Assessing the influence of cannabis and alcohol use on different visual functions: A comparative study.

This study aimed to assess and compare the influence of alcohol intake and cannabis smoking on different visual functions. A total of 64 young and healthy volunteers took part in the study. All undertook several randomised experimental sessions in which different visual functions, namely distance stereopsis, retinal straylight, visual discrimination capacity, and contrast sensitivity, were tested. Cannabis smokers (N = 30) took a baseline session and a session after smoking a cannabis cigarette, whereas alcohol users (N = 34) underwent a baseline session, a session after a low alcohol intake (Alcohol 1), and a session after a moderate to high alcohol intake (Alcohol 2). All visual functions were impaired by cannabis and alcohol use, particularly for the Cannabis and Alcohol 2 groups. The deterioration of all visual variables was higher for the Alcohol 2 than for the Alcohol 1 and Cannabis groups, except for retinal straylight, the deterioration of which was equal for the Cannabis group, and distant stereopsis, which was more impaired for the Cannabis group. The Alcohol 2 group experienced the most impairing conditions, although very similar to the cannabis group, and that factors other than the experimental conditions, such as sex and age, also influenced these visual changes. Alcohol and cannabis use clearly impair vision. The deterioration caused by cannabis is similar to, but slightly lower than, that produced by a moderate to high alcohol intake, with the experimental conditions, sex and age all having an impact on the variability of visual deterioration.

Comparison of the effects of alcohol and cannabis on visual function and driving performance. Does the visual impairment affect driving?

BACKGROUND: Alcohol and cannabis are the most widely consumed psychoactive substances worldwide. This study compared the effects of alcohol and cannabis on visual function and driving performance, as well as self-perceived effects. Also, the relationship between visual effects under the influence and driving performance was studied. METHODS: Sixty-four young drivers, with a history of alcohol and/or cannabis use were included. Of these, 33 were allocated to the alcohol group and 31 to the cannabis group. All participants were evaluated in a baseline session. The alcohol group underwent two sessions: after drinking 300 ml and 450 ml of red wine (A1 and A2). The cannabis group attended one session after smoking cannabis (C). Visual function was evaluated at the contrast sensitivity, stereoacuity, and intraocular straylight level. Participants drove a driving simulator. A general score (overall visual score, OVS; overall driving performance score, ODPS) was obtained for both visual functioning and driving performance. RESULTS: The evaluation of visual function demonstrated a significant impairment in OVS for all conditions studied (A1, p = 0.005; A2, p < 0.001; C, p < 0.001) with respect to the baseline session. General driving performance (ODPS) demonstrated a significant worsening for the A2 condition (p = 0.003). Finally, a significant relationship between driving performance and visual function was found (rho=0.163, p = 0.039 and χ2 = 4.801, p = 0.028). CONCLUSIONS: Cannabis and alcohol use negatively impact visual function. However, driving performance was only significantly affected by the higher alcohol dose. This impairment in visual function was significantly associated with worse driving performance.

Effect of interocular differences on binocular visual performance after inducing forward scattering.

PURPOSE: To assess binocular visual performance by means of binocular summation on visual function after inducing monocular forward scattering, and to study the influence of interocular differences on ocular parameters. METHODS: Seven young healthy subjects were recruited. Four Bangerter foils and five fog filters were used to induce monocular forward scattering. To analyse the impact of the scatter, visual acuity, contrast sensitivity, visual discrimination capacity and distance stereoacuity were measured binocularly with the filter placed over the dominant eye. Additionally, interocular differences were calculated for four ocular parameters: the Objective Scatter Index (OSI), Strehl ratio (SR), modulation transfer function cut-off (MTF cut off) and straylight (log[s]). Binocular summation was determined for these visual functions. RESULTS: A statistically significant deterioration in visual acuity, contrast sensitivity and stereoacuity was seen for all of the filter conditions with respect to the natural state (baseline), with the largest change being recorded for the Bangerter foils. Similarly, the interocular difference for the three retinal image quality parameters (OSI, SR and MTF cut-off) and log(s) increased significantly for the Bangerter foil condition, but not for the fog filters (except log(s)). Binocular summation declined gradually with the Bangerter foils, but not for the fog filters. Statistically significant correlations were found, that is, the greater the interocular differences, the lower the binocular summation of the visual functions and the greater the distance stereoacuity. CONCLUSION: Increased forward scattering in the dominant eye resulted in interocular differences, which reduced the overall binocular visual performance, including the binocular summation of several visual functions and distance stereoacuity. The results suggest that marked interocular differences in ocular parameters should be avoided in cases of ocular pathology, amblyopia and emmetropisation procedures (such as refractive surgery) or a monovision correction for presbyopia.

