Vertical vergence adaptation does improve with practice.

PURPOSE: To investigate the effect of repeated testing on adaptation to a 2 Delta vertical prism in subjects with normal binocular single vision. METHODS: Subjects were required to have good visual acuity and normal binocular single vision. The residual deviation was measured after a 1-min period of adaptation to a 2 Delta vertical prism using a modified Maddox Rod technique. This measurement was repeated 10 times, with a 5-min rest period between each trial. RESULTS: For eight young adult subjects, the mean residual deviation at 1 min reduced with consecutive trials, and this effect was statistically significant (p < 0.0001). No significant correlation was present between the amplitude of vertical vergence and the increase in adaptation with repeated demand. CONCLUSIONS: A practice effect for vertical vergence adaptation appears to be present in young adult subjects with normal binocular single vision.     

Empirical fitting of soft or rigid gas-permeable contact lenses for the correction of moderate to severe refractive astigmatism: A comparative study

BackgroundThis study aims to validate the fitting of contact lenses derived from refractive and keratometric values in a group of subjects with moderate (2.50 diopters [D] to 5.00 D) to severe (>5.00 D) astigmatism. It aims also to show whether soft or rigid gas-permeable (GP) contact lenses offer the best correction and to determine which modality is preferred by subjects.MethodsTwenty subjects were randomly fitted with both soft and GP lenses. Group A was first fitted with soft lenses then switched to GPs and vice versa for group B. For each type of lens worn, low- and high-contrast visual acuity (VA) and stereoscopy were evaluated at both near and far. Each subject was asked to select the lens type of choice and to rate quality of vision in day-to-day activities through a questionnaire.ResultsThere was no significant difference in objective binocular VA between current spectacles and empirically calculated soft toric lenses and GP toric/bi-toric contact lenses at all distances. That was also true for stereoscopy. Subjectively, most of the subjects preferred rigid contact lenses because of the quality of their vision in day-to-day activities, and a majority of them decided to continue with that modality.ConclusionEmpirical fitting of toric soft or GP contact lenses leads to very good results, which suggests that each type of lens might constitute a viable option.     

Evaluation of “high-cylinder” toric soft contact lenses

The purpose of this study was to evaluate lens performance, vision, and initial clinical success achievable with custom toric soft contact lenses fitted to patients with high amounts of astigmatism. Eleven subjects were fitted with high-water-content custom toric soft lenses for daily wear. Assessment/measurements of the lens-mark position on the eye, lens movement, visual acuity, wearing time, eye response to lens wear, and subjective evaluation of visual quality and stability were performed during the initial wearing/adaptation period. Nine subjects having an average of 3.16 D of astigmatism successfully wore the lenses on a full-time basis for 2 weeks of daily wear. The data indicated good visual acuity, but with great variability in subjective ratings of stability and quality of vision. Alignment of lenses on the eye was very good, ocular response was unremarkable, and seven of nine (78%) of the subjects elected to continue with lens wear after the initial 2 weeks of wear. The results suggest that high-cylinder toric hydrogels can provide reasonable vision and patient acceptance even while stability and overall quality of vision may be a challenge. Toric soft lenses in higher cylinder amounts, such as those utilized in this study, may be considered a reasonable vision correction option and one that can be provided in a straightforward and predictably successful manner in most cases.     

Disconjugate adaptation to long-standing, large-amplitude, spectacle-corrected anisometropia

