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Biomedical subjects

Nathan Efron

Publications and source records attributed to Nathan Efron.

At least 19 recordsLinked to original sources
PubMed2006

A longitudinal case series investigating cellular changes to the transplanted cornea using confocal microscopy.

PURPOSE: To perform a longitudinal evaluation of subjects who had undergone penetrating keratoplasty, using slit scanning confocal microscopy. METHODS: In vivo confocal microscopy was used to evaluate the central cornea of four subjects who had recently undergone penetrating keratoplasty. Subjects were examined on four occasions over a 12-month period after surgery. Quantitative and qualitative aspects of corneal morphology were compared against data from normal control subjects. RESULTS: The epithelium varied in appearance between subjects and took at least 12 months to return to a similar arrangement to that seen in normal eyes. Bowman's layer was viewed as an acellular layer immediately after surgery with no evidence of nerve fibres, although nerve components were apparent 12 months after surgery. Stromal nerves were not visible immediately after surgery. One year following penetrating keratoplasty there was evidence of thin nerves running a straight course through the central stroma. Keratocyte density in the anterior and posterior stroma was lower in the transplanted cornea but appeared to remain constant over a period of 1 year. Activated keratocytes were seen in the anterior stroma of all subjects; they appeared to be responsible for significant levels of corneal haze. The time period within which this keratocyte activation occurred varied between individuals. Endothelial cell density decreased at an accelerated rate over the 12-month period. CONCLUSIONS: Confocal microscopy allows cellular changes to be monitored in vivo following penetrating keratoplasty and may assist clinicians in understanding postoperative recovery.

Adult↗
PubMed2006

A decade of contact lens prescribing trends in the United Kingdom (1996-2005).

PURPOSE: To document contact lens prescribing trends in the United Kingdom over the past decade (between 1996 and 2005). METHODS: An annual survey of contact lens prescribing trends was conducted each year by asking a random selection of optometrists and dispensing opticians to provide information relating to 10 consecutive contact lens fits between January and March. RESULTS: Over the 10-year survey period, 1251 practitioners returned survey forms representing a total of 12,050 contact lens fits. The mean (+/-standard deviation) age of lens wearers was 33+/-13 years of which 64% were female. Over the survey period, rigid lens new fits decreased from 22% to 4%. Low water content lenses reduced from 20% to 2% of new soft lens fits. Soft toric lenses gradually increased to the point where they accounted for the expected proportion of patients with astigmatism>or=1.00DC (i.e. >20% of soft lens fits). Monthly and daily disposable lenses accounted for >90% of all soft lens fits between 2003 and 2005. The proportion of new soft fits and refits prescribed as extended wear has gradually increased, stabilizing at about 5% of new fits and 12% of refits. Multi-purpose lens care solutions increased from 60% of all care systems in 1997 to 91% in 2005. Rigid lenses and monthly replacement soft lenses are predominantly worn on a full time basis, whereas daily disposable soft lenses are mainly worn part time. CONCLUSIONS: This survey indicates that technological advancements such as the development of new lens materials, manufacturing methods and lens designs have had a significant impact on the contact lens market over a relatively short period of time.

Adolescent↗
PubMed2006

Assessment of stromal keratocytes and tear film inflammatory mediators during extended wear of contact lenses.

PURPOSE: To monitor quantitative changes in stromal keratocyte density and the level of tear film inflammatory mediators following extended contact lens wear. METHODS: Twenty-two subjects aged 32 +/- 11 years participated in this cross-sectional study. Eleven subjects had worn silicone hydrogel (Si-H) lenses on a 30-day continuous wear basis for 12 months. Eleven subjects had worn rigid gas permeable lenses on the same basis for 12 months. Eleven age-matched control subjects were also recruited. Ultrasound pachometry, confocal microscopy, and tear fluid sample collection were performed on all subjects. Tear samples were assayed for epidermal growth factor (EGF), hepatocyte growth factor (HGF) and interleukin (IL)-8. RESULTS: Corneal thickness was similar for all subject groups. Total keratocyte density was not different between the 3 groups; however, keratocyte density was lower for rigid lens wearers in the anterior to mid stroma and lower for Si-H lens wearers in the posterior stroma compared with control subjects. Rigid lens wearers exhibited an irregular keratocyte distribution across the corneal stroma. EGF concentration and rate of release was greater in the tears collected from the rigid lens wearers and Si-H lens wearers, and IL-8 concentration was higher in the samples collected from the rigid lens wearers compared with the samples collected from the control subjects. CONCLUSIONS: Mechanical stimulation of the corneal surface due to the physical presence of a contact lens and the consequent release of inflammatory mediators may account for a loss or redistribution of keratocytes.