Effects of cannabis on visual function and self-perceived visual quality.

Cannabis is one of the most used drugs of abuse in the world. The objective of this study was to analyze the effects of smoking cannabis on vision and to relate these to those perceived by the user. Thirty-one cannabis users participated in this study. Visual function assessment was carried out in a baseline session as well as after smoking cannabis. We evaluated static visual acuity, contrast sensitivity, stereoacuity, accommodative response, straylight, night-vision disturbances (halos) and pupil size. The participants were also divided into two groups depending on whether they perceived their vision to have worsened after smoking cannabis. A logistic regression analysis was employed to identify which visual test could best predict self-perceived visual effects. The study found that smoking cannabis has significant adverse effects on all the visual parameters analyzed (p < 0.05). Self-perceived visual quality results revealed that about two thirds of the sample think that smoking cannabis impairs their vision. Contrast sensitivity, specifically for the spatial frequency 18 cpd, was identified as the only visual parameter significantly associated with self-perceived visual quality (Odds Ratio: 1.135; p = 0.040). Smoking cannabis is associated with negative effects on visual function. Self-perceived visual quality after smoking cannabis could be related to impaired contrast sensitivity.

Effects of Smoking Cannabis on Visual Function and Driving Performance. A Driving-Simulator Based Study.

Cannabis is the most widely used illegal drug in the world. Limited information about the effects of cannabis on visual function is available, and more detail about the possible impact of visual effects on car driving is required. This study investigated the effects of smoking cannabis on vision and driving performance, and whether these effects are correlated. Twenty drivers and occasional users were included (mean (SE) age, 23.3 (1.0) years; five women). Vision and simulated driving performance were evaluated in a baseline session and after smoking cannabis. Under the influence of cannabis, certain visual functions such as visual acuity (p < 0.001), contrast sensitivity (p = 0.004) and stereoacuity (far, p < 0.001; near, p = 0.013) worsened. In addition, there was an overall deterioration of driving performance, with the task of keeping the vehicle in the lane proving more difficult (p < 0.05). A correlation analysis showed significant associations between driving performance and visual function. Thus, the strongest correlations were found between the distance driven onto the shoulder and stereoacuity, for near (ρ = 0.504; p = 0.001) and far distances (ρ = 0.408; p = 0.011). This study provides the first evidence to show that the visual effects of cannabis could impact driving performance, compromising driving safety. The results indicate that information and awareness campaigns are essential for reducing the incidence of driving under the influence of cannabis.

Percutaneous closure of an acquired and iatrogenic left ventricular-right atrium communication (Gerbode defect) with an Amplatzer Vascular Plug II.

Gerbode defect is defined as an abnormal left ventricle-right atrium shunting which may have congenital or acquired origin, first described by Thurman in 1838, representing 0.08% of intracardiac shunts and <1% of the congenital heart diseases. The acquired defect can be classified as iatrogenic or non-iatrogenic, with previous cardiac surgery being the most common cause. Gerbode defect is classified depending on its position with respect to the tricuspid valve in supravalvular, infravalvular, or intermediate. Our purpose was to report a rare case of an iatrogenic and acquired Gerbode defect in a 10-year-old male patient following surgical correction of a partial anomalous pulmonary venous return of the right pulmonary veins to the right atrium. The defect was successfully closed percutaneously with an Amplatzer™ Vascular Plug II device. Percutaneous closure of acquired Gerbode defects could be considered as a good option using soft devices to reduce the possibility of severe complications such as complete heart block due to the location of the defect. .

Stereopsis Simulating Small-Aperture Corneal Inlay and Monovision Conditions.

