The topography of the anterior surface of the cat's cornea

The topography of the cornea in nine unanaesthetised domestic cats was studied by the computer analysis of photokeratographs obtained using a Wessley Jessen P.E.K. 2000 photokeratoscope . Mean figures were obtained for: Central corneal radius in the steeper (9.06 mm) and flatter (9.20 mm) corneal meridians. Corneal astigmatism (0. 61D ). Corneal shape factor in the steeper (0.33) and flatter (0.31) corneal meridians and the diameter of the corneal cap in the vertical (6.23 mm) and horizontal (7.08 mm) meridians. The results are discussed and compared with previous such estimates for corneal topography. Dimensions for an hydrophilic contact lens suitable for general therapeutic or research use in the cat are suggested.     

Lateral spatial interaction in humans with abnormal visual experience

Foveal increment sensitivity has been determined using a small flashing test spot on a background with and without the presence of a steadily presented satellite light patch. The satellite was arranged at different distances from the test spot along vertical, horizontal, and oblique meridians. Normal subjects and those whose visual development was probably abnormal due to severe astigmatism (meridional amblyopes) were tested. Increment sensitivity for the test spot alone is considerably lower for the amblyopes than for normal subjects. The presence of the satellite patch depresses sensitivity for small separations and is alternately threshold-lowering and threshold-raising for larger separations. The influence of the satellite differs along the three meridians tested both in the normal and abnormal subjects.     

使用全景超声生物显微镜观察年龄相关性白内障超声乳化手术后前房直径的改变

目的探讨使用全景超声生物显微镜（ultrasound biomicroscopy,UBM）观察白内障患者手术前后前房直径的改变。方法对109例（128眼）年龄相关性白内障患者行超声乳化白内障吸除联合折叠型人工晶状体植入术,分别于术前、术后第2个月利用全景UBM测量水平前房直径和垂直前房直径,观察其变化情况。结果年龄相关性白内障患者术前水平前房直径为（11.58±0.43）mm,术后为（11.82±0.35）mm;术前垂直前房直径为（11.59±0.44）mm,术后为（11.87±0.33）mm。术前垂直前房直径与水平前房直径相差（0.01±0.23）mm,术后相差（0.06±0.25）mm。术后水平、垂直前房直径均较术前增加,差异有统计学意义（P〈0.01）。术前与术后水平前房直径存在正相关（r=0.68,P〈0.01）,回归方程为Y=5.3945＋0.55438x。结论白内障患者垂直前房直径略大于水平前房直径;年龄相关性白内障超声乳化吸除人工晶状体植入术后水平前房直径及垂直前房直径均增加。可以用术前的前房直径预测出术后前房直径,为选择适合大小的前房型人工晶状体提供参考。     

Plasticity of convergence-dependent variations of cyclovergence with vertical gaze.

Binocular alignment of foveal images is facilitated by cross-couplings of vergence eye movements with distance and direction of gaze. These couplings reduce horizontal, vertical and cyclodisparities at the fovea without using feedback from retinal image disparity. Horizontal vergence is coupled with accommodation. Vertical vergence that aligns tertiary targets in asymmetric convergence is thought to be coupled with convergence and horizontal gaze. Cyclovergence aligns the horizontal retinal meridians during gaze elevation in symmetrical convergence and is coupled with convergence and vertical gaze. The latter vergence-dependent changes of cyclovergence have been described in terms of the orientation of Listing's plane and have been referred to as the binocular extension of Listing's law. Can these couplings be modified? Plasticity has been demonstrated previously for two of the three dimensions of vergence (horizontal and vertical). The current study demonstrates that convergence-dependent changes of the orientation of Listing's plane can be adapted to either exaggerate or to reduce the cyclovergence that normally facilitates alignment of the horizontal meridians of the retinas with one another during gaze elevation in symmetrical convergence. The adaptability of cyclovergence demonstrates a neural mechanism that, in conjunction with the passive forces determined by biomechanical properties of the orbit, could play an active role in implementing Listing's extended law and provide a means for calibrating binocular eye alignment in three dimensions.     

Calculating the surgically induced refractive change following ocular surgery.