Adult↗
PubMed2006

Can subtypes of contact lens-associated corneal infiltrative events be clinically differentiated?

PURPOSE: A schema has recently been described for clinical differentiation among 4 symptomatic subtypes of contact lens-associated corneal infiltrative events (CIEs): microbial keratitis (MK), contact lens-induced peripheral ulcer (CLPU), contact lens-induced acute red eye (CLARE), and infiltrative keratitis (IK). The clinical utility of this schema has been challenged in the literature. The aim of this study is to determine whether it is possible to clinically differentiate among these conditions. METHODS: Criteria for MK, CLPU, CLARE, and IK were applied to a data set of 111 contact lens-associated CIEs, spanning a wide range of clinical severities, presenting consecutively to a hospital clinic. A Venn diagram analysis was used to determine the extent to which these conditions can be clinically differentiated. RESULTS: Of the 111 CIEs, 20% could be classified unambiguously as MK, CLPU, CLARE, or IK, 56% could be classified as 1 of 2 conditions, 13% could be classified as 1 of 3 conditions, and 0% could be classified as 1 of 4 conditions. Eleven percent of CIEs could not be classified as any of the 4 conditions. CONCLUSIONS: Although the etiology of CIEs is multifactorial, the considerable overlap between the clinical presentation of MK, CLPU, CLARE, and IK is such that it is not possible to clinically differentiate between them with any degree of certainty. A preferred approach might be to consider CIEs as part of a disease continuum whereby these events can manifest in various degrees of severity, depending as well on the point at which the condition is observed in the course of the natural history of the disease.

Contact Lenses↗
PubMed2006

Corneal hydration control in contact lens wearers with diabetes mellitus.

PURPOSE: The purpose of this study was to assess the acute swelling and recovery response to contact lens-induced corneal hypoxia in diabetic patients who wear contact lenses. METHODS: A thick, low water content, soft contact lens was fitted under a light patch to one eye of 23 diabetic patients and one eye of 23 nondiabetic control subjects in a single-masked, controlled clinical study. After 2.5 hours an ultrasonic pachymeter was used to measure the induced corneal edema and the rate at which the cornea recovered to baseline thickness. RESULTS: The induced corneal edema was significantly less for the diabetic patients compared with the nondiabetic control subjects (p = 0.004). The corneas of the diabetic patients were found to recover from the induced edema at a similar rate to the corneas of the nondiabetic control subjects (p = 0.28). CONCLUSIONS: Diabetes mellitus alters aspects of corneal hydration control.

Adult↗
PubMed2006

Impact of differences in diagnostic criteria when determining the incidence of contact lens-associated keratitis.

PURPOSE: The purpose of this study is to examine the effect of differences in within-study and between-study diagnostic criteria in determining the incidence of contact lens-associated keratitis. METHODS: We applied the sets of criteria for "microbial keratitis" as described in five previous studies to the dataset of Morgan et al., which documents 118 cases of contact lens-associated keratitis across a wide range of clinical severities. For each set of criteria, the incidence of contact lens-associated keratitis was calculated for the following five lens type/modality combinations: daily-wear rigid, daily-wear daily disposable hydrogel, daily-wear hydrogel, extended-wear hydrogel, and extended-wear silicone hydrogel. The effect of varying the clinical severity score for the differentiation of nonsevere versus severe keratitis was also examined with respect to the dataset of Morgan et al. RESULTS: The size and location of the corneal infiltrative events identified as representing "microbial keratitis" for each of the different sets of criteria are illustrated in a series of cartograms. A key between-study difference in the incidence values calculated for the various sets of criteria relates to the categories of extended-wear hydrogel and extended-wear silicone hydrogel lenses. Specifically, the incidence of "microbial keratitis" was found to be statistically significantly greater for extended-wear hydrogel compared with extended-wear silicone hydrogel lenses when the set of criteria of Morgan et al. was applied, but not when the other sets of criteria were applied, to the dataset of Morgan et al. Increasing the threshold clinical severity criterion for differentiating between nonsevere and severe keratitis within this dataset resulted in lower incidence values; however, such changes in threshold had a minimal impact on relative risk values. CONCLUSIONS: The choice of criteria for diagnosing contact lens-associated "microbial keratitis" has a significant impact on calculations of the incidence of this condition.

