正视和近视青少年对比度视力与像差的关系

目的 比较初发性近视、进展性近视以及正视青少年明、暗环境下对比度视力（CVA）的差异,及其与像差和瞳孔的相关性.方法 横断面群组研究.58名年龄为12～16岁的青少年根据屈光状态及近视发生时间分为3组：正视组18人,等效球镜度（0.00±0.20）D;初发性近视21人,等效球镜度（-1.03±0.33）D;进展性近视19人,等效球镜度（-2.67±0.77）D.记录受试者左眼CVA、瞳孔直径和全眼波前像差.采用配对t检验、重复测量方差分析、单因素方差分析和Pearson相关分析对获得的数据进行处理.结果 初发性近视组的CVA低于进展性近视组和正视组（F=199.17、234.54,P＜0.01）,在低对比度（25％、10％）和暗环境下更为明显.3组青少年受试者明环境下全眼总像差（除去一阶和二阶离焦）、高阶像差、四阶球差以及彗差的均方根值[分别为（0.205±0.108）μm、（0.101±0.057）μm、（0.028±0.039）μm 以及（0.066±0.056）μm],低于暗环境下的各像差值[分别为（0.599±0.257）μm、（0.355±0.141）μm、（0.148±0.122）μm 以及（0.195±0.034）μm],差异具有统计意义（t=14.94、16.71、7.89、6.28,P＜0.05）.在同一亮度环境下,近视组像差与正视组之间差异无统计学意义.除明环境100％对比度下,CVA与总高阶像差存在负相关关系（r=-0.275,P＜0.05）外,其余情况下,CVA与高阶像差、瞳孔之间不存在相关性.结论 初发性近视者CVA低于进展性近视和正视者,差异在低对比度和暗环境下更明显.初发性近视CVA的下降与视网膜成像质量下降无直接关系,可能为皮层因素起主导作用.     

青少年正视眼与近视眼调节微波动的差异及其与波前像差的关系

背景 人眼在观察外界的物体时,调节反应呈现出持续波动状态.青少年阶段是近视发生和发展的关键时期,通过研究这一人群的调节微波动的特点及眼球像差的分布情况,将有助于我们理解近视的发生和进展.目的 研究持续阅读情况下青少年正视眼与近视眼调节微波动的差异及其与眼球像差之间的关系,探讨产生微波动差异的原因及其对近视发生和发展的影响.方法 前瞻性对照研究.纳入2010-2011年在温州医科大学附属眼视光医院进行定期眼科常规检查的12～15岁青少年54人,包括正视者19人和近视者35例,受试者均进行扩瞳后客观和主觉验光,然后根据受试者近2年来近视屈光度的变化情况将近视眼分为初发性近视组18例和进展性近视组17例.受试者分别在25、33和50 cm距离处阅读计算机显示屏上的文字,使用WAM-5500红外验光仪测量受试者阅读过程中的调节反应和调节微波动,每个注视距离检测5 min.将测得的调节反应值经频谱傅里叶分析后将微波动能量按频率划分为低频段组分(LFC) (0 ～0.6 Hz)、中频段组分(MFC)(0.6～0.9 Hz)和高频段组分(HFC)(1.0～1.4 Hz)进行计算和分析.采用i-Trace波前像差仪测量受试者全眼像差,用Humphrey角膜地形图仪采集和计算角膜像差,比较正视眼组、初发性近视组和进展性近视组受试眼调节反应、调节微波动和波前像差的差异,对受试者调节指标与波前像差间的关系进行分析.结果 在25 cm和33 cm的阅读距离下,正视眼组调节反应值分别为(2.78±0.35)D和(2.19±0.27)D,明显高于进展性近视组的(2.44±0.33)D和(1.89±0.35)D,差异均有统计学意义(P=0.002、0.003).受试者的LFC、MFC及HFC随阅读距离的缩短而增加,差异均有统计学意义(F阅读距离=8.480、14.270、21.400,均P＜0.01),但仅LFC值在3个组间总体差异有统计学意义(F分组=4.115,P＜0.05),其中进展性近视眼组LFC能量高于正视眼组,差异均有统计学意义(25 cm:P=0.044;33 cm:P=0.038;50 cm:P=0.032),3个组间MFC以及HFC值的差异均无统计学意义(F分组=0.859、0.682,均P＞0.05).在25 cm和33 cm阅读距离下,LFC值与角膜彗差、眼内彗差、全眼总高阶像差和眼内总高阶像差间均呈正相关(均P＜0.05),而MFC和HFC与像差间均无明显相关性.结论 青少年正视眼的调节反应强于进展性近视眼,而正视眼和初发性近视眼调节微波动能量小于进展性近视眼.近距离阅读下,调节微波动中仅LFC能量与人眼的高阶像差相关.     

