Biomedical subjects

M S Rahhal

Publications and source records attributed to M S Rahhal.

12 recordsLinked to original sources

PubMed2006

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) microm 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.

Adult↗

PubMed2005

Caucasian emmetropic aged subjects have reduced corneal thickness values: emmetropia, CCT and age.

We aimed to analyze the possible changes in corneal thickness values according to age in emmetropic subjects. The central corneal thickness values of 100 emmetropic subjects (n = 100) were analyzed with the DGH 2000 AP ultrasonic pachymeter (DGH Technology, Inc., San Diego, CA, USA) by one experienced physician. The mean age of the subjects was 40.6 +/- 12.1 years old (range, 21-64). Analysis of the central corneal thickness (CCT) values by age subgroups indicated that subjects aged between 20 and 30 years had the higher CCT values. Differences in CCT values between the age groups were significant (p < 0.001; 1-way ANOVA test). A significant correlation between CCT values and age was found (r = -0.974; p < 0.001). In sum, it seems that there is a decrease in CCT values with age in emmetropic subjects.

Adult↗

PubMed2005

Reduced corneal thickness values in postmenopausal women with dry eye.

PURPOSE: To study and compare the corneal thickness values of postmenopausal women with dry eye and postmenopausal women without dry eye. METHODS: The corneal thickness value of 30 postmenopausal women with dry eye (dry eye group; aged 52 to 55 years) and 32 postmenopausal women without dry eye (normal group; aged 51 to 55 years) was analyzed with the Orbscan Topography System II. Each woman underwent a tear breakup test, the Schirmer test, fluorescein staining of the cornea, and an analysis of the meibomian gland by slit lamp before corneal thickness measurement. The statistical analysis was performed by means of the unpaired Student t test. RESULTS: The mean corneal thickness value was significantly decreased in postmenopausal women with dry eye (P < 0.001 at each corneal location). The central cornea had the thinnest mean values in dry eyes and normal eyes (533.10 +/- 4.74 microm and 547.63 +/- 15.11 microm, respectively), whereas superonasal cornea had thicker mean values in both groups (632.43 +/- 6.11 microm and 648.78 +/- 14.98 microm in dry eye and normal eyes, respectively). CONCLUSIONS: Postmenopausal women with dry eye have lower corneal thickness values than postmenopausal women without dry eye. Special care must be taken with these reduced corneal thickness values when selecting postmenopausal women for surgery involving corneal photoablation.

Body Weights and Measures↗

PubMed2005

Corneal endothelial cell density decreases with age in emmetropic eyes.

PURPOSE: To analyze the corneal endothelial cell density in healthy adult emmetropic subjects. METHODS: We analyzed the corneal endothelial cell density of a group made up of 225 emmetropic subjects (n=225). As age-matched control groups we analyzed two other groups, one made up of myopic subjects (n=209) and the other made up of hyperopic subjects (n=203). We recorded the mean of three consecutive measurements of the corneal endothelial cell density using the Topcon SP-2000P non-contact specular microscope (Topcon Corp., Tokyo, Japan). RESULTS: The mean age was 38.6+/-11.8 years, 40.7+/-12.2 years, and 39.2+/-10.5 years for emmetropic, myopic and hyperopic subjects respectively (p=0.994). No significant differences (p=0.920) in endothelial cell density values were found between emmetropic (2985+/-245 cells/mm2), myopic (2936+/-258 cells/mm2) and hyperopic eyes (2946+/-253 cells/mm2). Lower corneal endothelial cell density values were found in older emmetropic (p<0.001), myopic (p<0.001), and hyperopic subjects (p<0.001). A significant correlation between endothelial cell density and age was found in emmetropic (r=-0.958; p<0.001), myopic (r= -0.954; p<0.001) and hyperopic subjects (r= -0.948; p<0.001). CONCLUSIONS: In healthy emmetropic subjects there is a reduction in corneal endothelial cell density with age although there are no differences in corneal endothelial cell density values between emmetropic, myopic and hyperopic subjects.