Contact Lenses↗
PubMed2006

Rethinking contact lens associated keratitis.

This review presents a critical analysis of the literature relating to the use of binomial and polynomial classification schemes for categorising corneal infiltrative events (CIEs) associated with contact lens wear and the epidemiology of such events. The results of the Manchester Keratitis Study-a 12-month, prospective, hospital-based epidemiological study of contact lens wearer suffering from CIEs-are used as a tool to challenge and test traditional thinking in relation to contact lens associated keratitis. An innovative aspect of this study is the use of a novel clinical severity matrix to systematically score the severity of CIEs based on 10 key signs and symptoms. The ambiguities inherent in using binomial classification schemes (such as, microbial versus sterile, ulcerative versus non-ulcerative etcetera) are highlighted. The failure of a polynomial scheme-due to extensive classification overlap between proposed sub-types of CIEs-is demonstrated using a Venn diagram. A cartographic analysis reveals that infiltrates tend to occur in the superior cornea of patients wearing extended wear silicone hydrogel lenses, in the central cornea of patients wearing daily wear hydrogel daily disposable lenses and in the peripheral cornea of patients wearing daily wear hydrogel (excluding daily disposable) lenses. Infiltrates that occur more towards the limbus are less severe. The incidence of CIEs is higher when contact lenses are worn overnight. Logistic analysis reveals that the risk of developing a severe CIE is five times greater with conventional hydrogel extended wear versus silicone hydrogel extended wear. The male gender, smoking, a healthy eye and body, and the late Winter months are associated with an increased risk of developing CIEs. The rate of significant visual loss as a result of developing a CIE is low. Two key conclusions are drawn from this work, which represent a radical rethinking of this potentially sight-threatening condition. CIEs should be considered as a continuous spectrum of ocular disease. If a contact lens wearer presents with a sore eye that is becoming progressively worse and a CIE is observed in that eye, lens wear should be suspended and anti-microbial therapy initiated immediately.

Bacteria↗
PubMed2006

Dynamic wettability of pHEMA-based hydrogel contact lenses.

Standard methods of contact angle analysis include sessile drop, captive bubble and Wilhelmy plate techniques; however, these methodologies are not particularly well suited for assessing the wettability of the surfaces of formed hydrogel contact lenses. This paper describes two methodologies that are adaptations of previously described techniques. The maximum adherent force method is an adaptation of the dynamic Wilhelmy plate technique that allows the assessment of whole, finished contact lenses. The dynamic photographic method allows the simultaneous assessment of the front and back surfaces of strip samples for the assessment of advancing and receding contact angles. Lenses investigated were made from polyhydroxyethyl methacrylate, hydroxyethyl methacrylate/methacrylic acid and hydroxyethyl methacrylate/glycerol methacrylate. The lenses were manufactured by lathing, spin-casting or cast-moulding techniques. Overall, both techniques demonstrated few differences between the wettability of different lens materials and no differences between materials of the 'same' lens type but manufactured by different methods. These findings are consistent with the results of clinical studies, which have shown little difference between contact lens surface wettability in vivo, which may be due to the apparent natural surface wettability-enhancing properties of the pre-lens tear film.

Biocompatible Materials↗
PubMed2005

Comparative clinical performance of rigid versus soft hyper Dk contact lenses used for continuous wear.