快速序列视觉呈现方式阅读状态下不同屈光组调节反应的差异

目的研究快速序列视觉呈现方式（rapid serial visual presentation．RSVP）阅读状态下进展性近视、稳定性近视和正视之间调节反应的差异，探讨调节因素在近视发生、发展过程中的表达。方法45例受试者参加本实验，分为进展性近视、稳定性近视和正视组，各15例。阅读材料为位于距受试者左眼角膜平面25cm处的电脑显示屏上的一篇中文短文．通过RSVP软件呈现单个字符．字体大小为9pt，文字呈现速度为150字／min。使用SEIKO—WV500自动验光仪测量其开放视野阅读状态下左眼的调节反应。结果所有受试者在4D的调节刺激下，均存在一定程度的调节滞后，个体差异较大。进展性近视组的调节反应低于正视组[（2．32±0．43）0VS（3．19±0．53）0，P〈0．01]，进展性近视组的调节反应亦低于稳定性近视组[（2．32±0．43）0VS（3.07±0．34）D，P〈0．01]，而正视组和稳定性近视组差异无显著性（P=0．441）。结论近距离阅读状态下进展性近视有较高的调节滞后，远视性离焦造成的模糊斑可能是近视的发生发展的促成因素，随着近视发展的稳定．调节反应恢复至一般水平。     

反应性AC/A等眼动参数在迟发性近视中作用的研究

目的探讨调节和辐辏的关系在迟发性近视发生发展中的作用和机制。方法本研究对象为34例在校大学生,其中包括11例正视者和23例迟发性近视者（-2．00- -6．00D,迟发性稳定性近视者14例、迟发性进展性近视者9例）。眼动参数测量包括远、近距隐斜、调节反应、调节性辐辏及正、负相对调节,对每组的反应性、计算性AC／A等眼动参数进行分析比较。结果迟发性进展性近视组的反应性AC／A明显高于正视组或迟发性稳定性近视组（P〈0．05）,而计算性AC／A的差异则无统计学意义（P〉0．05）;在高需求时（3．00D视标）,正视组的调节反应A均明显高于迟发性进展性、稳定性近视组（P〈0．05）;远近隐斜、正相对调节的各组资料均服从近似正态分布（P〉0．05）,迟发性近视组和正视组的远、近隐斜及负相对调节差异无统计学意义（P〉0．05）,但迟发性近视组的近隐斜较正视组有内隐斜倾向,迟发性近视组的正相对调节其绝对值显著低于正视组（P〈0．05）。结论调节、辐辏及其相互作用在迟发性近视发生发展中起重要作用,反应性AC／A为关键参数,高反应性AC／A的迟发性近视者在近距工作时存在视网膜成像离焦倾向。     

