Simplified fitting procedures for toric soft contact lenses

This pilot study assessed a simplified procedure for fitting toric soft contact lenses without the use of a diagnostic fitting set. The sample consisted of 12 patients (21 eyes) who has astigmatic refractive effects of -0.75 D.C. to -2.50 D.C. and who ranged in age from 21-38 years. Patients were fit using a standard protocol. Using the criteria of success as defined in this paper, 17 of the 21 eyes were successfully fit with Hydromarc toric soft contact lenses.     

Localized edema with soft toric contact lenses

Soft toric contact lenses had provided a good correction for this patient for 3 1/2 years. An acute episode of slightly decreased vision and lens discomfort was accompanied by corneal irritation, edema, irregular distorted keratometric mires, and a change in refractive cylinder. It is of interest that the areas of most corneal disturbance were in continuous apposition to the areas of most deposits on the non-rotating toric contact lenses.     

Reliability of power measurement of toric soft contact lenses

We studied the reliability of lensometer measurements of hydrated toric soft contact lenses in air and compared them to similar measurements of toric hard contact lenses and a spherocylindrical spectacle lens. Twenty measurements were made of each of five soft lenses, three hard lenses, and one spectacle lens. One-half of the measurements used an eyepiece lensometer and one-half a projection lensometer. The reliability of the technique was found to be lower for soft lenses than for hard lenses and highest for the spectacle lens. Reliability was sufficiently high for hydrated toric soft lenses with either type of lensometer to support recommendation of a standard tolerance of +/-0.25 D when applied to the mean of five measurements.     

Vision with disposable toric contact lenses and daily-wear toric contact lenses

The study compared the vision, the use and evaluation criteria in a group of students with corrective daily-wear toric contact lenses and disposable toric contact lenses, in order to ascertain which of the two optical systems is more advantageous. We fitted 114 subjects with daily-wear and disposable lenses to be worn for 12 months, one type of lens in one eye and the other type in the fellow eye. The results reveal no significant differences between the two systems in terms of visual acuity attained; both lenses centred well and were comfortable. Nevertheless, the deposits were significantly greater in the daily-wear lenses. The ocular reactions were less with the disposable toric lenses. In conclusion, the disposable lenses led to fewer deposits and less ocular reactions, but are limited in parameters. However, both optical systems were appropriate for correcting for astigmatism, and provided good visual acuity.     

散光软镜的旋转性评估分析

目的 研究散光软镜配适中代表镜片稳定性的评估因素及这些因素之间的相关性.方法 非干预性、观察性研究.32名散光软镜配戴者,经角膜接触镜的常规验配前检查,给予双眼配戴一种低旋智动定位设计的频繁更换型散光软镜,20 min后进行稳定性的评估,评估因素包括戴镜视力、镜片定位、活动度、散光轴旋转方向、旋转度数、旋转稳定性、鼻侧旋转恢复速度和颞侧旋转恢复速度.随机选择一眼数据,采用SPSS 13.0软件,对配适评估因素之间进行Partial相关性分析.结果 散光软镜配戴者中,旋转方向为偏颞侧者占59%,所有配戴者的平均旋转度数为（10.56±7.77）°：鼻侧旋转恢复速度和整体评估之间呈负相关（r=-0.49,P=0.005）,镜片配适越松,旋转恢复速度越快：旋转度数与旋转方向之间存在正相关（r=0.48,P=0.006）,向颞侧旋转时的旋转度数少于向鼻侧旋转时的旋转度数：旋转度数与旋转稳定性之间呈正相关（r=0.45,P=0.010）,旋转度数越少,旋转稳定性越好.结论 目前国内临床应用较多的频繁更换型散光软镜相对容易向颞侧旋转,其整体配适以相对偏松为主,旋转程度偏大,临床验配中应该引起重视;散光软镜配戴者的配适评估因素之间存在一定的相关性,影响镜片稳定性的主要因素包括整体配适评估和旋转度数,提示在临床运用中应该更加重视散光软镜的整体配适评估结果和旋转程度等问题.     

Now soft toric contact lenses; silicone hydrogel lens for astigmatism

Soft toric contact lenses are a good alternative for the optical correction of astigmatism. They provide a wide visual field, quick adaptation process, negligible aniseikonia, together with enhanced comfort and reduced incidence of complications introduced by the lenses for frequent replacement. Still practitioners do not recommend them proactively and the satisfaction obtained by the patients is not high enough. This paper presents two recent studies that investigate the opinions of specialists and contact lens wearers and introduce a new contact lens, with an original design, born after 30 years of domination of only 2 modalities of rotational stabilization: prism ballast and dual thin zones. The lens is manufactured using a silicon-hydrogel material of 2-nd generation that provides sustained comfort and better oxygenation.     

Rotational stability of toric soft contact lenses during natural viewing conditions.

