Visual field does not affect steady-state accommodative response and near-work induced transient myopia

To investigate whether or not peripheral retinal defocus contributes to the refractive development of myopia by influencing the overall accommodative function. The steady-state accommodative stimulus response curve (ASRC) and the near-work induced transient myopia (NITM) after a near visual task were compared between different visual field conditions in emmetropes (EMMs), stable myopes (SMs) and progressing myopes (PMs). Results showed that visual field had no effect on the ASRC and NITM but PMs exhibited greater NITM than EMMs and SMs. The results of this study suggest that peripheral defocus does not influence the overall accommodative system so its probable contribution to myopia development is not via the accommodative system.     

Additivity of near work-induced transient myopia and its decay characteristics in different refractive groups

PURPOSE: To determine the additive effect, if any, of NITM after 1 and 2 hours of reading in different refractive groups. METHODS: Fifteen early-onset myopes (EOMs), 14 late-onset myopes (LOMs), and 15 emmetropes (EMMs), as well as progressive myopes (PMs) and stable myopes (SMs), were tested. Subjects read binocularly for 2 hours at a distance of 35 to 40 cm. Distance refractive state of the right eye was assessed every 2 seconds for 30 seconds after the first hour of reading, and then every 2 seconds for 120 seconds after the second hour of reading. NITM was calculated as the difference in posttask distance refractive state compared with the pretask distance refractive state after each hour. RESULTS: Initial NITM values (mean +/- SE) recorded at the end of the near work tasks were 0.22 +/- 0.03 D and 0.29 +/- 0.03 D for the EOMs, 0.14 +/- 0.02 D and 0.20 +/- 0.03 D for the LOMs, 0.14 +/- 0.02 D and 0.15 +/- 0.02 D for the EMMs, 0.20 +/- 0.03 D and 0.27 +/- 0.03 D for the PMs, and 0.09 +/- 0.04 D and 0.20 +/- 0.05 D for the SMs, after the first and second hours of reading, respectively. After the second hour, only in the EOMs and LOMs was NITM significantly greater than that found after the first hour. Seventy percent of the myopes (EOMs and LOMs) but only 47% of the EMMs exhibited increased NITM in the second hour compared with the first hour. Only EOMs exhibited longer decay duration after the second hour of reading. NITM was increased in progressive myopes (PMs), but not in stable myopes (SMs), after the first hour of reading only. Within the PMs, NITM was increased after the second hour compared with the first hour. The time constant for decay was greater in the PMs than in the SMs. Lastly, many myopes (up to 46%) did not experience decay to baseline after the near task over the 120-second posttask period. CONCLUSIONS: EOMs and LOMs demonstrated larger NITM than the EMMs and exhibited NITM additivity, but the EOMs also exhibited prolonged decay of NITM compared with the EMMs and LOMs. PMs, but not SMs, exhibited additivity of NITM. These findings may be attributed to impaired sympathetic function in the subjects with myopia. It is speculated that with repeated cycles of near work, residual NITM may contribute to the progression of permanent myopia.     

Differential refractive susceptibility to sustained nearwork

PURPOSE: A possible role for nearwork-induced transient myopia (NITM) (i.e. transient myopia at distance following sustained nearwork) in the development and/or progression of permanent myopia has been suggested. If certain refractive groups are more susceptible to NITM than others, then measures may be implemented to prevent or retard the occurrence of myopia in these individuals. In a recent study (Ciuffreda and Wallis, 1998), it was found that young-adult late-onset myopes (LOM) and early-onset myopes (EOM) were highly susceptible to this NITM accommodative after-effect, while emmetropes (EMMs) were only moderately susceptible, and hyperopes (HYP) were particularly insusceptible, following short periods (10 min) of sustained nearwork at a very close distance (20 cm, 5 D). In the current study, this was extended to encompass a much longer period of nearwork under more naturalistic conditions. METHODS: Young-adult subjects (n = 16) performed a reading task for a continuous period of 4 h at their habitual working distance under naturalistic conditions, i.e. binocular viewing with blur-related visual feedback present. Distance refractive state (binocular viewing) was assessed objectively using a Canon R-1 autorefractor immediately before (pre-task), every hour during the task, and immediately after (post-task) to assess NITM and its subsequent decay to pre-task refractive levels. Subjects were divided into the four refractive subgroups as above, which were each of equal size (n = 4). RESULTS: The NITM was induced in all subjects, except for the hyperopes in which there was a hyperopic refractive shift. The LOMs (0.12 D) and EOMs (0.13 D) were highly susceptible, while the HYPs were especially insusceptible (0.44 D hyperopia), and the EMMs were only moderately susceptible (0.09 D). CONCLUSIONS: The present study extended our earlier investigation by demonstrating the differential refractive susceptibility over a longer period of sustained nearwork, which may be the result of reduced sympathetic activation. It has been speculated that NITM may be a factor in myopigenesis, with a possible mechanism being time-integrated increased retinal defocus from NITM at both distance and near, in conjunction with the normal lag of accommodation during sustained nearwork, thereby causing axial elongation. Hence, a future longitudinal investigation specifically targeting this retinal defocus hypothesis is warranted.     

