Recovery from monocular stimulus deprivation amblyopia in the kitten.

A review of experimental studies on recovery from monocular stimulus deprivation amblyopia in the kitten is presented. Physiologic, anatomic, and behavioral results are reported for two kinds of recovery experiments: (1) those in which reverse deprivation is employed and (2) those utilizing a recovery period of binocular vision. Data from these investigations are discussed in relation to current thinking regarding the role of synaptic competition during the development of the visual system. The conclusions drawn from these experimental studies of monocular deprivation suggest a possible approach to the treatment of human amblyopia.     

Optical development of the kitten cornea

The kitten eye undergoes considerable growth during a period when there is a high neural susceptibility to the effects of visual experience. We have monitored growth of the cornea in cats of different ages using photokeratoscopy. Qualitatively, the corneal surface of the youngest kittens studied (20 days old) is sometimes irregular and photokeratographs are correspondingly partially distorted. In older kittens the general surface quality appears to be improved. Quantitatively, corneal curvature is very steep centrally in the youngest kittens and it flattens with age at a higher rate than in the pericentral region. In the adult cats, radii of curvature of central and pericentral areas are approximately equal so that a relatively large region of the cornea is spherical.     

Fixational ocular motor control is plastic despite visual deprivation

The aim of this study was to assess the plasticity of human voluntary fixational eye movement control in relation to visual experience/chronic visual deprivation. Twelve blind adults participated (self-reported vision < or = light perception in each eye; age range = 23-56 years; visual experience range = 0-28 years; blindness duration range = 6-55 years). Infrared-based recordings of horizontal eye movements were made before, during, and immediately after three 30-s periods of auditory ocular motor feedback, while participants were instructed to look straight ahead and keep their eyes as steady as possible. Percent change in horizontal displacement of the eye during and after feedback was compared with the no-feedback baseline. Eleven of the 12 individuals demonstrated feedback-mediated increase in eye stability, which improved as a function of visual experience. Improved eye stability was inversely related to duration of blindness. Clearly, blind adults can use nonvisual external feedback to stabilize gaze. Thus, the fixational subsystem can exhibit improved voluntary control despite chronic visual deprivation. Possible cortical and subcortical mechanisms are discussed.     

视觉剥夺对不同发育期鸡近视性眼球生长的影响

目的 研究未成年期视觉剥夺引起鸡眼球近视性发育的变化,从中探讨与人类近视相似的机制。方法 新出生小鸡分3组：1组孵出第2天缝合左侧眼睑后再分I线生长到2周（鸡龄2周）,Ⅱ组生长到8周（鸡龄8周）;另1组为Ⅲ组生长到第8周后缝合左侧眼睑,经8周后（鸡龄16周）打开缝合眼睑,测量屈光度,眼球径（前后及赤道径）。结果 近视程度：I组＞Ⅱ组＞Ⅲ组;3组缝合眼眼球前后径的增长大于赤道径,3组眼球径增长率的比较,差异并不明显。结论 成年前期的不同发育期鸡视觉剥夺均可引起眼球生长近视化,但易感程度不同,生长早期视觉干扰对眼球生长影响明显高于少年期,如早期长期干扰视觉,肌体可能有部分代偿性机制的发生。这一结果提示鸡近视动物模型的研究成果可以应用到人类青少年近视的研究。     

早期形觉剥夺对眼球屈光状态的影响

目的：研究早期形觉剥夺对眼球发育及屈光状态的影响,探讨近视眼发病机理及近视发生的危险因素。方法：对先天性白内障８３例１０９眼和对照组老年性白内障９７例１０９眼的各屈光因子进行生物学测量,确定其屈光状态,并用多元线性和Ｌｏｇｉｓｉｃ回归的方法进行单因素和多因素分析。结果：先天组与老年组相比,先天组有较明显的近视倾向,平均屈光度相差－３．３０Ｄ。两组比较角膜屈光度差异无显著性意义;前房深度、晶状体厚度     

双眼或单眼慢性阿托品化幼猫的视功能发育

用幼猫双眼或单眼慢性阿托品化的方法 ,造成屈光不正或屈光参差的弱视动物模型 ,在整个视觉发育期 ,连续检测其条栅视力 (GA)和对比敏感度函数 (CSF) ,并与正常幼猫相比较。结果表明 :正常幼猫的GA 3 5周龄时为 1 4 8± 0 31c/d ,达到成年 (1 6周龄 )后为 3 67± 0 1 4c/d ,屈光不正组分别为 1 0 0± 0 2 5c/d和 2 1 5± 0 65c/d ,屈光参差组分别为 1 2 6± 0 30c/d和 2 0 5± 0 4 0c/d。在 1 6周龄屈光不正组或屈光参差组与正常组之间均有显著性差异 (t =4 839和 7 0 1 2 ,P均小于0 0 1 ) ,屈光不正组与屈光参差组之间却无显著性差异 (t=0 4 1 0 ,P >0 50 )。屈光不正组和屈光参差组猫CSF均低于正常 ,且以屈光参差组更明显。总之 ,人工模拟的屈光不正和屈光参差均造成幼猫GA和CSF的功能障碍 ,即弱视。两者所造成的视功能障碍无明显差异 ,可能意味着两者有相似的发病机制     

Refractive development in individuals with ocular and oculocutaneous albinism

International Ophthalmology - Albinism is known to disrupt emmetropisation in animal models. However, it is not clear if the same effect is seen in humans. This study aimed to investigate the...     

