ABSTRACT
Albinism is a genetic disorder that affects melanin synthesis of the human being. Although not very common, it has serious effects on the visual system, particularly reduced visual acuity. The pattern visual evoked potential is a reliable objective technique for diagnosing the latent and misrouting of this condition. The aim of this study was to use and evaluate the importance and accuracy of a single channel PVEP instead of common multichannel PVEP for detecting asymmetric responses between the latent and misrouting albinism and control group. In this cross sectional study, the pattern visual evoked potentials were measured using 60 min/arc check sizes with temporal frequency of 3 Hz in twenty four suspected albino people ages of 5 to 43 years [mean age of 19 years]. Amplitude and latencies time were measured for both the right and left, and then the results were compared with an age- and gender matched, normal group. The latency waves of N75, P100, N135 and P1N1 [N75-P100] amplitude between two eyes of the albino people showed a statistically significant difference. The asymmetric responses of PVEP between two of the albino people were significantly larger than than control group. There is a strong relation between asymmetric responses of single channel PVEP and other clinical signs of albinism, which make this method as a useful objective technique for diagnosing the latent albinism
ABSTRACT
To evaluate the effect of Hyperopia, Myopia and Astigmatism on measurement of color vision, we experimentally induced refractive errors by positive, negative and cylinder lenses and estimated this effect on measurement of color vision. From one hundred patients referred to optometry clinic, sixty subjects with distance corrected or uncorrected visual acuity of 6.6, and without any ocular pathology were selected. Color vision was measured by D15 test before and after introducing 2 to 14 diopter positive lenses, 4 to18 diopter minus lenses and 2 to 10 diopter positive cylinder lenses, to induce Hyperopia, myopia and astigmatism respectively. The age was between 15 to 45 years. Although the decrease in color vision [or increase in the mean errors] was significant by introducing 4 to 14 positive, 8 to 18 minus and 4 to 10 cylinder, but it was not statistically significant by introducing 3 D positive lenses, 3D cylinder lenses and 4 D minus lenses. Induced 4 D or more myopia and astigmatism reduces color vision measured by D-15 test. But induced 8D or more Hyperopia can cause reduction in color vision measurement? On the other hand myopia and astigmatism less than 4 diopters, and hyperopia less than 8 diopters have no effect on the measurement of color vision
ABSTRACT
Variations in sterioacuity may be used in an assessment of intermittent exotropia. Intermittent exotropia is divergent squint of eyes that is worsened due to daily visual tasks and its resultant tiredness therefore the amount of deviation increases. The purpose of this study is to determine the effect of daily work and resultant tiredness on near sterioacuity among intermittent exotropic patients. In this cross-sectional study, 600 dormitory students of Mashad University of Medical Sciences, ranging in age from 21 to 23 years, examined with alternate cover test to diagnose intermittent exotropic cases. 30 students had intermittent exotropia and along with 15 normal cases constituted the case-control group. Sterioacuity was measured twice, in the morning and at night, with Randot-SO 001 test. Suppression was checked with Bagoloni striate lens and 4 prism diopter base out test. Data were statistically analyzed with SPSS software [version 13]. The measured deviation in intermittent exotropic cases showed a significant difference between the deviation in the morning and late at night among 23.33% [7 cases] [P=0.00]. In addition, sterioacuity decreased significantly at night, [P=0.00] among these cases. Despite the increase in the deviation among 53.3% [16 cases] at night, steriacuity was not changed significantly. 23.33% [7 cases] did not show any changes in the morning and at night, both in deviation amount and sterioacuity measurement. In most intermittent exotropic cases, there is no significant correlation between intermittent exotropia and near sterioacuity variations after daily work and resultant tiredness [P<0.696]
ABSTRACT
