The relationship between the Stiles–Crawford effect of the first kind (SCE-I) and myopia

The Stiles-Crawford effect of the first kind (SCE-I) was measured on both emmetropic and myopic subjects at six different retinal locations. The results revealed a number of significant discrepancies in receptor alignment between the groups of different refractive errors. In myopic subjects, the receptors in the nasal retina (i.e. between the fovea and the optic nerve head) were found to be aligned nasally towards the optic nerve head, whereas the receptors in the temporal retina were aligned towards the centre of the exit pupil. In emmetropic subjects, the receptors across the retina were finely tuned towards the centre of the exit pupil. The magnitude of the receptor displacement in myopic subjects was found to be directly associated with the length of the eyeball.     

正视眼屈光要素与年龄关系的研究进展

综述2002～2007年有关正视眼屈光要素的研究文献,主要通过PubMed和万方数据库,对“emmetropia”和“optical components”两词进行检索,在2002年1月～2007年1月期间共有研究文献1228篇。本研究重点复习和讨论不同年龄正视眼与屈光要素的关系、影响屈光要素的因素等问题。     

正视眼与近视眼角膜前表面非球面性的分析

目的探讨我国正视眼与近视眼中青年人群的角膜前表面非球性参数(Q值)的分布及其与屈光度的关系。方法随机选择18～44岁行准分子激光角膜屈光手术的低、中、高度近视及正视眼患者,各组均取40例(80眼)。应用AstraMax三维角膜综合检查站行角膜地形图检查,记录Q值,并进行统计学分析。结果正视眼Q值均数为-0.1028±0.0712;近视眼总体Q值均数为-0.1600±0.1700,呈正态分布;近视眼Q值与屈光度之间存在线性相关关系(F=9.6665,P=0.0021);正视眼与近视眼Q值总体差异有统计学意义(t=19.7241,P<0.001);高度近视组和低度、中度组间的差异均有统计学意义(q=4.0037,P<0.05;q=3.1218,P<0.05);低度、中度近视眼组间差异无统计学意义(q=0.8818,P>0.05)。结论我国近视人群的Q值呈正态分布,大部分人群角膜为长椭球形。Q值与屈光不正程度相关。近视眼角膜前表面形态较正视眼更趋于长椭圆非球面形。     

角膜生物力学及校正眼压与青少年屈光状态的相关性

目的：探讨7～18岁青少年角膜生物力学及校正眼压与屈光状态的内在关系。方法：横断面研究。 选择2017年11月至2018年2月于中山大学中山眼科中心屈光门诊就诊的中国青少年325例,年龄7～18 岁,等效球镜度（SE）-10.25～+16.50 D。采用IOLMaster测量眼轴长度（AL）,Corvis ST测量角膜生 物力学参数及生物力学校正眼压（bIOP）,Pentacam测量眼前节生物学参数。按照右眼SE将受检者 分为高度近视、中低度近视、正视和远视组。采用Pearson或Spearman相关分析SE与角膜生物力学 参数的相关性。用协方差分析比较4组的角膜生物力学参数差异,用方差分析比较4组间的bIOP差异。 结果：SE越偏向近视,第二次压平速率（VA2,r=0.180,P=0.001）越快,峰值距离（PD,r=-0.273, P<0.001）和形变幅度（DA,r=-0.167,P=0.002）越大。AL越长,PD（r=0.355,P<0.001）越大,VA2 （r=-0.138,P=0.021）越快。4组间PD（F=9.372,P<0.001）、DA（F=4.425,P=0.005）和VA2（F=4.961, P=0.002）的总体差异有统计学意义,进一步比较发现,PD、DA和VA2绝对值在高度近视、中低度 近视、正视、远视组间依次下降,差异均有统计学意义（均P<0.05）。高度近视组（102.04±19.59）和 中低度近视组（98.95±16.62）的角膜硬度参数（SP-A1）差异无统计学意义,但中低度近视组比正视 组（107.49±18.66,P=0.010）和远视组（108.98±20.20,P=0.004）的SP-A1低,差异有统计学意义。 眼压（IOP）和bIOP均与SE无相关性。结论：7～18岁青少年SE越偏向近视,角膜硬度越低。无论是 否校正角膜生物力学因素的影响,眼压均与屈光度无关。     

Static accommodative responses following adaptation to differential levels of blur

PURPOSE: To investigate the effects of two levels of blur adaptation on visual resolution and steady-state accommodation responses in emmetropes and myopes. METHODS: Eleven emmetropes (mean refractive error +0.01 +/- 0.31 DS) and 11 early-onset myopes (EOM, mean refractive error -4.44 +/- 1.64 DS) fixated monocularly at 4 m in three trials of 45 min duration with either: optimal refractive correction, +1 DS defocus, or +3 DS defocus. Monocular logMAR visual acuity (VA) was measured at 10 min intervals during each trial, and immediately following completion of the trial. Accommodative stimulus-response function (ASRF), refractive error and pupil size were measured before and after each trial. RESULTS: Blur adaptation was found to have no effect on pupil size or baseline refraction, irrespective of the power of the blurring lens. Adaptation to +1 DS of defocus yielded an improvement in VA of -0.16 +/- 0.07 logMAR and -0.17 +/- 0.11 logMAR in the emmetropes and myopes respectively. An improvement in VA of -0.20 +/- 0.18 logMAR in the emmetropes and -0.26 +/- 0.17 logMAR in the myopes was observed following adaptation to +3 DS of defocus. The changes in acuity became significant following 30 min of exposure to defocus. Blur adaptation was found to have no effect on the ASRF gradient or individual steady-state accommodative responses. CONCLUSIONS: Following blur adaptation, visual resolution was found to increase in both emmetropes and myopes. The magnitude of the blur level did not produce significantly different increases in resolution. Blur adaptation failed to affect either the steady-state responses to an accommodative stimulus or ASRF gradient.     

