Vision of low astigmats through thick and thin lathe-cut soft contact lenses

Addressing common myths and misconceptions in soft contact lens practice

Advances in contact lens technology over the past 50 years since the commercialisation of the first soft lenses in 1971 have been incredible, with significant changes in contact lens materials, frequency of replacement, care systems and lens designs occurring. However, despite the widespread availability of contact lenses, penetration rates for those who need vision correction remain in the low single digits and many practitioners seem to hold on to concepts around the potential value of contact lenses that appear based in the dim and distant past and are certainly no longer valid today. This review addresses 10 common 'myths and misconceptions' around soft contact lenses using an evidence-based approach that can hopefully dispel some of these incorrect assumptions.

Low toric soft contact lens acceptance study

PURPOSE

The aim of the study was to evaluate the objective and subjective visual performance of custom toric contact lenses (TL) and their spherical off-the-shelf counterparts (SL) in subjects with low amounts of astigmatism.

METHODS

Twenty-three habitual soft lens wearers (40 eyes, 25-35 years) manifesting 0.50-1.00DC and ≤±3.00DS were recruited. Air Optix Aqua (Lotrafilcon B) was fit using the spherical equivalent of the manifest refraction. Intelliwave toric in Efrofilcon A (Definitive) was fit using the manifest refraction and keratometric data. Comprehensive visual performance tests were done through manifest refraction in a trial frame; in SL; and in TL. A subjective evaluation of quality of vision was also obtained.

RESULTS

ANOVA revealed that, at the morning visit (AM), high contrast logMAR distance visual acuity (HCDVA) was significantly better (p<0.01) in spectacles as compared to SL. A similar trend was noted at the afternoon visit (PM). In addition, at the PM visit, HCDVA was significantly better (p<0.01) for TL as compared to their SL. ANOVA revealed that, at the PM visit, low contrast distance visual acuity (LCDVA) was significantly better (p=0.05) in spectacles as compared to SL. None of these differences were clinically significant. In addition, no statistically significant difference (p>0.05) in subjective vision rating scores was noted between SL and TL.

CONCLUSIONS

The present investigation found no clinically significant difference in visual performance between spherical and toric soft contact lenses in low astigmats.

A literature review: the impact of rotational stabilization methods on toric soft contact lens performance

Toric soft contact lenses have been in the marketplace for more than 30 years. Over this period of time, substantial improvements have been made in the areas of lens reproducibility, lens material permeability, frequency of lens replacement, and availability of lens design and parameter options. This article will review the methods used to stabilize lens rotation and their effectiveness as reported in the literature.

Success rates in the correction of astigmatism with toric and spherical soft contact lens fittings

Objectives:

To evaluate success rates in the correction of astigmatism with toric and spherical soft contact lens fitting.

Methods:

30 patients with soft toric lenses having more than 1.25 D of corneal astigmatism (25 eyes; Group A) or having 0.75–1.25 D of corneal astigmatism (22 eyes; Group B) and 30 patients with soft spheric lenses having 0.75–1.25 D of corneal astigmatism (28 eyes; Group C) or less than 0.75 D of corneal astigmatism (23 eyes; Group D) were included in the study. Corrected and uncorrected monocular visual acuity measurement with logMAR, biomicroscopic properties, autorefractometry and corneal topography were performed for all patients immediately before and at least 20 minutes after the application of contact lenses. Success of contact lens fitting was evaluated by three parameters: astigmatic neutralization, visual success, and retinal deviation.

Results:

After soft toric lens application, spheric dioptres, cylindric and keratometric astigmatism, and retinal deviation decreased significantly in Groups A and B (P < 0.05). In Group C, spheric dioptres and retinal deviation decreased (P < 0.05), while cylindric and keratometric astigmatism did not change significantly (P > 0.05). In Group D, spheric dioptres, retinal deviation, and cylindric astigmatism decreased (P < 0.05). Keratometric astigmatism did not change significantly (P > 0.05) and astigmatic neutralization even increased.

Conclusions:

Visual acuity and residual spherical equivalent refraction remained between tolerable limits with the use of toric and spheric contact lenses. Spherical lenses failed to mask corneal toricity during topography, while toric lenses caused central neutralization and decrease in corneal cylinder in low and moderate astigmatic eyes.

Inefficacy of Aspheric Soft Contact Lenses for the Correction of Low Levels of Astigmatism

PURPOSE

The purpose of this article is to compare the visual performance of a toric soft (TS) contact lens (SofLens 66 Toric; Bausch & Lomb, Rochester, NY), an aspheric soft (AS) contact lens (Frequency Aspheric; CooperVision, Fairport, NY) and a spectacle correction (SC) in subjects with low levels of astigmatism.

METHODS

One eye of 30 subjects with refractive astigmatism of -0.75 DC or -1.00 DC was tested. After pupil dilation, each subject was fitted with all three forms of correction in random order. Subjects were masked from the contact lens type. High-contrast visual acuity (HCVA) and low-contrast visual acuity (LCVA) were recorded for each correction using 2-mm, 4-mm, and 6-mm artificial pupils.

RESULTS

With a 2-mm pupil, HCVA was similar for the TS lens and the SC (p = 0.13); better HCVA was demonstrated with the TS lens than with the AS lens (p = 0.001). With 4-mm and 6-mm pupils, HCVA was poorer with the AS lens than with the SC (p < 0.002) and TS lenses (p < 0.0001). The difference in HCVA between the TS and AS lenses was two letters, three letters, and one line with pupil sizes of 2 mm, 4 mm, and 6 mm, respectively. LCVA was similar for the three refractive conditions with the 2-mm pupil size. With 4-mm and 6-mm pupils, LCVA was similar for the TS lens and SC, but better than the AS lens by approximately one line in each case (all p < 0.0001).

CONCLUSIONS

For small pupil sizes, there is little difference in HCVA and LCVA between various refractive corrections. However, for larger pupils, HCVA and LCVA are superior with TS contact lenses and SC versus AS contact lenses by approximately a half-line or more, which is considered to be clinically significant. Superior vision can be achieved for low astigmatic contact lens wearers using TS rather than AS contact lenses.

Repeatability of the Waterloo Four-Contrast LogMAR Visual Acuity chart and Near Vision Test card on a group of normal young adults

PURPOSES

To investigate the repeatability of logMAR visual acuity (VA) with the Waterloo Four-Contrast LogMAR Visual Acuity (FCLVA) chart and the Near Vision Test (NVT) card. The differences and agreements between near logMAR VA using horizontally- and vertically-presented letters were also determined.

METHODS

Visual acuity of one eye (55 subjects) was first assessed by using the FCLVA chart, comprising four charts of varying contrast, and then with the NVT card (comprising four charts of two contrasts and two presentations). Measurements were repeated after 3 or 4 weeks.

RESULTS

No significant between-visit differences were observed for any of the charts used. The repeatability coefficient for the distance 90, 60, 30 and 10% charts were 0.07, 0.11, 0.15 and 0.16 log units, respectively. The repeatability coefficients of the near vision charts were 0.06, 0.04 (high contrast), 0.11 and 0.10 (low contrast) log units. The agreements between horizontally- and vertically-presented letters were good. The differences were similar to the repeatability coefficient of each chart.

CONCLUSIONS

The repeatability coefficient of the high contrast distance and near chart was about half a line. Repeatability coefficients increase with decreasing contrasts for both distance and near charts, with coefficients of one line or more for low contrast charts. Variabilities in both distance and near VA increase with decrease in contrast. The presentation of the letters does not affect near VA and the agreement between horizontally- and vertically-presented letters (both high and low contrast) was within the repeatability coefficient of each chart.