Adult↗

PubMed2005

[Orbscan pachymetry: differences between observers when carrying out measurements of the corneal thickness].

PURPOSE: To study the corneal thickness and the inter-observer variability of corneal thickness measurements by means of Orbscan pachymetry. METHODS: We analysed the central and para-central corneal thickness of 30 subjects, whose age ranged from 19 to 38 years (mean 27.27, S.D. 5.25), with the Orbscan Topography System II (Orbscan, Inc., Salt Lake City, UT, USA). The mean of five consecutive measurements of the corneal thickness were obtained by two different observers and the results obtained were compared. RESULTS: No significant differences in mean corneal thickness between observers were found at central (p=0.749), nasal (p=0.931), supero-nasal (p=0.847), infero-nasal (p=0.930), temporal (p=0.918), supero-temporal (p=0.912) and infero-temporal (p=0.760) regions of the cornea. The maximum mean corneal thickness was found most commonly at the supero-nasal cornea (14 of 30 eyes for observer 1, and 16 of 30 eyes for observer 2). The difference between the central thickness and the maximum para-central thickness was 117 (S.D. 22) and 117 (S.D. 23) microns for observers 1 and 2 respectively (p=0.974). The difference between the central thickness and the minimum para-central thickness was 40 (S.D. 20) and 39 (S.D. 19) microns for observers 1 and 2 respectively (p=0.846). The difference between the minimum and the maximum para-central thickness was 76 (S.D. 24) and 77 (S.D. 23) microns for observers 1 and 2 respectively (p=0.895). CONCLUSIONS: Orbscan pachymetry allows central and para-central corneal studies to be carried out by different observers without any significant differences being found between them.

Adult↗

PubMed2004

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 microm center; 603 to 678 microm nasal; 620 to 689 microm superonasal; 600 to 669 microm inferonasal; 571 to 639 microm temporal; 601 to 669 microm superotemporal; and 572 to 647 microm inferotemporal. In each individual the difference between the central thickness and the maximum paracentral thickness ranged from 85 to 107 microm (mean +/- SD, 99.21 +/- 3.80). The difference between the central thickness and the minimum paracentral thickness ranged from 36 to 59 microm (48.97 +/- 4.23 microm). The difference between the minimum paracentral corneal thickness and the maximum paracentral corneal thickness ranged from 37 to 58 microm (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.

Adult↗

PubMed2003

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.

Adult↗

PubMed2003

[Comparative clinical study of visual results between two different types of bifocal intraocular lenses].

PURPOSE: To compare visual results after cataract surgery in patients who underwent bilateral implantation of two different types of bifocal intraocular lenses: the model 811E (Pharmacia), and the model MF4 (Ioltech). METHODS: This prospective study comprised 99 patients who underwent phacoemulsification with bifocal IOL implantation. The model 811E was implanted in forty-seven eyes of 47 patients (group I) and the model MF4 in fifty-two eyes of 52 patients (group II). Visual acuity (distance and near), complications, and adverse events were measured. The postoperative follow-up in all patients was of 6 months. Patient satisfaction was also valued using a questionnaire. RESULTS: There was no significant difference in uncorrected distance visual acuity between both groups, which was respectively 0.63 (S.D.: 0.2) for group I and 0.58 (S.D.: 0.16) for group II (p=0.17). Nonetheless a significant difference was found when measuring corrected distance visual acuity, which was 0.86 (S.D.: 0.1) for group I and 0.77 (S.D.: 0.12) for group II (p=0.01). Mean uncorrected near visual acuity was statistically better in group I: J2.00 (S.D.:1.16) in comparison with J2.48 (S.D.:0.83) for group II (p=0.021). Subjectively, both groups indicated high levels of satisfaction, without significant difference between them, being respectively 78% (group I) and 73.4% (group II). CONCLUSIONS: Our results reveal a superiority of the bifocal diffractive lens over the refractive bifocal lens for corrected distance visual acuity and distance-corrected near visual acuity. Postoperatory complications and satisfaction degree were similar for both IOL models.

