks [1-5]. The SCN expresses many functionally important neuropeptides, including vasoactive intestinal peptide (VIP), which drives light entrainment, synchrony, and amplitude of SCN cellular clocks and organizes circadian behavior [5-16]. The transcription factor LHX1 drives SCN Vip expression, and cellular desynchrony in Lhx1-deficient SCN largely results from Vip loss [17, 18]. LHX1 regulates many genes other than Vip, yet activity rhythms in Lhx1-deficient mice are similar to Vip^-/- mice under light-dark cycles and only somewhat worse in constant conditions. We suspected that LHX1 targets other than Vip have circadian functions overlooked in previous studies. In this study, we compared circadian sleep and temperature rhythms of Lhx1- and Vip-deficient mice and found loss of acute light control of sleep in Lhx1 but not Vip mutants. We also found loss of circadian resistance to fever in Lhx1 but not Vip mice, which was partially recapitulated by heat application to cultured Lhx1-deficient SCN. Having identified VIP-independent functions of LHX1, we mapped the VIP-independent transcriptional network downstream of LHX1 and a largely separable VIP-dependent transcriptional network. The VIP-independent network does not affect core clock amplitude and synchrony, unlike the VIP-dependent network. These studies identify Lhx1 as the first gene required for temperature resistance of the SCN clockworks and demonstrate that acute light control of sleep is routed through the SCN and its immediate output regions.

Evaluating Access to Eye Care in the Contiguous United States by Calculated Driving Time in the United States Medicare Population

PURPOSE

To quantify the proximity to eye care in the contiguous United States by calculating driving routes and driving time using a census-based approach.

DESIGN

Cross-sectional study based on United States (US) census data, Medicare payment data, and OpenStreetMap.

PARTICIPANTS

2010 US census survey respondents older than 65 years.

METHODS

For each state in the United States, the addresses of all practicing ophthalmologists and optometrists were obtained from the 2012 Medicare Provider Utilization and Payment Data from the Centers for Medicare and Medicaid Services (CMS). The US census data from 2010 then were used to calculate the geolocation of the US population at the block group level and the number of people older than 65 years in each location. Geometries and driving speed limits of every road, street, and highway in the United States from the OpenStreetMap project were used to calculate the exact driving distance and driving time to the nearest eye care provider.

MAIN OUTCOME MEASURES

Driving time and driving distance to the nearest optometrist and ophthalmologist per state.

RESULTS

Driving times for 3.79×10⁷ persons were calculated using a total of 3.88×10⁷ available roads for the 25 508 optometrists and 17 071 ophthalmologists registered with the CMS. Nationally, the median driving times to the nearest optometrist and ophthalmologist were 2.91 and 4.52 minutes, respectively. Ninety percent of the population lives within a 13.66- and 25.21-minute drive, respectively, to the nearest optometrist and ophthalmologist.

CONCLUSIONS

While there are regional variations, overall more than 90% of the US Medicare beneficiary population lives within a 30-minute drive of an ophthalmologist and within 15 minutes of an optometrist.

Ocular Photoreception for Circadian Rhythm Entrainment in Mammals

Circadian rhythms are self-sustained, approximately 24-h rhythms of physiology and behavior. These rhythms are entrained to an exactly 24-h period by the daily light-dark cycle. Remarkably, mice lacking all rod and cone photoreceptors still demonstrate photic entrainment, an effect mediated by intrinsically photosensitive retinal ganglion cells (ipRGCs). These cells utilize melanopsin (OPN4) as their photopigment. Distinct from the ciliary rod and cone opsins, melanopsin appears to function as a stable photopigment utilizing sequential photon absorption for its photocycle; this photocycle, in turn, confers properties on ipRGCs such as sustained signaling and resistance from photic bleaching critical for an irradiance detection system. The retina itself also functions as a circadian pacemaker that can be autonomously entrained to light-dark cycles. Recent experiments have demonstrated that another novel opsin, neuropsin (OPN5), is required for this entrainment, which appears to be mediated by a separate population of ipRGCs. Surprisingly, the circadian clock of the mammalian cornea is also light entrainable and is also neuropsin-dependent for this effect. The retina thus utilizes a surprisingly broad array of opsins for mediation of different light-detection tasks.