A 12-yr-old anisometropic patient had worn corrective eyeglasses (right eye, -0.50 +1.50 x 125; LE, -9.75 +2.50 x 60) for 7 yr, and then changed to contact lenses. Eye movements were recorded before and after the change to contact lenses using binocular search coils. In habitual spectacle viewing, the patient showed disconjugate adaptation. During monocular viewing, for example, ocular alignment changed by as much as 4 degrees during a 20 degrees saccade. Also, during monocular viewing, with either eye, placing the spectacle lens in front of the eye caused an increase in the disconjugate adaptive response compared with viewing without lenses. This finding emphasizes the context specificity of adaptive responses. After switching to contact lenses, the patient still wore his spectacles for 20-40 min each day. Although there was little residual disconjugate adaptation for vertical saccades, he showed considerable adaptation for horizontal saccades, especially for gaze changes that required divergence. The persistence of a partial state of disconjugate adaptation allowed the patient to use immediate, disparity-induced, horizontal vergence to aid ocular alignment in either the contact-lens-viewing or the spectacle-viewing condition. A more complete reversion to conjugacy occurred after nine days of exclusive use of his contact lenses. Then, in a short-term experiment, two minutes of binocular viewing through the eyeglasses induced a considerable reversion toward the previous state of disconjugate adaptation (up to 1.25 degrees of vergence change during monocular viewing). Finally, the waveform of the adapted (to spectacles) intrasaccadic vergence change with monocular viewing was similar to the waveform of the unadapted intrasaccadic vergence change during binocular refixations between targets that required a combined saccade and vergence. This finding suggests a common mechanism for adaptation to spectacle-corrected anisometropia and for normal binocular vergence-saccade interactions.     

Evaluation of the binocularity of 147 unilateral and bilateral pseudophakic patients

Tests of binocular functions were performed on a group of 147 patients with unilaterally or bilaterally implanted intraocular lenses. The quality of the binocular vision achieved was significantly better than that of unilateral aphakic patients wearing contact lenses. Compared to the normal population, the stereoscopic threshold in the pseudophakic population was found to be slightly poorer. Visual acuity, anisometropia, lens fixation, and vertical deviation were analyzed in relation to stereopsis.     

Vergence adaptation maintains heterophoria in normal binocular vision

This investigation sought to determine whether vergence adaptation serves to maintain orthophoria or heterophoria in normal binocular vision. While wearing prisms which neutralized their nearpoint (40 cm) heterophorias, 27 of 30 nonstrabismic subjects adapted from their prismatically created orthophoria toward their habitual heterophoria. Three subjects showed no adaptive response. A symptom questionnaire distributed to these subjects determined that the maintenance of heterophoria by vergence adaptation is: characteristic of normal and comfortable binocular vision, and neither an entirely necessary nor sufficient condition for normal and comfortable binocular vision.     

Visual outcome of Soflens Daily Disposable and Soflens Daily Disposable for Astigmatism in subjects with low astigmatism

Purpose: To compare the visual outcome of Soflens Daily Disposables and Soflens Daily Disposable for Astigmatism (Bausch & Lomb, Rochester, NY, USA) when worn by subjects with low astigmatism. Methods: Forty‐one subjects (aged 19 to 40 years) with myopia between 0.50 D to 6.00 D and astigmatism not more than ‐1.25 D in at least one eye were recruited and fitted with spherical and toric soft contact lenses in this double‐masked, non‐dispensing cross‐over study. High and low contrast logMAR visual acuities were measured over the lenses. At the end of the study, each subject was asked to complete a questionnaire on vision, initial comfort and ease of handling of the two lens types. Results: Monocular and binocular high and low contrast logMAR visual acuities were significantly better with the toric lenses compared with the spherical lenses (p < 0.01). Results from the questionnaire showed a significantly higher grade for vision with the toric lenses than with the spherical lenses (p = 0.003) but no significant differences in initial comfort and ease of handling between spherical and toric lenses (p > 0.21). Conclusions: The results of the present study show that both subjective and objective vision in myopic subjects with low astigmatism improves significantly when corrected with toric lenses compared with spherical lenses.     

