ABSTRACT
Evaluation of the corneal curvature, central thickness and volume three months after fitting the Rigid Gas Permeable [RGP] contact lens in keratoconic eyes. Corneal topography maps of 25 keratoconic eyes with a negative history of using the RGP lens were evaluated by Oculus Pentacam. Corneal curvature in both surfaces of the cornea, central corneal thickness and corneal volume were evaluated before and three months after fitting the aspheric RGP lens. Three months after using the contact lens, decrease in central corneal thickness [-3.43 micro m, P=0.127], decrease in flattest anterior corneal surface power [-0.43D, P=0.339], decrease in anterior corneal steep power [-1.54D, P=0.358], decrease in posterior corneal flat power [-0.1D, P=0.121], an increase in posterior corneal steep power [0.02D, P=0.710] and an increase in corneal volume [0.27 mm[3] P=0.331] were not statistically significant. Lack of significant changes in corneal topographical parameters three months after using the RGP lens may indicate the non progressive nature of keratoconus in this period. Further studies with longer follow-up periods are suggested to obtain more accurate results
ABSTRACT
Convergence insufficiency [CI] is one of the most important binocular vision disorders. Because there is no previous report on CI prevalence in an Iranian population, the purpose of this study is to estimate the frequency of CI in a population of 18 to 30 years old university students in the rehabilitation faculty of Iran University of Medical Sciences. 160 students aged 18 to 30 years [mean +/- SD = 21.7 +/- 2.8 age] that had no glasses or had worn glasses or contact lenses>/= 1 month with corrected or uncorrected visual acuity of 20/30 or better in both eyes and uncorrected refractive error less than or equal to -0.5 D to + 1.00 D, or /= 10 cm, exophoria at near >/=4 delta more than far measurements, insufficient fusional convergence amplitude according to sheard criterion, normal amplitude of accommodation according to Hofstetter formula [minimum age appropriate amplitude of accommodation= 15- 0.25 x age in years]. The prevalence of CI was calculated based on the abovementioned data. Regardless of accommodative condition, 10% of the study population showed CI disorder. 25% of this population showed lower amplitudes of accommodation compared to the normal accommodative values. Indeed, 7.5% were CI and 2.5% were pseudo CI. The results of the present study demonstrated a high frequency of CI in population of university students. Because of the symptoms of CI during near work activities such as reading and using computer, screening and applying appropriate treatments seem to be essential
ABSTRACT
Optic neuritis causes some deficits in visual function in the affected eye and there are some differences in these functions between the affected and unaffected eyes. The purpose of the study is to compare visual functions of both eyes to demonstrate the minimum and maximum value of affection in patients with acute unilateral optic neuritis. Thirty patients [23 female, 7 male aged between 18 and 45 years] who 22 patients with retro-bulbar and 8 patients with anterior optic neuritis, enrolled in the study and their affected and unaffected eyes underwent visual function assessments. Visual acuity [VA], contrast sensitivity [CS], color vision [CV], and visual field [VF] [consist of MA and PSD] were examined for both eyes of all the patients and the significance of the differences between two eyes were calculated and compared by Independent T-test. According to our results, all the investigated visual functions consist of VA [t-test, t=7.29, P=0.00], CS [t-test, t=9.20, P=0.00], CV [t-test, t= -21.95, P=0.00], MD [t-test, t=5.29, P=0.01] except PSD [t-test, t=0.67, P=0.71] were affected by optic neuritis and there was a significant difference between the affected and unaffected eyes [P<0.01]. The most significant difference were found for contrast sensitivity with letters [P=0.00] and there wasn't any significance in the difference between two eyes for PSD parameter in VF [P=0.71]. Considering the most significant difference of contrast sensitivity between affected and unaffected eyes in patients with acute unilateral optic neuritis, it is suggested to pay more attention to the test in evaluating, diagnosis and follow up patients with acute unilateral optic neuritis
Subject(s)
Humans , Female , Male , Visual Acuity , Vision, Ocular , Sensitivity and Specificity , Diagnostic Techniques, Ophthalmological , Optic Neuritis/pathology , Contrast SensitivityABSTRACT
