In order to understand how the biomechanical properties of rabbit cornea change over time after corneal ablation, 21 healthy adult rabbits were used in this study, with the left eye as experimental side and the right eye as the control side. Firstly, a lamellar knife was used to remove a portion of the anterior corneal surface tissue (30%~50% of the original corneal thickness) from the left eye of each rabbit, as an animal model simulating corneal refractive surgery. Secondly, postoperative experimental rabbits were kept for one, three, or six months until being euthanized. Strip specimens were produced using their corneas in vitro to perform a uniaxial tensile test with an average loading-unloading rate of approximately 0.16 mm/s. Finally, the visco-hyperelastic material constitutive model was used to fit the data. The results showed that there was a significant difference in the viscoelastic parameters of the corneas between the experimental and the control eyes at the first and third postoperative months. There was a difference in tangential modulus between the experimental and the control eyes at strain levels of 0.02 and 0.05 at the third postoperative month. There was no significant difference in biomechanical parameters between the experimental and the control eyes at the sixth postoperative month. These results indicate that compared with the control eyes, the biomechanical properties of the experimental eyes vary over postoperative time. At the third postoperative month, the ratio of corneal tangential modulus between the experimental and the control eyes significantly increased, and then decreased. This work lays a preliminary foundation for understanding the biomechanical properties of the cornea after corneal refractive surgery based on rapid testing data obtained clinically.
Objective To observe the distribution of macular thickness and its relationship with axial length, gender, refraction status and race in six-year-old children. Methods 1543 six-year-old children from 34 schools in Sydney were randomly selected. The thickness of center macula（CM）, inner macula（IM）and outer macula（OM）were measured by optical coherence tomography（OCT）, the differences of macular thickness between different genders and races were comparatively analyzed. The axial length and refraction status of all children were measured by IOL Master and autorefractor RK-F1 respectively. Results The CM, IM and OM thickness of all those six-year-old children were normally distributed，on average they were 193.6, 264.3 and 236.9 mu;m respectively,the differences were statistically significant（t=0.40,0.08,0.20;P＜0.05）. The CM,IM and OM average thickness was 194.2,264.9,229.0 mu;m for boys and 189.3,262.5,231.5 mu;m for girls respectively. CM and IM thickness of boys were thicker than those in girls（t=0.15,0.11;P＜0.05）. The CM,IM and OM average thickness was 196.0,265.2,237.5 mu;m for White kids,186.0,262.3,236.5 mu;m for East Asia kids and 19.4,263.7,233.8 mu;m for Central East kids respectively. The CM and IM thickness of White and Central East children were significantly thicker than East Asia children (t=0.12,0.15;Plt;0.05）. There was no difference between these three races in OM thickness（t=0.16,P=0.6）. The IM and OM were thinner with longer axial length (Plt;0.05). The CM,IM and OM thickness was thicker with higher hyperopic degrees (Plt;0.05). Conclusions Macular thickness was normally distributed in six-year-old children and was significantly affected by gender, race, axial length and refraction status.
Objective To observe visual field outcome and refractive status of patients with retinopathy of prematurity (ROP) treated by laser photocoagulation. Method The data of 39 ROP patients (73 eyes) who received laser photocoagulation were retrospectively analyzed and compared with 13 normal control subjects (25 eyes) whose age and sex were matched with ROP group. There were 24 males (45 eyes) and 15 females (28 eyes) in ROP group, with an average age of (7.0±1.28) years. The first laser treatment was carried out at postnatal age (PA) of (38.74±3.82) weeks, the birth weight (BW) of (1402.33±369.61) g and the number of laser burns was (517.86±277.40). The control group included 7 females (13 eyes) and 6 males (12 eyes), with an average age of (7.17±0.96) years. The age (t=0.691) and gender (χ2=1.425) were comparable between the two groups (P=0.491, 0.233). The data of patients and controls were retrospectively analyzed including best corrected visual acuity, refractive examination, automated perimetry test. The differences of the mean deviation (MD) of visual field and the spherical equivalent (SE) between these two groups were comparatively observed. ROP patients were divided into no VF loss group (MD≤2 dB) and VF loss group (MD＞2 dB), mild VF loss group (MD≤6 dB) and moderate VF loss group (MD＞6 dB) according to the results of automated perimetry test, the differences of gestational age (GA), PA, BW, number of laser burns and SE between these groups were comparatively observed. Results The MD in ROP group and control group were 4.87±5.12 dB and 1.27±3.34 dB, respectively; the difference between the two groups was statistically significant (t=–4.01,P＜0.001). The subgroup analysis showed that BW, number of laser burns, and SE were significantly different between no VF loss group and VF loss group (t=2.074, –1.996, –2.162;P=0.042, 0.026, 0.034); while the GA was not significantly different between these two groups (t=1.973,P=0.052). The difference of PA was not statistical significant different between mild VF loss group and moderate VF loss group (t=2.03,P=0.051) and SE was significantly different between the above two groups (t=3.283,P=0.002). For refractive outcomes, the BW and ROP stage correlated with SE significantly (r=–0.304, –0.387;P=0.015, 0.002). The mean BCVA in ROP group was 0.84±0.23, and 59 eyes (91.2%) with BCVA better than 0.5. Conclusion Laser treatment for ROP tends to have less effect on long term refractive status and VF loss, with good visual outcome.