Dynamic accommodation and myopia.

PURPOSE: Accommodative effort during nearwork is thought to be a causative factor in the development of myopia. It has been proposed that an anomaly in autonomic control may be a precursor to the development of myopia. In the present study the closed-loop accommodation response after variations in fixation period was investigated in emmetropes, early-onset myopes and late-onset myopes to determine characteristics of reflex accommodation for each refractive group. METHODS: Closed-loop accommodation responses were measured in a group of emmetropes (n = 7), early-onset myopes (n = 7), and late-onset myopes (n = 7) by use of a dynamic tracking infrared optometer. A variation in fixation period (10 seconds, 60 seconds, and 180 seconds) before an accommodative step was used to stimulate the accommodation control mechanism differentially. RESULTS: Group results of accommodative response times showed that late-onset myopes were significantly affected by the duration of fixation before the change in stimulus vergence. Accommodative response times after 3 minutes of sustained near vision were significantly longer than those observed for other groups for the near-to-far condition. Reaction time appears to be independent of refractive grouping, prior fixation period, and direction of step change. CONCLUSIONS: Late-onset myopes showed significantly extended accommodation response times after a sustained near vision task that was demonstrable under well-controlled experimental conditions. The extended response times observed in the present study were consistent with previous reports of refractive shifts in late-onset myopes and early-onset myopes and provide a corollary between reflex and adaptive components of the accommodation response. Potential mechanisms are discussed in an attempt to explain the resultant hysteresis under closed-loop viewing conditions.     

The effect of common reductions in letter size and contrast on accommodation responses in young adult myopes and emmetropes.

PURPOSE: Accommodation errors during reading and the subsequent near work-induced transient myopia (NITM) that occurs have been implicated in the development and progression of myopia. This study investigated the effects of two letter variables, size and contrast, on accommodation accuracy during the near task and on NITM and its subsequent decay. These were varied so as to mimic what might occur when students photocopy and reduce reading materials. METHODS: Based on their refractive errors, young adult subjects (18-25 years) were classified into three groups: emmetropes (n = 19), stable myopes (n = 17), and progressing myopes (n = 17). Three print sizes (N4, N6, and N8) and two print contrasts (90% and 60%) were used to give six different reading targets. Targets were presented in random order at 25 cm (4 D demand) and the text read for comprehension for 3 minutes. For each target, accommodation accuracy and NITM and its decay were measured using the free space Shin-Nippon SRW-5000 autorefractor. RESULTS: When data for all subjects were pooled, there was a significant effect of letter size (p = 0.030) but not contrast (p = 0.898) on accommodation accuracy; however, differences were small and unlikely to be clinically relevant. NITM (p = 0.033) and its decay (p = 0.012) also varied with letter size. NITM was greater and decay longer for larger letters. We found no effect of refractive error group on accommodation accuracy. In contrast, there was a significant difference in the magnitude of NITM and its decay for emmetropic and myopic subjects (although no effect of progression status); myopes had larger NITM values and longer decay times to baseline than emmetropes (NITM myopes: 0.37 +/- 0.14D vs. emmetropes: 0.19 +/- 0.17 D, p = 0.005; decay time myopes: 15.12 +/- 6.58 seconds vs. emmetropes 7.10 +/- 4.82 seconds, p = 0.0045). The differences in NITM and its decay between the two refractive groups were of similar magnitude for all six combinations of letter size and contrast. CONCLUSIONS: Our data do not support the suggestion that common reductions in letter size or contrast of reading material (as might occur for photocopied reading materials) cause greater accommodation inaccuracy and greater near work-induced adaptation effects that would exacerbate myopia development in young adults.     