Accommodation in strabismus

This paper describes clinical observations of optico-sensori-motor symptomatology prior to and during treatment for strabismus. These findings were compared with theoretical data of the binocular visual function. We consider that binocular function has the structure and the working of a "set" in cybernetic sense. In this psycho-physiological set, the accommodative system constitutes a "sub-set". The classification of accommodative disturbances as "pure or impure" and "typical or atypical" arises from the fact that a rebuilding of the visual function has occurred. Thus in "pure" accommodative strabismus the disturbances of accommodation results from "peripheral" accommodation and is easily reversible. In this situation ocular deviation has been perfectly corrected for and binocular vision normally built up since there is enough compensation of the whole optical correction. In "impure" accommodative strabismus the perturbation of accommodation affects the whole accommodation system and also the sensorial motor system. Thus there is a restructuring of the optico-sensori-motor set that is more or less reversible due to a variety of factors. From these investigations we conclude: every strabismus is accommodative in the sens that in every strabismus there is a disturbance of accommodative mechanism. Furthermore, we oppose believers of "all sensorial" and "all motor" mechanisms. Considering that strabismus is a disturbance of optico-sensori-motor binocularity, nothing can be only "accommodative", only "sensorial" and only "motor". From this it follows that treatment should not be only "motor", only "accommodative" or only "sensorial".     

Accommodation and presbyopia

The mechanism of accommodation has been studied for at least four hundred years. The most interesting aspect of accommodation is that its time course is well in advance of other physiological functions – it begins to decline by adolescence and is lost about two-thirds of the way through the normal line span. The state of presbyopia is reached when accommodation has declined sufficiently to interfere with close tasks requiring acute vision. Presbyopia is generally considered to originate with the 'plant' of the accommodative system, either within the lens and its capsule or within their support structures. One of the lenticular theories, the Hess–Gullstrand theory, is distinguished from other theories by its claim that as age increases there is an increasing excess amount of ciliary muscle contraction beyond the ability of the lens and capsule to respond to it. For all other theories, the maximum possible amount of ciliary muscle contraction is always necessary to produce maximum accommodation, at least beyond the age at which it reaches its peak. From my review of the present understanding of the mechanisms of accommodation and the theories of the development of presbyopia, I conclude that there is overwhelming evidence against the Hess–Gullstrand theory and that it is unlikely that changes in the ciliary muscle contractility contribute significantly to the development of presbyopia.     

Effects of lens vertex distance on ocular accommodation demand for reading

Accommodation demand for near work varies on changes of spectacle vertex distance. Equations relating ocular accommodation, spectacle vertex and working distance are derived. These equations show that increase in vertex distance will reduce demand for ocular accommodation in some conditions only.     

飞秒激光在眼科手术中的应用

飞秒激光具有切面平整、精准度高、损伤小及应用范围广等优点,其应用已成为近年眼屈光手术研究的热点.飞秒激光可以替代机械角膜刀,用于准分子激光角膜磨镶术制作角膜瓣,实施全程飞秒激光角膜屈光手术;还可用于老视、青光眼、白内障、角膜病等诸多方面的手术治疗.本文就飞秒激光的切削原理、临床应用以及研究进展作一综述.     

Changes in connexin43 in early ocular surface development

PURPOSE: In the limbo-corneal epithelium the stem and early precursor epithelial cell pool is confined to the limbal rim. Among the features associated with this spatial segregation is the general paucity of connexin43 (Cx43) within the limbal basal cell population and its complete absence in resident stem cells. The limbo-corneal epithelial lineage derives from a Cx43-positive (Cx43+) embryonic outer ectoderm. Accordingly, as a means of identifying the process through which limbal cell phenotypes emerge, we investigated the expression of Cx43 in the ocular surface of embryonic rats. METHODS: Ocular surface expression of Cx43 or K12 was determined in cryostat sections of rat embryos and eyes using immunohistological methods. RESULTS: Changes in Cx43 expression revealed the early phenotypic divergence of three main epithelial cell phenotypes of the ocular surface. An analysis of the level and distribution pattern of Cx43 puncta lead to the identification of two distinct domains by embryonic day 10 (E10), a stage that occurs soon after formation of the lens vesicle. Additionally, at E12, ectodermal cells directly adjacent to the edges of the developing retina no longer express connexin. A comparison of anatomical and expression changes throughout embryonic development demonstrated that the two early zones represent the rudiments for the epithelia of the central cornea and conjunctiva, respectively, and that the isolated Cx43-negative (Cx43-) cells represent the precursors of the basal and, putatively, stem cells of the limbal epithelium. CONCLUSIONS: Changes in Cx43 expression revealed that the phenotypic divergence of ocular surface epithelial cells and the generation of limbo-corneal stem cell precursors takes place at a very early stage in ocular development, ahead of the establishment of any identifiable anatomical or differentiation features for these domains.     