PURPOSE: To compare objectively the rotational stability of two differently designed toric soft contact lenses over a range of natural viewing conditions using a novel infrared, video-based technique. METHODS: Two contact lenses using different methods of stabilization were assessed: Accelerated Stabilization Design (ACUVUE ADVANCE for ASTIGMATISM) and Lo-Torque Design (B&L SofLens Toric). Four tasks involving saccades were performed: settling time with free viewing, reading, visual search, and execution of large versional tasks. Lens position (degrees of rotation) was continuously recorded with a head mounted, infrared, video-based system and a digital photo slit-lamp in 20 adult subjects. All measurements were obtained from the left eye under binocular viewing conditions with contact lenses on both eyes. RESULTS: The ACUVUE lens was significantly more stable during the settling time and large saccadic versional tasks than the SofLens. For the two other tasks (reading, visual search), performance was similar. CONCLUSION: The ACUVUE design was superior in stability for two of the four conditions tested. This resulted in a more stable lens immediately after insertion as well as during some visual tasks involving either naturally occurring or programmed large versional eye movements. Both lens designs provided acceptable performance in terms of induced astigmatism produced by off-axis rotation.     

Vertical imbalance induced by prism-ballasted soft toric contact lenses fitted unilaterally.

Fitting a prism-ballasted soft toric contact lens unilaterally may potentially induce a vergence error that the subject cannot compensate. In the present study, a prism-ballasted (1.5Delta base down) soft toric contact lens was fitted in the right eye only of 10 subjects with normal binocular vision. The effect on binocular vision was evaluated by measuring vertical phoria adaptation and vertical fixation disparity adaptation. The results show that the vertical vergence error induced was well compensated and fully adapted to. However, care might be needed when fitting these lenses unilaterally in subjects with vertical phoria-related problems.     

Rotational characteristics of toric contact lenses

Prospective data from 11 patients (18 eyes) each fit with five soft toric contact lens designs were analyzed for lens rotation at fitting, at dispensing, and at a 1-week follow-up. The purpose was to determine which lens designs has the best performance when comparing mean rotation among diagnostic lens, lens ordered, and postdispensing lens. The study also obtained subjective data on comfort, visual acuity, consistency of vision, handling, and overall satisfaction of each of the lens designs in the study. Rotational characteristics of a lens design often determine the practitioner's success in fitting a particular astigmatic patient. The back-surface toric-designed lenses showed the best performance as indicated by the lowest mean rotations when compared to the other toric lens-stabilizing designs, although all lenses showed consistency with time.     

Stability characteristics of toric soft lenses

The interblink stability of front toric, back toric, thin zone, thin zone/prism, and prism ballast hydrogel toric contact lens designs were assessed on 40 eyes. Subjects were placed in one of four categories, based upon corneal curvature. Lenses were videotaped in stitu video biomicroscopy through 10 normal blinks. Rotation was assessed with a protractor template aligned with enhanced manufacturer's markings to determine rotational amounts. The results indicate that there is no statistically significant difference between the interblink stability of the four lens designs investigated in this study. This confirms results of related studies previously conducted.     

Dynamic simulation of the effect of soft toric contact lenses movement on retinal image quality.

PURPOSE: To report the development of a tool designed to dynamically simulate the effect of soft toric contact lens movement on retinal image quality, initial findings on three eyes, and the next steps to be taken to improve the utility of the tool. METHODS: Three eyes of two subjects wearing soft toric contact lenses were cyclopleged with 1% cyclopentolate and 2.5% phenylephrine. Four hundred wavefront aberration measurements over a 5-mm pupil were recorded during soft contact lens wear at 30 Hz using a complete ophthalmic analysis system aberrometer. Each wavefront error measurement was input into Visual Optics Laboratory (version 7.15, Sarver and Associates, Inc.) to generate a retinal simulation of a high contrast log MAR visual acuity chart. The individual simulations were combined into a single dynamic movie using a custom MatLab PsychToolbox program. Visual acuity was measured for each eye reading the movie with best cycloplegic spectacle correction through a 3-mm artificial pupil to minimize the influence of the eyes' uncorrected aberrations. Comparison of the simulated acuity was made to values recorded while the subject read unaberrated charts with contact lenses through a 5-mm artificial pupil. RESULTS: For one study eye, average acuity was the same as the natural contact lens viewing condition. For the other two study eyes visual acuity of the best simulation was more than one line worse than natural viewing conditions. CONCLUSIONS: Dynamic simulation of retinal image quality, although not yet perfect, is a promising technique for visually illustrating the optical effects on image quality because of the movements of alignment-sensitive corrections.     

Theoretical optics of toric hydrogel contact lenses

Toric hydrogel contact lenses are used when spherical lenses prove inadequate at correcting refractive error due to astigmatism. A model of hydrogel contact lens flexure effects allows theoretical investigation of the in situ optical power of toric soft contact lenses. Total meridional power is believed to be the sum of meridional lens power and entrapped tear layer power if any, and not due to lens form or flexure when considering low-minus powered lenses. The clinician should reduce astigmatic power correction both to allow for minus tear lens effects in thicker meridians and to decrease variable visual results due to misrotation.