PURPOSE: The purpose of this study is to investigate the comparative clinical performance of two hyper Dk contact lenses: a silicone hydrogel lens (Focus Night & Day, Ciba Vision) and a rigid lens (Z-alpha, Menicon Co. Ltd.) when worn for up to 30 days of continuous wear (CW). The rigid lens was worn on an unplanned replacement basis, whereas the soft lens was replaced monthly. METHODS: One hundred subjects were recruited. Fifty neophyte subjects were randomly assigned into one of the lens types (25 subjects per lens type). Twenty-five existing daily wear (DW) rigid lens users wore the rigid study lens and 25 existing DW soft lens users wore the soft study lens. Visual acuity, lens fit, keratometry, refraction, lens surface assessment, physiological response, and subjective response were investigated at baseline and after 1 week of DW and 24 hours, 1 week, and 1, 3, 6, 9, and 12 months of CW. Analysis compared lens type (rigid vs. soft) and subject group (experienced vs. neophyte). RESULTS: Sixty-eight subjects completed the study. Visual acuity was similar for the two lens types and subject groups. Lens fit was judged to be adequate in all subjects. Corneal curvature of subjects in the rigid groups became flatter by 0.13 mm compared with 0.04 mm for subjects in the soft lens groups (F = 14.7, p = 0.0003); the refractive findings mirrored these corneal changes. The increasing rate of deposition on rigid lenses was consistent with the fact that these lenses were not replaced during the study. Conjunctival hyperemia and staining were similar for the two lens types but greater among experienced wearers at baseline (F = 13.8, p = 0.0005; F = 5.3, p = 0.02, respectively). Corneal staining was higher for the rigid lens wearers (F = 5.6, p = 0.02) but this was mainly the result of the initial higher scores in the rigid lens experienced group. The change in papillary conjunctivitis was greater for subjects in the soft lens groups than rigid lens groups (F = 4.6, p = 0.04). Comfort was initially lower for the rigid lens neophyte group (F = 4.2, p = 0.0001), but after the CW phase started, there were no differences between groups. CONCLUSIONS: Notwithstanding subtle differences in physiological responses, continuous wear hyper Dk rigid and soft silicone-containing contact lenses can be successfully worn by both those with previous contact lens experience and those with no history of contact lens wear.

Adult↗
PubMed2005

Empirical versus trial set fitting systems for accelerated orthokeratology.

PURPOSE: To compare the short-term clinical performance of two reverse-geometry rigid contact lens systems for accelerated orthokeratology with different fitting approaches and designs: an experimental lens that was fitted empirically (No. 7 Contact Lens Laboratory, Ltd.) and a more established lens using a trial set system, the BE lens (NKL). METHODS: Twenty-four subjects were enrolled in a clinical study in which the two reverse-geometry lenses were worn contralaterally for seven nights. The No. 7 lens was manufactured based on subject keratometric readings, refraction, and horizontal visible iris diameter. The BE lens was fitted in accordance with fitting guidelines provided by the manufacturer and included the use of proprietary computer software in addition to an overnight trial before lens ordering. Data were collected at baseline, day 1, and day 7 (morning and afternoon). Unaided visual acuity, best-corrected visual acuity, subjective refraction, corneal topography, biomicroscopy (corneal staining), and subjective reaction were recorded at each visit. RESULTS: Nine subjects (18 eyes) completed the study. All eyes fitted with the No. 7 lens and 67% of the eyes fitted with the BE lens were within +/-1.00 diopter of the attempted correction after seven nights of lens wear. There was more myopic reduction (F = 16.2, P=0.0002), better unaided high-contrast visual acuity (F = 8.7, P=0.005) and low-contrast visual acuity (F = 9.5, P=0.003), and more change in corneal numerical eccentricity (F = 8.6, P=0.005) with the BE lens than with the No. 7 lens. There were no significant differences between the lenses for best-corrected visual acuity, change in apical radius, corneal staining, and subjective reaction. DISCUSSION: Both lens types investigated in this study were effective in temporarily reducing myopia and in providing good unaided visual acuity during the day (without lenses) in subjects with low levels of myopia. Subjective reaction showed that the lenses were perceived as being equally effective, but clinical data showed that the BE lens effected more myopic reduction and better unaided visual acuity than did the No. 7 lens during the 7-day period investigated.