Effect of Vitamin A Depletion on Nonvisual Phototransduction Pathways in Cryptochromeless Mice

Mice exhibit multiple nonvisual responses to light, including 1) photoentrainment of circadian rhythm; 2) “masking,” which refers to the acute effect of light on behavior, either negative (activity suppressing) or positive (activity inducing); and 3) pupillary constriction. In mammals, the eye is the sole photosensory organ for these responses, and it contains only 2 known classes of pigments: opsins and cryptochromes. No individual opsin or cryptochrome gene is essential for circadian photoreception, gene photoinduction, or masking. Previously, the authors found that mice lacking retinol-binding protein, in which dietary depletion of ocular retinaldehyde can be achieved, had normal light signaling to the SCN, as determined by per gene photoinduction. In the present study, the authors analyzed phototransduction to the SCN in vitamin A-replete and vitamin A-depleted rbp-/- and rbp-/-cry1-/-cry2-/- mice using molecular and behavioral end points. They found that vitamin A-depleted rbp-/- mice exhibit either normal photoentrainment or become diurnal. In contrast, while vitamin A-replete rbp-/-cry1-/-cry2-/- mice are light responsive (with reduced sensitivity), vitamin A-depleted rbp-/-cry1-/-cry2-/- mice, which presumably lack functional opsins and cryptochromes, lose most behavioral and molecular responses to light. These data demonstrate that both cryptochromes and opsins regulate nonvisual photoresponses.

Clean Thoughts about Dirty Genes

The mouse has joined the fruit fly, bread mold, and cyanobacteria as a tractable genetic system for studying mechanisms of circadian rhythms. The circadian rhythms of “knock-out” mice for specific clock genes, however, have demonstrated significant variability between laboratories. In this brief review, the authors discuss possible sources of this variability, focusing particularly on questions of modifier loci of circadian rhythms that vary between inbred mouse strains. They conclude with a short list of recommendations for researchers working on circadian rhythms in mixed-strain mice.

Primed Mycobacterial Uveitis (PMU): Histologic and Cytokine Characterization of a Model of Uveitis in Rats

PURPOSE

The purpose of this study was to compare the histologic features and cytokine profiles of experimental autoimmune uveitis (EAU) and a primed mycobacterial uveitis (PMU) model in rats.

METHODS

In Lewis rats, EAU was induced by immunization with interphotoreceptor binding protein peptide, and PMU was induced by immunization with a killed mycobacterial extract followed by intravitreal injection of the same extract. Clinical course, histology, and the cytokine profiles of the aqueous and vitreous were compared using multiplex bead fluorescence immunoassays.

RESULTS

Primed mycobacterial uveitis generates inflammation 2 days after intravitreal injection and resolves spontaneously 14 days later. CD68+ lymphocytes are the predominant infiltrating cells and are found in the anterior chamber, surrounding the ciliary body and in the vitreous. In contrast to EAU, no choroidal infiltration or retinal destruction is noted. At the day of peak inflammation, C-X-C motif ligand 10 (CXCL10), IL-1β, IL-18, and leptin were induced in the aqueous of both models. Interleukin-6 was induced 2-fold in the aqueous of PMU but not EAU. Cytokines elevated in the aqueous of EAU exclusively include regulated on activation, normal T cell expressed and secreted (RANTES), lipopolysaccharide-induced CXC chemokine (LIX), growth-related oncogene/keratinocyte chemokine (GRO/KC), VEGF, monocyte chemoattractant protein-1 (MCP-1), macrophage inflammatory protein-1α (MIP-1α), and IL-17A. In the vitreous, CXCL10, GRO/KC, RANTES, and MIP-1α were elevated in both models. Interleukin-17A and IL-18 were elevated exclusively in EAU.

CONCLUSIONS

Primed mycobacterial uveitis generates an acute anterior and intermediate uveitis without retinal involvement. Primed mycobacterial uveitis has a distinct proinflammatory cytokine profile compared with EAU, suggesting PMU is a good complementary model for study of immune-mediated uveitis. CXCL10, a proinflammatory cytokine, was increased in the aqueous and vitreous of both models and may be a viable therapeutic target.

Comparative Proteomic Analysis of Two Uveitis Models in Lewis Rats

PURPOSE

Inflammation generates changes in the protein constituents of the aqueous humor. Proteins that change in multiple models of uveitis may be good biomarkers of disease or targets for therapeutic intervention. The present study was conducted to identify differentially-expressed proteins in the inflamed aqueous humor.

METHODS

Two models of uveitis were induced in Lewis rats: experimental autoimmune uveitis (EAU) and primed mycobacterial uveitis (PMU). Differential gel electrophoresis was used to compare naïve and inflamed aqueous humor. Differentially-expressed proteins were separated by using 2-D gel electrophoresis and excised for identification with matrix-assisted laser desorption/ionization-time of flight (MALDI-TOF). Expression of select proteins was verified by Western blot analysis in both the aqueous and vitreous.

