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Purpose: To investigate the relationship between age, gender, corneal diameter, central corneal curvature, central corneal thickness (CCT) and intraocular pressure in Nigerians with normal intraocular pressure. Methods: One hundred and thirty eyes from 130 subjects (mean age = 47.8 ± 16.8 years) including 77 males and 53 females were recruited. CCT was measured by ultrasound pachymetry, intraocular pressure was determined by non-contact tonometry, horizontal and vertical corneal diameters were measured with a ruler and central corneal curvature was measured by keratometry. Results: The mean values obtained were as follows: CCT = 548.97 ± 34.28 μm, IOP = 15.61 ± 2.69 mmHg, average corneal curvature (AVK) = 42.98 ± 1.19 D, horizontal corneal diameter (HVID) = 11.39 ± 0.69 mm and vertical corneal diameter (VVID) = 10.51 ± 0.50 mm. There was a significant effect of age on CCT (r = −0.35, p

Purpose: To investigate the effects of physical size on refractive error and the dimensions of optical components in sickle cell disease (SCD). Methods: The design was cross sectional. Height and weight of adult patients suffering from SCD were measured, and body mass index (BMI) was calculated. Anterior chamber depth (ACD), lens thickness (LT), vitreous chamber depth (VCD) and axial length (AL) were measured using A-scan ultrasonography. Corneal radius of curvature (CR) was measured using a keratometer. Non-cycloplegic refractive error was determined subjectively. Results: Subjects with SC genotype were significantly taller than those with SS genotype. In the unadjusted data, height was correlated with VCD [p = 0.02, 0.44 mm deeper per 10 cm increase in height, 95% CI (0.65, 8.25)] and AL [p = 0.03, 0.42 mm longer for every 10 cm increase in height, 95%CI (0.49, 7.99)]. The relationship between height, VCD and AL was absent after adjustment for age, gender, genotype and weight. BMI (kg m−2) was correlated with AL/CR ratio in both unadjusted (p = 0.04, −0.10 decrease per 1 kg m−2, 95% CI (−0.018, −0.001) and adjusted data (p = 0.05, −0.10 decrease per 10 kg m−2, 95% CI (−0.0189, 0.0001). Refractive error was not related to height, weight or BMI. Conclusions: Physical size does not affect refractive error or optical components in adult patients with SCD.

We investigated the relationship between myopia and peripheral refraction for distance and near vision by measuring peripheral refractive errors in 10 myopic and 10 emmetropic participants at viewing distances of 2.5 and 0.4 m. Measurements were made at the fovea, and at eccentricities of 10 degrees , 20 degrees and 30 degrees in the temporal and nasal hemispheres of the horizontal visual field. Our results showed that peripheral astigmatism increased with increasing eccentricity, but there was no significant difference between refractive error groups except at 30 degrees eccentricity in the temporal retina. Considering the Mean Spherical Equivalent errors, emmetropes became relatively myopic at peripheral eccentricities, but there was little change in myopes. The effect of viewing distance on astigmatism or Mean Spherical Equivalent error was not significant. Our results do not support the view that myopia is associated with changes in peripheral refraction during distance or near vision.

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.

Background: The average value of some facial and ocular dimension varies with race, age and gender. The upper eyelid margin-to-corneal reflex distance (ULCRD) is used to define and quantify the degree of blepharoptosis. Evidence from previous studies indicates that both the vertical width of the palpebral fissure (VWPF) and the ULCRD are age-dependent. This study was carried out to investigate the average value of the ULCRD in Saudi Arabian boys and to determine the relationship between the ULCRD and the VWPF. This information will be useful in diagnosing and quantifying the degree of ptosis among Arabian boys. Methods: Measurements of the ULCRD and the VWPF were obtained from projected slide photographs taken of boys aged between six and 15 years. The measured distances were converted to actual values by multiplying by a constant magnification factor. Results: The average value of the ULCRD was 3.05 mm ± 0.79 while that of the VWPF was 8.83 mm ± 1.14. The ULCRD was directly proportional to the VWPF. Approximately 44.0 per cent of the variation in the ULCRD among our subjects was accounted for by the differences in the VWPF. The two variables were related by the equation: ULCRD = 0.45 VWPF -0.91. A maximum asymmetry of 1.0 mm was obtained between the ULCRD of the two eyes. Conclusions: The average value of the ULCRD of Arab boys is lower than previously reported averages obtained on predominantly Caucasian adult subjects. This finding may be related to age and racial differences. The ULCRD is closely related to the VWPF. Generally, the ULCRD is similar in both eyes. Asymmetry greater than 1.0 mm should be investigated further for evidence of blepharoptosis or exophthalmos.