Adaptation model of nearwork-induced transient myopia

A nearwork model was developed to determine whether variation in accommodative adaptation gain, KA, can account for the differences in the dynamic decay timecourse following near work in hyperopes (HYP), emmetropes (EMM), early-onset myopes (EOM), and late-onset myopes (LOM). The model incorporated a proximal component into a previously-developed adaptation model of accommodation and vergence. It was used to simulate the nearwork-induced transient myopia (NITM) response following 10 min of congruent binocular near viewing (5 D, 5 MA). The accommodative adaptation gain, KA, value was varied from 1.0 to 6.0 in increments of 0.5. For the hyperopes, an additional constraint was imposed wherein the accommodative response was biased on the under-accommodated side of the deadspace operator (i.e., depth-of-focus). In addition, the effect of prolonged nearwork was simulated by alternating between 1 hr of congruent near viewing (3 D, 3 MA) and 5 min of congruent far viewing (0.25 D, 0.25 MA) over a 160 hr period representing one work-month with 40 hours of nearwork per week. The steady-state rms value of the accommodative error was measured as a function of KA. It was found that the NITM timecourses for HYP, EMM, EOM, and LOM could be simulated accurately using KA values of 2.0, 2.5, 4.0 and 5.5, respectively. The long-term final steady-state rms of the accommodative error was found to increase from 0.182 D to 0.188 D as KA increased from 1 to 6. This indicated a small and progressive increase in residual accommodative error for higher KA values, which was associated with EOM and LOM. Thus, NITM for the different refractive groups could be quantified by the accommodative adaptation gain element, with KA for the HYP, EMM, and EOM and LOM groups having lower, intermediate, and higher values, respectively. The larger rms for higher KA values suggests that a myopic individual may have a predisposition to exhibit a slightly larger long-term accommodative error, which may stimulate axial elongation and in turn promote the progression of axial myopia.     

阅读中文简体字与繁体字人眼短暂性近视量及其回退时间的差异

目的 研究正视人群与近视人群阅读中文简体字与繁体字时产生的短暂性近视的量,以及其回退时间的差异.方法 实验研究.随机选择18～28岁的近视者18人,等效球镜度为(-3.74±1.22)D;正视者18人,等效球镜度为(-0.14±0.22)D.应用Grand-Seiko WAM-5500分别测量阅读两种大小(12 pt;8 pt)中文简体字与繁体字4组视标短暂性近视的量及其回退时间,要求阅读距离40 cm(调节需2.5 D),每组视标阅读时间为5 min.结果 阅读繁体字,近视组的短暂性近视量为(0.61±0.34)D,大于正视组短暂性近视量(0.42±0.25)D (t=2.556,P＜0.05);近视组阅读繁体字短暂性近视的量为(0.61±0.34)D大于简体字短暂性近视的量(0.53±0.33)D (t=2.298,P＜0.05),正视组阅读两种不同字体差异无统计学意义(t=0.789,P＞0.05).阅读引起近视组短暂性近视回退时间为(15.88±19.53)s,大于正视组的短暂性近视回退时间(9.04±12.62)s,差异有统计学意义(t=2.555,P＜0.05);但阅读各组视标间近视组和正视组短暂性近视回退时间差异无统计学意义.结论 从短暂性近视方面研究,阅读中文繁体字与简体字引起的短暂性近视的量存在差异,近视组更容易受到阅读不同字体的影响,这种不同的阅读字体引起不同的短暂性近视量可能是近视发生率地域性差异形成的一种环境因素.     