ObjectiveTo explore the distribution of choroidal thickness and its influence factors in university students.MethodsA cross-sectional study. A total of 896 eyes of 896 college students were included in the study. Among them, there were 350 males (350 eyes) and 546 females (546 eyes). All the eyes were right eyes. The average age was 19.18 ± 1.36 years old. According to the spherical equivalent refraction (SER), the eyes were divided into non-myopia group, low myopia group, moderate myopia group and high myopia group, which were 59, 251, 356 and 230 eyes, respectively. The subfoveal ChT (SFCT) was measured using a swept-frequency source optical coherence tomography scanner. According to the ETDRS, the choroid within 6 mm of the fovea was divided into three concentric circles centered on the fovea of the macula, which were the central area with a diameter of 1 mm, the inner ring area of 1-3 mm and the outer ring area of 3-6 mm. The outer ring area of 3-6 mm has a total of 9 zones. The inner ring and outer ring 4 regions were superior, inferior, nasal and temporal, respectively. The distribution characteristics of ChT in different regions, genders and diopter groups were observed. Bivariate correlation analysis were used to analyze the correlation of ChT and SER, axial length (AL).ResultsThe average SFCT of 896 eyes was 221.28±67.35 μm. The mean SFCT of males and females were 227.20±69.38 and 217.50±65.80 μm, respectively. The difference of SFCT between different genders was statistically significant (t=2.075, P=0.038). Compared with the central region ChT, there was no significant difference in ChT between the outer ring and the outer region (t=0.086, P=0.932). The difference of ChT in other regions was statistically significant (t=-21.973, -5.818, 36.328, -3.065, -18.017, -10.595, 57.007; P＜0.001, ＜0.001, ＜0.001, ＜0.002, ＜0.001, ＜0.001, ＜0.001). In the horizontal direction, ChT gradually thickens from nasal to temporal (F=2 251.558, P＜0.001); in the vertical direction, ChT gradually decreases from superior to the central, but have a little increased from central to inner inferior, then decreased to outer inferior again (F=45.425, P＜0.05). Correlation analysis showed that SFCT was negatively correlated with AL (r=0.478, P＜0.01) and a negative correlation with axial length (r=?0.395, P＜0.01), and positively correlated with SER (r=0.478, P＜0.01). SFCT decreased by 12.29 μm for every in myopic refractive error of 1 D, or by 20.14 μm for every increase in AL of 1 mm.ConclusionsChT is changed by different location. The horizontal direction is gradually thickened from nasal to temporal. The vertical direction is thicker than the center. The inferior inner ring area is thicker than the outer ring area. Gender, SER and AL are the influencing factors of SFCT.
Purpose To investigate the influence of ametropia on stereopsis and its mechanism by using the disparity evoked potential testing. Methods A new set of static random dot stereograms was utilized as a stimulation to elicit the disparity evoked potentials in 21 ametropes and 40 stereo normal subjects. Rezults The P250 wave,which was related to stereoscopic stimulation in ametropes,was recorded in both the ametropes and emetropic stereo normal persons in this series,and the characteristic changes of P250 wave with increasing visual disparity in ametropes were similar to those in normal subjects.The differences of mean amplitudes and latencies of P250 waves between myopes and hyperopes were not significant. Conclusion Ametropia in full correction dose not significanly affect the function of stereopsis. (Chin J Ocul Fundus Dis,1998,14:225-227)
Purpose To investigate the association between the macular volume and thickness, as assessed by optical coherence tomography (OCT), with refraction state and axial length (AL) in children. Methods A total of 100 normal children whose right eyes were randomly selected were divided into five groups due to their refraction, comprising hyperopia, emmetropia, low myopia, moderate myopia, high myopia. The AL of the eyes was measured by IOL mas ter measuring machine. Then the macular volume and thickness were measured by OCT. Results Children with high myopia have smaller macular volume and thinner parafoveal retinal thickness (especially out-ring macular). The minimum thickness and average thickness of the fovea were not significantly different among the five groups. The macular volume ,total average macular thickness and quadrant-specific macular thickness(except the nasal inner quadrants) were positively associated with refraction and negatively associated with AL, while t here were no correlation between minimum foveal thickness, the average foveal th ickness and refraction or AL. Conclusions In Chinese children, increasing axial length was associated with reduced macular volume and thickness (except the foveal region and the nasal inner quadrant). (Chin J Ocul Fundus Dis,2008,24:114-117)