不同阅读距离的调节反应在近视发生发展中的表达

目的检测近视眼在不同距离调节刺激下的调节反应等参数。研究其在正视眼、稳定性近视眼和进展性近视眼中的表达。方法38名志愿者，根据屈光状态分组，测量在不同调节刺激下的调节反应（AR）和调节性辐辏（AC／A），并分析结果。结果进展性近视组的AR／AS斜率显著低于正视组（P〈0．05），进展性近视组的AC／A高于正视组和稳定性近视组（P〈0．01）。进展性近视组在高调节刺激水平（2D，3D）下所表现的调节反应显著低于正视组（P〈0．05）。结论进展性近视组在高调节需求下有较低的调节反应，较高的调节滞后导致视网膜模糊像，长期的视网膜模糊像可能是引发眼轴近视化发展的主要因素。     

调节滞后与青少年近视的关系

目的 探讨调节滞后与近视的关系以及与近视进展的关系，双眼调节与单眼调节的不同。方法 56例青少年受试者分成三个组：稳定的近视（n=20）、进展的近视（n=21）、正视（n-15），戴框架镜矫正屈光不正，用双眼分光检影装置分别测定三组在单眼、双眼注视离角膜顶点35cm、20cm距离视标时的调节反应。结果 ①进展的近视调节滞后大于稳定的近视和正视组（P〈0．01），稳定的近视眼与正视眼的调节滞后差异无显著性（P〉0．05）。②双眼调节大于单眼调节，双眼调节滞后小于单眼调节滞后（P〈0．01）。③20cm距离的调节滞后大于35cm距离的调节滞后（P〈O．01）。结论 近视眼进展与调节滞后存在一定的联系，调节滞后随着调节需要的增加而增大，双眼调节优越于单眼调节。     

青少年近视在不同阅读距离调节状态下眼前段结构的变化

目的分析和探讨不同程度青少年近视在不同阅读距离诱导的调节状态下眼前段结构的变化。方法收集我院屈光门诊14～18岁间青少年近视95例（95眼），正视眼34例（34眼）作对照，其中男66例，女63例。所有被试者行主觉验光、调节幅度测定，眼前节OCT测量在不同阅读距离诱导的调节状态下（OD、3D、6D）的前房深度、晶状体厚度及瞳孔直径，采用SPSS11．5forWindows行统计学分析。结果①在调节放松情况下，随着近视度数增加，暗瞳直径明显减小（P〈0．05），各组间晶状体厚度差异无显著性，前房深度差异有显著性（P〈0．05）。（D随着阅读距离的减小，调节运用的增加，各组前房深度变浅值、晶状体厚度变厚值、暗瞳直径变小值均显著增加（P〈0．01）。③随着近视度数增高，诱发3D调节时前房深度变浅值显著增加（P〈0．01），晶状体厚度变厚值明显增加（P〈0．05），暗瞳直径变小值差异无显著性。④随着近视度数增高，诱发6D调节时前房深度变浅值显著增加（P〈0．01），晶状体厚度变厚值明显增加（P〈0．05），暗瞳直径变小值显著增加（P〈0．01）。结论在青少年中，随近视程度加深，阅读距离减小，运用调节量的增加可引起眼前房显著变浅，晶状体明显变厚：暗瞳直径缩小值在诱发6D调节时随近视度数增高而增大。     

进展性近视与正视儿童眼调节功能特征比较

目的：比较儿童进展性近视眼与正视眼的调节功能特征,探讨调节对近视的潜在影响。方法：病例对照研究。选择2015年12月至2016年5月于温州医科大学附属眼视光医院就诊的68例儿童,进展性近视组[（等效球镜度（SE）≤-0.75 D）]与正视组（+0.50 D≥SE≥-0.50 D）各34例,测量内容包括主观调节幅度、远距调节灵活度及调节刺激-反应曲线（ASRC）。采用独立样本t检验比较2组间调节功能的差异。结果：正视组、进展性近视组SE分别为（0.18±0.28）D、（-2.88±1.03）D,差异有统计学意义（t=-16.72,P<0.001）。进展性近视组的主观调节幅度低于正视组（t=-2.22,P=0.03）。2组间的远距调节灵活度与ASRC斜率差异均无统计学意义（t=-0.82,P=0.41;t=1.58,P=0.12）。进展性近视组和正视组在0～6 D调节刺激范围的调节滞后面积分别为（7.35±1.54）D2 、（6.48±1.05）D2 （t= 2.74,P=0.01）;且在不同调节刺激水平下（1、2、3、4、5 D）,进展性近视比正视眼的调节滞后量大（t=2.40、2.78、2.79、2.49、2.12,P<0.05）。而进展性近视组在6 D刺激水平的调节滞后量比正视组稍高,但差异无统计意义（t=1.83,P=0.07）。结论：儿童进展性近视眼的调节反应特征与正视眼不完全一致,其中进展性近视眼的调节滞后量高于正视眼,提示调节滞后可能在近视发生中具有一定的作用。     

