Local dioptric power matrix in a progressive addition lens

In this paper we use the formalism of the Dioptric Power Matrix to visualise and characterise the properties of a Progressive Addition Lens. For progressive addition lenses, the dioptric power matrix is point-dependent, and we have measured its elements over the lens surface by means of an automatic focimeter. We show the obtained contour plots corresponding to the matrix elements, and we compare them with the traditional sphere and cylinder graphs. Although the two representations give the same information, the advantages and disadvantages between them are analysed. The dioptric power matrix method turns out to be specially useful for the computation of prismatic effects along the lens surface.     

Eye and head movement alterations in naïve progressive addition lens wearers

Aims: To examine adaptation to progressive addition lenses (PALs) by investigating eye and head movement strategies of individuals naïve to PAL wear; to determine whether adaptation is a short‐term change in strategy or is maintained with continued PAL wear; to determine if adaptation strategies are different between PAL designs. Methods: Ten presbyopic individuals participated in a double‐blind crossover study. Participants wore one PAL design for ≤4 weeks, had approximately 1 week without PAL wear and then wore the second PAL for ≤4 weeks. Eye and head movements were recorded at the beginning and end of each period of PAL wear in response to several visual tasks. Visual tasks were a flash discrimination task at 2 m and 40 cm, and reading text aloud. Quantitative analysis was undertaken for eye and head movement dynamics (latency, duration, peak velocity, etc.). Categorical analysis used eye and head movement metrics to classify participants as eye‐movers, head‐movers or mixed at each visit. Results: There was significant between‐participant variability. A number of eye/head movement parameters exhibited carry‐over effects. The number of vertical head movements for the distance task showed a significant increase between the first and second visit (F_1,9 = 5.578; p = 0.042), irrespective of lens design. Categorical analysis showed that participants employed task dependent strategies for all tasks. Participants that altered their strategy tended to include more head movements. Seven of the 10 participants preferred the second PAL worn. Conclusions: Participants recruited more head movements for flash discrimination tasks and for reading text during adaptation to PAL wear. The many and various eye and head movement parameters analysed were unable to discriminate differences dependent on PAL design.     

老视渐变镜的近视眼配戴者年龄和近附加的关系

目的研究成功验配渐进多焦点镜片（渐变镜,progressive addition lenses,PALs）的近视患者的年龄与其近附加（presbyopic add,ADD）的关系。方法将本中心2005年1月1日至2008年6月15日间成功验配渐变镜、资料完整的近视验配者69例（双眼均为近视眼,等效球镜〉-0．50 D）．按照每5岁分为一组,共分5组（40～45岁为第1组．46～50岁为第2组,51～55岁为第3组,56～60岁为第4组,61岁及以上为第5组）,线性回归分析年龄与最终成功验配的渐变镜近附加的关系。结果随着年龄的增加,近附加逐渐增加,年龄和近附加呈线性回归（t=9．662,P〈0．01）,得出公式：近附加=-0．697＋0．051×年龄（年龄≥40岁）。5组患者的近附加分别为（1.44±0．27）D、（1.73±0.32）D、（2.08±0.28）D、（2.38±0.38）D和（2．52±0．38）D,各组之间差异有非常显著的统计学意义（F=21．303,P〈0．01）。结论从昆明地区验配近视眼渐变镜的中老年人近视眼的现状可知,该人群每5年增加约0．25 D的近附加是初步成功验配的基础：     

Verifying and evaluating progressive addition lenses in clinical practice.

BACKGROUND: Despite the fact that more than 50% of multifocal lenses dispensed in the United States are progressive addition lenses, adequate methods for clinical verification of these lenses have been lacking. Using automated lens meter techniques, the author describes a simplified method for verification of these complex lenses. METHODS: Thirty pairs of progressive lenses were measured in a modified method using a Humphrey 330 Lens Analyzer. Fifteen pairs were "premium-quality" progressive lenses: fifteen pairs were "non-premium-quality" progressives. Five criteria were assessed on each lens: Distance Zone Width (DZW). Intermediate Zone Width (IZW), Near Zone Width (NZW), Drop Distance (DD), and Maximum Astigmatic Distortion (MAD). RESULTS: "Premium-quality" progressive lenses failed to demonstrate clear-cut superiority over "non-premium-quality" progressive lenses in the five specified criteria. Individual measurements indicate considerable product inconsistency affected every brand tested. CONCLUSIONS: Premium- and non-premium-quality progressive lenses demonstrated similar performance characteristics in this study. Zone size variation in these lenses was found to be considerable, a characteristic that seemed to cut across brand lines. The AO Compact lens seemed to demonstrate a shorter drop distance than other lenses, which does enhance its suitability for use with small frames. A comparison of the Essilor Natural PAL to the Younger Image lens showed little difference in the categories measured, although peripheral distortions seemed closer to the reading zone in the image. A comparison of the MAD of lenses in this study to lenses tested in 1986 indicates a considerable improvement has been made in that important characteristic.     