Color blindness is a common disorder. The congenital type of tcolor blindness is sex-linked and the genes are located on the X chromosome. The prevalence of color blindness among males and females are 5-8% and 0.5%, respectively. Color blindness may affect daily activities and could be considered as a disability. Therefore, the aim of this study was to investigate the prevalence of color blindness and its effect on contrast sensitivity and depth perception among school children in Mashhad. Four thousand four hundred school children [2408 males and 1992 females] were selected randomly and tested by Ishihara for color blindness detection. At the second step, students with color blindness were examined at optometry clinic by the Ishihara test again. Two hundred students were also selected randomly to allocate into a control group. Cambridge and Titmouse tests were taken on the case and control groups. Among 4400 schoolchildren, 3% suffered from color blindness [5.1% in boys and 0.4% in girls]. Ishihara test showed 2.2% deuteranopia, 0.8% protanopia and 0.6% suspect. The results indicate that the congenital color blindness has no significant effect on contrast sensitivity and depth perception. The present report provides valuable information regarding color vision defectiveness among schoolchildren. Effective detection of this anomaly is expected to prevent from substantial effects on their education and future job. It is strongly recommended to perform color vision test at the beginning of a child's education
ABSTRACT
To determine the prevalence rates of refractive errors in Mashhad, Iran. In this population-based study, random cluster sampling was performed on the urban population of Mashhad and of 4453 selected individuals, 70.4% participated in the study. Refractive errors were assessed using cycloplegic refraction in participants who were 15 years of age. The prevalence of myopia and hyperopia in individuals 15 years of age was 22.36% [95% CI: 24.66 to 20.06] and 34.21% [95 CI: 36.85 to 31.57], respectively. The prevalence of astigmatism and anisometropia were 25.64% and 5.84, respectively. Astigmatism and anisometropia were significantly more [p=0.005] and less [p=0.048] prevalent in females, respectively. Anisometropia, astigmatism and hyperopia were found to be increased with age. This study highlighted the valuable information on refractive errors in Mashhad. Hyperopia was the most common refractive error. In addition to subjects who were between 5 to 15 years of age, refractive errors were also prevalent among older people; therefore, more attention should be paid to the correction of refractive errors in these groups
ABSTRACT
Amblyopia is a relatively common condition in which visual acuity through an eye is subnormal despite no overt pathology. Pattern visual evoked potential [PVEP] can detect any defect from optic nerve to occipital cortex and pattern electroretinogram [PERG] can detect retinal defects specially the ganglion layers. This study was performed to evaluate the cortical and retinal activity in strabismic and anisometropic amblyopia. PVEP and PERG were recorded simultaneously in 40 amblyopes [20 strabismics and 20 anisometropics] and 20 normal control subjects. Normal subjects were age and sex matched with patients. The P100 latency in PVEP was increased in both groups of patients but the P100 amplitude was reduced only in anisometropic group. In PERG, the amplitude of P50 was reduced in all patients with no significant change in latency. Beside reduced PVEP responses in strabismic and anisometropic amblyopia, the activity of retina reduced too. It is likely that retinal impulses can affect the development of visual system
Subject(s)
Humans , Male , Female , Evoked Potentials, Visual , Anisometropia , Strabismus , Visual AcuityABSTRACT
Refractive errors [myopia, hyperopia and astigmatism] could lead to an impaired quality of life affect a large proportion of the population worldwide, irrespective of age, sex and ethnic group. Such refractive errors can be easily diagnosed, measured and corrected with spectacles or other refractive corrections to attain normal vision. Since there is paucity of information in school children in Iran we aimed to investigate the distribution pattern of refractive status and prevalence of refractive errors in school-age children in Shiraz. A random sampling strategy in geographically defined clusters was used to identify children aged 6-15 years in Shiraz between 2008-2209. We carried out a school survey and actual eye examinations, including visual acuity measurements, stereopsis examination, anterior segment and eyeball movements, fundus examinations, and cycloplegic retinoscopy with 1% cyclopentolate. Of 3065 selected individuals, 2683 were participated in the study [response rate 86.6%]. According to cycloplegic refraction, 4.85% [95% [CI], 3.52 to 6.16] of the primary and middle school students were myopic and 4.64% [95% CI, 3.52 to 6.19] were hyperopic. For high school students, these rates were 22.19 and 11.4% respectively. Myopia and hyperopia were shown to be correlated with age. Prevalence of anisometropia, amblyopia and strabismus were 2.51%, 2.31[95%CI 1.51-3.11] and 1.83% [95%CI 1.15-2.50]. Compared to other published reports, the rate of myopia in the school children of Shiraz seems relatively high