Calculating the surgically induced refractive change following ocular surgery is important for evaluating the results of keratore-fractive procedures, smaller incisions and various wound closures for cataract surgery, and the effect of suturing techniques and suture removal following corneal transplant surgery. We present a ten-step method of calculating the spherical- and cylindrical-induced refractive change in a manner suitable for a programmable calculator or personal computer. Several applications are given including (1) adding the overrefraction to the spectacle correction, (2) determining the surgically induced refractive change from the preoperative and postoperative refractions, (3) determining the surgically induced refractive change from the K-readings, (4) rotating axes, (5) determining the power at meridians oblique to the principal meridians of a spherocylinder, (6) determining the coupling ratio, and (7) averaging axes. Standard methods for calculating and reporting aggregate results are also given.     

Toroidal surface assessment by curvature measurements in three fixed meridians

A method is described to evaluate the sphero-cylindrical components of a toroidal surface by curvature measurement along three fixed meridians which are orientated at 60 degrees to each other.     

Converting principal meridional representation of power to the coordinates of the power matrix using the matrix similarity transform

General or local variations of the refractive elements in the eye, called irregular astigmatism, may manifest as non-orthogonal meridians when each principal meridian on the front surface of a cornea is independently aligned with the focussed mires of a keratometer. These are examples of astigmatic systems that are thick. The representation of power along the principal meridians is not suitable for quantitative work. The purpose of this research note is to convert power along principal meridians that can be non-orthogonal, to the coordinates of the power matrix that are suitable for quantitative analysis.     

Measurement of posterior corneal surface toricity

We describe a method in which posterior corneal surface toricity can be determined by photographing catoptric (Purkinje) images in three fixed meridians simultaneously using infrared light sources. Keratometry, the comparison of anterior and posterior corneal catoptric (Purkinje) images and pachometric results, are applied to three meridional analysis equations, allowing the posterior corneal surface to be described in spherocylindrical form. The technique is evaluated on five subjects with anterior corneal radii varying from 7.11 to 8.52 mm.     

Tri-meridional analysis using arbitrary meridians: a new solution

A new solution is presented for the evaluation of the spherocylindrical components of curvature or refraction from measurements taken along three distinct, arbitrary, meridians. Unlike previous approaches, the axis direction is found first, thereby making sphere and cylinder evaluation relatively simple. The derivation of the solution is reasonably uncomplicated using straightforward trigonometrical operations.     

An analysis of three meridional keratometric measurement of the anterior corneal surface

Analysis of measurements taken in three meridians of a toroidal optical surface can produce a spherocylindrical result without having to locate the principal meridians. This technique is assessed for the anterior corneal surface using keratometry. Good agreement is found with measurements taken in the principal meridians making this a suitable method for the assessment of the eye's optical surfaces by Purkinje image measurement.     

Qualitative effect of zonular tension on freshly extracted intact human crystalline lenses: implications for the mechanism of accommodation

PURPOSE: To determine the topographic effects of zonular tension on the anterior surface of the human crystalline lens. METHODS: Real-time topography of the anterior surface of seven fully relaxed, freshly extracted intact, clear, human crystalline lenses aged 3, 17, 45, 54, 54, 56, and 56 years was qualitatively obtained before, during, and after the application of zonular traction. Zonular traction was applied manually either by grasping a group of zonules 180 degrees apart with tying forceps (three lenses), or with micrometers by clamping four portions of the ciliary body that were 90 degrees apart (four lenses). RESULTS: Zonular tension began with the lenses in the fully relaxed, baseline state. As zonular tension was increased across one meridian of all seven lenses, the center of the anterior surface steepened while the periphery of the anterior surface flattened across that meridian of traction. When the tension was reduced across that meridian of traction, the center of the lens flattened while the periphery steepened in that meridian. Four-point zonular traction applied 90 degrees apart produced symmetrical central steepening (four lenses). Reduction of zonular tension across both orthogonal meridians caused symmetrical central flattening. CONCLUSIONS: These observations reveal that when zonular tension is applied to the fully relaxed lens, the center steepens and its periphery flattens in the meridian (or meridians) in which zonular tension is applied. The reverse of this process demonstrates that as tension is reduced, the center of the lens flattens while the periphery steepens either in the meridian of relaxation or symmetrically when zonular tension is released from two orthogonal meridians. These results are opposite to what would have been predicted on the basis of Helmholtz's theory of accommodation.     