Analysis of refractive state ratios and the onset of myopia

PURPOSE: To develop formulae for the refractive state ratios, axial length growth and the age of onset (A*) of myopia. Calculated results are compared with measurements. METHODS: Using an image equation, the axial length in the ametropic state (L) is related to the length in the emmetropic state (L*) and refractive error (D) by a rate of change M (D mm(-1)). Three refractive state ratios are defined: C1 = L/r1, C2 = L/L* and C3 = L/H, where r1 and H are the anterior surface radius of the cornea and the transverse dimension of the eye, respectively. The age of onset A* is calculated by the rate of change of refractive error (M) and the axial growth rates N and N* in the ametropic and emmetropic states, respectively. RESULTS: The three ratios C1, C2 and C3 are increasing function of the myopia power, for example, C1 = 3.4, 3.1, 2.9 for D = -8, 0, +4 dioptres, respectively. The calculated C1* (for the emmetropic state) varies between 3.08 and 3.14, depending on corneal shape, and C3 = 0.985, 1.0, 1.04 for D = +3, 0, -3 dioptres: these values are consistent with measured data. For a typical system with effective focal length F = 22.25 mm, L* = 24.2 mm and L = 23.4, 24.9, 25.9 mm for D = +2, -2, -5 dioptres, respectively. The calculated rates of change of refractive error M = 2.3-2.9 D mm(-1) for F = 22-23 mm are also consistent with measured values 2.4-2.7 D mm(-1). The age of onset A* is calculated to be proportional to 1/(M dN), where dN = N-N* is the axial growth rate difference between the ametropic and emmetropic states and may be used as a better predictor for myopia onset than the conventional ratio L/r1. The A* is given by the crossing of L and L* curves, in which myopia onset occurs earlier for larger M dN. CONCLUSION: The theory provides formulae to calculate various refractive state ratios, which are consistent with measurements. By defining two rate functions, M and N, the onset of myopia can be predicted.     

Stiles-Crawford effect of the first kind (SCE-I) in post-photorefractive keratectomy and anisometropic subjects

The Stiles-Crawford effect of the first kind (SCE-I) was measured on both post-photorefractive keratectomy (PRK) and anisometropic subjects at six different locations of retina. The eye that underwent the PRK procedure showed results that were typical of myopic eyes, although the vision in that eye has been maintained at 6/5 (or 20/15) since the operation. The anisometropic subject had one eye that was emmetropic and the other eye was myopic with a refractive error of -3.00 DS. The emmetropic eye showed the normal well-centered SCE-I functions across the retina, whereas the myopic eye of the same subject showed the nasal tilting of receptors in the nasal retina, which has been the typical finding among myopic subjects.     

正视和近视儿童调节幅度的三种测定方法比较

目的分析正视和近视儿童用不同测量方法测量的眼调节幅度的差异(amplitude of accommodation,AMP)并初步探讨不同方法测量对眼AMP测量的影响。方法随机选取9岁~13岁的40例受试者,分为正视组(17例)和近视组(23例)。应用移近法、负镜片法和红外电脑验光仪法分别测定受试者的单眼AMP。结果①正视和近视儿童三种方法测量AMP值分别为:(14.13±2.16)D,(9.15±1.99)D,(7.36±1.23)D和(14.39±2.94)D,(9.79±1.65)D,(8.32±0.66)D。②在正视组移近法、负镜片法和红外视力计法测量的AMP值三者之间差异有显著性(P值分别为0.000,0.000,0.003),近视组三种测量方法之间的AMP差异也具有显著性(P值分别为0.002,0.002,0.036)。③正视组和近视组之间仅红外视力计法测量时两者AMP差异有显著性(P=0.006)。结论不同测量方法会影响AMP,使用移近法测量AMP倾向于高估AMP值,使用负镜片法及红外电脑验光测量的方法则倾向于低估AMP值。近视儿童的AMP与正视儿童的有一定的差异性。     

儿童正视眼与近视眼角膜地形图比较

目的 :研究儿童正视眼与儿童近视眼的角膜地形图特征并进行比较。方法 :应用计算机辅助的角膜地形图检测分析了 115只儿童正视眼和 115只儿童轻中度近视眼。结果 :儿童近视眼Simk2 值较正视眼高(P <0 .0 1) ,SF值较正视眼低 (P <0 .0 5 )。而角膜中心屈光度、Simk1值、CIM值两组差异无显著意义 (P >0 .0 5 )。结论 :儿童近视眼角膜垂直方向屈光度较正视眼明显增加 ,近视眼角膜周边变扁平的趋势相对不明显