Subject(s)
Humans , Child , Adolescent , Prevalence , Students , Visual Acuity , Myopia/epidemiologyABSTRACT
To determine the effect of occluding a normal eye on visual acuity, contrast sensitivity and stereopsis in amblyopic school children. Amblyopic children from primary schools of region 2 in Mashhad were identified and referred to Optometry Clinics of Mashhad Medical University through a screening program. Informed consent was obtained from the parents. All subjects underwent an ophthalmologic examination including visual acuity, subjective refractive error, biomicroscopy and funduscopy. Best-corrected visual acuity [BCVA], contrast sensitivity and stereopsis were measured by Snellen E chart, Cambridge low contrast chart and Titmus stereotest, respectively. All tests were repeated 2 weeks, 1 month and 3 months after initial examination. Of 1,947 children, 289 [14.8%] were amblyopic of whom 62 subjects were eventually enrolled for the study. BCVA in the amblyopic eye was less than 3/10 in 25.8% of subjects before treatment however all children had BCVA of 3/10 or better afterwards. Mean BCVA in amblyopic eyes significantly increased from 0.53 +/- 0.26 logMAR to 0.24 +/- 0.23 logMAR after 2 months of treatment [P<0.001]. Mean contrast sensitivity in amblyopic eyes was 68.3 before treatment which improved to 152.5, 138.2 and 198 after 2 weeks, 1 month and 2 months of treatment, respectively [P<0.001]. Contrast sensitivity may provide better assessment of visual function as compared to visual acuity. Changes in contrast sensitivity are more sensitive to occlusion therapy as compared to visual acuity. Therefore, contrast sensitivity may yield better evaluation of subclinical changes not detectable by testing visual acuity
ABSTRACT
For good stereopsis, the two retinal images should have similar clarity, shape, and size. Anisometropia is one of the factors which has affect on stereopsis. The purpose of this study was investigation of induced anisometropia effect on binocular function and stereopsis. In this semi experimental study, a total of 135 students from Zahedan University of Medical Sciences who had inclusion criteria were selected randomly. At the beginning of the work, the refractive errors of the subjects were determined and corrected with retinoscop and their stereopsis measured using T.N.O test. Subsequently, this hyperopic and myopic anisometropia induced by use of negative and positive spherical lenses [power 1, 2, 3 diopter] in trial frame in front of one eye and in each state stereopsis measured again. In agreement and against the rule astigmatic anisometropia induced by positive cylindrical lenses in 180 and 90 degree axes and stereopsis measured again. Data were analyzed by SPPS. 14 software using within subjects factorial and repeated measurement ANOVA test. This study showed that both type and amount of anisometropia had significant effect on stereopsis [P<0.001]. The mean of stereopsis before intervention was [36.42 +/- 12.65]. The most and least reduction of stereopsis were related to 3D hyperopic anisometropia [339.42 +/- 125.1] and 1D with the rule astigmatic anisometropia [36.57 +/- 12.6], respectively. The mean of stereopsis before and after different type and amount of induced anisometropia were significantly different [P<0.001]. The result of this study showed that with increasing of anisometropia, stereoacuity decreases. Therefore, low degree of anisometropia, even 1D, can decrease both stereopsis and binocular function and thus, the amendment of stereopsis is necessary
Subject(s)
Humans , Depth Perception , Vision, Binocular , Refractive ErrorsABSTRACT
