Reanalysis of refractive growth in pediatric pseudophakia and aphakia.

BACKGROUND: The current model of refractive growth in children (RRG2) is calculated as the slope of aphakic refraction at the spectacle plane versus the logarithm of adjusted age. However, this model fails in infants because of the optical effect of vertex distance of a spectacle lens on the effective power at the cornea. In this study, we developed a new model of refractive growth (RRG3) that eliminates the optical effect of vertex distance on the RRG2 model. METHODS: We calculated RRG3 values for pseudophakic and aphakic eyes previously analyzed for RRG2. Inclusion criteria were age ≤10 years at the time of cataract surgery and follow-up time between measured refractions of at least 3.6 years and at least the age at first refraction plus 0.6 years. For both pseudophakic and aphakic eyes, we compared RRG3 values in children who had cataract surgery before age 6 months with those in children aged 6 months or older. RESULTS: A total of 78 pseudophakic and 70 aphakic eyes met the inclusion criteria. Ages at surgery ranged from 0.25 to 9 years, with a 9.5-year mean follow-up time. The mean RRG3 value was not significantly different between the surgical age groups for both pseudophakic eyes (P = 0.053) and aphakic eyes (P = 0.59). CONCLUSIONS: The RRG3 values were not significantly different between the surgical age groups for both pseudophakic and aphakic eyes. Consequently, RRG3 is theoretically applicable even in the small eyes of infants having surgery before 6 months of age.

Hypophosphorylation of aqueous humor sCD44 and primary open-angle glaucoma.

PURPOSE: The ectodomain of CD44, the principal receptor for hyaluronic acid (HA), is shed as a 32-kDa fragment-soluble CD44 (sCD44)-which is cytotoxic to trabecular meshwork (TM) cells and retinal ganglion cells (RGCs) in culture. The purpose of this study was to characterize sCD44 further by determining the phosphorylation of aqueous humor sCD44 in normal and primary open-angle glaucoma (POAG). METHODS: Aqueous humor samples of patients were subjected to CD44 enzyme-linked immunosorbent assay (ELISA) and two-dimensional (2-D) polyacrylamide gel electrophoresis, followed by Western blot analysis with anti-CD44, anti-serine/threonine, and anti-tyrosine phosphospecific antibodies, to determine sCD44 concentration, isoelectric point (pI), and phosphorylation, respectively. The bioactivity of hypophosphorylated sCD44 was tested in cell culture and HA affinity columns. RESULTS: Two-dimensional Western blot analysis revealed that the representative pI of the 32-kDa sCD44 was 6.96 +/- 0.07 in POAG versus 6.38 +/- 0.08 in normal (P < 0.0004). Enzymatic dephosphorylation of sCD44 resulted in a basic shift in the pI. The normal aqueous humor sCD44 was positive for serine-threonine phosphorylation; however, POAG sCD44 was hypophosphorylated. Hypophosphorylated sCD44 was more toxic to TM and RGC cells than standard sCD44, and hypophosphorylated sCD44 had decreased affinity to HA, particularly with increased pressure. CONCLUSIONS: POAG aqueous is characterized by posttranslational change in the pI of sCD44 and hypophosphorylation, which clearly distinguished POAG from normal aqueous humor. The high toxicity and low HA-binding affinity of hypophosphorylated sCD44 may represent specific pathophysiologic features of the POAG disease process.

Reconstitution of trabecular meshwork GAGs: influence of hyaluronic acid and chondroitin sulfate on flow rates.

PURPOSE: This study was undertaken to determine whether the concentration of hyaluronic acid (HA) and of chondroitin sulfate (CS) occurring in the normal and the primary open-angle glaucoma (POAG) trabecular meshwork (TM) influences flow rates in vitro as a function of pressure. METHODS: We tested 100, 500, and 4000 kDa molecular weight HA, CS, reconstituted normal and POAG TM HA-CS and juxtacanalicular connective tissue (JCT) HA-CS in a micro test chamber to determine initial and steady-state flow rates. The resistance and permeability (Ko) were calculated; Linear Newtonian mechanics were used to determine the possible contributions of the hydrophobic interactions of HA. RESULTS: Initial flow rates increased in the pressure range of 5 to 20 mm Hg for the three HA preparations and the flow rates declined in the pressure range of 20 to 40 mm Hg. Flow rates of reconstituted normal TM and JCT were optimum at 10 mm Hg and then declined with increasing pressure. Flow rates of reconstituted POAG TM and JCT were optimum only at 5 mm Hg and then declined. The steady-state rate of POAG JCT HA-CS at 10 mm Hg was slow: the transition time (ie, the time required to start an increase in flow rate) was 29 hours and the lag time (ie, the time required to obtain steady-state flow rate) was 17 hours. The maximum flow rate in POAG JCT HA-CS decreased by 37.2% from the normal JCT HA-CS. The calculated resistance of reconstituted POAG JCT HA-CS was approximately 18% of the total resistance of the human JCT compared with 10% in the normal JCT. CONCLUSIONS: Hyaluronic acid and CS contribute to flow resistance and influence flow rate in vitro. The influence of HA is particularly sensitive to an increase in the pressure gradient, which may be caused by unfolding of the hydrophobic interactions of HA polymers that further entangles the HA polymer. The POAG JCT HA-CS concentrations represent a significant factor in outflow resistance in POAG, particularly at higher pressures.