近距离计算机工作对不同类型近视眼波前像差的影响

背景 近视眼近距离工作时存在的调节异常及高阶像差均与视网膜图像模糊相关,因此研究稳定性和进展性近视眼近距离工作前后高阶像差的变化具有重要意义. 目的 观察进展性近视和稳定性近视在近距离工作,如计算机工作前后高阶像差的变化,同时评估不同类型近视眼高阶像差的变化.方法 采用病例对照研究设计.60例受试者按年龄、性别匹配的原则进入进展性近视组及稳定性近视组,每组各30例.使用框架眼镜矫正屈光不正,然后持续使用计算机1h,阅读距离为40 cm,暗环境、自然最大瞳孔状态下使用COAS波前像差仪测量右眼计算机工作前后的波前像差,分别导出3、4、5 mm瞳孔直径下各阶像差的变化,分析计算机工作和近视类型对波前像差的影响,各阶高阶像差(3～6阶)以均方根(RMS)表示.结果 直径3、4、5 mm瞳孔下受试者使用计算机工作前后高阶像差的差异均无统计学意义(均P＞0.05).直径3mm瞳孔时进展性近视和稳定性近视的高阶像差RMS差异均无统计意义(均P＞0.05);直径4 mm瞳孔下进展性近视3、5、6阶RMS和总高阶RMS显著高于稳定性近视,差异均有统计学意义(F=5.985,P=0.016;F=3.975,P=0.049;F=8.130,P=0.005;F=6.493,P=0.012);直径5 mm瞳孔下进展性近视3、5、6阶RMS和总高阶RMS显著高于稳定性近视,差异均有统计学意义(F=13.132,P=0.000; F=4.032,P=0.047;F=4.393,P=0.038;F=10.508,P=0.002).各瞳孔直径下进展性近视组球差均大于稳定性近视组,但差异均无统计学意义(P＞0.05).结论 进展性近视眼高阶像差大于稳定性近视眼,但近距离工作,如从事计算机工作,不引起近视眼高阶像差的显著变化.     

早发性近视和迟发性近视张力性调节的比较

目的:通过一种测量张力性调节的方法,了解迟发性近视、早发性近视和正视眼的张力性调节表现。探讨张力性调节与近视的相互关系。方法:志愿参加本实验者54例,正视组18例,屈光度(-0.25～ 0.50)D之间,早发性近视组18例,平均为(-6.50±2.40)D,迟发性近视组18例,平均为(-3.00±1.75)D。在完全黑暗的环境下,用偏振光游标式调节检测仪对受试者进行张力性调节的测量,比较迟发性近视、早发性近视和正视眼的张力性调节的差异。结果:在缺乏任何视觉刺激的状态下,调节处于一定的静息状态,所有受试者张力性调节的平均值为(0.90±0.76)D。其中正视组的张力性调节平均为(0.80±0.64)D,早发性近视组的张力性调节为(1.32±0.80)D,迟发性近视组的张力性调节平均为(0.62±0.46)D。早发性近视的张力性调节高于正视组和迟发性近视组的张力性调节,差异有非常显著性(P<0.001);正视组和迟发性近视组的张力性调节,差异无显著性(P>0.05)。结论:早发性近视者有较强睫状肌的基础张力水平,易导致牵拉眼球而使近视进展。     

Variability of the accommodation response in early onset myopia.