配戴多焦点硬性角膜接触镜对近视患者双眼视功能的影响

目的：探讨多焦点设计的硬性角膜接触镜对近视患者双眼视功能的影响。

方法：自身前后对照研究。于2020-07/08在川北医学院招募近视学生15人作为试验者,试验者首先配戴框架眼镜行双眼视功能检查,然后分别配戴单焦点与多焦点硬性角膜接触镜(间隔1wk),每种镜片配戴2wk后行双眼视功能检查。采用单因素方差分析比较多焦点硬性角膜接触镜(MFRGP)、单焦点硬性角膜接触镜(SVRGP)和框架眼镜双眼视功能的差异。

结果：三种镜片立体视、远距水平隐斜、远距正融像性聚散、远距负融像性聚散、近距正融像性聚散、聚散灵活度、集合近点、调节幅度、调节灵活度、负相对调节比较均无差异(P>0.05)。与框架眼镜相比,配戴MFRGP近距水平隐斜、近距负融像性聚散、调节滞后、正相对调节增大,AC/A降低(P=0.023、0.048、0.001、0.013、0.046); 与SVRGP相比,MFRGP近距水平隐斜、调节滞后、正相对调节增大,AC/A降低(P=0.014、<0.001、0.001、0.009)。

结论：配戴MFRGP会引起近距水平隐斜、调节滞后、正相对调节增大和AC/A降低,这些变化可能对配戴者近距离用眼产生一定影响,在临床应用中要考虑这些预期的变化,以便正确评估和管理患者。     

Rotational position of toric soft contact lenses on the eye—Clinical judgments

This study investigated the accuracy and reliability of experienced contact lens practitioners in estimating the rotational position of a toric soft contact lens on the eye. The study also evaluated whether some markings of selected round toric soft lenses are superior to others in assisting clinicians who are making lens rotational position judgments.Estimates of on-the-eye landmark position of toric soft contact lenses were found to be within 1 to 12 degrees of true position. The subject, rather than the type of lens marking, accounted for most of the error in lens rotation judgment.     

Communication:A bitoric rigid contact lens with base down prism to eliminate binocular vertical diplopia

Prism base down can be incorporated into a rigid gas permeable contact lens to align the diplopic images in a patient who has a significant vertical phoria. A rigid lens may also incorporate both vertical base down prism and a toroidal back surface—the vertical prism to correct the heterophoria and the toric back surface to improve the physical fit of the lens on a highly toric cornea. This paper presents a case where vertical diplopia due to a post‐surgical left hyperphoria of about four prism dioptres was eliminated by the incorporation of the appropriate amount of base down vertical prism into a bitoric rigid gas permeable contact lens.     

Clinical evaluation of toric soft lens reproducibility.

PURPOSE: The manufacturing variability of frequent replacement toric soft lenses is such that some resulting variation in clinical performance can be expected. The purpose of this study was to evaluate the effect of manufacturing variability on the clinical performance of three frequent replacement toric soft contact lenses. METHODS: This was a three-part study in which 12 to 14 subjects were enrolled for each part. In each part, subjects were preadapted to the lens type 1 month prior to the assessment visits. Subjects wore a total of 12 test lenses in one eye and, in each case, the clinical performance was compared with a control lens of the same type worn in the other eye that was removed between assessments but not replaced. The study lenses were Acuvue Toric (Vistakon), Focus Toric (Ciba Vision) and FreshLook Toric (Wesley lessen). RESULTS: Two lens types (Focus Toric and FreshLook Toric) showed significantly greater variability with the test lenses compared with the nonreplaced control lenses with several variables: lens fit, visual acuity, and subjective vision quality. One lens (Focus Toric) also showed greater variability of orientation position, and another (Acuvue Toric) showed greater variability in subjective vision quality. CONCLUSIONS: The study demonstrated variability in aspects of clinical performance, which appear to be linked to variability of manufacturing output. With toric soft lenses used on a frequent replacement basis, better reproducibility is needed if consistent clinical performance is to be maintained.     

