Juan A. Sanchis-Gimeno

THE RELATIONSHIP BETWEEN CENTRAL CORNEAL THICKNESS AND GOLDMANN APPLANATION TONOMETRY

Background: The aim of this study was to investigate the relationship between Goldmann applanation tonometry and central corneal thickness in a large sample of healthy eyes.

Corneal Thickness Values Before and After Oxybuprocaine 0.4% Eye Drops

Purpose To determine changes in corneal thickness after topical anesthesia. Methods Corneal thickness was measured before and 3 minutes after administration of two drops of oxybuprocaine 0.4% to 26 patients (26 eyes). We analyzed the corneal thickness of a control group, which was made up of 26 patients (26 eyes) before and 3 minutes after administration of two drops of saline solution. Corneal thickness was measured with the Orbscan Topography System II (Bausch Lomb Surg., Barcelona). Results Variations higher than ± 10 &mgr;m were found following the instillation of 2 oxybuprocaine eye drops in eight eyes (30.76%) at the inferonasal cornea, in six eyes (23.08%) at the superotemporal, temporal and inferotemporal cornea, in five eyes (19.23%) at the nasal cornea, in three eyes (11.53%) at the central cornea, and in two eyes (7.69%) at the superonasal cornea. Nevertheless, no significant differences in the mean corneal thickness at each corneal location between the first and the second corneal thickness measurements were found in anesthetized eyes. Conclusions Some individuals can present important increases and decreases in corneal thickness values after anesthetic eye drops. This effect of anesthetic eye drops must be considered by refractive surgeons when carrying out preoperative laser in situ keratomileusis corneal thickness measurements.

Intraobserver reproducibility of retinal nerve fiber layer measurements using scanning laser polarimetry and optical coherence tomography in normal and ocular hypertensive subjects.

Purpose To evaluate quantitatively the intraobserver reproducibility of measurements of the retinal nerve fiber layer (RNFL) in healthy subjects and an ocular hypertensive population using two nerve fiber analyzers. Methods Sixty eyes of normal (n=30) and ocular hypertensive subjects (n=30) were consecutively recruited for this study and underwent a complete ophthalmologic examination and achromatic automated perimetry. RNFL were measured using scanning laser polarimeter (GDx-VCC) and optical coherence tomography (OCT Model 3000). Reproducibility of the RNFL measurements obtained with both nerve fiber analyzers were compared using the coefficient of variation. Results In both groups the authors found fair correlations between the two methods in all ratio and thickness parameters. The mean coefficient of variation for measurement of the variables ranged from 2.24% to 13.12% for GDx-VCC, and from 5.01% to 9.24% for OCT Model 3000. The authors could not detect any significant differences between healthy and ocular hypertensive eyes, although in normal eyes the correlations improved slightly. Nevertheless, the test–retest correlation was slightly better for GDx-VCC than for OCT Model 3000 (5.55% and 7.11%, respectively). Conclusions Retinal mapping software of both nerve fiber analyzers allows reproducible measurement of RNFL in both healthy subjects and ocular hypertensive eyes, and shows fair correlations and good intraobserver reproducibility. However, in our study, GDx showed a better test–retest correlation.

Assessment of applanation tonometry after hyperopic laser in situ keratomileusis.

Purpose. To determine the reliability and identify pitfalls in intraocular pressure measurement by Goldmann applanation tonometry after hyperopic laser in situ keratomileusis (LASIK). Methods. Prospective non-masked case series at University of Valencia, Faculty of Medicine and Rahhal Ophthalmology Clinic, Valencia, Spain. One hundred three patients (103 eyes) treated with hyperopic LASIK were evaluated. The main treatment was hyperopic LASIK using a microkeratome Chiron Hansatome (Chiron Vision Corp, Claremont, CA) and the excimer laser Chiron Technolas 217-C LASIK (Chiron Technolas GmbH, Dornack; Germany). Central Goldmann applanation tonometric readings before surgery and 1, 3, and 6 months after surgery were analyzed. Results. After hyperopic LASIK, a significant decrease in intraocular pressure was observed in the postoperative controls. In the low hyperopia patients (range: 1.00–3.00 D) a decrease of 2.43 mmHg was observed at the 6-month follow-up (p < 0.001). In the moderate hyperopia group (range: 3.25–6.00 D) a decrease of 2.05 mmHg was observed at the 6-month follow-up (p < 0.001). There were no significant differences between low and moderate hyperopia (p = 0.812). There was no statistically significant correlation between the magnitude of decrease in tonometry and gender, age, treated spherical equivalent, pachymetry, and anterior chamber depth (ACD). Conclusions. This clinical study displays that postoperative tonometry after hyperopic LASIK was significantly lower than the preoperative, hence modifying the reliability of Goldmann tonometry, and causing an intraocular pressure underestimation. A correcting factor should be applied when using applanation tonometry to measure postoperative intraocular pressure in patients who have undergone hyperopic LASIK.