PURPOSE: Hyperopic retinal defocus (blur) is thought to be a cause of myopia. If the retinal image of an object is not clearly focused, the resulting blur is thought to cause the continuing lengthening of the eyeball during development causing a permanent refractive error. Both lag of accommodation, especially for near targets, and greater variability in the accommodative response, have been suggested as causes of increased hyperopic retinal blur. Previous studies of lag of accommodation show variable findings. In comparison, greater variability in the accommodative response has been demonstrated in adults with late onset myopia but has not been tested in children. This study looked at the lag and variability of accommodation in children with early onset myopia. METHODS: Twenty-one myopic and 18 emmetropic children were tested. Dynamic measures of accommodation and pupil size were made using eccentric photorefraction (PowerRefractor) while children viewed targets set at three different accommodative demands (0.25, 2, and 4 D). RESULTS: We found no difference in accommodative lag between groups. However, the accommodative response was more variable in the myopes than emmetropes when viewing both the near (4 D) and far (0.25 D) targets. Since pupil size and variability also varied, we analyzed the data to determine whether this could account for the inter-group differences in accommodation variability. Variation in these factors was not found to be sufficient to explain these differences. Changes in the accommodative response variability with target distance were similar to patterns reported previously in adult emmetropes and late onset myopes. CONCLUSIONS: Children with early onset myopia demonstrate greater accommodative variability than emmetropic children, and have similar patterns of response to adult late onset myopes. This increased variability could result in an increase in retinal blur for both near and far targets. The role of accommodative variability in the etiology of myopia is discussed.     

Accommodative lag before and after the onset of myopia

PURPOSE: To evaluate accommodative lag before, during the year of, and after the onset of myopia in children who became myopic, compared with emmetropes. METHODS: The subjects were 568 children who became myopic (at least -0.75 D in each meridian) and 539 children who were emmetropic (between -0.25 D and +1.00 D in each meridian at all visits) participating between 1995 and 2003 in the Collaborative Longitudinal Evaluation of Ethnicity and Refractive Error (CLEERE) Study. Accommodative lag was measured annually with either a Canon R-1 (Canon USA., Lake Success, NY; no longer manufactured) or a Grand Seiko WR 5100-K (Grand Seiko Co., Hiroshima, Japan) autorefractor. Subjects wore their habitual refractive corrections while viewing a letter target accommodative stimulus of 4 D (either in a Badal system or at 25 cm from the subject, designated Badal and near, respectively) or of 2 D (Badal only). Refractive error was measured with the same autorefractor in subjects under cycloplegia. Accommodative lag in children who became myopic was compared to age-, gender-, and ethnicity-matched model estimates of emmetropic values for each annual visit from 5 years before, through 5 years after, the onset of myopia. RESULTS: In the sample as a whole, accommodative lag was not significantly different in children who became myopic compared with model estimates in emmetropes in any year before onset of myopia for either the 4-D or 2-D Badal stimulus. For the 4-D near target, there was only a greater amount of accommodative lag in children who became myopic compared with emmetropes 4 years before onset (difference, 0.22 D; P = 0.0002). Accommodative lag was not significantly elevated during the year of onset of myopia in any of the three measurement conditions (P < 0.82 for all three). A consistently higher lag was seen in children after the onset of their myopia (range, 0.13-0.56 D; P < 0.004 for all comparisons). These patterns were generally followed by each ethnic group, with Asian children typically showing the most, African-American and white children showing the least, and Hispanic children having intermediate accommodative lag. CONCLUSIONS: Substantive and consistent elevations in accommodative lag relative to model estimates of lag in emmetropes did not occur in children who became myopic before the onset of myopia or during the year of onset. Increased accommodative lag occurred in children after the onset of myopia. Elevated accommodative lag is unlikely to be a useful predictive factor for the onset of myopia. Increased hyperopic defocus from accommodative lag may be a consequence rather than a cause of myopia.     

