The effect of in vivo retinal cooling on the electroretinogram of the rabbit

Experimental Models of Glaucoma: A Powerful Translational Tool for the Future Development of New Therapies for Glaucoma in Humans-A Review of the Literature

Glaucoma is a common complex disease that leads to irreversible blindness worldwide. Even though preclinical studies showed that lowering intraocular pressure (IOP) could prevent retinal ganglion cells loss, clinical evidence suggests that lessening IOP does not prevent glaucoma progression in all patients. Glaucoma is also becoming more prevalent in the elderly population, showing that age is a recognized major risk factor. Indeed, recent findings suggest that age-related tissue alterations contribute to the development of glaucoma and have encouraged exploration for new treatment approaches. In this review, we provide information on the most frequently used experimental models of glaucoma and describe their advantages and limitations. Additionally, we describe diverse animal models of glaucoma that can be potentially used in translational medicine and aid an efficient shift to the clinic. Experimental animal models have helped to understand the mechanisms of formation and evacuation of aqueous humor, and the maintenance of homeostasis of intra-ocular pressure. However, the transfer of pre-clinical results obtained from animal studies into clinical trials may be difficult since the type of study does not only depend on the type of therapy to be performed, but also on a series of factors observed both in the experimental period and the period of transfer to clinical application. Conclusions: Knowing the exact characteristics of each glaucoma experimental model could help to diminish inconveniences related to the process of the translation of results into clinical application in humans.

Intraoperative Electroretinograms before and after Core Vitrectomy

PURPOSE

To evaluate retinal function by intraoperative electroretinograms (ERGs) before and after core vitrectomy.

DESIGN

Retrospective consecutive case series.

METHOD

Full-field photopic ERGs were recorded prior to the beginning and just after core vitrectomy using a sterilized contact lens electrode in 20 eyes that underwent non-complicated vitreous surgery. A light-emitted diode was embedded into the contact lens, and a stimulus of 150 ms on and 350 ms off at 2 Hz was delivered. The amplitudes and latencies of the a-, b-, and d-waves, photopic negative response (PhNR), and oscillatory potentials (OPs) were analyzed. The intraocular temperature at the mid-vitreous was measured at the beginning and just after the surgery with a thermoprobe.

RESULTS

The intraocular temperature was 33.2 ± 1.3°C before and 29.4 ± 1.7°C after the vitrectomy. The amplitudes of the PhNR and OPs were significantly smaller after surgery, and the latencies of all components were prolonged after the surgery. These changes were not significantly correlated with the changes of the temperature.

CONCLUSION

Retinal function is reduced just after core vitrectomy in conjunction with significant temperature reduction. The differences in the degree of alterations of each ERG component suggests different sensitivity of each type of retinal neuron.

Structural and functional maturation of the retina of the albino Hartley guinea pig

PURPOSE

Altricial animals, such as rats and mice, are born with their eyes closed, compared to precocial animals, such as guinea pigs and humans, which have their eyes opened at birth. The purpose of this study was to investigate if the retina of guinea pigs (precocial animal) is subjected to a postnatal maturation process similar to that previously reported for rodents.

METHODS

Photopic and scotopic electroretinograms (ERG) and retinal histology were obtained from albino guinea pigs aged P1 to P75.

RESULTS

Photopic ERG responses reached maximal amplitudes at P5 (a-and b-waves), that is 5 days (b-wave) to 10 days (a-wave) earlier than scotopic responses. However, the postnatal gain in b-wave amplitude was significantly (P < 0.05) more important for the cone (73.38 +/- 4.4%) signal than for the rod (15.23 +/- 3.96%), suggesting that the rod function is more mature at birth. Similarly, the short latency photopic oscillatory potential (ie: OP2) reached its maximal value 5 days (P10) earlier than its scotopic equivalent (P15), while the long latency OPs (ie: OP3, OP4), reached their maximal values nearly 20 days sooner in scotopic condition. Finally retinal histology revealed a thinning of the retina with age, the latter being most pronounced at the level of the ganglion cell layer (GCL).

CONCLUSION

Our results thus confirm that despite its relative maturity at birth (compared to rodents), the retina of newborn albino guinea pigs undergoes significant postnatal maturation modifying its structure as well as its function, albeit not as extensive as that previously documented for altricial animals.

Features of visual function in the naked mole-rat Heterocephalus glaber

The eyes and visual capacity of the naked mole-rat, Heterocephalus glaber, a subterranean rodent, were evaluated using anatomical, biochemical, and functional assays, and compared to other rodents of similar body size (mouse and gerbil). The eye is small compared to mouse, yet possesses cornea, lens, and retina with typical mammalian organization. The optic nerve cross-sectional area and fiber density are approximately 10% and approximately 50% that of gerbil, respectively. Levels per unit retinal area of 11-cis and all-trans retinal, derivatives of vitamin A associated with the visual cycle, are comparable to mouse. The corneal electroretinogram (ERG) exhibits early and late negative components that scale with flash strength; raising the body temperature of this poikilothermic animal from 30 degrees C (normal for H. glaber ) to 37 degrees C (normal for mouse) revealed an ERG response with typically mammalian features, but greatly attenuated and with slower kinetics. Leaving the nest chamber was a behavior correlated with light onset displayed preferentially by breeding females. Optical models of five mole-rat eyes suggest reasonable, but variable, image formation at the retina, possibly related to age. Results are consistent with amorphous light detection, possibly useful for circadian entrainment or escape behavior in the event of tunnel breeches.

The effect of body temperature on the murine electroretinogram

PURPOSE

To study the effect of body temperature on the murine electroretinogram (ERG).

METHODS

The corneal ERG elicited by a strobe flash from dark-adapted mice was recorded using a saline wick electrode while measuring rectal temperature continuously. The mouse was placed within a cylindrical coil of tubing through which water circulated from a temperature controlled bath. The body temperature of the mouse was changed stepwise between 30 and 37 degrees C.

RESULTS

ERGs of approximately normal configuration were recorded at body temperature ranging between 30 and 37 degrees C. The maximum amplitude of the a- and b-waves varied linearly with temperature. The rate of change of b-wave amplitude was about 100 microV/degree. At 30 degrees C, maximum b-wave amplitude was about 400 microV; at 37 degrees C it was about 1000 microV. A change in body temperature produced a rapid change in ERG amplitude.

CONCLUSION

The murine ERG is very sensitive to changes in temperature. In order to monitor the ERG accurately over time, continuous recording of body temperature is essential.