Comparison of pachymetry pattern of OCT finding in Keratoconus [KCN] suspect and normal subjects. Thirty-two KCN suspect eyes and Thirty- eight normal eyes in young subjects [20-30 year- old] were evaluated. Pachymetry pattern of frequency domain OCT [Visante] in different parts of cornea [thinnest point, inferior - superior thickness difference, inferior temporal - superior nasal thickness difference and thinnest point in 0-2 millimeter decent ration] were measured. There was a significant [p<0.0001] difference in normal and KCN suspect patients in all measurements. KCN suspects showed thinner cornea and more differences in corneal thickness measurements. Anterior frequency domain OCT seems to be suitable for evaluation of KCN suspect patients. It may be critical for refractive surgery candidate and may be used as Pentacam or OrbScan corneal imaging systems
ABSTRACT
Corneal sensitivity is one of the indicators for corneal health which may be affected by some factors such as age and geographical area. The purpose of this study was to measure normal central corneal sensitivity in different age groups with healthy cornea in Tehran. Central corneal sensitivity of the right eye of 596 volunteers [age ranged 15-81] was measured using a Cochet-Bonnet aesthesiometer. Subjects were divided into six age groups of 1-6 based on age ranges of 15-25, 26-35, 36-45, 46-55, 56-65 and >65 years, respectively. All measurements were performed by the same optometrist in 18 degrees of centigrade temperature, 35% humidity and between 2-5 p.m. There was a significant main effect of age group [f=92.22, p=0.000]. There was statistically significant difference of central corneal sensitivity among all age groups [p
ABSTRACT
To evaluate optometrist and ophthalmologist approach in KCN diagnosis. A questionnaire was introduced randomly to Iranian ophthalmologist and optometrist in two national and international congresses. The questionnaire consisted of 16 questions that some of them has related to KCN early diagnosis and lens fitting. Cronbach's Alpha was 0.594 in ophthalmologists and 0.603 among optometrist groups. 36.2% of optometrists and 18% of ophthalmologists believed that retinoscopic reflex is very important in KCN diagnosis. Bio-microscopy was believed to be important in 53.7% of optometrists and 48.7% of ophthalmologists. Corneal imaging was important in early diagnosis of KCN 55.8% of optometrists and 57.7% of ophthalmologists. Most of optometrists believed that retinoscopy is most important in KCN diagnosis. Both groups believed that bio-microscopy and corneal imaging are very important in KCN diagnosis. Educational courses should be considered for contact lens fitting, both for optometrists and ophthalmologists. Regular congresses and symposiums may be recommended
ABSTRACT
To evaluate the effect of vertical prism induced stress on binocular visual evoked potentials. Using checkerboard stimulus patterns in two spatial frequencies [SFs] of 0.48 cpd as a low SF and 2.18 cpd as a moderate SF reversing with temporal frequency of 4 Hz, the effect of increasing visual stress using vertical prisms of 0, 1, 2 and 3 prism diopters on binocular visual evoked potentials was investigated. The project was performed on 23 participants [11 male and 12 female] with normal binocular visual function, i.e., vertical prism vergences and stereo acuities were within normal limits. The amplitude and latency of N75, P100 and N135 components were measured during different vertical prism induced stresses in all cases. To compare mean amplitude and latency with different vertical prism induced stresses, the repeated measure ANOVA statistical method was used. The amplitude of N75, P100 and N135 components showed reduction as a function of vertical prism induced stress at both low and moderate SFs [P<0.001]. This reducing trend was more severe with increasing intensity of prism stress, while the latency of these components showed an increase as a function of vertical prism induced stress at both low and moderate SFs [P<0.001]. Based on clinical findings, ocular symptoms are caused by the vertical prism induced stress; in visual evoked potential as a paraclinical test, amplitude and latency of all components of the VEP wave, are affected by this stress
ABSTRACT