Anatomic study of the corneal thickness of young emmetropic subjects

Purpose To study the corneal thickness of young emmetropic subjects. Methods One thousand eyes of 1000 young healthy emmetropic subjects were analyzed with the Orbscan Topography System II (Orbscan, Inc, Salt Lake City, UT) from January 2001 to May 2003. The age of the subjects ranged from 20 to 30 years old (mean ± SD = 27.12 ± 2.86). The mean of 5 consecutive measurements of the corneal thickness in the center of the cornea and at temporal, superotemporal, inferotemporal, nasal, inferonasal, and superonasal cornea were recorded. Results The corneal thickness at the following areas ranged as follows: 518 to 589 μm center; 603 to 678 μm nasal; 620 to 689 μm superonasal; 600 to 669 μm inferonasal; 571 to 639 μm temporal; 601 to 669 μm superotemporal; and 572 to 647 μm inferotemporal. In each individual the difference between the central thickness and the maximum paracentral thickness ranged from 85 to 107 μm (mean ± SD, 99.21 ± 3.80). The difference between the central thickness and the minimum paracentral thickness ranged from 36 to 59 μm (48.97 ± 4.23 μm). The difference between the minimum paracentral corneal thickness and the maximum paracentral corneal thickness ranged from 37 to 58 μm (50.24 ± 4.30). The tonometry was statistically correlated with the corneal thickness (P < 0.05 at each corneal location analyzed). Conclusions In emmetropic corneas the difference between the minimum paracentral thickness and the maximum paracentral thickness was similar to the difference between the central thickness and the minimum paracentral thickness.

Quantitative anatomical differences in central corneal thickness values determined with scanning-slit corneal topography and noncontact specular microscopy

Purpose: This study was designed to analyze the differences in central corneal thickness values determined with noncontact specular microscopy and scanning-slit corneal topography. The measurements were performed on the same eye. Methods: We analyzed the central corneal thickness values of 93 patients (n = 93) by means of noncontact specular microscopy (Topcon SP-2000P noncontact specular microscope, Topcon Corp., Tokyo, Japan) and scanning-slit corneal topography (Orbscan Topography System II, Orbscan Inc., Salt Lake City, UT). One experienced physician performed 3 consecutive central corneal thickness measurements with both devices. Results: The central corneal thickness values obtained by means of Orbscan pachymetry were 17 ± 2.7 (range, 12-24) μm greater. A significant correlation was observed between scanning-slit corneal topography and noncontact specular microscopy (Pearson correlation coefficient, r = 0.976; P < 0.001). Conclusions: Researchers should know of the existence of this difference between noncontact specular microscopy and Orbscan pachymetry when interpreting central corneal thickness values.