运用正切曲率半径分析角膜前表面的Q值规律

目的运用正切曲率半径探讨人眼角膜前表面360°子午线Q值规律性。方法中度近视无散光中国青年55人,采集0rbscan—Ⅱ角膜地形图上360条子午线、距角膜顶点0．3mm为间隔的点的前表面曲率值。建立以角膜顶点为原点的笛卡儿空间三维坐标,绕Z轴旋转坐标．形成新的三维空间坐标系。采集正切图的前表面曲率,代入方程376/F=4/a1^2[a1^2/4＋（1＋a2）y^2]^3/2,各解出一套二次曲线公式x2=a2z^2＋a1z（前表面截痕）,确定各切面偏心率Q值及截痕特性,并统计比较其差异性,从各子午线的截痕的曲线特征归纳角膜前表面曲面空间形态的数学表达式。结果55人0°和180°子午线上的平均Q值分别为-0．211±0．22和-0．138±0．20,90°和270°子午线上的平均Q值分别为0．243±0．28和0．224±0．24。水平子午线的Q值趋向于-1,垂直子午线趋向于0°比较两种方法计算出来Q值的差异性,结果示在水平方向上的Q值没有差异性（P〉0．05）,在垂直方向上的Q值有差异性（P〈0．01）。结论本研究分析了运用正切曲率半径值建立人眼前表面角膜数学模型的科学性,显示角膜前表面水平子午线方向非球面性趋向于长椭圆,垂直子午线方向非球面性趋向于扁椭圆．说明人眼角膜的非球面性特性主要由水平子午线实现。     

Study of spatial function using the contrast sensitivity function. Cases of presbyopic subjects fitted with progressive glasses

The spatial properties of the global visual system were measured on the basis of the contrast sensitivity function, in three presbyopic observers. Shape alterations of the contrast sensitivity curves were found depending on the experimental conditions: foveal vision, in far, intermediary and near vision, along central, 13 degrees nasal and 13 degrees temporal meridians (according to three parallels and three meridians), peripheral vision, in far and near vision, at 13 degrees and 26 degrees retinal eccentricities using the central or nasal part of the lens. The central meridian was found to be the most efficient part of the progressive lenses. These results strengthen the observations reported by ophthalmologists and progressive lens wearers.     

Comparison of ocular component growth curves among refractive error groups in children

PURPOSE: To compare ocular component growth curves among four refractive error groups in children. methods Cycloplegic refractive error was categorized into four groups: persistent emmetropia between -0.25 and +1.00 D (exclusive) in both the vertical and horizontal meridians on all study visits (n = 194); myopia of at least -0.75 D in both meridians on at least one visit (n = 247); persistent hyperopia of at least +1.00 D in both meridians on all visits (n = 43); and emmetropizing hyperopia of at least +1.00 D in both meridians on at least the first but not at all visits (n = 253). Subjects were seen for three visits or more between the ages of 6 and 14 years. Growth curves were modeled for the persistent emmetropes to describe the relation between age and the ocular components and were applied to the other three refractive error groups to determine significant differences. results At baseline, eyes of myopes and persistent emmetropes differed in vitreous chamber depth, anterior chamber depth, axial length, and corneal power and produced growth curves that showed differences in the same ocular components. Persistent hyperopes were significantly different from persistent emmetropes in most components at baseline, whereas growth curve shapes were not significantly different, with the exception of anterior chamber depth (slower growth in persistent hyperopes compared with emmetropes) and axial length (lesser annual growth per year in persistent hyperopes compared with emmetropes). The growth curve shape for corneal power was different between the emmetropizing hyperopes and persistent emmetropes (increasing corneal power compared with decreasing power in emmetropes). conclusions Comparisons of growth curves between persistent emmetropes and three other refractive error groups showed that there are many similarities in the growth patterns for both the emmetropizing and persistent hyperopes, whereas the differences in growth lie mainly between the emmetropes and myopes.     

Interconverting the matrix and principal meridional representations of dioptric power in general including powers with nonorthogonal and complex principal meridians

The principal meridians of the powers of thick astigmatic systems, like the eye, are not necessarily at right angles. The consequence is a class of phenomena included in the category commonly described as irregular astigmatism. The conventional principal meridional representation of power, however, is unsuited to quantitative analysis. This paper presents equations for converting from the principal meridional form of power to a representation, the dioptric power matrix, which is amenable to quantitative analysis. It generalizes an earlier paper which treated only powers of a conventional form in which the principal meridians are always at right angles. It copes in particular with what are known as asymmetric powers. A routine is also presented for converting in the reverse direction, from the power matrix to the principal meridional form of power. The principal meridional form of power turns out not always to be unique, there being distinct powers (they are asymmetric) with the same principal powers and meridians. Thus, in general, the dioptric power matrix is a satisfactory representation of power while the principal meridional representation is not.     

