CENTRAL CORNEAL THICKNESS AND INTRAOCULAR PRESSURE CHANGES POST- PHACOEMULSIFICATION SURGERY IN GLAUCOMA PATIENTS WITH CATARACT.

AIMS: To compare the changes of central corneal thickness (CCT) and intraocular pressure (IOP) post-phacoemulsification between cataract patients with and without pre-existing glaucoma. MATERIALS AND METHODS: A prospective cohort study of 86 patients with visually significant cataract: 43 with pre-existing glaucoma (GC group) and 43 without pre-existing glaucoma (CO group). CCT and IOP were evaluated at baseline (pre-phacoemulsification), as well as at 2 hours, 1 day, 1 week and 6 weeks post-phacoemulsification. RESULTS: The GC group have significantly thinner CCT pre-operatively (p = 0.003). There was a steady increase of CCT with the highest peak at 1 day post-phacoemulsification, followed by a steady decline of CCT and back to baseline at 6 weeks post-phacoemulsification in both groups. The GC group demonstrated a significant difference in CCT at 2 hours (mean difference 60.2 µm, p = 0.003) and 1 day (mean difference 70.6 µm, p = 0.002) post-phacoemulsification, compared to the CO group. There was a sudden increase in IOP at 2 hours post-phacoemulsification measured by GAT and DCT in both groups. This was followed by a gradual reduction of IOP, with significant reduction at 6 weeks post-phacoemulsification in both groups. However, there was no significant difference in IOP between the two groups. IOP measured by GAT and DCT showed strong correlation (r > 0.75, p < 0.001) in both groups. There was no significant correlation between GAT-IOP and CCT changes; nor between DCT-IOP and CCT changes in both groups. CONCLUSIONS: CCT changes post-phacoemulsification in patients with pre-existing glaucoma were similar, in spite of having thinner CCT pre-operatively. IOP measurement was not affected by CCT changes in glaucoma patients post-phacoemulsification. IOP measurement using GAT is comparable with DCT post-phacoemulsification.

Full thickness macular hole: Early intervention is an important factor in visual prognosis.

Full thickness macular hole is an eye disease, which can cause permanent visual impairment. Current advancement in vitreoretinal surgery has high success rates in repairing them, leading to a significant visual improvement, especially if patient presents early. In this article, three cases of idiopathic full thickness macular hole with different visual outcomes have been presented. All cases were referred by the primary care practitioners and had undergone macular hole surgery with the same vitreoretinal surgeon. The visual outcome was best in the patient who had the earliest presentation and referral. Early detection and referral of these patients is vital so that early surgical intervention can be carried out to improve their vision.

The utility of Ki-67 and BrdU as proliferative markers of adult neurogenesis.

Adult animals continue to produce new neurons in the dentate gyrus of hippocampus. Until now, the principal method of studying neurogenesis has been to inject either tritiated thymidine or 5'-Bromo-2-deoxyuridine (BrdU) intraperitoneally followed by autoradiographic or immunohistochemical detection methods respectively. However, such exogenous markers may produce toxic effects. Our objective was to determine whether Ki-67, a nuclear protein expressed in all phases of the cell cycle except the resting phase, can be used as an alternative, endogenous marker. Using immunohistochemistry, we examined Ki-67 and BrdU expression pattern in rats. Ki-67 was expressed within the proliferative zone of the dentate gyrus and its expression pattern mimicked that of BrdU when examined soon after exogenous BrdU administration. Quantitative comparison of BrdU and Ki-67-positive cells showed 50% higher numbers of the latter when examined 24 h after the BrdU injection. This was expected, since BrdU can be incorporated into DNA only during the S-phase of the mitotic process, whereas Ki-67 is expressed for its whole duration. Experimental increases (by ischemia) or reductions (by radiation) in the number of mitotic cells produced parallel changes in BrdU and Ki-67 signals. Thus, Ki-67 is an effective mitotic marker and has most of the benefits of BrdU and none of the costs. This study provides evidence for Ki-67 to be used as a marker of proliferation in the initial phase of adult neurogenesis.

Effects of adult neurogenesis on synaptic plasticity in the rat dentate gyrus.