Scheimpflug imaging to determine intraocular lens power in vivo

PURPOSE: To assess the feasibility of determining intraocular lens (IOL) power by measurement of the central optic thickness using clinically available Scheimpflug imaging (Pentacam, Oculus). SETTING: King's College Hospital Ophthalmology Department, London, United Kingdom. METHODS: Sixty-seven eyes were assessed 1 month after uneventful phacoemulsification with in-the-bag implantation of AcrySof MA60AC IOLs (Alcon). The correlation between IOL thickness measurement and IOL power was calculated. Repeatability of central optic thickness measurement was determined from 10 successive scans of 4 patients. RESULTS: Within-subject standard deviation increased with the subject mean. The coefficient of variability was 1.4%. Measured lens thickness was highly correlated with lens power (R(2) = 0.94, P<.001). Over the measured range, 95% confidence intervals varied between +/-0.83 diopters (D) and +/-0.92 D. CONCLUSIONS: Central IOL thickness measurements with the Pentacam Scheimpflug camera were highly repeatable and closely correlated with the known IOL power. The IOL power, calculated from a regression equation, is likely to be less than +/-1.00 D away from the actual power. Approximate in vivo IOL power determination is feasible with clinically available Scheimpflug imaging. This could be applied clinically in cases of unexplained postoperative refractive error.     

硅油填充眼A超眼轴测算及人工晶状体度数计算

目的:评价声速调整法测量硅油眼眼轴、测算人工晶状体度数的准确性。方法:对2003/2008年于我院治疗的24例硅油填充术后并发性白内障患者,采取坐位眼轴测量并改变硅油眼中超声波的传播速度来修正眼轴长度,再将计算所得眼轴长度代入SRKII公式计算拟植入的人工晶状体度数。行硅油取出术联合白内障摘除+人工晶状体植入术。术后3mo测量眼轴及屈光状态。对手术前后眼轴长度进行对比,将术后屈光状态与术前预期值比较。结果:硅油取出术前平均眼轴长度为25.25±0.65mm,术后平均眼轴长度为24.80±0.67mm,取油前后眼轴长度均值差异无统计学意义。手术后屈光度与术前预期值差值平均为1.50±0.40D,差异无统计学意义。结论:通过坐位测量并调整超声波在硅油中的传导速度,可准确测量硅油填充眼眼轴,较传统方法测算人工晶状体度数准确率更高。     

Meridional profiles of variance—covariance of dioptric power, Part 2. Profiles representing variation in one or more of sphere, cylinder and axis

Meridional profiles of variation of dioptric power are constructed. Using the basic theory developed in an accompanying paper, samples are selected in a systematic way to illustrate variation only in sphere, only in cylinder and only in axis, and in all possible combinations of sphere, cylinder and axis. For each of the seven samples, scatter plots are constructed together with ellipsoids that represent the estimated distribution of powers in the population from which the sample was taken. The surfaces of the ellipsoids are surfaces of constant probability density within which 95% of the population is calculated to lie. The scatter plots and distribution ellipsoids are plotted in a three-dimensional space called h-space. Meridional profiles of variation are constructed for each of the samples. Properties of the profiles are discussed. Meridional profiles are also presented for eyes before and after radial keratotomy. Among other things, the profiles show meridians of greatest and least variation and are intuitively satisfying. They are potentially useful for the researcher and clinician including the surgeon. They may help to improve surgical and therapeutic techniques. Certain patterns may prove to be characteristic of physiological or pathological conditions, in which case meridional profiles may have use as a diagnostic tool.     

Using the lens haptic plane concept and thick-lens ray tracing to calculate intraocular lens power

PURPOSE: To develop a methodology for intraocular lens (IOL) power calculation in which the task of predicting the postoperative position of the IOL is separated from the calculation itself. SETTING: Pharmacia, Groningen, The Netherlands. METHODS: The minimum biometry input needed for IOL power calculation is the mean anterior corneal radius and axial length of the eye. The lens haptic plane (LHP) is the plane where the IOL haptics make contact with eye tissue. It is an anatomical site (eg, the equator of the capsular bag) and is independent of the IOL model. The position of the IOL optic in relation to the LHP is determined from the exact design of the IOL. Gullstrand's eye model is adopted to obtain the posterior corneal radius, thickness of the cornea, and refractive indices of the eye media. Thick-lens ray tracing in the paraxial limit is used for the optical calculation. RESULTS: A spreadsheet is given for the calculation. CONCLUSIONS: The methodology developed allows for IOL power calculation from first principles (ie, using true physical distances, radii, and refractive indices as input for the optical calculation).     