Aged↗

PubMed2001

[Rational management of applanation tonometry in myopia after LASIK].

PURPOSE: To determine the accuracy and to identify pitfalls when intraocular pressure is measured in myopic patients after laser in situ keratomileusis (LASIK). METHODS: A retrospective study of intraocular pressure (IOP) measured with a Goldmann applanation tonometer in 103 eyes of 52 myopic patients who underwent LASIK was performed. Patients without ocular hypertension or glaucoma were selected. The same surgeon carried out a standard LASIK technique using a microkeratome Chiron Hansatome and the Technolas Chiron 217-C Lasik. IOP was measured pre-operatively, and at 1, 3 and 6 months post-operatively. RESULTS: After LASIK, a significant decrease was observed in the IOP in the post-operative controls, with a mean decrease of 2.69+/-1.69 mm Hg (p<0.001). This was related with the degree of myopia (p=0.05) and the characteristics of the excimer-laser treatment parameters, such as corneal ablation (p=0.04). No correlation was observed between this decrease and age or gender. CONCLUSIONS: Our retrospective review showed that the post-operative intraocular pressure measured after LASIK was lower than the pre-operative ones, which changed the Goldmann tomometer accuracy, thus causing it to underestimate the IOP.

Adult↗

PubMed2000

Influence of refraction on tonometric readings after photorefractive keratectomy and laser assisted in situ keratomileusis.

PURPOSE: To determine the decrease of Goldmann tonometry after photorefractive keratectomy (PRK) and laser assisted in situ keratomileusis (LASIK) according to refraction prior to surgery. METHODS: Prospective simultaneous comparative case series of 53 myopic eyes (53 patients) that underwent PRK and 50 (50 patients) that underwent LASIK using the Summit Excimed SVS plus (Summit Technology, Inc., Walthan, MA, U.S.A.). PRK and LASIK were subdivided by refractive error into two subgroups of more than or less than -5 diopters (D). Central tonometric readings were taken prior to surgery and 12 months after surgery. RESULTS: In LASIK and PRK subgroups of more than -5 D, 85.7% (24) and 69.6% (24), respectively, gave lower readings than those taken before surgery. In LASIK and PRK subgroups of less than -5 D, 77.3% (17) and 53.3% (16), respectively, gave lower readings. The difference between the two is significant (p < 0.001). Average tonometry falls by 2.8 mmHG in the LASIK subgroup of more than -5 D (p < 0.001) and by 2.8 mmHG in the LASIK subgroup of less than -5 D (p < 0.001) and by 1.7 mmHG in the PRK subgroup of more than -5 D (p < 0.010). In PRK subgroup of less than -5 D, the tonometric changes are not significant (p = 0.971). CONCLUSIONS: High previous refraction (in PRK) and technique used determines lower final tonometric readings, bringing about more frequent and significant decreases in LASIK than in PRK for errors of more than and less than -5 D.

Adolescent↗

PubMedDate not supplied

Quantitative corneal anatomy in emmetropic subjects.

PURPOSE: Currently there is little information available about the corneal thickness values of healthy emmetropic subjects. Therefore, the authors decided to analyze the corneal thickness in healthy emmetropic subjects. METHODS: The authors analyzed the difference in thickness values between the thinnest corneal site and the central and paracentral cornea in 124 eyes of 124 healthy emmetropic white subjects. RESULTS: The mean difference between the thinnest site of the cornea and the thickness values obtained in the areas analyzed was as follows: 12+/-6 microm center; 140+/-19 microm superonasal; 133+/-23 microm nasal; 117+/-26 microm inferonasal; 122+/-19 microm superotemporal ; 89+/-22 microm temporal; and 99+/-29 microm inferotemporal (p<0.001; one way analysis of variance test). CONCLUSIONS: In healthy emmetropic white subjects the thinnest site of the cornea is statistically lower than the central and paracentral cornea.

Adolescent↗

PubMedDate not supplied

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.

Adult↗