近视儿童调节滞后与隐斜状态及相关因素研究

目的 研究近视儿童近距注视下的调节滞后和隐斜量,分析近视儿童调节滞后与近隐斜的关系及相关因素.方法 受试者为250名近视儿童,等效球镜屈光力范围为-0.50～-5.25D.采用MEM动态检影法测量受试者右眼近距的调节滞后;分别采用Howell测量法(HT)和改良Thorington测量法(MTT)测量近隐斜;通过问卷调查受试者父母的屈光状态.各重复测量三次,取均值.结果 受试者近距调节滞后为(+0.97±0.43)D,近隐斜为(-0.94±4.55)△(外隐斜,HT)和(-1.71±4.85)△(外隐斜,MTT).伴近内隐斜者占28.0％(HT)和22.8％(MTT).伴近内隐斜者的调节滞后和内隐斜呈正相关(r=0.353,P=0.003,HT;r =0.461,P＜0.001,MTT);受试者调节滞后和近视程度呈负相关(r=-0.241,P＜0.001).23％近视者父母均为近视,其调节滞后显著大于其父母组儿童(F =4.90,P=0.009).结论 近视儿童在近距注视状态下调节滞后较高.近隐斜状态和遗传因素都可能影响近视儿童的调节滞后,调节滞后量与近视程度可能存在相互作用.临床上应将近距调节反应和隐斜测量纳入儿童的常规视功能检查项目.     

儿童和青少年近视调节功能的临床分析

目的 探讨发病早期的儿童和青少年近视的调节功能状态,分析主导眼和非主导眼的调节功能水平.方法 应用动态检影法和移近法分别测量50例发病1～2年的学龄期儿童和青少年近视患儿调节滞后和调节幅度;同样方法测量20例正视儿童和25例远视屈光不正患儿;检测其主导眼和非主导眼.结果 近视患儿的主导眼和非主导眼的调节幅度和调节滞后与正视儿童均差异无统计学意义;而其主导眼和非主导眼的调节幅度比远视患儿明显更大(t=2.21,P=0.03＜0.05;t=2.83,P=0.006＜0.05);两组的调节滞后差异无统计学意义.50例近视患儿主导眼和非主导眼的调节滞后值分别为(0.73±0.31)D和(0.81±0.38)D,主导眼和非主导眼间差异有统计学意义(t=2.14,P=0.038＜0.05);调节幅度分别为(13.39±3.51)D和(13.26±3.60)D,差异无统计学意义.95例观察对象(近视、正视和远视患儿)的主导眼的调节滞后度为(0.68±0.36)D,非主导眼调节滞后度为(0.75±0.34)D,主导眼和非主导眼间的差异有统计学意义(t=2.06,P=0.042＜0.05);主导眼调节幅度(12.9±3.09)D,非主导眼为(12.6±3.09)D,差异无统计学意义(t=1.49,P=0.14).结论 发病早期的儿童和青少年近视的调节滞后值和调节幅度与正视儿童无明显差别;调节幅度比远视儿童的更大.儿童和青少年主导眼的调节滞后比非主导眼的更小,进行调节滞后相关研究时应注意主导眼和非主导眼的区别.     