Horizontal and vertical prism adaptation are different mechanisms

As part of a study on subjects with convergence insufficiency (CI), their vertical and horizontal vergence adaptation was assessed and compared with age matched controls in order to investigate whether the horizontal adaptation system can be regarded as being independent of the vertical adaptation system. Using a flashed Maddox rod technique horizontal vergence adaptation was found to be reduced in CI subjects whereas no difference could be found in vertical adaptation. These results confirm that the vertical and horizontal adaptation systems can be treated as independent mechanisms.     

Ophthalmic practice during COVID-19 pandemic

AIM: To compare the visual acuity (VA), comfort, and patient preference in a soft toric contact lens (TCL) versus soft spherical contact lens (SCL) in low astigmatic subjects during the contact lens (CL) trial. METHODS: This subject-masked, block randomized, 2×2 crossover study recruited 40 neophyte subjects (80 eyes) aged 18 to 33y with astigmatism in the range of 0.75-1.25 D with or without spherical power from -6.00 D to +6.00 D. The participants were scheduled for two days CL trial and were fitted with the best-fit SCL and TCL. After 4h of wear, they were assessed objectively for high contrast VA and subjective vision, comfort, and preference. RESULTS: The responses of 36 subjects (response rate 90%) with a mean age of 23.02±2.97y (range 18 to 33y) were analysed. One-line improvement of monocular VA in the logMAR chart was reported to TCL as compared to SCL (-0.044±0.06 vs 0.04±0.03 logMAR, P=0.01) but the binocular vision remained similar (-0.12±0.07 vs -0.14±0.04 logMAR, P=0.38). Subjects felt a noticeable difference in clarity when shifted to TCL as compared to the SCL. The satisfaction with vision (vision quality) was significantly better with TCL (P=0.03). The fatigue with TCL was graded less at 2.5±0.6, compared to SCL at 4.6±1.3 (P=0.04). Thirty-three participants (91.6%) preferred to use contact lens of which 26 participants (79%) preferred TCL. CONCLUSION: The findings suggest that VA and comfort are better with TCL as compared to SCL which is only observed if the patient was offered both offering SCL with spherical equivalent power alone as the first option can mislead the practitioner; TCL trial should be the first choice of the lens in low-to-moderate astigmatism.     

Does offering only the spherical contact lens trial to the low astigmats mislead the practitioners?

AIM: To investigate the association of axial length and ocular factors on axial length elongation. METHODS: A retrospective chart review of patients who underwent two or more axial length examinations for more than two years. Totally 4 groups were divided according to initial axial length (<24mm, 24-26mm, 26-28mm, ≥28mm). Initial fundus photograph was used to find risk factors associated axial length elongation. RESULTS: The mean age of the patients was 47.21±7.79y. Axial length remained almost unchanged in the groups with axial length < 24mm and 24 ≤ axial length < 26mm. On the contrary, axial length increased by 0.011 mm/y in the group with 26 ≤ axial length < 28 mm and 0.035 mm/y in the group with axial length ≥ 28mm (P<0.001). In high myopia, axial length elongation increased in eye with longer axial length (r=0.003, P=0.024), female gender (r=0.014, P=0.019), eye with larger peripapillary chorioretinal atrophic area (r=0.002, P=0.019), and smaller vascular arcade angle (r=-0.004, P=0.006). The risk of elongation 0.03 mm/y in high myopia was increased in female gender (P=0.040), and gradually increased in eye with large peripapillary chorioretinal atrophy area (P<0.010). CONCLUSION: Axial length elongate significantly in the eye with longer axial length, female gender, and the eye with larger atrophic area and smaller arcade angle on fundus photography.     