Adult↗
PubMed2005

An investigation of the discrete and continuum models of water behavior in hydrogel contact lenses.

PURPOSE: To investigate the water behavior in hydrogels of differing equilibrium water content (EWC) and to use these results to investigate the opposing discrete model (thermodynamically different classes of water exist in hydrogels) and continuum model (water behaves as a consequence of nonequilibrium conditions) of nonfreezing water in swollen hydrogels. METHODS: Differential scanning calorimetry (DSC) was used to obtain melting thermograms for five lenses of each of 12 hydrogel lens types. The gravimetric content of the nonfreezing water was subsequently determined from an integrated endotherm for water. The effect of anneal time on the amount of nonfreezing water obtained in samples was investigated before undertaking these measurements. The glass transition temperature (Tg) of each of the lens types was obtained with DSC to investigate how the Tg was related to the amount of nonfreezing water found in the hydrogels. RESULTS: Melting enthalpy increased with increasing anneal time and leveled off at 6 hours. Low-EWC lenses showed endotherms with a single melting peak at 0 degrees C. Materials with a higher EWC showed more complicated melting endotherms, with a broad shoulder occurring at temperatures below 0 degrees C. There was a statistically significant positive correlation between EWC and freezing water (R=0.95, P<0.0001), but the amount of nonfreezing water was similar for all lens materials. There was a statistically significant positive correlation between the Tg of the hydrogels and the theoretically derived weight fraction of nonfreezing water in the hydrogels required to bring the Tg of the gels down to 0 degrees C (R=0.99, P<0.0001) but not with the experimentally derived values (R=0.29, P=0.07). CONCLUSIONS: Low-EWC hydrogels have the lowest free-to-bound water ratios. That the experimentally derived values of nonfreezing water are different from the theoretically derived values creates doubt with the continuum model theory. The best model probably employs a combination of the discrete and continuum theories.

Calorimetry↗
PubMed2005

Observations of banding patterns (Vogt striae) in keratoconus: a confocal microscopy study.

PURPOSE: To investigate Vogt striae in keratoconus using confocal microscopy. METHODS: The central cornea of 51 eyes of 29 subjects with keratoconus was observed using a slit-lamp biomicroscope, slit-scanning confocal microscope (TOMEY Confoscan 1), and corneal topographer (EyeSys 2000). RESULTS: Alternating dark and light bands were seen in the stromal images of 23 eyes examined. The bands corresponded with the appearance of Vogt striae on slit-lamp biomicroscopy examination. Bands were found most commonly in the posterior stroma. Posterior bands varied in width, ran mainly in a nearly vertical direction, and appeared to run a straight course through individual image frames. Keratocyte nuclei were located in between the bands. Posterior keratocyte density was unaffected by the presence of bands. Nerve fibers appeared to run a straight course through the bands. When present, bands in the anterior stroma showed greater variability in width and direction within a single frame. Bands were only present in the anterior stroma in more severe levels of keratoconus. The difference in banding pattern noted between the anterior and posterior stroma parallels the known collagen fiber arrangement in the anterior and posterior stroma. CONCLUSIONS: The bands apparent on confocal microscopy of the stroma of the keratoconic cornea correspond with Vogt striae on slit-lamp microscopy. It appears that these bands (and hence Vogt striae) represent collagen lamellae under stress. The stress pattern appears to radiate from the center of the cone and is consistent with the direction of striae when viewed with the confocal microscope.

Adolescent↗
PubMed2005

Correlation of the appearance of the keratoconic cornea in vivo by confocal microscopy and in vitro by light microscopy.