Differences in corneal anatomy in a pair of monozygotic twins due to continuous contact lens wear

Purpose. To study the differences in the corneal anatomy in a pair of 31-year-old monozygotic female twins, one of whom has been a contact lens wearer for the past 15 years and the other is a nonwearer. Methods. We analyzed the corneal thickness and the corneal endothelial cell density of the monozygotic twins and of two age-matched control groups, one made up of non–contact lens wearers (35 eyes of 35 patients; mean age, 29.32 ± 2.83 years) and the other made up of soft contact lens wearers (30 eyes of 30 patients; mean age, 33.08 ± 3.72 years; mean duration of contact lens use, 10.62 ± 4.32 years). Five corneal thickness measurements were carried out with the Orbscan Topography System II. Three consecutive measurements of the corneal endothelial cell density were carried out with the Topcon SP-2000P noncontact specular microscope. Results. Lower central corneal endothelial cell densities were found in both eyes of the monozygotic contact lens–wearing twin. The greater corneal thickness was shown at superonasal cornea except in the right cornea of the monozygotic contact lens twin. Moreover, significant differences in corneal thickness values were found between the monozygotic twins. Conclusions. The differences between the monozygotic twins seem to confirm that daily use of soft contact lenses can modify normal corneal anatomy.

Possible Further Evidence of Low Genetic Diversity in the El Sidrón (Asturias, Spain) Neandertal Group: Congenital Clefts of the Atlas

We present here the first cases in Neandertals of congenital clefts of the arch of the atlas. Two atlases from El Sidrón, northern Spain, present respectively a defect of the posterior (frequency in extant modern human populations ranging from 0.73% to 3.84%), and anterior (frequency in extant modern human populations ranging from 0.087% to 0.1%) arch, a condition in most cases not associated with any clinical manifestation. The fact that two out of three observable atlases present a low frequency congenital condition, together with previously reported evidence of retained deciduous mandibular canine in two out of ten dentitions from El Sidrón, supports the previous observation based on genetic evidence that these Neandertals constituted a group with close genetic relations. Some have proposed for humans and other species that the presence of skeletal congenital conditions, although without clinical significance, could be used as a signal of endogamy or inbreeding. In the present case this interpretation would fit the general scenario of high incidence of rare conditions among Pleistocene humans and the specific scenariothat emerges from Neandertal paleogenetics, which points to long-term small and decreasing population size with reduced and isolated groups. Adverse environmental factors affecting early pregnancies would constitute an alternative, non-exclusive, explanation for a high incidence of congenital conditions. Further support or rejection of these interpretations will come from new genetic and skeletal evidence from Neandertal remains.

Difficulties in distinguishing between an atlas fracture and a congenital posterior atlas arch defect in postmortem analysis.

We found one atlas from a sample of 148 skeletons (0.67%) that presented different anatomical variations which made it difficult to determine whether the vertebra had an atlas fracture, an unusual Type B posterior atlas arch defect, or a combination of both. We carried out a stereomicroscopy, radiographic, and computerized tomography scan study that revealed that the dry atlas we found presented a very uncommon congenital Type B posterior atlas arch defect, simulating a fracture. In short, the present paper has revealed that differentiating Type B posterior atlas arch defects from fractures in post-mortem dry vertebrae is more difficult than expected. Thus we believe that it can be easier than expected to mistake Type B posterior arch defects for fractures and vice versa in postmortem studies.

Corneal thickness differences between sexes after oxybuprocaine eye drops.

Purpose We aimed to analyze the corneal thickness (CT) values of female and male subjects before and after instillation of oxybuprocaine 0.4% anesthetic eye drops. Methods The CT of 30 female subjects and 28 male subjects was measured using scanning-slit corneal topography (Orbscan Topography System II, Orbscan, Inc, Salt Lake City, UT). Measurements were carried out before and 3 minutes after the instillation of oxybuprocaine 0.4% eye drops. Results The difference between the baseline values and those obtained after anesthesia ranged as follows: male subjects: central, −26 to +24 &mgr;m; superior, −24 to +23 &mgr;m; inferior, −19 to +20 &mgr;m; nasal, −25 to +30 &mgr;m; and temporal, −21 to +20 &mgr;m; female subjects: central, −16 to +24 &mgr;m; superior, −19 to +32 &mgr;m; inferior, −14 to +34 &mgr;m; nasal, −19 to +33 &mgr;m; and temporal, −36 to +16 &mgr;m. No significant differences were found in any corneal location in male subjects. The differences were significant at inferior (p = 0.001) and nasal (p = 0.011) corneal sites in female subjects. Conclusions Oxybuprocaine anesthetic eye drops induce significant CT increases in female subjects but not in male subjects.