Background: Some pathological conditions of the eyelids are known to induce corneal astigmatism. In general, North American Indians and persons of oriental origin have a higher prevalence and greater magnitude of corneal astigmatism compared with persons of other racial background. This is thought to be related to the thicker upper eyelid of orientals, among other factors. An experiment was conducted to study the relationship between lid thickness and corneal astigmatism. Method: A blepharometer used to measure lid thickness was designed and built from commercially available components. The thickness of both upper eyelids of 70 subjects was measured. Corneal astigmatism was calculated from the measurements made with a Reichert (Bausch and Lomb type) keratometer. Results: There were no significant differences in lid thickness and corneal astigmatism between the right and left eyes. The average thickness of the right upper eyelid was 4.13 mm ± 0.40 while the average corneal astigmatism was -1.14 DC ± 0.69. Eyes with corneal astigmatism equal to or greater than -2.00 DC are associated with thicker eyelids. Conclusions: Eyes with high degrees of corneal astigmatism tend to have thicker eyelids. However, this association does not necessarily prove a cause-effect relationship. (Clin Exp Optom 1997; 80: 1: 35–39)

Aims: Gujarati is the main spoken language of a large proportion of the population of India. The aim of this study was to develop and validate a new Minimum Angle of Resolution (logMAR) visual acuity chart in the Gujarati language. Materials and Methods: A new Gujarati visual acuity chart was designed to logMAR specifications using Gujarati optotypes experimentally selected to have similar relative letter legibility under spherical and cylindrical defocus. The chart validation study was carried out using 153 adult subjects in a large clinical setting in India. Subjects who were literate in English and Gujarati participated in the study. Visual acuity was measured with the new Gujarati logMAR chart and a modified Early Treatment of Diabetic Retinopathy Study-(m-ETDRS) logMAR chart. The method of presentation was randomized between the charts. Repeat visual acuity was measured on a subsequent day with a second version of the Gujarati logMAR chart. Results: The Gujarati chart correlated highly with the m-ETDRS logMAR chart (r2 = 0.974). The mean visual acuity difference (Gujarati - m-ETDRS logMAR) was equal to three letters (-0.06 logMAR). The Gujarati logMAR chart also proved to be highly repeatable (r2 = 0.994, test-retest) with 95% CI of ± 0.04 logMAR. Conclusions: The new Gujarati logMAR visual acuity chart provides a valid and repeatable tool for the measurement of visual acuity in native Gujarati language speakers.

Background: Gaze-related changes in the magnitude and type of phoria have important clinical implications with respect to the attainment and maintenance of comfortable single binocular vision. Previous investigations were either limited to the mid-vertical and lateral directions of gaze or involved head positions with input from neck proprioceptors. The results of such studies have been ambiguous. Method: The Hess-Lancaster screen was used to study the variations of near horizontal phoria in nine positions of gaze among subjects with normal binocular vision. Head movement was restrained by a head support system. Subjects were divided into orthophoric, esophoric and exophoric groups based on their phoria in the primary position. Results: The orthophoric and esophoric subjects demonstrated small but insignificant increases in esophoria at secondary and tertiary positions of gaze. However, the changes for the exophoric subjects were significant and ranged from 0.34 prism dioptres less exophoria at right gaze to 2.61 prism dioptres less exophoria at down and left gaze. Conclusions: Significant gaze-related changes in phoria were obtained among exophoric subjects at non-primary positions of gaze. Possible explanations for this finding include horizontal and vertical muscle involvement and differences in perceived size of objects at non-primary positions. The results indicate the need to measure phoria at all major positions of gaze.

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.

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.

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.

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.

Background: The slitlamp can be used to estimate the anterior chamber depth (ACD). The length of a slit object is increased until the corneal and iris/lens images appear to just touch. Multiplying the just-touching-slit-length (JTSL) by a conversion factor gives an estimate of the ACD as measured by ultrasonography. The purpose of this study was to determine if central corneal thickness (CCT) affects the accuracy of this technique. Methods: The ACD of 50 subjects was measured by A-scan ultrasonography and estimated by the slitlamp technique. CCT was measured by ultrasonic pachometry. The refractive error was determined subjectively. Results: The average ultrasonographic ACD for all subjects was 3.32 ± 0.65 mm. The average JTSL was 2.46 ± 0.38 mm. The conversion ratio between the ultrasonographic ACD and the average JTSL was 1.35. The predicted ACD using the regression equation of JTSL on the ultrasound anterior chamber depth (USACD) was 3.32 ± 0.54 mm. The corresponding value using the regression equation of JTSL and CCT on USACD was exactly the same, that is, 3.32 ± 0.54 mm. Conclusion: Incorporation of CCT into a regression equation does not improve the accuracy of the Smith technique.

