Cerebrospinal fluid pressure is significantly lower in primary open-angle glaucoma patients compared with that in nonglaucomatous controls, according to a large case-control study at the Duke University Eye Center and the Mayo Clinic, Rochester, Minn. The data supports the notion that CSF pressure may play an important contributory role in the pathogenesis of POAG, the authors conclude.

The authors write that the optic nerve is exposed to two independent pressurized regions: the intraocular space anteriorly and the subarachnoid space posteriorly. The lamina cribrosa is the primary structure that separates the two regions. The pressure difference between them, the translaminar pressure, can cause changes in the optic disc if the pressure becomes abnormal.

Their study analyzed 28 patients who had POAG and 49 patients who did not from a group of 31,786 subjects who underwent lumbar puncture between 1996 and 2007, and compared cerebrospinal fluid pressure in patients with POAG with that in nonglaucomatous patients. Demographics (age and gender), medical history, medication use, indication for LP, intraocular pressure, cup-to-disc ratio, visual field assessment and CSF pressure were recorded. The mean CSF pressure ±SD was 13.0 ±4.2 mmHg in nonglaucoma patients and 9.2 ±2.9 mmHg in POAG patients (p<0.00005). The CSF pressure was lower in POAG patients regardless of indication for lumbar puncture or age. Linear regression analysis showed that cup-to-disc ratio correlated independently with IOP (p<0.0001), CSF pressure (p<0.0001), and the translaminar pressure difference (p<0.0001). Multivariate analysis demonstrated that larger cup-to-disc ratio (p<0.0001) was associated with lower CSF pressure.

(Ophthalmology 2008;115:761-2)

Berdahl JP, Allingham RR, Johnson DH.


Effects of CCT on the Efficacy of Topical Ocular Hypotensive Meds

When dosed with intraocular pressure-lowering drugs, eyes with thinner corneas had lower IOPs than eyes with thicker corneas, according to a University of Nebraska study. This suggests a reduced efficacy of some glaucoma medications in ocular hypertensive patients with thick corneas, the authors say.

The retrospective study analyzed research records of 115 patients with ocular hypertension and 97 ocular normotensive (ONT) volunteers. Central corneal thickness was measured by slit-lamp pachymetry and IOP by pneumatonometry. The OHT patients were divided into Thick (>540 µm, n=52) and Thin (≤540 µm, n=63) Cornea groups. Measurements in the OHT group were made after washout of all IOP-lowering drugs and at one week of treatment with latanoprost, dorzolamide, brimonidine, apraclonidine, pilocarpine or unoprostone to one eye and vehicle contralaterally. ONT volunteers also were divided into Thick (n=34) and Thin (n=63) Cornea groups. Results were compared between groups using unpaired t tests or nonparametric Wilcoxon tests and within groups using linear regression analyses.

Baseline IOPs were not different between CCT groups of OHT patients or of ONT volunteers. After one week of drug treatment, IOP was significantly (p=0.02) lower in the OHT Thin Cornea group (16.0 ±3.0 mmHg, mean ±SD) than the OHT Thick Cornea group (17.4 ±2.8 mmHg). There was a positive correlation between IOP and CCT (R2=0.06, p=0.007) in OHT drug-treated eyes, but not OHT vehicle-treated or ONT untreated eyes. The final IOP was significantly lower in the Thin than the Thick Cornea group treated with brimonidine (p=0.02) but not with latanoprost (p=0.91).

(J Glaucoma 2008;17:89-99)

Johnson T, Toris C, Fan S; Camras C.


Increasing Prevalence of MRSA in  Ocular Infections

Multidrug-resistant methicillin resistant Staphylococcus aureus is increasing in serious ocular infections, reports a group at Mount Sinai School of Medicine, New York. Based on the rate of increase in their database, MRSA cultures from serious ocular infections could be more common than methicillin-susceptible S. aureus within two to three years.

The group reviewed data on S. aureus submitted to The Surveillance Network (TSN) by more than 200 laboratories in the United States from January 2000 to December 2005. From this they determined the prevalence of methicillin resistance in S. aureus ocular infections and in vitro susceptibility to antibiotic agents commonly used to treat or prevent ocular infections. The proportion of S. aureus infections culture-positive for methicillin-resistant S. aureus increased from 29.5 percent in 2000 to 41.6 percent in 2005. The MRSA ocular isolates were multidrug resistant, that is, in vitro resistance to three antibiotic agents or more, including all fluoroquinolones tested. The researchers call for large-scale national surveillance programs to monitor in vitro antimicrobial resistance trends in ocular isolates.

(J Cataract Refract Surg 2008;34: 814-8)

Asbell PA, Sahm DF, Shaw M, Draghi DC, Brown NP.


Blue-Light Filtering IOL: No Change in Color Contrast

In an intraindividual comparison, the implantation of a blue-light-filtering intraocular lens did not lead to a clinically significant change in color contrast sensitivity, say surgeons at the Medical University of Vienna, in Austria.

Thirty-one patients (62 eyes) were randomized to receive an AF-1 (UV) IOL (Hoya) in one eye and an AF-1 (UY) IOL (Hoya) in the contralateral eye after phacoemulsification and primary posterior curvilinear capsulorhexis. Three months postop, the best distance-corrected visual acuity was evaluated. Before color contrast sensitivity testing, a heterochromatic flicker test was performed in both eyes to avoid error in brightness matching. Central and peripheral tritan color contrast sensitivities were evaluated using the Moorfields Vision System (CH Electronics).

Visual acuity did not differ significantly between the two groups. The central color contrast sensitivity threshold also did not differ significantly between eyes with a clear IOL and eyes with a yellow IOL at any tested spatial frequency. The peripheral color contrast sensitivity test showed slightly higher color contrast sensitivity thresholds in eyes with a yellow IOL, although the differences were not statistically significant. Two patients independently reported subjective changes in color perception in the eye with the yellow IOL.

(J Cataract Refract Surg 2008;34: 769-73)

Schmidinger G, Menapace R, Pieh S.


LASIK Ectasia Screening System Validated

The Ectasia Risk Score System is a valid and effective method for detecting eyes at risk for ectasia after LASIK and represents a significant improvement over previously utilized screening strategies, according to a report from Emory University.

The Ectasia Risk Score System assigns points in a weighted fashion to the following variables: topographic pattern, predicted residual stromal bed thickness, age, preoperative corneal thickness and manifest refraction spherical equivalent. This retrospective case-control study looked at 50 eyes that developed ectasia and 50 control eyes with normal postoperative courses after LASIK.

In the series, 46 eyes (92 percent) with ectasia were correctly classified as being at high risk for the development of ectasia, while three controls (6 percent) were incorrectly classified as being at high risk for ectasia (p<1 x 10^-10). Significantly more eyes were classified as high risk by the ectasia risk score than by traditional screening parameters relying on abnormal topography or RSB thickness less than 250 µm (92 percent vs. 50 percent; p<.00001). There was no difference in the sensitivity or specificity of the Ectasia Risk Score System in the population from which it was derived and this independent population of ectasia cases and controls.

(Am J Ophthalmol 2008;145:813-8)

Randleman J, Trattler W, Stulting R.