Ongoing neurogenesis in the adult hippocampal dentate gyrus (DG) generates a substantial population of young neurons. This phenomenon is present in all species examined thus far, including humans. Although the regulation of adult neurogenesis by various physiologically relevant factors such as learning and stress has been documented, the functional contributions of the newly born neurons to hippocampal functions are not known. We investigated possible contributions of the newly born granule neurons to synaptic plasticity in the hippocampal DG. In the standard hippocampal slice preparation perfused with artificial cerebrospinal fluid (ACSF), a small (10%) long-term potentiation (LTP) of the evoked field potentials is seen after tetanic stimulation of the afferent medial perforant pathway (MPP). The induction of this ACSF-LTP is resistant to a N-methyl-D-aspartate (NMDA) receptor blocker, D,L-2-amino-5-phosphonovaleric acid (APV), but is completely prevented by ifenprodil, a blocker of NR2B subtype of NMDA receptors. In contrast, slices perfused with picrotoxin (PICRO), a GABA-receptor blocker, revealed a larger (40--50%), APV-sensitive but ifenprodil-insensitive LTP. The ACSF-LTP required lower frequency of stimulation and fewer stimuli for its induction than the PICRO-LTP. All these characteristics of ACSF-LTP are in agreement with the properties of the putative individual new granule neurons examined previously with the use of the whole cell recording technique in a similar preparation. A causal relationship between neurogenesis and ACSF-LTP was confirmed in experiments using low dose of gamma radiation applied to the brain 3 wk prior to the electrophysiological experiments. In these experiments, the new cell proliferation was drastically reduced and ACSF-LTP was selectively blocked. We conclude that the young, adult-generated granule neurons play a significant role in synaptic plasticity in the DG. Since DG is the major source of the afferent inputs into the hippocampus, the production and the plasticity of new neurons may have an important role in the hippocampal functions such as learning and memory.

Enhanced neurogenesis after transient global ischemia in the dentate gyrus of the rat.

The dentate gyrus is one of the few areas of the mammalian brain where new neurons are continuously produced in adulthood. Certain insults such as epileptic seizures and ischemia are known to enhance the rate of neuronal production. We analyzed this phenomenon using the temporary occlusion of the two carotid arteries combined with arterial hypotension as a method to induce ischemia in rats. We measured the rate of cell production and their state of differentiation with a mitotic indicator, bromodeoxyuridine (BrdU), in combination with the immunohistochemical detection of neuronal markers. One week after the ischemic episode, the cell production in dentate gyrus was increased two- to threefold more than the basal level seen in control animals. Two weeks after ischemia, over 60% of these cells became young neurons as determined by colabeling with BrdU and a cytoplasmic protein (CRMP-4) involved in axonal guidance during development. Five weeks after the ischemia, over 60% of new neurons expressed calbindin, a calcium-binding protein normally expressed in mature granule neurons. In addition to more cells being generated, a greater proportion of all new cells remained in the differentiated but not fully mature state during the 2- to 5-week period after ischemia. The maturation rate of neurons as determined by the calbindin labeling and by the rate of migration from a proliferative zone into the granule cell layer was not changed when examined 5 weeks after ischemia. The results support the hypothesis that survival of dentate gyrus after ischemia is linked with enhanced neurogenesis. Additional physiological stimulation after ischemia may be exploited to stimulate maturation of new neurons and to offer new therapeutic strategies for promoting recovery of neuronal circuitry in the injured brain.

Receptor protein tyrosine kinases in perinatal developing rat kidney.

We have identified receptor protein tyrosine kinases (PTKs) that are expressed and/or activated during kidney development. mRNA from fetal rat kidneys in late gestation (embryonic day 21), was used to prepare a cDNA template for polymerase chain reaction amplification with primers based on conserved regions of PTKs, and products were subcloned and sequenced. Among 346 clones, we identified epidermal growth factor receptor (EGF-R), Tie-2, platelet-derived growth factor receptor (PDGF-R)-alpha, PDGF-R beta, Flk-1, Flt-4, fibroblast growth factor receptor (FGF-R)-1, FGF-R3, FGF-R4, Met, and RYK/Nbtk-1. PTK expression was studied by immunoprecipitation and immunoblotting of kidney membrane proteins with specific antibodies. EGF-R, PDGF-R alpha, FGF-R1, FGF-R3, Met, and in some cases Tie-2 protein expression was greater in fetal kidneys, as compared with kidneys from 12-week-old adult rats (controls). Flk-1, PDGF-R beta, and FGF-R4 proteins were expressed comparably, however, Flt-4 was not detected. As a reflection of receptor PTK activity, we assessed endogenous tyrosine phosphorylation, and in vitro autophosphorylation. EGF-R and PDGF-R alpha displayed activity in fetal, but not adult kidneys. FGF-R3 and Flk-1 were active in some fetal kidneys, and the other PTKs were not active. Thus, in late gestational rat kidney, there are distinct patterns of receptor PTK expression and activity. EGF-R, PDGF-R alpha, FGF-R3 and Flk-1 are among the PTKs that are activated, and they may mediate perinatal development of renal epithelial, interstitial, or vascular structures.