Biomedical subjects

E P Osuobeni

Publications and source records attributed to E P Osuobeni.

17 recordsLinked to original sources

PubMed2003

The effect of illumination-microscope angle on slit lamp estimate of the anterior chamber depth.

PURPOSE: The anterior chamber depth can be estimated by the slitlamp without additional attachments. The method involves increasing the length of a horizontal slit focused on the cornea until the corneal and iris/lens images appear to just touch. For a slitlamp angle of 60 degrees, multiplying the just-touching slit length (JTSL) by 1.4 gives an estimate of the anterior chamber depth as measured by ultrasonography. The purpose of this study was to determine whether the slitlamp angle affects the accuracy of the procedure. METHODS: The anterior chamber depth of 63 adult male and female subjects aged between 19 and 44 years was measured by A-scan ultrasonography and estimated by the slitlamp technique. The angle between the illumination and microscope systems was varied at 10 degrees intervals from 30 degrees to 70 degrees. RESULTS: The average ultrasonographic anterior chamber depth for all subjects was 3.23 +/- 0.38 mm. The average JTSL was as follows: 30 degrees = 1.5 mm, 40 degrees = 1.7 mm, 50 degrees = 2.1 mm, 60 degrees = 2.3 mm, and 70 degrees = 2.5 mm. The conversion ratio between the ultrasonographic anterior chamber depth and the average JTSL was as follows: 30 degrees = 2.2, 40 degrees = 1.9, 50 degrees = 1.5, 60 degrees = 1.4, and 70 degrees = 1.3. The ultrasonic anterior chamber depth was best estimated at 60 degrees. The 95% limits of agreement between the estimated and measured anterior chamber depth were as follows: 30 degrees = -0.76 to +0.84 mm, 40 degrees = -0.75 to +0.63 mm, 50 degrees = -0.36 to +0.46 mm, 60 degrees = -0.26 to +0.28 mm, and 70 degrees = -0.45 to +0.41 mm. CONCLUSIONS: These results experimentally confirm Smith's suggestion that the optimum slitlamp angle at which to accurately estimate the anterior chamber depth is 60 degrees. At this angle, estimates of the anterior chamber depth are minimally deviated from the gold standard (A-scan ultrasonography). At a slitlamp angle of 60 degrees, the JTSL can be converted to an estimate of the ultrasonic anterior chamber depth by multiplying it by 1.40.

Adult↗

PubMed2000

Intra-observer repeatability and inter-observer agreement of the Smith method of measuring the anterior chamber depth.

The Smith (1979) method provides a means of estimating the anterior chamber depth without additional attachments to the slit lamp [Smith, R. J. H. (1979). A new method of estimating the depth of the anterior chamber. Br. J. Ophthalmol. 63, 215-220]. In this study, the 95% intra-observer limits of repeatability and the 95% inter-observer limits of agreement of this method have been determined. The intra-observer limits of repeatability were determined by plotting the difference vs the mean of the estimated anterior chamber depth obtained in two different sessions by each of two examiners, while the inter-observer limits of agreement are represented by a plot of the difference vs the mean estimated anterior chamber depth between the two examiners. For one examiner, the 95% intra-observer limits of repeatability was -0.36 to 0.58 mm, while for the other examiner the 95% intra-observer limits of repeatability was -0.25 to 0.37 mm. The 95% inter-observer limits of agreement were -0.31 to 0.23 mm and -0.41 to 0.25 mm for the first and second sessions respectively. The intra-observer limits of repeatability are comparable with those reported for A-scan ultrasonographic measures of the anterior chamber depth. These results imply that the Smith method can be used with a high degree of repeatability and agreement to clinically monitor longitudinal changes in anterior chamber depth.

Adult↗

PubMed1999

Ocular components values and their intercorrelations in Saudi Arabians.