RESULTS

The inflamed aqueous from both models demonstrated an increase in total protein concentration when compared to naïve aqueous. Calprotectin, a heterodimer of S100A8 and S100A9, was increased in the aqueous in both PMU and EAU. In the vitreous, S100A8 and S100A9 were preferentially elevated in PMU. Apolipoprotein E was elevated in the aqueous of both uveitis models but was preferentially elevated in EAU. Beta-B2-crystallin levels decreased in the aqueous and vitreous of EAU but not PMU.

CONCLUSIONS

The proinflammatory molecules S100A8 and S100A9 were elevated in both models of uveitis but may play a more significant role in PMU than EAU. The neuroprotective protein β-B2-crystallin was found to decline in EAU. Therapies to modulate these proteins in vivo may be good targets in the treatment of ocular inflammation.

A Rayleigh Scatter-Based Ocular Flare Analysis Meter for Flare Photometry of the Anterior Chamber

PURPOSE

Existing flare photometers are based on the Tyndall effect, which requires sophisticated laser photometry. The ocular flare analysis meter (OFAM) is a nonlaser photometer that uses quantitative Rayleigh scatter and absorption from visible light to compute a flare value. This study is designed to correlate OFAM measurements with qualitative measurements of flare in vitro and in vivo.

METHODS

Following validation of the device on artificial anterior chambers containing known protein concentrations, flare readings were obtained from 90 subjects (46 with and 44 without uveitis) in one eye. Subjects were graded by the Standardization of Uveitis Nomenclature (SUN) working group flare scoring system and received the OFAM flare measurements.

RESULTS

The OFAM showed linear response in vitro to protein concentrations ranging from 0 to 0.5 mg/ml. In clinical use in subjects ranging from SUN flare scores of 0+ to 2+, OFAM showed statistically significant measurement accuracy (P = 0.0008 of flare 0 versus flare 2; P = 0.031 of flare 0 versus flare 1). Distinction of SUN scores 1 and 2 was borderline significant (P = 0.057).

CONCLUSION

The OFAM photometry correlates with the standard SUN scoring system. This method may provide an objective method to diagnosis and monitor uveitis. Further longitudinal studies are warranted.

TRANSLATIONAL RELEVANCE

Currently, ocular flare is assessed qualitatively in most clinical settings. The existing methodology uses only Tyndall effect to measure flare. The OFAM uses an alternate, nonlaser means for measurement of anterior chamber flare by measure of Raleigh scatter. This pilot clinical study suggests that the OFAM device may be useful in measurement of uveitis activity.

Vision Science: Can Rhodopsin Cure Blindness?

Outer retinal degeneration is the leading cause of blindness in the developed world. A new study now demonstrates that ectopic expression of human rhodopsin in the inner retina, mediated by viral gene therapy, can restore light sensitivity and some vision to mice blind from outer retinal degeneration.

Type I intrinsically photosensitive retinal ganglion cells of early post-natal development correspond to the M4 subtype

Background

Intrinsically photosensitive retinal ganglion cells (ipRGCs) mediate circadian light entrainment and the pupillary light response in adult mice. In early development these cells mediate different processes, including negative phototaxis and the timing of retinal vascular development. To determine if ipRGC physiologic properties also change with development, we measured ipRGC cell density and light responses in wild-type mouse retinas at post-natal days 8, 15 and 30.

Results

Melanopsin-positive cell density decreases by 17 % between post-natal days 8 and 15 and by 25 % between days 8 and 30. This decrease is due specifically to a decrease in cells co-labeled with a SMI-32, a marker for alpha-on ganglion cells (corresponding to adult morphologic type M4 ipRGCs). On multi-electrode array recordings, post-natal day 8 (P8) ipRGC light responses show more robust firing, reduced adaptation and more rapid recovery from short and extended light pulses than do the light responses of P15 and P30 ipRGCs. Three ipRGC subtypes – Types I-III – have been defined in early development based on sensitivity and latency on multielectrode array recordings. We find that Type I cells largely account for the unique physiologic properties of P8 ipRGCs. Type I cells have previously been shown to have relatively short latencies and high sensitivity. We now show that Type I cells show have rapid and robust recovery from long and short bright light exposures compared with Type II and III cells, suggesting differential light adaptation mechanisms between cell types. By P15, Type I ipRGCs are no longer detectable. Loose patch recordings of P8 M4 ipRGCs demonstrate Type I physiology.