Membrane addition to photoreceptor outer segments: progressive reduction in the stimulatory effect of light with increased temperature.

Previous studies have indicated that temperature and light regimens affect the rates of membrane addition to rod outer segments in amphibia. However, it is not known how membrane renewal responds to simultaneous alterations of these two environmental factors. In the present study, the rates of membrane addition have been assessed in adult Rana pipiens maintained in three lighting conditions (constant light, constant darkness, and cyclic light) at three different temperatures by following the displacement of a radioactive band in autoradiographs after 3H-leucine injection. At 16 degrees, 21 degrees, and 26 degrees C, constant light increases the rate of membrane addition in red rods above the rates which occur in darkness by 39%, 14%, and 9%, respectively, whereas in the green rods, the rates of increase were 41%, 22%, and 8%. This progressive reduction in the stimulatory effect of light suggest that at the higher temperatures, rod outer segment renewal is proceeding at near maximal rates and can no longer be further accelerated by light stimulation.     

Induction of mitosis in the cultured rabbit lens initiated by the addition of insulin to medium KEI-4.

The epithelium of lenses cultured in KEI-4, a completely defined medium formulated with specific reference to the biochemistry and physiology of the rabbit lens, exhibits a pattern of cell division similar to that noted for the organ in situ. Initial fluctuations in mitotic activity occurred in the area of the germinative zone during the first 24 hr of culture. Mitosis decreased at 1 hr, was extremely low at 3 hr and returned to values comparable for lens in vivo by 22 hr. The precipitous drop in mitosis noted at 3 hr is in part attributable to the isolation of the lens from adjoining tissue. The addition of insulin to KEI-4 triggers a parasynchronous burst of DNA synthesis throughout the central lens epithelium. The activation requires the intact hormone; neither proinsulin nor the A and/or B chains of insulin, nor glucagon nor zine chloride can initiate mitosis. The gamma-globulin-rich fraction of rabbit serum can also stimulate mitosis. The addition of dibutyryl adenosine 3′:5′ cyclic monophosphate (DBcAMP) plus theophylline to KEI-4-insulin inhibits mitosis and prevents the cells from entering the synthetic phase of the cell cycle. Theophylline alone or DBcAMP alone brings about a 90% reduction in the insulin-induced mitotic responses.Lenses exposed to insulin show a marked increase in RNA synthesis and also exhibit an increased binding of tritiated actinomycin D at 1 and 3 hr of culture relative to KEI-4 controls. The hormone apparently activates the genome including those genes governing cell division. The system is amenable for long-term culture of the mammalian lens and since the constituents of the medium are known it should be possible to determine the factor(s) in the medium which, in conjunction with insulin, are needed for the induction of cell division.     

Corneal curvature and supplemental power effect of the Bausch and Lomb SOFLENS contact lens.

The supplemental power effect (SPE) of F series Bausch and Lomb SOFLENS (polymacon) Contact Lenses was determined for a sample of 54 eyes. The mean value was +0.34 D=S.D.+/-0.37 D, range zero to +1.00 D. A significant correlation was present between the SPE and the apical lens-cornea bearing relationship. (p less than 0.01). The results of this study provide refractive evidence that a central lens-cornea alignment is achieved when the posterior apical radius of the lens is about 0.5 mm flatter than the flat radius of the cornea, S.D.+/-0.35 D. This information is clinically useful in assessing the patient's visual response as well as the fit of the lens.     

Immunopathology of the lens. III. Humoral and cellular immune responses to autologous lens antigens and their roles in ocular inflammation.

In experimental rabbits it has been shown for the first time that autologous lens protein is antigenic when injected with Freund's complete adjuvant. Although lens haemagglutinins were detected in 6 out of 7 rabbits, in only 3 of the 6 animals did the titre reach a maximum of 1:640. A weak agar precipitation reaction was obtained with only 1 of the 3 sera. It would appear, therefore, that the passive haemagglutination test is superior for the detection of autologous lens antibodies. The response to autologous lens antigen both in magnitude as well as in duration varied in different rabbits, which suggested to us the possible role played by a central control mechanism involving the immune-response (Ir) and immune-associated (Ia) genes which are part of the major histocompatibility complex. Alternatively, this variation may be the result of an antigenic competition between various autologous crystallins. Antibodies to autologous lens protein as detected by immunofluorescence and immunoperoxidase techniques were shown to be of the IgG class. Systemic autologous immunisation produces only a mild uveitis and does not lead to a granulomatous intraocular inflammation. Intravitreal injections of autologous lens protein in pre-immunised animals, however, produced an Arthus type of acute endophthalmitis. Autologous lens antisera showed limited cross-reactivity with ocular and extraocular tissues, which could be detected only by such sensitive techniques as immunofluorescence and immunoperoxidase methods.     