There are no previous studies on the dimensions of ocular components and their intercorrelations in adult Saudi Arabians. In this study ocular components were measured by ultrasonography and keratometry in 152 adult Saudis. Their ages ranged from 16 to 50 years. The males had significantly longer anterior chamber depth (ACD), vitreous chamber depth (VCD), axial length (AL) and axial length/corneal radius ratio (AL/CR) than females. However, females had non-significantly steeper corneas than males. The AL/CR ratio had the highest correlation with refractive error. Corneal radius of curvature was positively correlated with VCD and AL. Lens thickness was negatively correlated with the VCD, AL and AL/CR ratio. Myopes had significantly deeper ACD, VCD, and higher AL/CR ratio than nonmyopes. Myopes had significantly thinner lenses than hyperopes. The average values of the optical components and their intercorrelations are similar to reported values obtained from subjects of other races but with comparable refractive errors.

Adolescent↗

PubMed1999

Ultrasonographic determination of the dimensions of ocular components in enucleated eyes of the one-humped camel (Camelus dromedarius).

The refractive status and visual capabilities of the one-humped camel are not currently known. Schematic eyes are important tools in studying the optical characteristics and refractive status of an eye. The variables required in developing a schematic eye for a particular animal species include the dimensions of the optical components. We have employed A-scan ultrasonography to measure the dimensions of optical components in freshly enucleated eyes of the one-humped camel. Measurements were made in eyes immersed in distilled water kept at 20 degrees C. The average values of the optical components were as follows: anterior chamber depth = 5.27 mm, lens thickness = 10.93 mm, vitreous chamber depth = 14.85 mm and axial length = 31.05 mm. The uncorrected average corneal thickness was 0.76 mm. These values would have to be confirmed in live animal subjects before they can be used to design a schematic eye for the one-humped camel.

Animals↗

PubMed1996

Prevalence of congenital red-green color vision defects in Arab boys from Riyadh, Saudi Arabia.

The prevalence of congenital red-green color vision defects (CVDS) is both racial and gender dependent. Red-green color vision defects (CVDS) have been screened for among Arab boys from Riyadh, Saudi Arabia, by using both the Ishihara plates and the D 15 test. The results indicate a prevalence of 2.93%. Deutan defect was present in 1.95% of the subjects, protan defect in 0.49% and unclassified color defect in 0.49%. This result confirms the previously reported low prevalence of congenital red-green CVDS among adult Arab males from the central region of Saudi Arabia.

Adolescent↗

PubMed1995

Normal values of ocular protrusion in Saudi Arabian male children.

The extent of ocular protrusion from the orbit is an important sign in the diagnosis and management of ocular and orbital diseases. Ocular protrusion is dependent, among other factors, on ethnic origin, age, gender, high refractive error, axial length, inter outer orbital distance (IOOD), and interpupillary distance (IPD). The purpose of this study was to provide normal absolute and relative ocular protrusion values for Saudi Arabian male children of Arab origin and to furnish regression equations relating ocular protrusion to age, IOOD, and IPD. A cross-sectional study was designed and ocular protrusion and IOOD were measured using a Hertel prism exophthalmometer. The IPD was measured by using a corneal reflection pupillometer. The data were analyzed using t-test and analysis of variance tests. The average absolute ocular protrusion of the right and left eye was 15.4 mm +/- 1.6 and 15.2 mm +/- 1.6, respectively. The maximum difference in protrusion between the eyes was 2.0 mm. Saudi Arabian male children of Arab origin who have ocular protrusion values outside the 95% confidence intervals should be advised to undergo additional diagnostic tests. A relative ocular protrusion value greater than 2.0 mm may be indicative of unilateral proptosis among these subjects. On the average, Arab children have more ocular protrusion than Caucasians but less than Chinese children.

Aging↗

PubMed1994

Ocular and facial anthropometry of young adult males of Arab origin.

