[Comparative study of the effect of pilocarpine and tropicamide eye drops on corneal topography]

This study was conducted to evaluate the effect of contraction and relaxation of ciliary muscle caused by pilocarpine and tropicamide eye drops on corneal radius, central corneal power and corneal astigmatism. This prospective study was performed on sixty normal and healthy eyes of sixty volunteers with a mean age of 38.19 year [range 18 to 49 years] and without any ocular pathology. Volunteers divided into 2 groups of thirty, in the first group corneal topography of both eye were measured before and 30 minutes after instillation of topical tropicamide 0.5% in only one eye, and the other eye was the control eye and no drop was given. In the second group, the same routine was performed, except that subject received on drop of pilocarpine 1% in one eye. Statistical comparison between groups for the central corneal power, corneal radius and corneal astigmatism were performed using paired t test. In group 1, no significant changes were found in corneal radius, power and astigmatism, however, in group 2 subjects who have received pilocarpine eye drop, mean corneal radius value decreased significantly by 0.05 mm and mean corneal power increased by a plus power of + 0.32 D. There was no significant change in corneal astigmatism in both groups. It seems that pilocarpine induced ciliary muscle contraction which may cause pressure on corneal limbus of cornea and scleral spur that resulted in changes in corneal curvature. But tropicamide eye drop did not affect corneal radius and other corneal parameters and corneal topography can be carried out after instillation of tropicamide eye drop

[Evaluation of pattern reversal visual evoked potential components in albinism]

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

[Evaluation of depth perception and heterophoria among laboratory sciences students in Mashhad, 2011]

Normal stereopsis as the highest level of binocular vision is required for most of clinical works such as working with microscope and some jobs, like piloting and surgery. The aim of this study was to evaluate, depth perception and hetrophoria in Mashhad laboratory sciences students in 2011. In this cross sectional study from 153 Mashhad laboratory sciences students, 42 subjects were selected randomly. Eye examinations including subjective and objective refraction and measurement of hetrophoria by cover test and prism bar were performed. The stereopsis was then determined with the T.N.O stereo test at 40 distance observation. Data were analyzed using SPSS version 11.5 software. Patients with amblyopia, cataract, and other ocular pathology were excluded from the study. Mean stereoacuity of the subjects was 147/14 +/- 129/76. Among this population, 14 subjects [%33.3] used microscope monocularly and 28 subjects [% 66.7] used it bionocularly. There was no significant difference between mean stereopsis and hetrophoria and other relative effective factors such as refractive error, way of using microscope, near point of convergence age and sex [p>0.05]. Comparison between mean monocular and binocular stereopsis was not significant [p>0.05]. There was no statictically significant difference between mean stereopsis and hetrophoria and other relative factors. However due to working too much with microscope, most of the laboratory sciences students had anomaly of binocular vision like intermittent exotropia and abnormal near point of convergence. This indicates the necessity of more research in anomaly of binocular vision in laboratory sciences students

[Evaluation of the effect of daily work and resultant tiredness on near steroacuity in intermittent exotropic patients]

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]

[ prevalence of congenital color blindness and its effect on contrast sensitivity and depth perception]

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

Simultaneous pattern visual evoked potential and pattern electroretinogram in strabismic and anisometropic amblyopia

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

[Effect of age on stereopsis]

To evaluate the effect of age on stereopsis. We evaluated stereoacuity using TNO and titmus test after full correction of refractive errors in 87 randomly selected subjects aged 5-80 years. There was a significant relashionship between stereopsis and age such that stereoacuity increased with aging [ANOVA, P<0.001]. Stereopsis decreases with aging and therefore age of the patient should be considered in this regard

[ prevalence of refractive errors in a Mashhad, Iran]

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

[ prevalence of visual problems in school children, Shiraz, Iran]

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

[Effect of occlusion therapy on visual acuity, contrast sensitivity and stereopsis in amblyopia]

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

[Age- and gender-specific prevalences of refractive errors in an elderly population in Mashhad]

To determine the prevalence of refractive errors among elderly residents of Mashhad during 2006 based on age and gender. Through proportionate cluster random sampling, urban residents of Mashhad aged 55 years or more were invited to attend the Vision Clinic of Mashhad Medical University for an eye examination including autorefraction and subjective refraction. Of 1,540 invited persons, 1,440 persons [response rate= 92.5%] participated in the study of whom 1,367 individuals including 883 [64.6%] male and 484 [35.4%] female subjects with mean age of 63.7 +/- 7.1 [range 55-92] years were examined. The prevalence of myopia was 27.2% [95% confidence interval [CI], 24.8-29.5%] overall, 29.6% in men and 22.5% in women [P<0.001]. The rate of myopia showed an increase with age [P<0.001]. The prevalence of hyperopia was 51.6% [95%CI, 48.9%-54.3%] overall, 48.3% in men and 57.6 in women [P<0.001]. The rate of hyperopia showed a significant decrease with age [P=0.009]. The overall prevalence of astigmatism was 37.5% [95% CI, 34.9-40.0%]. Refractive errors are a major issue among the elderly and their prevalence rates varies greatly depending on age and gender

[Prevalence of amblyopia in school children in Mashhad]

To determine the prevalence of amblyopia and its determinants in students of region 1 in Mashhad, 2006. Using randomized cluster sampling, 2510 students were selected to undergo ophthalmologic examinations. Amblyopia was defined as corrected visual acuity of 8/10 or less in either eye. Of the 2510 selected student, 2150 were examined [85.6% participation rate]. The prevalence of amblyopia was 1.9% [95% confidence interval [CI], 0.94 to 2.9] including 2.1% in female and 1.7% in male subjects [P=0.620]. Amblyopia was detected in right eye in 31.7%, left eye in 41.5% and both eyes in 26.8%. About 66% of amblyopic cases had refractive errors. The prevalence of amblyopia in students of region 1 in Mashhad is comparable to that of other parts of the country. Refractive error is a significant risk factor for occurring amblyopia

[Visual acuity and contrast sensitivity in pseudophakic patients after cataract surgery]

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

Abnormal Cambridge low-contrast grating sensitivity results associated with diabetic retinopathy as a potential screening tool

Contrast sensitivity is proposed as a potential screening tool for the early detection of diabetic retinopathy. A cross-sectional study was performed in a tertiary referral university eye centre. A total of 80 diabetes patients were recruited and tests were performed on 154 eyes. Contrast sensitivity was checked using Cambridge low-contrast grating. Abnormal contrast sensitivity was observed in 27.1% of eyes with diabetic retinopathy, compared with 9.0% in unaffected eyes, a statistically significant difference. Cambridge low-contrast grating is a potential screening tool for early detection of diabetic retinopathy by non-ophthalmologistsp