Optical blur due to refractive errors causes reducing retinal image quality and induces changes in how visual system responds. The purpose of this study was to evaluate the effect of myopic optical blur on visual cortex response by functional magnetic resonance imaging [fMRI]. Five healthy volunteers with various degrees of myopia and age range 18-25 years [two females and three males] participated in this study. The results of functional magnetic resonance imaging of 18 emmetropic people [without refractive error] participated in a recent fMRI study with the same scanning conditions were applied as the control data. The functional scans were obtained by a Phillips scanner using a sine-wave grating visual task with spatiotemporal frequency of 2cpd/8Hz. The percentage of BOLD [Blood-Oxygen-Level-Dependent] signal change and number of activated voxels in different scan series were compared with each other after image processing. Non-linear reduction of visual cortex response due to increasing optical blur was observed in this study. The number of activated voxels and the percentage of BOLD signal change were both reduced in different amounts of myopia. Considering the effect of optical blur on visual cortex responses in different amounts of myopia, it is better to provide the optimum optical correction during cognitive neuroscience fMRI research and FMRI study of neurologic diseases using patterned visual stimuli
ABSTRACT
The brain response to temporal frequencies [TF] has been already reported, but with no study reported for different TF with respect to various spatial frequencies [SF]. fMRI was performed by 1.5T GE-system in 14 volunteers during checkerboard, with TFs of 4, 6, 8 and 10Hz in low and high SFs of 0.5 and 8cpd. Average percentage BOLD signal change demonstrated the amplitude of the fMRI response to different TFs was maximal in 6Hz for high SF of 8cpd, while, it was maximal at TF of 8Hz for low SF of 0.5cpd. The results are useful for vision therapy [such as the treatment of Amblyopia] and visual task selecting in fMRI studies
Subject(s)
Humans , Male , Female , Magnetic Resonance Imaging , Photic Stimulation , Vision, OcularABSTRACT
The brain response to temporal frequencies [TF] has been already reported. However, there is no study on different TF with respect to various spatial frequencies [SF]. Functional magnetic resonance imaging [fMRI] was done by a 1.5 T General Electric system for 14 volunteers [9 males and 5 females, aged 19'26 years] during square-wave reversal checkerboard visual stimulation with different temporal frequencies of 4, 6, 8 and 10 Hz in 2 states of low SF of 0.4 and high SF of 8 cycles/degree [cpd]. All subjects had normal visual acuity of 20/20 based on Snellen's fraction in each eye with good binocular vision and normal visual field based on confrontation test. The mean luminance of the entire checkerboard was 161.4 cd/m2 and the black and white check contrast was 96%. The activation map was created using the data obtained from the block designed fMRI study. Pixels with a Z score above a threshold of 2.3, at a statistical significance level of 0.05, were considered activated. The average percentage blood oxygenation level dependent [BOLD] signal change for all activated pixels within the occipital lobe, multiplied by the total number of activated pixels within the occipital lobe, was used as an index for the magnitude of the fMRI signal at each state of TF and SF. The magnitude of the fMRI signal in response to different TF's was maximum at 6 Hz for a high SF value of 8 cpd; it was however, maximum at a TF of 8 Hz for a low SF of 0.4 cpd. The results of this study agree with those of animal invasive neurophysiologic studies showing SF and TF selectivity of neurons in visual cortex. These results can be useful for vision therapy and selecting visual tasks in fMRI studies
Subject(s)
Humans , Male , Female , Photic Stimulation , Visual CortexABSTRACT
Purpose: to evaluate the effect of prism induced heterophoria including esophoria and exophoria on binocular visually evoked potentials [BVEP]
Methods: esophoria and exophoria were induced with base-in and base-out prisms, respectively. Binocular visual evoked potentials for different heterophoia values were recorded using pattern reversal visual stimuli with a 6.5 min arc check size. Amplitude and latency of P[100] component of the potential waves were evaluated
Results: the present study showed that heterophoia significantly causes increase in latency of BVEP, P[100] and decrease in amplitude of P[100] peak [p<0.001]
Conclusion: BVEP may be a useful technique to evaluate and measure heterophoria values, namely BVEP phorometry