This study was designed to determine the role of intraocular lens implantation in visual acuity and contrast sensitivity in pseudophakic patients. This case control study was done in the year 2004 in Mashhad Ophthalmology Center of Khatam- al- Anbia. with convenience sampling method based on object visual acuity and contrast sensitivity in 85 pseudophakic patients [110 eyes] with a mean age of 63.83, and 20 age - matched phakic subjects [40 eyes] were compared. The visual acuity and contrast sensitivity at distance after correction of refractive disorders were measured by Snellen chart and Cambridge Low Contrast grating chart at 6 meter. Individual data, surgery date, visual acuity, and contrast sensitivity were gathered in a questionnaire and analyzed by descriptive statistics and frequency distribution tables. Statistical test showed that the best corrected visual acuity in IOL group had no significant difference from that in the phakic group [p=0.36]. But the contrast sensitivity reduces in the pseudophakic group comparing with the phakic group [p=0.004]. These patients often complain of blur vision, despite of good visual acuity. Contrast sensitivity reduced significantly with increase of age in both groups of normal and pseudophakic patients. No improvement in contrast sensitivity and visual acuity was found over the time [P[va]=0.174, P[cs]=0.257]. This study showed that intraocular lenses could provide good visual acuity for distance but there was slight reduction in contrast sensitivity. Contrast sensitivity test is an important tool for evaluation of visual function; especially age related changes or intraocular differences, which may not have been detected by visual acuity tests
ABSTRACT
Binocular vision anomalies are the most common visual problems that are along with several symptoms such as headache, asthenopia, and pain in the eyes, intermittent diplopia, intermittent blur vision, print swimming and other symptoms. Because of high prevalence of these anomalies a regular examination and visual screening program including on some tests for assessment and determination of these anomalies is necessary. The aim of this study was assessment of relationship between near point of convergence [NPC] and near binocular vision symptoms. In this cross sectional study 124 students of different majors in paramedical and health faculty of Mashhad University of medical sciences that had inclusion criteria were studied. The subjects were selected using simple random sampling. The subjects were divided to two groups [with and without symptoms] according to their own reporting. Visual acuity, refractive errors and NPC were determined using snellen chart, retinoscopy [cyclopentolat 1% if necessary] and small isolated letter [E] of approximately 20/30 [6/9] size from snellen reduced chart. The data were analyzed by SPSS version 13 using descriptive and analytical [Mann-Withney test and ROC curve] statistics. The subjects were 60% [75] female and 40% [49] males. In this study 61.1% [82] and 33.9% [42] of subjects were with and without symptom respectively. The mean of NPC in with and without symptoms group were 11.7 +/- 6.01 and 8.4 +/- 3.95 centimeters respectively. The difference in near point of convergence was statistically significant in the two groups. The cut-off point of NPC was determined 9.5 cm using ROC curve. According to high prevalence of binocular vision anomalies especially in students, determination of NPC has an important role in differentiation of symptomatic from asymptomatic subjects. Hence, NPC is suggested to be evaluated specially in persons that have long near vision tasks. Cut-off point 9.5 cm is suggested to binocular vision screening
Subject(s)
Humans , Male , Female , Convergence, Ocular , Accommodation, Ocular , Vision Disorders , Cross-Sectional StudiesABSTRACT
Some studies have shown that eyes undergo a hyperopic shift after the presbyopia, whereas others have reported a myopic shift. The purpose of this study was to determine types and the degree of refractive errors before and after presbyopia. This was a cross sectional study carried out at the department of optometry[Mashhad University of Medical Sciences] in2001.Followingroutineoptometricexamination, the type and degree of refractive errors of 500 patients before and after presbyopia were statically analyzed using X[2] and student t-tests. The prevalence of hyperopia was 19.4% before presbyopia which later increased to40.1% [p<0.001]. Following the occurrence of presbyopia, against-the-rule astigmatism increased to 12.3% whereas the with-the-rule astigmatism decreased to 12.9% [p<0.001]. The distribution of oblique astigmatism was3.7%and3.4%beforeandafter presbyopia, respectively. The gender had no effect on refractive errors before and after presbyopia. The presbyopia caused a reduction in optical power of eyes and also increase dhyperopia. Reduced rigidity of the upper tarsal plate associated with presbyopia, caused an increase in the against-the-rule astigmatism