Conclusions

Type I ipRGCs are found only in early development. In addition to their previously described high sensitivity and rapid kinetics, these cells are uniquely resistant to adaptation and recover quickly and fully to short and prolonged light exposure. Type I ipRGCs correspond to the SMI-32 positive, M4 subtype and largely lose melanopsin expression in development. These cells constitute a unique morphologic and physiologic class of ipRGCs functioning early in postnatal development.

Electronic supplementary material

The online version of this article (doi:10.1186/s13064-015-0042-x) contains supplementary material, which is available to authorized users.

Photochemical approaches to vision restoration

Photoswitches are traditional pharmacologic agonists, antagonists, or channel blockers that are covalently modified with an azobenzene derivative. Azobenzene undergoes wavelength-dependent isomerization between cis and trans conformation. For some photoswitches, only one of these configurations is biologically active, resulting in light-dependent activation or inhibition of function. Photoswitches that feature a quaternary ammonium coupled to the azobenzene moiety cause light-dependent neuronal depolarization due to blockage of voltage-gated potassium channels. Two photoswitch strategies have been pursued. In the one-component strategy, the photoswitch is applied to native receptors; in the two-component strategy, the photoswitch is combined with virally-mediated expression of a genetically modified receptor, to which the photoswitch may covalently bind. The former approach is simpler but the latter allows precise anatomic targeting of photoswitch activity. Acrylamide-azobenzene-quaternary ammonium (AAQ) is the prototypical first-generation one-component photoswitch. When applied to retinas with outer retinal degeneration, ganglion cell firing occurs in response to blue light, and is abrogated by green light. In vivo, AAQ restored pupillary light responses and behavioral light responses in blind animals. DENAQ is a prototypical second generation one-component photoswitch. It features spontaneous thermal relaxation so cell firing ceases in dark, and features a red-shifted activation spectrum. Interestingly, DENAQ only photoswitches in retinas with outer retinal degeneration. MAG is a photoswitched glutamate analog which covalently binds to a modified ionotropic glutamate receptor, LiGluR. When applied together, MAG and LiGluR also rescue physiologic and behavioral light responses in blind mice. Together, photoswitch compounds offer a potentially useful approach to restoration of vision in outer retinal degeneration.

Identification of torque teno virus in culture-negative endophthalmitis by representational deep DNA sequencing

PURPOSE

To test the hypothesis that uncultured organisms may be present in cases of culture-negative endophthalmitis by use of deep DNA sequencing of vitreous biopsies.

DESIGN

Single-center, consecutive, prospective, observational study.

PARTICIPANTS

Aqueous or vitreous biopsies from 21 consecutive patients presenting with presumed infectious endophthalmitis and 7 vitreous samples from patients undergoing surgery for noninfectious retinal disorders.

METHODS

Traditional bacterial and fungal culture, 16S quantitative polymerase chain reaction (qPCR), and a representational deep-sequencing method (biome representational in silico karyotyping [BRiSK]) were applied in parallel to samples to identify DNA sequences corresponding to potential pathogens.

MAIN OUTCOME MEASURES

Presence of potential pathogen DNA in ocular samples.

RESULTS

Zero of 7 control eyes undergoing routine vitreous surgery yielded positive results for bacteria or virus by culture or 16S polymerase chain reaction (PCR). A total of 14 of the 21 samples (66.7%) from eyes harboring suspected infectious endophthalmitis were culture-positive, the most common being Staphylococcal and Streptococcal species. There was good agreement among culture, 16S bacterial PCR, and BRiSK methodologies for culture-positive cases (Fleiss' kappa of 0.621). 16S PCR did not yield a recognizable pathogen sequence in any culture-negative sample, whereas BRiSK suggested the presence of Streptococcus in 1 culture-negative sample. With the use of BRiSK, 57.1% of culture-positive and 100% of culture-negative samples demonstrated the presence of torque teno virus (TTV) sequences, compared with none in the controls (P=0.0005, Fisher exact test). The presence of TTV viral DNA was confirmed in 7 cases by qPCR. No other known viruses or potential pathogens were identified in these samples.

CONCLUSIONS

Culture, 16S qPCR, and BRiSK provide complementary information in presumed infectious endophthalmitis. The majority of culture-negative endophthalmitis samples did not contain significant levels of bacterial DNA. "Culture negativity" does not seem to be due to failure of growth of fastidious bacteria. The small DNA virus TTV was unexpectedly found in all culture-negative samples and some culture-positive samples. This study cannot distinguish whether TTV is a direct intraocular pathogen, an adjuvant for inflammation, a general marker of inflammation, or a commensal virus but provides a testable hypothesis for a pathogenic mechanism in culture-negative endophthalmitis.