Nearwork-induced transient myopia in preadolescent Hong Kong Chinese

PURPOSE: To compare the magnitude and time course of nearwork-induced transient myopia (NITM) in preadolescent Hong Kong Chinese myopes and emmetropes. METHOD: Forty-five Hong Kong Chinese children, 35 myopes and 10 emmetropes aged 6 to 12 years (median, 7.5), monocularly viewed a letter target through a Badal lens for 5 minutes at either 5.00- or 2.50-D accommodative demand, followed by 3 minutes of viewing the equivalent target at optical infinity. Accommodative responses were measured continuously with a modified, infrared, objective open-field autorefractor. Accommodative responses were also measured for a countercondition: viewing of a letter target for 5 minutes at optical infinity, followed by 3 minutes of viewing the target at a 5.00-D accommodative demand. The results were compared with tonic accommodation and both subject and family history of refractive error. RESULTS: Retinal-blur-driven NITM was significantly greater in Hong Kong Chinese children with myopic vision than in the emmetropes after both near tasks, but showed no significant dose effect. The NITM was still evident 3 minutes after viewing the 5.00-D near task for 5 minutes. The magnitude of NITM correlated with the accommodative drift after viewing a distant target for more than 4 minutes, but was unrelated to the subjects' or family history of refractive error. CONCLUSIONS: In a preadolescent ethnic population with known predisposition to myopia, there is a significant posttask blur-driven accommodative NITM, which is sustained for longer than has previously been found in white adults.     

Facility of accommodation in myopia

PURPOSE: Myopes have been shown to have abnormal accommodative characteristics. This study investigated the characteristics of accommodation facility in myopic and emmetropic students. METHODS: Distance and near positive and negative accommodation response time components of facility were measured over a 1 min period using a -2.00 D/zero lens pair for distance responses and a +/-2.00 D lens pair for near responses. 79 students (37 myopes and 42 emmetropes) aged 18-27 years acted as subjects. Subjects were masked, and the results were analysed in a masked fashion. RESULTS: Mean distance facility was significantly lower (9.7 cycles per minute (cpm)) in the myopic group compared with the mean distance facility in the emmetropic group (15.6 cpm; p < 0.005). There was no significant difference in the near facilities of the two groups (11.5 cpm in myopes vs 12.9 cpm in emmetropes). Positive accommodation response time for distance vision was greater than 4 s in 45% of myopes and in 9% of emmetropes. CONCLUSIONS: Our findings confirm that myopes tend to have abnormal accommodation responses to blur. Distance facility, but not near facility of accommodation is more frequently reduced in myopes than in emmetropes.     

Retinotopic accommodation responses in myopia

PURPOSE: A reduced sensitivity to retinal image blur has been reported in myopes. Diminished blur detection reduces the error signal to the retinotopic (blur-induced) accommodation system and results in impaired accommodation responses under retinotopic conditions. This study was conducted to investigate retinotopic accommodation responses in emmetropia and myopia under dynamic conditions. METHODS: Static accommodation responses to a blur-only target with vergences of 0 to 4.5 D were measured with an optometer. Microfluctuations of accommodation were recorded with the subject viewing the target at a vergence of 4 D, and dynamic step responses were measured for step stimuli from 2.5 to 3.5 D and 2.0 to 4.0 D, with the optometer in dynamic recording mode. Measurements were obtained from a group of 32 visually normal emmetropes (EMMs) and subjects with progressing myopia. RESULTS: Stimulus-response curves were not significantly different between the refractive groups. Subjects with late-onset myopia (LOMs) demonstrated significantly larger accommodation microfluctuations compared with emmetropes and subjects with early-onset myopia (EOMs). Fourier analysis revealed that the increase in the magnitude of the fluctuations was mediated by the low-frequency components. Accommodation step responses revealed longer reaction times in LOMs. Further analysis showed that LOMs responded to accommodation step stimuli only between 43% and 64% of the time. In contrast, the other groups showed a response rate of almost 100%. CONCLUSIONS: The experiments demonstrate a reduction in retinotopic processing in LOMs, which results in an increased variability in their dynamic accommodation response to stationary near targets and reduced performance for dynamic step tasks. The results demonstrate a reduced blur appreciation under dynamic conditions in these refractive groups that may lead to periods of retinal image blur of varying magnitude during near work.     

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.     

Differences in the accommodation stimulus response curves of adult myopes and emmetropes

While the accommodation system has been implicated in myopia development, the nature of this relationship remains obscure. This study investigated the differences in accommodation stimulus response curves between adult myopes and emmetropes. Myopic subjects were classified according to age of onset and stability of their myopia. Accommodation stimulus response curves were measured using three different methods: (i) real targets presented at viewing distances of 4 m to 0.25 m, (ii) a target at 4 m viewed through negative lenses of increasing power, and (iii) a target at 0.25 m viewed through positive lenses of decreasing power. A Canon Autoref R-1 measured the accommodation responses at 5 levels of demand (increasing from 0 D to 4 D in 1 D steps). We found significant differences between the three methods used to stimulate an accommodation response in all subject groups, for example, accommodation lags at high accommodative demands were greatest for the negative lens series and least for the positive lens series. In addition, while differences between early-onset myopes, late-onset myopes and emmetropes were not observed, we did observe differences when myopic subjects were reclassified according to whether their myopia was progressing or stable. A reduced accommodation response to negative lens-induced accommodative demand was found in progressing myopes but not in stable myopes. These results provide further evidence for the link between myopia progression and inaccurate accommodation. The data also suggest that adult myopes with stable refractive errors show accommodation responses similar to that of emmetropes.     