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.

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.

BACKGROUND: There are no previous reports on the velocity of ultrasound through the aqueous and vitreous humours of the one-humped camel. This information is required for determination of the depth of the aqueous and vitreous chambers and therefore the axial length. This knowledge together with other, yet to be determined, ocular dimensions will ultimately be used in drawing up a schematic eye for the camel. This will provide a tool for studying the visual capability of this animal. METHOD: A-mode ultrasonography was used to determine the velocity of sound through the aqueous and vitreous fluids of the one-humped camel. The fluids were obtained from freshly enucleated eyes. RESULTS: The average velocity of ultrasound through 20 aqueous and 22 vitreous humour samples kept at 20 degrees Celsius was 1,499 +/- 23 m/s and 1,497 +/- 24 m/s, respectively. CONCLUSION: We recommend that at 20 degrees Celsius a common value of 1,498 m/s should be adopted as the velocity of ultrasound through the aqueous and vitreous humours of the one-humped camel. This value is slower than in humans but similar to that of the cow and pig.

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.

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.

Purpose.: To test the efficacy of a novel dual treatment for improving accommodative accuracy and dynamics in young persons with myopia. Methods.: Ninety-three young persons with myopia (mean spherical equivalent, −3.0 ± 1.8 D; age 16.8 ± 2.1 years; spherical aberration +0.06 ± 0.04 μm) participated in the study. Custom-designed soft contact lenses were used to alter ocular SA to −0.10 μm to improve accommodative accuracy and reduce any lag of accommodation. A vision training regimen was performed for 18 minutes per day for up to 6 weeks to improve speed of dynamic accommodation. Control groups had contact lenses with no added SA and/or no exercises. To avoid any effects of natural levels of negative aberration on the results of the study, all participants who had negative SA were excluded. Results.: The treatment contact lenses produced a significant reduction in lag of accommodation (P < 0.05) at all proximal viewing distances measured. The vision training measurement and treatment resulted in a significant increase in distance facility rate for all groups compared with their own baselines (P < 0.05). Near facility rate improved in the vision training treatment group only compared with its baseline (P < 0.05). Both positive and negative response times for distant viewing were significantly shorter in all groups after training compared with their baseline values (P < 0.05). At near, the positive response times were decreased significantly (P < 0.05) in both groups, whereas the negative response times decreased significantly only in the vision training treatment group. Conclusions.: After 3 months, the dual treatments (altering SA and vision training) used in the study were effective in modifying accommodation. The static accommodative response to targets at proximal distances was increased by the altered SA contact lenses and rates of dynamic accommodation improved with vision training.

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.

Purpose: To investigate relative letter legibility of Punjabi optotypes. Methods: In experiment 1, the influence of font type on letter legibility was studied on nine subjects optically defocused using a +1.00 DS lens in front of one eye. Two Punjabi font types used in widely read Punjabi language newspapers and magazines were selected. Legibility was determined according to the method of Strong and Woo (1985). In experiment 2, a single Punjabi font (selected from experiment 1) was used to investigate relative letter legibility in 10 subjects who were optically defocused with a +1.00 DS, +2.00 DC, axis 180 and 90. The Punjabi letters were modified to fit into a 5 × 5-grid using Coral draw and presented on a standard PC monitor at high contrast using Powerpoint. The method of Strong and Woo (1985) was used to determine relative letter legibility. Results: The results of experiment 1 showed no effect of font type on letter legibility (anova, p > 0.05). The results of experiment 2 were analysed in two ways. Firstly, anova revealed an interaction between blur condition (sphere, cyl axis 90, cyl axis 180) and letter legibility (p

La stereoacuite a ete mesuree a des taux de difference de luminance variables et egalement au point d'isoluminance, lorsque la cible et le fond sont de luminance egale. Les resultats de l'experience montrent que l'acuite a l'isoluminance est 3 fois plus mauvaise que la valeur obtenue lorsqu'il y a un contraste maximal entre la cible et le fond. On a recherche les raisons possibles de ces constatations. Les resultats des experiences de controle montrent que ni l'aberration chromatique, ni la reponse d'accommodation deficiente ne pouvaient etre responsables de cela