Clinical performance and factors affecting the physical fit of a soft toric frequent replacement contact lens

Background: Differences in ocular parameters between Chinese and Caucasian eyes, may lead to differences in the success rate of soft contact lens fittings. As most disposable or frequent replacement lenses are manufactured based on data of Caucasian eyes, the aim of this study was to investigate the clinical performance and factors affecting die preliminary fitting of a ‘one‐fit’ bi‐weekly replacement soft toric lens on Hong Kong (HK)‐Chinese. Method: Forty‐one HK‐Chinese were fitted with Acuvue soft toric lenses (on one eye only). The success rate, die comfort, vision and die effects of central corneal curvature, horizontal visible iris diameter (HVID) and palpebral aperture size (PAS) on the physical fit of die toric lenses were determined. Results: Twenty‐four of 41 eyes (58.6 per cent) attained acceptable fit and satisfactory vision with these lenses. The main reason for unsuccessful lens fit was loose fitting. Only central corneal curvatures were significandy correlated (statistically) to the looseness of the lens. Discussion: The results showed diat about 40 per cent of our subjects were unable to obtain acceptable fit with this one‐fit frequent replacement lens, the main reason for which was loose fit. This was expected due to the steeper corneas of the Chinese eyes and we would expect similar results widi odier one‐fit soft lenses. Only die central corneal radii were significandy correlated widi die looseness of the lens fit. However, this factor was not die main factor affecting die contact lens fitting. HVID and PAS did not appear to play any significant role in die physical fit of diis lens. As tiiere are individual variations of lens fitting behaviour, trial lens fitting assessment is die most suitable way to select the appropriate lens.     

Dynamics of horizontal vergence movements: interaction with horizontal and vertical saccades and relation with monocular preferences

We studied the dynamics of pure vergence shifts and vergence shifts combined with vertical and horizontal saccades. It is known from earlier studies that horizontal saccades accelerate horizontal vergence. We wanted to obtain a more complete picture of the interactions between version and vergence. Therefore we studied pure version (horizontal and vertical), pure vergence (divergence and convergence) and combinations of both in five adult subjects with normal binocular vision and little phoria (< 5 degrees). The visual targets were LED's in isovergence arrays presented at two distances (35 and 130 cm) in a dimly lit room. Two targets were continuously lit during each trial and gaze-shifts were paced by a metronome. The two subjects with a strong monocular preference made vergence eye movements together with small horizontal saccades during pure vergence tasks. The other subjects, who did not have a strong monocular preference, made pure vergence movements (without saccades). These findings, suggest that monocular preferences influence the oculomotor strategy during vergence tasks. Vergence was facilitated by both horizontal and vertical saccades but vergence peak-velocity during horizontal saccades was higher than during vertical saccades.     

Increasing the proportion of binocular vision makes horizontal prism adaptation complete

In previous phoria adaptation experiments on normal subjects adaptation tends to reach only approximately 2/3 of the prism-induced phoria while clinical experience indicates that prism adaptation is usually complete. The present data show that increasing the proportion of binocular experience through the phoria-inducing prism allows adaptation to become complete. Longer periods of binocular vision give a better indication of vergence adaptation function. This is particularly important in experiments where normal and abnormal adaptive abilities are being compared.     

Vertical fixation disparity curve and the effects of vergence training in a normal young adult population.

BACKGROUND: The vertical forced vergence fixation disparity (VFD) curve represents the amount of vertical fixation disparity, the steady-state vertical bifixation error of the eyes, at various levels of vertical vergence demand. The main aim of the present study was to examine the effects of vertical vergence training on the slope of the VFD curve in a normal, young adult population. METHODS: Forty-five subjects with normal vision and binocular function underwent vertical vergence training for 1 week. The training was done using a vertical prism bar, and the vertical fixation disparity was measured using the Disparometer. RESULTS: The mean slope of the VFD curve in a normal, young adult population was 1.103 min arc/delta. The slope of the VFD curve decreased significantly after the training and remained flattened for at least 3 months. There was no evidence to support the idea that the decrease in the VFD slope was related to the increase of vertical fusional amplitude. CONCLUSIONS: Vertical prism bar training provided a long-term effect, both increasing the vertical fusional amplitude and flattening the slope of the VFD curve. The decrease in the slope of the VFD curve was thought to be independent of the increase of vertical fusional amplitude.