Accommodation and presbyopia : part 1: physiology of accommodation and development of presbyopia

Accommodation is a dynamic change in the dioptric power of the eye. According to the widely accepted and experimentally confirmed theory of Helmholtz, it is achieved by release of zonular tension with contraction of the ciliary muscle and consecutive modelling of the shape of the crystalline lens by the elastic lens capsule. The ability to accommodate is gradually lost with age (presbyopia). Because of difficulties in examining the accommodative apparatus in vivo, many theories, in part contradictory, about the mechanism of accommodation and the origin of presbyopia have been developed. In recent years experimental studies have greatly increased the knowledge about the acommodative apparatus and suggest a multifactorial aetiology of presbyopia. A better understanding of the physiology of accommodation and presbyopia can contribute to the development of effective treatments.     

Influence of deprivation on axial ocular growth: A novel mechanism of emmetropization

A 24-year-old myopic woman with familial, bilateral, congenital cataracts underwent cataract extraction and intraocular lens implantation in her left eye, with resulting 20/20 visual acuity. She postoponed cataract surgery on her right eye for 4 years. Axial myopia progressed in the right eye from 27.99 to 29.11 mm, and the left eye also elongated, from 28.25 to 28.72 mm, as indicated by A-scan ultrasonography. Axial elongation apparently is not a purely local phenomenon. Presented as a poster presentation at the Association for Research in Vision and Ophthalmology meeting, Fort Lauderdale, Fla. May 13, 1997.     

Manganese-enhanced MRI studies of alterations of intraretinal ion demand in models of ocular injury

PURPOSE: To provide proof-of-concept that the extent of intraretinal manganese uptake after systemic MnCl(2) injection, detected with manganese-enhanced MRI (MEMRI), assesses alterations in intraretinal ion demand in models of ocular insult. METHODS: In Sprague-Dawley rats, retinal ion demand and thickness were measured from MEMRI data collected before, 4 hours after, or 1, 3, and 7 days after intraperitoneal injection of MnCl(2). Choroidal contribution or blood-retinal barrier permeability surface area product (BRB PS') was determined using MRI after Gd-DTPA injection. Ocular injury was evaluated 24 hours after intravitreal injection of phosphate-buffered saline (PBS, vehicle) or PBS + ouabain, or after intraperitoneal injection of sodium iodate. Manganese retinal toxicity was assessed by comparing full-field, white-flash electroretinographic (ERG) data obtained before and after systemic MnCl(2) administration. Rat choroidal thickness was measured from cross-sections prepared from paraformaldehyde-perfused adult rats. RESULTS: Comparing pre- and post-Gd-DTPA images demonstrated minimal choroidal contribution to intraretinal analysis. Intraretinal signal intensity returned to baseline by 7 days after MnCl(2) injection. After ouabain injection, receptor and postreceptor uptake of manganese were subnormal (P < 0.05). After sodium iodate exposure, intraretinal manganese uptake was supernormal (P < 0.05) and did not increase with increasing BRB PS'. ERG data did not show any effect of MnCl(2) on photoreceptor a-wave and postreceptor b-wave relative to baseline at either observation time. CONCLUSIONS: MEMRI measurements of uptake of systemically administered and nontoxic doses of manganese appear to be a powerful approach for measuring alteration in intraretinal ion demand in models of ocular injury.     

Accommodation in pseudophakic eyes

PurposeToday, many patients who have undergone cataract surgery want to enjoy good non-spectacle corrected distant vision and nonspectacle corrected near vision with glasses independence. According to the literature, the implantation of an accommodative intraocular lens (AIOLs) can achieve the level of vision after cataract surgery. However, there is a debate regarding the true accommodative capability of the AIOLs (i.e., whether the IOLs can move forward when attempting to accommodate like the natural crystalline lens of a phakic eye). This review aims to answer the following questions: (1) Can pseudophakic eye accommodate? (2) If pseudophakic eyes can accommodate, how long does this accommodation last? (3) Is there pseudoaccommodation?MethodsThis is a systematic review of randomized and nonrandomized controlled trials that have compared different IOLs in accommodation using subjective and objective methods of testing accommodation. All peer reviewed randomized and nonrandomized controlled trials that compared different IOLs in accommodation were included.ResultsThere was evidence of pseudophakic accommodation up to 12 months postoperatively for AIOLs (mostly 1CU): subjective accommodation [95% confidence interval (CI), 0.36–0.98], objective optic shift (95% CI, 0.12–0.76). However, accommodation decreased at 12 months postoperatively (95% CI, 0.55–1.00). In addition, several papers have reported evidence of pseudoaccommodation.ConclusionThere is pseudophakic accommodation up to 1 year post cataract surgery, mostly 1CU AIOL. Pseudoaccommodation may coexist.