Wenyi Guo

The critical role of the conjunctiva in glaucoma filtration surgery

This review considers the critical role of the conjunctiva in determining the success or failure of glaucoma filtration surgery. Glaucoma filtration surgery can be defined as an attempt to lower intraocular pressure (IOP) by the surgical formation of an artificial drainage pathway from the anterior chamber to the subconjunctival space. Many types of glaucoma filtration surgery have been developed since the first attempts almost 180 years ago. The wide range of new techniques and devices currently under investigation is testament to the limitations of current techniques and the need for improved therapeutic outcomes. Whilst great attention has been paid to surgical techniques and devices to create the drainage pathway, relatively little attention has been given to address the question of why drainage from such artificial pathways is often problematic. This is in contrast to normal drainage pathways which last a lifetime. Furthermore, the consequences of potential changes in aqueous humour properties induced by glaucoma filtration surgery have not been sufficiently addressed. The mechanisms by which aqueous fluid is drained from the subconjunctival space after filtration surgery have also received relatively little attention. We propose that factors such as the degree of tissue damage during surgery, the surrounding tissue reaction to any surgical implant, and the degree of disruption of normal aqueous properties, are all factors which influence the successful formation of long term drainage channels from the conjunctiva, and that these channels are the key to successful filtration surgery. In recent years it has been suggested that the rate of fluid drainage from the subconjunctival space is actually the determining factor in the resultant IOP reduction. Improved knowledge of aqueous humour induced changes in such drainage pathways has the potential to significantly improve the surgical management of glaucoma. We describe for the first time a novel type of drainage surgery which attempts to minimise surgical trauma to the overlying conjunctiva. The rationale is that a healthy conjunctiva allows drainage channels to form and less opportunity for inflammation and scar tissue formation which are a frequent cause of failure in glaucoma filtration surgery. Successful drainage over extended periods of time has been demonstrated in monkey and rabbit eyes. Long lasting drainage pathways were clearly associated with the presence of lymphatic drainage pathways. A new philosophy in glaucoma drainage surgery is proposed in which minimisation of surgical trauma to the conjunctiva and the encouragement of the development of conjunctival drainage pathways, particularly lymphatic pathways, are central pillars to a successful outcome in glaucoma filtration surgery.

Induction of retinal ganglion-like cells from fibroblasts by adenoviral gene delivery

Central nervous system neurons fail to regenerate after birth, which greatly hampers the effective treatment of many neurodegenerative diseases. Neurons differentiated from induced pluripotent stem cells have been considered a possible option for cell-based therapies. Recent discoveries have revealed that fibroblasts can be directly converted into neurons without a transition through a pluripotent state. This approach might serve as a more efficient and convenient method for the cellular therapy of neurodegenerative diseases. Currently, several types of neurons have been directly generated from fibroblasts, including dopamine neurons, motor neurons and neural progenitor cells. In our study, by screening a series of candidate genes, we found that the adenovirus-mediated transduction of Ascl1, Brn3b and Ngn2 can directly convert mouse fibroblasts to retinal ganglion-like cells. The induced retinal ganglion-like cells co-express multiple retinal ganglion cell markers, and exhibit membrane properties of functional neurons. The reprogramming mediated by adenoviruses occurs much sooner than that mediated by lentiviruses. Furthermore, the induced retinal ganglion-like cells that are produced via adenoviral gene delivery are free of exogenous gene integration. Retinal ganglion-like cells that are induced by adenoviruses demonstrate great potential applicability in clinical therapy and provide a novel platform for the research of retinal degenerative diseases.

Effect of acute intraocular pressure elevation on blood flow velocity and resistance in the rabbit ophthalmic artery

OBJECTIVE To determine the effect of intraocular pressure (IOP) on blood flow velocity and resistance in the rabbit ophthalmic artery. ANIMALS Ten adult New Zealand White rabbits were used. PROCEDURES Right eyes were cannulated and the IOP was raised in a stepwise manner from 20 to 70 mmHg. Peak systolic velocity (PSV), end diastolic velocity (EDV) and resistive index (RI) in the ophthalmic artery were measured by color Doppler imaging. Values of PSV, EDV and RI were compared at various IOPs via the analysis of variance (anova) of a randomized block design with post hoc Bonferroni test. RESULTS Significant differences of PSV, EDV and RI at different IOP points (all P < 0.001) were observed. Over the entire IOP range, linear regression showed a negative correlation between IOP and both PSV and EDV (β = -0.07434, P = 0.0020 and β = -0.07829, P < 0.001, respectively), as well as a positive correlation between the RI and IOP (β = 0.00221, P < 0.001). Moreover, line plots identified a point with IOP = 40 mmHg, splitting the IOP range with different regression slopes. Piecewise linear regression indicated no correlation between PSV, EDV, RI and IOP when the IOP was elevated from 20 to 40 mmHg (P = 0.1832, P = 0.5932 and P = 0.5819, respectively). However, piecewise linear regression detected a stronger negative correlation between PSV, EDV and IOP (β = -0.15760, P = 0.0011 and β = -0.11872, P = 0.001, respectively) and a stronger positive correlation between RI and IOP (β = 0.00273, P = 0.0015) during the stage from 40 to 70 mmHg. CONCLUSIONS The ophthalmic artery in the rabbits was capable of maintaining normal blood velocity and resistance when IOP was below 40 mmHg. However, the autoregulatory capacity was greatly limited when IOP was over 40 mmHg.

Astrocytic responses in the lateral geniculate nucleus of monkeys with experimental glaucoma.