OBJECTIVE: To compare morphologic features of keratoconus as observed in vivo with a slit scanning confocal microscope and in vitro using light microscopy. METHODS: Slit scanning confocal microscopy (CM) was used to evaluate the central cornea of 29 keratoconic subjects (mean age, 31 +/- 10 years; range, 16-49). Light microscopy (LM) examination was performed on 2 of the keratoconic corneas post-keratoplasty. RESULTS: With CM, the epithelium appeared more abnormal with increasing severity of keratoconus. In severe disease, the epithelium displayed the following characteristics: superficial cells were elongated and spindle shaped, wing cell nuclei were larger and more irregularly spaced, and basal cells were flattened. These findings were confirmed by LM. Images obtained using CM revealed disruption to Bowman's layer and the occasional presence of epithelial cells and stromal keratocytes. This was shown with LM to be due to breaks in Bowman's layer. Stromal haze and hyperreflectivity observed with CM corresponded with apical scarring seen on slit-lamp biomicroscopy. Hyperreflective keratocyte nuclei observed with CM are thought to indicate the presence of fibroblastic cells seen with LM. Increasing levels of haze detected with CM were found with LM to be due to fibroblast accumulation and irregular collagen fibers. Descemet's membrane appeared normal with both CM and LM. Evidence of endothelial cell elongation was apparent in 1 subject with CM. CONCLUSIONS: The current study confirms the application of CM for assessing morphologic alterations to the epithelium, Bowman's layer, and stroma in keratoconus. Many of the tissue changes observed with CM could be reconciled with observations made using LM. This work provides a framework against which tissue changes in keratoconus can be studied in a clinical context in vivo using CM.

Adolescent↗
PubMed2005

The size, location, and clinical severity of corneal infiltrative events associated with contact lens wear.

PURPOSE: The purpose of this study is to determine the relationship between the size, location, and clinical severity of corneal infiltrative events (CIEs) associated with contact lens wear. METHODS: We examined a series of contact lens wearers, presenting consecutively to a large hospital clinic, who had any form of CIE. The severity of the CIE was quantified using a clinical severity matrix based on scores attributed to each of 10 signs and symptoms. The infiltrate was accurately drawn on a schematic diagram of the ocular surface, and from this, we determined its size (i.e., largest dimension) and distance from the limbus. Cartograms were constructed to illustrate the size and location of the corneal infiltrates according to wearing modality and lens type. RESULTS: Useable data pertaining to 111 patients were analyzed. A significant positive correlation was found between the distance of the infiltrate from the limbus versus clinical severity (p = 0.002), but not between the distance of the infiltrate from the limbus versus infiltrate size (p = 0.97). The cartograms revealed a tendency for infiltrates to occur in the superior cornea of patients wearing extended wear silicone hydrogel lenses (p = 0.0002) in the central cornea of patients wearing daily wear hydrogel daily disposable lenses (p = 0.007) and in the peripheral cornea of patients wearing daily wear hydrogel (excluding daily disposable) lenses (p = 0.0006). CONCLUSIONS: These data statistically validate the previously held anecdotal notion that CIEs which occur in the peripheral cornea are less clinically severe than those which occur in the central cornea. Consideration of the distribution of CIEs may facilitate a better understanding of the etiology of these events and can serve to alert practitioners as to their likely clinical presentation.

Adult↗
PubMed2005

Adverse events and discontinuations with rigid and soft hyper Dk contact lenses used for continuous wear.

PURPOSE: The purpose of this study was to assess the relative clinical success of hypertransmissible rigid and soft contact lenses in terms of the rates of adverse events and clinical discontinuations. METHODS: One hundred subjects (50 experienced wearers and 50 neophytes) were fitted with either the Z-alpha lens (Menicon) or the Focus Night & Day lens (CIBA Vision), which were worn on a 30-day continuous wear basis. The rates of adverse events and clinical discontinuations were monitored over 12 months. RESULTS: There were 20 adverse events that were categorized as being serious or significant--four with rigid lenses and 16 with soft lenses (p = 0.003). There was no significant difference between the experienced (10) and the neophyte (10) groups (p = 1.00). There were 23 clinical discontinuations--13 with rigid lenses and 10 with soft lenses (p = 0.46). Fewer experienced wearers (five) discontinued than neophytes (18) (p = 0.002). CONCLUSIONS: Practitioners should anticipate fewer adverse events with rigid versus soft lenses prescribed for continuous wear. Experienced wearers are less likely to discontinue compared with neophytes.

Adult↗
PubMed2005

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.

Adolescent↗