Immunopathology of the lens. II. Humoral and cellular immune responses to homologous lens antigens and their roles in ocular inflammation.

It has been possible for the first time to demonstrate antibodies to homologous lens proteins in rabbits without the addition of adjuvant. By means of immunofluorescence and immunoperoxidase methods it has been possible not only to show for the first time that homologous lens antibodies cross-react with extraocular tissues but that the cross-reacting antigens are related to the cell mitochondria, microsomes, and the proteins associated with contractile organelles. The rabbits did not produce antibodies to gamma-crystallins even when the whole lens homogenate was injected with Freund's complete adjuvant. This suggests that gamma-crystallins are non-antigenic in homologous situations, and this may be related to both B- and T-cell tolerance. Alternatively, the failure of gamma-crystallins to induce antibody production may be due to intermolecular antigenic competition with other crystallins. The presence of mycobacteria in an adjuvant is essential for an antibody response to be detectable by agar diffusion techniques. The response to homologous lens antigens, both in magnitude as well as in duration, varied in different rabbits, which suggested to us that a central control mechanism involving the immune response (Ir) genes may plan an important role. Antibodies to homologous lens proteins as detected by immunofluorescence and immunoperoxidase methods were shown to be of the IgG class. This is the first time that the kinetics of the immune response to the same homologous lens antigen in saline with or without incomplete or complete adjuvant has been examined and their relative merits compared. Systemic homologous immunisation followed by discission of the lens led to a marked Arthus type reaction in and around the lens, but a typical granulomatous phakoallergic endophthalmitis was not produced. It seems likely that the rabbit is not suitable for the production of an experimental model of this condition.     

Immunopathology of the lens. I. Humoral and cellular immune responses to heterologous lens antigens and their roles in ocular inflammation.

In experimental rabbits heterologous soluble lens proteins consisting of alpha-, beta-, and gamma-crystallins were found to be antigenic; they stimulated a marked antibody response compared to a rather weak T-cell response. The serum antibodies to alpha-crystallins appeared first, to be followed by antibodies to beta- and gamma-crystallins in that order. The rabbits did not respond to heterologous gamma-crystallins unless these were injected with Freund's adjuvant containing mycobacteria. Incomplete Freund's adjuvant (i.e., without mycobacteria) was found to be an inferior immunoaccelerator so far as lens antigens are concerned. The response to lenticular antigens in both magnitude and duration varied in different rabbits, which suggested to us the important role played by a central control mechanism involving the immune response (Ir) genes. Some of the antibodies in potent lens antisera cross-reacted with mitochondria, endoplasmic reticulum (i.e., microsomes), contractile organelles, and cell nuclei. This explains for the first time at least in part the reasons for the widely observed phenomenon of the reactivity of lens antisera with ocular and extraocular structures. Antibodies to soluble lens proteins as detected by immunofluorescence and immunoperoxidase techniques were shown to be of the IgG class. Systemic heterologous immunisation followed by discission of the lens does not lead to the typical changes of phakoallergic endophthalmitis in the rabbit.     

非球面人工晶状体度数计算的最优化

目的：：通过评价非球面人工晶状体( intraocular lens, IOL)屈光度的可预测性,初步开发一种计算屈光度( PIOL )的优化算法。方法：本研究纳入植入非球面 IOL ( LENTIS L-313, Oculentis GmbH)65眼,并分为2组：A组8例12眼,PIOL≥23.0D;B组35例53眼,PIOL<23.0D。术后3mo进行屈光度可预测性评价。参考角膜屈光力估计所致的可变性屈光指数计算出校正的IOL度数( PIOLadj )及屈光结果,根据年龄和解剖学因素得出校正的有效晶状体位置( adjusted effective lens position, ELPadj )。结果：术后A、B两组等效球镜度数分别为-0.75~+0.75 D、-1.38~+0.75D。 A、B两组的PIOLadj和实际晶状体屈光度(PIOLReal)之间无统计学差异(P=0.64、0.82)。 Bland-Altman分析显示A、B两组PIOLadj和PIOLReal之间的一致性区间分别为+1.11~-0.96 D和+1.14~-1.18 D。 Hoffer Q公式和Holladay I公式计算PIOLadj和PIOL之间存在临床和统计学上的显著差异(P<0.01)。结论：植入非球面IOL白内障手术的屈光可预测性可通过平行轴光学联合线性法则使角膜屈光力及晶状体位置相关误差最小化。