Other investigators have provided normal values of facial and ocular dimensions of subjects of different ethnic backgrounds. Our main reason for carrying out this study was to provide a data base of similar measurements for the male Arab (Saudi) population. A projected photographic technique was used. Measurements from the photographs were transformed to real life distances by multiplying by a constant factor. The results of our investigations show that Japanese have wider inter-outer canthal distance (IOCD) than Arabs and Caucasians, both of whom have similar IOCD. Arabs have wider inter-inner canthal distance (IICD) than Caucasians. African-Americans and Japanese have wider inter pupillary distance (IPD) than Arabs. Percentile values of the measured distances will aid in syndrome diagnosis among male Arabs.

Adolescent↗

PubMed1994

Differences between anatomical and physiological interpupillary distance.

BACKGROUND: The interpupillary distance (IPD) is usually measured between the centers of the pupils (anatomical IPD) or between the visual axes (physiological IPD). We have investigated the differences between the two methods of measuring IPD. METHODS: A millimeter ruler was used to measure the distance between the nasal and lateral limbus of 400 male Arab subjects (anatomical IPD). An Essilor corneal reflex pupillometer was employed to also measure the inter visual axes distance (physiological IPD) of the same group of subjects. RESULTS: The anatomical IPD is on the average 0.10mm and 0.30mm wider than the physiological IPD at distance and near respectively. The calculated near physiological IPD is significantly different from the measured near physiological IPD. CONCLUSIONS: Although individual differences between anatomical and physiological IPDs could be clinically significant, generally, there is good agreement between the two. It is preferable to employ the monocular components of the physiological IPD in ophthalmic procedures.

Adolescent↗

PubMed1993

Induced prismatic effect in spectacle prescriptions sampled in Saudi Arabia.

We determined the prevalence of prescription glasses-induced prismatic effect among a sample of 100 patients in the Kingdom of Saudi Arabia. All the glasses sampled had a certain degree and type of induced prismatic effect. A small percentage (5%) of the subjects complained about their glasses. Prism adaptation is thought to be the reason why the number of patients complaining about improperly fitted glasses does not reflect the frequency of the problem. Simple ways of eliminating these inaccuracies are suggested.

Eyeglasses↗

PubMed1993

Interpupillary distance of females of Arab origin.

We have investigated the distant and near interpupillary distance (IPD) of three groups of females of Arab origin. Average values and range of values have been determined for children, young adults, and older adults. Average distant interpupillary distance (FIPD) measurements are compared to those of females of Caucasian (European and American), African-American, and Chinese (Hong Kong and mainland China) origin. Different experimental techniques and some unavailable information about previously studied subjects make conclusive statements about the ethnic variation of IPD difficult to draw.

Adolescent↗

PubMed1993

Gender differences in interpupillary distance among Arabs.

Information about the normal values of interpupillary distance (IPD) for a particular age group, sex, and ethnic background has important clinical implications. Normative values of IPD could be useful in the diagnosis of certain syndromes and also in surgery after facial trauma. Our main reason for carrying out this study was to provide normal values and ranges of IPD for the male Arab population. The distance between the temporal limbus of one eye and the nasal limbus of the other was measured by a ruler. We have provided average values and range of values of normal IPD for Arab boys, young adults, and older adults. Arab males have IPD on the average 2.0 mm wider than females. Different experimental techniques and ages of subjects make conclusive statements about the ethnic variation of IPD difficult.

Adolescent↗

PubMed1993

Ocular and facial dimensions of male Arab children.

BACKGROUND: Photographic measurements of facial and ocular distances of 200 normal male Arab children have been undertaken. METHODS: Measurements include inter inner canthal distance (IICD), inter outer canthal distance (IOCD), length of the palpebral fissure (LPFOD), width of the palpebral fissure (WPFOD), horizontal corneal diameter (HVDOD), vertical brow-nasal distance (VBND), interpupillary distance (IPD), bridge height (BH) and frontal angle (AANG). RESULTS: Percentile values of the measured distances have been given. These values will aid in syndrome diagnosis. CONCLUSIONS: They will also be useful to manufacturers of spectacle frames and lenses. Our values have been compared to those obtained from young males of other racial backgrounds.