Synkinesis of accommodation and vergence in late-onset myopia

The accommodative response (AR) to disparity-vergence and blur stimuli was determined for 45 subjects; 15 emmetropes, 15 late-onset myopes (LOM's), and 15 early-onset myopes (EOM's). The accommodative response was measured at approximately 1-s intervals for 50 s using an objective infrared optometer. Disparity-driven accommodation was induced by a 4 delta base-out prism at accommodative stimulus levels of 2.50 and 3.25 D. LOM's show significantly higher levels of disparity-induced accommodation when compared with the other two refractive groups. Blur-induced accommodation was produced by increasing the accommodative stimulus from 2.50 to 3.25 D with no concomitant change in vergence stimulus. EOM's exhibit less blur-induced accommodation compared with LOM's and emmetropes. These results are discussed with reference to differences in accommodation-vergence synkinesis between LOM's and EOM's, and in relation to the etiology of late-onset myopia.     

Repeatability of post-task regression of accommodation in emmetropia and late-onset myopia

The characteristics of post-task regression of accommodation to pre-task ionic accommodation (TA) levels have been examined in a number of studies to clarify the nature of the within-task facility for accommodative adaptation. Of special interest is the recent observation that significant attenuation of post-task regression occurs in late-onset myopes (LOMs) when compared with emmetropes(EMMs). These findings have led to speculation that such attenuation may reflect a deficit in inhibitory sympathetic innervation to ciliary smooth muscle in late-onset myopia and hence a predisposition to sustained accommodative adaptation which then acts as a precursor to the induced myopia. A consequence of this study was that post-task regression may have some value in predicting those individuals who may be susceptible to post-task accommodative hysteresis. A pre-requisite for such a predictive value is that for a given individual the variation in inter-trial regression patterns is not significant. The aim of this study is principally to Investigate the inter-trial variability of post-task regression for individual subjects following a sustained near vision task, and to confirm further differences that have been reported between EMMs and LOMs with respect to the time course of post-task regressions, A modified Canon Rl infrared optometer was used to measure accommodation objectively throughout a near task and for 2 min post-task. Accommodative level was measured following 3 min fixation of a high contrast photopic Maltese cross target placed 3 D above the subject's baseline TA. Repeatability of post-task regression in 10 EMMs and 10 LOMs was assessed by taking measurements on three separate occasions, A significant difference in the post-task regression patterns between EMMs and LOMs was observed which supports previously reported work; the rate of regression to pre-task TA being slower in the LOMs. Within-subject analysis showed that for both EMMs and LOMs the differences between time-course of post-task regressions were not significant. The repeatability of post-task regression patterns thus justifies their use as indices of within-task adaptation.     

Evaluation of inner retinal function in myopia using oscillatory potentials of the multifocal electroretinogram

PURPOSE: Oscillatory potentials have been suggested to arise from the inner retina at the level of amacrine cells and inner plexiform layer and they are thought to provide a non-invasive assessment of inner retinal function. We sought to investigate the response dynamics of the inner retina of adult emmetropes and myopes by analysing the oscillatory potentials of the multifocal electroretinogram (mfERG) in these groups. METHODS: Eleven emmetropes and 18 myopes underwent mfERG testing using VERIS 5.1.5X. Myopes were further separated based on whether their myopia was stable (n=9) or progressing (n=9). Oscillatory potentials were recorded using a modified mfERG stimulation technique, the slow flash paradigm, and they were extracted using band-pass filtering from 100 to 300 Hz. The slow flash mfERG stimulus array consisted of 103-scaled hexagons and flickered according to a pseudorandom binary m-sequence (2(13)-1). Amplitudes and implicit times of the first-order oscillatory potentials were analysed. RESULTS: There were significant differences in the implicit time of the oscillatory potentials of the emmetropes, stable myopes and progressing myopes (F(2,25)=3.663, p=0.043). Progressing myopes had significantly shorter implicit times compared to emmetropes (p=0.026 by 1.0-4.7 ms) and stable myopes (p=0.043 by 0.8-1.3 ms), whereas implicit times of stable myopes and emmetropes were similar. There were no statistically significant differences in amplitude of the oscillatory potentials between the groups (F(2,25)=0.890, p=0.426). CONCLUSIONS: Significant differences in multifocal oscillatory potentials between stable and progressing myopes were found. This finding is further evidence of an inner retinal involvement in human myopia progression and may suggest an underlying alteration to dopaminergic or GABAergic retinal systems.     