OBJECTIVE   To investigate the responses of lateral geniculate nucleus (LGN) astrocytes to experimental glaucoma in monkeys. ANIMAL STUDIED   Rhesus monkeys (Macaca mulatta). PROCEDURES   Unilateral chronic elevation of intraocular pressure (IOP) was induced in six rhesus monkeys by laser photocoagulation of the trabecular meshwork. Four normal monkeys were used as controls. Immunohistochemistry with antibodies to glial fibrillary acidic protein (GFAP), S100β and parvalbumin was used to specifically label astrocytes and neurons in the LGN. The relative immunointensity (RI) of GFAP was defined as the ratio of intensity between each region of interest to a reference field and compared between the experimental and control groups as a function of percentage optic nerve fiber loss. Ultrastructural changes of LGN astrocytes were examined by transmission electron microscopy. RESULTS   An increase in GFAP and S100β immunoreactivity was observed in the LGN layers receiving projections from the experimental glaucoma eyes. Quantitative analysis revealed that the RI of GFAP in both the magnocellular and parvocellular layers connected to the glaucomatous eyes increased in a linear fashion with increasing optic nerve fiber loss. Compared to controls, the RI of GFAP was also moderately elevated in LGN layers connected to the fellow nonglaucomatous eyes. Ultrastructurally, accumulation of glial filaments that occurred throughout the perikaryon and extended into the process in reactive astrocytes was observed in LGN layers of glaucomatous monkeys. CONCLUSIONS   Reactive astrogliosis occurs in the magnocellular and parvocellular LGN layers of monkeys with unilateral glaucoma. Astrocytes may play an important role in the regulation of LGN microenvironment in glaucoma.

Glaucoma club: a successful model to educate glaucoma patients.

patient should be seated (in the case of infants, on the parent’s lap) at arms’ length from the examiner, in a room with dim lighting. The Krimsky test is first performed using the light source of the ophthalmoscope (Figs 1,2). When the angle of the squint is measured as accurately as possible, the ophthalmoscope is elevated and the Bruckner reflex sought (Fig. 3). The prism power may need to be adjusted to equalize the fundus red reflexes such that the Bruckner reflex becomes negative. In essence, the Bruckner reflex becomes negative (i.e. symmetrical) when viewed through the correct power prism(s). If possible, the accuracy of the measurement can be confirmed by using the prism cover test, but with experience this step is usually not necessary. A satisfactory surgical outcome for strabismus surgery depends, in part, on accurate measurement of the angle of misalignment. We have found that combining the Krimsky test and the Bruckner reflex makes measurement of the angle of strabismus much easier in infants than the prism cover test, especially when combining loose prisms in front of both eyes to measure infants with large angle strabismus. A search of PubMed and Embase using the terms ‘Bruckner reflex’ and ‘Krimsky test’ did not find any papers describing the combination of these tests. The technique that we are describing seems to distress infants much less than moving the hand from one eye to another during the performance of the prism cover test and offers the potential benefit of more accurate measurement. We recommend it as part of the strabismologists’ repertoire.

Structure and function of myelinated nerve fibers in the rabbit eye following ischemia/reperfusion injury.

The rabbit eye presents a valuable model to study the effects of vascular occlusion on the function and structure of myelinated nerve fibers. The rabbit eye has a band of myelinated nerve fibers within the intraocular compartment that are supplied by a narrow band of retinal vasculature. These vessels were transiently occluded ( approximately 8 hours) using laser photocoagulation and the transmission of electrical signals along the nerve fibers was assessed by recording the visual evoked response (VER). Morphological damage was assessed by histological techniques. The ischemic insult produced no permanent change in retinal function as assessed by electroretinography, but the VER was suppressed, indicating failure of nerve fiber transmission. Histologically, the visible damage to the region supported by the retinal vasculature worsened following reperfusion, showing evidence of demyelination and necrosis followed by macrophage responses and gliosis. This rabbit model of ischemia/reperfusion of the retinal vasculature offers a rare opportunity to reliably study the response of myelinated nerve fibers to ischemia/reperfusion insults and has demonstrated the susceptibility of myelinated nerve fibers to such insults.

Vulnerability study of myelinated and unmyelinated nerve fibers in acute ocular hypertension in rabbit

In the current study, it was aimed to evaluate the changes in myelinated and unmyelinated nerve fibers in retinal ischemia-reperfusion injuries caused by acute ocular hypertension and to determine the sequence of these changes. Adult healthy New Zealand white rabbits were randomized to the hemodynamic group [n=12; used to determine the optimal intraocular pressure (IOP) for the subsequent experiments] and the hypertension group (n=6; 70-mmHg hypertension induced in one eye). IOP was adjusted using a cannula and saline. Doppler ultrasound was used to measure the velocity of the optic artery under different intraocular pressures. Immunohistochemistry for myelin basic protein (MBP) was performed. Apoptosis of retinal cells was detected by terminal deoxynucleotidyl transferase biotin-dUTP nick end labeling (TUNEL) assay. Electron microscopy was used to investigate the changes in myelinated and unmyelinated nerve fibers. IOP of the hypertension eyes was maintained at 70.2±1.0 mmHg, while IOP of control eyes was 7–14 mmHg. Doppler ultrasound demonstrated an obvious decline of peak systolic velocity and an increase of resistance index of retinal bloodstream under a 70-mmHg IOP. MBP immunohistochemistry and electron microscopy demonstrated obvious injuries to the myelin fibers. TUNEL indicated a significantly higher apoptosis rate in the hypertension eyes compared with control eyes. The apoptosis rate of retinal ganglion cells and bipolar cells in unmyelinated regions was higher than in myelinated regions. In conclusion, an IOP of 70 mmHg led to incomplete retinal ischemia but was the threshold for retinal ischemia, leading to obvious injuries to the myelin fibers.