Adolescent↗

PubMed1992

Monocular vernier acuity in normally binocular, monocular, and amblyopic subjects.

Previous experiments that have compared monocular vernier acuity in amblyopic, monocularly blind, and normal binocular subjects have been confined to the center of the retina. Based on brain changes that accompany the early disruption of form vision in one eye, monocularly blind subjects (that is, those who have completely lost the ability to process form vision in one eye) and amblyopic subjects are expected to have better vernier acuity in their normally functioning eye than subjects with normal binocular vision. Results from such studies have been ambiguous. This experiment was set up to study monocular vernier acuity in the central and peripheral retina of the three groups of subjects mentioned above. The results show that, at the center, monocularly blind subjects have the best vernier acuity followed by the amblyopic subjects and, finally, the normal binocular subjects have the worst acuity. In the peripheral retina, no significant differences were found between the three groups. A possible explanation has been provided for this finding.

Amblyopia↗

PubMed1991

Effect of chromatic aberration on isoluminance stereothreshold.

The results of a previous experiment have shown that stereothreshold varies as a function of the luminance difference between a target and its background. When the luminance of the target is the same as that of the background (isoluminance) the stereothreshold was elevated by a factor of 3 as compared with a situation where there was maximum luminance difference between the target and the background. Generally, if the target and the background have the same color, stereothreshold at a particular luminance difference level was lower (stereoacuity better) than if the target and the background have different colors. This indicates a possible effect of chromatic aberration on stereothreshold which could be responsible for the 3-fold increase in threshold at isoluminance. This possibility has been investigated in this experiment. The results show that even though stereothresholds are sensitive to chromatic aberration this factor cannot explain the elevated stereothreshold at isoluminance.

Color Perception↗

PubMed1991

Effect of reduced accommodative response on isoluminance stereothreshold.

A previous study has shown that stereothreshold varies as a function of the luminance difference between a target and its background. On the average, the stereothreshold at the isoluminance point is three times higher than when there is maximum luminance difference between the target and the background. One of the possible reasons for this finding is the effect of less than optimum accommodative response for isoluminant targets. This possibility has been investigated in this study. The results show that the suboptimal accommodative response cannot explain the high stereothreshold at isoluminance.

Accommodation, Ocular↗

PubMed1986

Chromatic and luminance difference contribution to stereopsis.

Stereoacuity has been measured at various luminance difference levels and also at the isoluminance point, where the target and the background have equal luminances. The results of the experiment show that acuity at isoluminance is three times worse than the value obtained when there is maximum contrast between target and background. possible reasons for these findings were investigated. Results of control experiments show that neither chromatic aberration nor defective accomodative response could be responsible for this finding.

Color↗

PubMedDate not supplied

Agreement between A-mode and B-mode ultrasonography in the measurement of ocular distances.

It is generally accepted that A-mode ultrasonography is more accurate than B-mode in measuring intraocular dimensions. Consequently, A-mode ultrasonography is the procedure of choice in ocular biometry while B-mode ultrasonography is used principally for diagnostic purposes. In this study, we investigated the agreement between measurement of intraocular distances using A- and B-mode ultrasonography on freshly enucleated camel eyes. Our results suggest that relative to average A-mode values, B-mode overestimates corneal thickness (bias = 0.06 mm) and anterior chamber depth (bias = 0.03 mm), while it underestimates lens thickness (bias = -0.11 mm), vitreous chamber depth (bias = -0.32 mm) and axial length (bias = -0.40 mm). In general, difference between A- and B-mode values is larger for deeper intraocular dimensions. This implies that the two methods are more likely to give different readings for measurements of lens thickness, vitreous chamber depth and axial length.

Animals↗