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.     

近视与眼相对调节力的相关性研究

目的：探讨近视眼患者正相对调节力( positive relative accommodation, PRA ),负相对调节力( negative relative accommodation,NRA)和 PRA/NRA 比值的特点及其与等效球镜度数、戴镜年数、戴镜习惯、度数进展情况和瞳孔大小的关系。方法：回顾性分析2014-08/11在泉州180医院就诊的患者90例90眼。将轻度、中度、高度近视眼和正视眼的PRA, NRA 和 PRA/NRA 比值进行比较。将近视眼患者PRA, NRA和PRA/NRA比值与等效球镜度数、戴镜年数、戴镜习惯、度数进展情况和瞳孔大小进行相关性分析。近视眼进展组和不进展组的PRA,NRA,PRA/NRA比值,、戴镜年数、戴镜习惯、瞳孔大小进行比较。结果：(1)在年龄、性别和眼压差别无统计学意义的情况下,轻度、中度和高度近视眼和正视眼分别比较, PRA和PRA/NRA比值均较低, NRA均较高;(2)在年龄、性别和眼压差别无统计学意义的情况下,轻度、中度和高度近视组间比较,PRA,PRA/NRA比值和NRA差别均无统计学意义,仅戴镜年数和戴镜习惯差别有统计学意义;(3)戴镜时间越长, PRA和PRA/NRA比值越大、NRA和瞳孔越小。 PRA/NRA比值越大、NRA越小,则瞳孔越小;(4)在年龄、屈光度和眼压无差异的条件下,不易进展组戴镜时间长,常戴镜者比率大;进展组戴镜时间短,不戴和偶戴镜者比率大。结论：近视眼和正视眼比较,PRA和PRA/NRA比值下降, NRA增大;但PRA,PRA/NRA比值与近视度数和近视进展无相关性,提示近视发生与发展无法用单一相对调节力改变来解释,而是多因素多机制共同作用的结果。及时准确配镜并坚持配戴可减轻近视眼PRA,PRA/NRA比值下降和减缓近视的进展。     

测量梯度性AC/A比值对青少年近视防治的意义

目的:探讨测量梯度性AC/A比值对青少年近视防治的意义。方法:选取60例青少年近视患者(30例早发性近视、10例迟发性近视和20例正视),测量他们的刺激性调节诱发的AC/A比值。结果:在早发性近视和迟发性近视与正视眼的反应性AC/A之间存在着显著性差异(P<0.05),早发性与迟发性近视组比较存在着显著性差异(t=2.84,P<0.01);早发性近视与正视组比较存在着显著性差异(t=2.71,P<0.01)。结论:早发性近视较迟发性近视和正视具有较高的反应性AC/A比值,提示高AC/A可能是近视发生发展的一个危险因素。     

Delayed mfERG responses in myopia

It has been suggested that changes in the multifocal electroretinogram (mfERG) responses in myopes are primarily due to the increased axial length that accompanies myopia development. We investigated the characteristics of mfERG responses between emmetropes and myopes and determined the contribution of axial length to the mfERG data in 30 subjects (10 emmetropes and 20 myopes) using VERIS I. The amplitude and implicit time of the first positive peak (P1) of the first-order kernel were analyzed. We found that P1 implicit time in myopes was significantly longer by 1.3-3.1 ms than that of the emmetropes and this was not explained by the myopes having greater axial lengths than the emmetropes. Axial length contributed to 15% of the implicit time total variance while refractive error accounted for 27%. Delayed mfERG responses observed in myopes were not attributable to the anatomical change that accompanies myopia and may suggest underlying differences in retinal function that result from being myopic.