复方中药散血明目片对兔视网膜静脉阻塞ET-1表达的影响

目的:探讨活血通脉利水明目之复方中药散血明目片对兔视网膜静脉阻塞RVO模型ET-1表达的影响。方法:取健康有色家兔36只,每组9只,分为A组:健康空白组,B组:模型组,C组:血栓通组,D组:散血明目片组。采用波长532nm的Nd:YAG激光光凝法建立RVO模型,连续灌胃,实验后7,14,21d分别处死家兔取材,石蜡包埋切片,用免疫组化法检测视网膜组织中ET-1表达活性,计算机系统图像分析结果并进行统计分析。结果:D组7,14,21d与A,B,C3组比较:ET-1表达活性明显低于B组(P<0.05),与C组差异无显著性;21d时D组ET-1表达活性与A组差异无统计学意义。结论:活血通脉利水明目之复方中药散血明目片能够明显降低兔视网膜静脉阻塞RVO模型ET-1表达,抗血栓形成,改善RVO后视网膜局部微循环,减轻缺血缺氧对血管内皮细胞的损害。     

散光对正常人眼角膜前表面调制传递函数的影响

目的用调制传递函数（MTF）客观分析散光对正常人眼角膜前表面光学质量的影响。方法回顾性系列病例研究。角膜前表面4 mm直径范围顺规散光456例（907眼）,依散光度分为A（散光度≤0.50 D）、B（0.50 D＜散光度≤1.00 D）、C（1.00 D＜散光度≤2.00 D）、D（2.00 D＜散光度≤3.00 D）、E（散光度＞3.00 D）5组;逆规散光19例（22眼）。用Sirius角膜地形图眼前节分析仪模拟角膜前表面中央4 mm直径范围垂直和水平子午线方向的MTF曲线,从曲线上可以得到5、10、15、20、25、30、35、40、45、50、55、60 c/d空间频率的MTF值,不同散光度同一频率下的MTF值的比较采用完全随机设计资料的方差分析,同一频率下垂直子午线的MTF值与水平子午线的MTF值比较采用配对资料t检验。结果顺规散光组：①随着散光度增大,水平和垂直子午线方位的MTF值均逐渐降低,散光度越大,降低的幅度越明显;②相同散光度组中垂直子午线各个频率的MTF值均低于水平子午线,差异有统计学意义;③不管是水平子午线还是垂直子午线,散光值对高频的影响最大,其次是中频,对低频部分影响较小。逆规散光组：垂直子午线各个频率的MTF值均高于水平子午线,差异有统计学意义。结论角膜散光对角膜前表面不同方位（垂直和水平子午线）的MTF值均有明显影响。     

Corneal topography of pellucid marginal degeneration

Our computer-based corneal topography analysis system was used to study the keratoscope photographs (keratograms) from two patients with classic pellucid marginal degeneration and a third patient with no inferior corneal thinning, whose keratoscope mire pattern was suggestive of the condition. All three patients showed marked flattening of the central cornea along a vertical axis and marked steepening of the inferior corneal periphery, which also extended into mid-peripheral inferior oblique corneal meridians. The mid-peripheral cornea gradually decreased in power above the inferior oblique meridians.     

Corneal astigmatism in applanation tonometry

PURPOSE: This short study aims at quantitatively correlating scale readings of the Goldmann tonometer to corneal curvatures in one and the same eye. METHODS: A total of 30 eyes of 21 adult patients who presented themselves in clinical practice for routine examination were arbitrarily selected. Corneal curvatures were measured in the horizontal and vertical meridians and then applanation tension measured in the same order. The data were submitted to statistical analysis by computer using Microsoft Excel and SAS System programs.Results All cases exhibited a strong positive correlation of tonometric readings to corneal curvature, that is, the flatter the curvature, the lower the reading on the scale of the tonomer, and vice versa. CONCLUSION: The numbers on the scale of the Goldmann tonometer may not represent true intraocular pressure in mmHg because their values depend on a number of variables of the globe, including corneal astigmatism. Attention to these influences may help interpret the tonometric record in difficult cases.