短时间平板电脑游戏对青少年近视患者调节反应和调节微波动的影响

背景 近距离使用电子平板设备是造成近视发生和进展的危险因素之一,研究此类设备对人眼调节系统的影响可能为近视防控提供新的思路. 目的 观察短时间进行平板电脑游戏前后青少年近视患者的调节反应值、调节微波动以及瞳孔直径的变化. 方法 采用前瞻性系列病例观察研究方法,纳入2014年8月至2015年4月于北京大学人民医院就诊的60例青少年近视患者,患者平均年龄(11.6±2.6)岁,平均等效球镜屈光度(SER)为(-2.38±1.08)D.采用随机数字表法将60例受试者随机分成不同游戏时间组,分别进行3、5和10 min iPAD电脑平板游戏,采用开放视野红外验光仪记录受试者游戏前后的瞳孔直径和调节数据,将采集的调节数据减去理论调节反应值计算为实际调节反应值,以实际调节反应值的均方根(RMS)作为调节微波动幅度,采用一维离散傅里叶变换法分析调节反应曲线的频谱特征.采用配对t检验对各组游戏前后的调节反应值、调节微波动幅度以及瞳孔直径进行比较.采用Wilcoxon符号秩检验对各组游戏前后调节反应曲线的高频信号占总信号功率百分比进行分析.结果 10 min组受试者游戏后的调节反应值为(0.74±0.27)D,明显低于游戏前的(0.81±0.29)D,差异有统计学意义(t=2.263,P=0.036),而3 min组和5 min组受试者游戏前后的调节反应值差异均无统计学意义(均P＞0.05).10 min组受试者游戏后调节微波动幅度(RMS)为(0.31±0.08)D,较游戏前的(0.27±0.09)D明显增加,差异有统计学意义(t=-2.259,P=0.036),而3 min组和5 min组受试者游戏前后的调节微波动幅度差异无统计学意义(均P＞0.05).3个组受试者游戏后调节微波动高频信号均高于游戏前,其中5 min组和10 min组受试者游戏前后高频信号比较差异均有统计学意义(Z=-2.213、-2.016,均P＜0.05).3个组受试者游戏后瞳孔直径较游戏前均缩小,其中5 min组和10 min组受试者游戏前后瞳孔直径的差异均有统计学意义(t=2.428,P=0.026;t=2.515,P=0.021). 结论 青少年近视患者进行短时间平板电脑游戏并不加重调节滞后,但是调节微波动幅度增加及调节反应曲线高频信号成分的增加均可能导致图像模糊,对控制近视进展不利.     

Aberrations and myopia

It has been suggested that high levels of axial aberration or specific patterns of peripheral refraction could play a role in myopia development. Possible mechanisms involving high levels of retinal image blur caused by axial aberrations include form deprivation through poor retinal image quality in distance vision, enhanced accommodative lags favouring compensatory eye growth, and an absence of adequate directional cues to guide emmetropization. In addition, in initially emmetropic eyes, hyperopia in the retinal periphery may result in local compensatory eye growth, which induces axial myopia. Evidence in support of these ideas is reviewed and it is concluded that, for any fixed pupil diameter, evidence for higher levels of axial aberration in myopes in comparison with other refractive groups is weak, making involvement of axial aberrations in myopization through image degradation at the fovea unlikely. If, however, some potential myopes had unusually large pupil diameters, their effective aberration levels and associated retinal blur would be larger than those of the rest of the population. There is stronger evidence in favour of differences in patterns of peripheral refraction in both potential and existing myopes, with myopes tending to show relative hyperopia in the periphery. These differences appear to be related to a more prolate eyeball shape. Longitudinal studies are required to confirm whether the retinal defocus associated with the peripheral hyperopia can cause patterns of eyeball growth which lead to axial myopia.     

Blur sensitivity in myopes.

PURPOSE: This study compared the ability of myopes and emmetropes to detect subjectively the presence of retinal defocus. METHODS: Subjects (12 myopes, 12 emmetropes) were cyclopleged and monocularly viewed a bipartite target through an appropriate near addition lens via a 2-mm artificial pupil. One-half of the target remained fixed while the other half was alternatively moved forward or backward until subjects first reported a difference in clarity between the two halves of the target. RESULTS: The mean blur threshold for the emmetropes and myopes was +/-0.11 and +/-0.19 D, respectively (p = 0.0001). CONCLUSIONS: These results demonstrate that myopes are less sensitive to the presence of blur, and may at least partially explain why previous reports have demonstrated a larger lag of accommodation in this refractive group. Additionally, the hyperopic retinal defocus resulting from the increased accommodative error may play a significant role in myopia development and progression.