PURPOSE: To analyze stereoscopic vision under a broad range of experimental conditions simulating small-aperture corneal inlay and monovision conditions. METHODS: A total of 10 patients participated in the study. The anisocoria generated by corneal inlays was simulated by using a small-aperture contact lens fitted on the non-dominant eye. Visual acuity, contrast sensitivity function, visual discrimination capacity (halo perception), and stereoacuity tests were performed under natural conditions or when the non-dominant eye wore the small-aperture contact lens under two conditions: induced anisocoria and induced anisocoria combined with monovision (using two add-powers: +0.75 and +1.25 diopters [D]). Stereoscopic vision and binocular summation were analyzed under those experimental conditions and for far, intermediate, and near vision. RESULTS: The results showed a deterioration in stereoacuity with respect to natural conditions, being significant mainly for near and intermediate distances. Results with other visual functions showed a deterioration of the binocular summation and therefore of visual performance, although not in a generalized way for all distances. Binocular visual acuity under the conditions that used the small-aperture contact lens was comparable to that of the natural eye. CONCLUSIONS: The deterioration of stereopsis and other binocular functions found in this study may be acceptable for patients who had this surgical technique because it is similar to the deterioration found in other surgical procedures of emmetropization. [J Refract Surg. 2018;34(7):482-488.].

Hyperopic Q-optimized algorithms: a theoretical study on factors influencing optical quality.

In this work, we analyze the way in which pupil size, optical zone, and initial hyperopic level influence optical quality for hyperopic Q-optimized corneal refractive surgery. Different Q-optimized algorithms and the Munnerlyn formula were tested to analyze the optical quality of the final retinal image for initial hyperopic errors from 1D to 5D. Three optical zones (5.5, 6, and 6.5 mm) and two pupil diameters (5 and 7 mm) were considered. To evaluate optical quality, we computed the modulation transfer function (MTF) and the area under MTF (MTFa). Q-optimized values at around Q = -0.18 were found to provide the best optical quality for most of the conditions tested. This optimum final asphericity for hyperopic ablation was not depending on the degree of hyperopia corrected, the optical zone or the pupil size being this information important for clinical practice.

Q-optimized Algorithms: Theoretical Analysis of Factors Influencing Visual Quality After Myopic Corneal Refractive Surgery.

PURPOSE: To model the effect of pupil size, optical zone, and initial myopic level on the retinal image quality after Q-optimized myopic corneal refractive surgery. METHODS: Different Q-optimized and paraxial Munnerlyn algorithms were tested using a schematic myopic eye model to analyze the optical quality of the final retinal image for initial myopic errors from -1.00 to -7.00 diopters (D). Different optical zones (5.5, 6, and 6.5 mm in diameter) and two pupil diameters (5 and 7 mm, mesopic-scotopic conditions) were included in the comparison. Modulation transfer function (MTF) and area under the MTF from 0 to 60 cycles per degree (MTFa) were calculated by ray tracing to evaluate this retinal image quality. RESULTS: The Q-optimized algorithm with Q = -0.45 provided the highest MTF and MTFa results for myopic corrections less than -5.00 D. For refractive errors greater than -5.00 D, Q = -0.26 provided the highest MTF and MTFa results. CONCLUSIONS: Q-optimized algorithms improve the visual outcomes with respect to the paraxial Munnerlyn algorithm for myopic corneal surgery. The results show that the Q value that optimizes the results of the Q-optimized algorithm depends on the degree of myopia to correct and the size of the pupil. [J Refract Surg. 2016;32(9):612-617.].

Optical quality and visual performance after cataract surgery with biaxial microincision intraocular lens implantation.

PURPOSE: To evaluate the time course of the optical quality and visual performance with a microincision monofocal intraocular lens (Incise). SETTING: Hospital Torrecárdenas, Almería, Spain. DESIGN: Prospective study. METHODS: The visual and refractive outcomes were evaluated in eyes with the microincision IOL preoperatively and 1, 3, and 6 months postoperatively. The modulation transfer function (MTF) cutoff frequency, Strehl ratio, and objective scatter index (OSI) were used to measure optical quality. The contrast sensitivity function (CSF) and the visual disturbance index characterized visual performance. RESULTS: In the 32 study eyes, the mean values preoperatively and 6 months postoperatively, respectively, were MTF cutoff frequency (11.40 cycles per degree [cpd] ± 8.39 [SD] and 23.33 ± 11.68 cpd; P < .001), Strehl ratio (0.078 ± 0.32 and 0.15 ± 0.07; P < .05), and OSI (7.44 ± 3.25 and 1.57 ± 0.26; P < .001). At each spatial frequency, the CSF significantly differed between preoperatively and postoperatively (P < .001). The mean visual disturbance index changed from 0.70 ± 0.28 to 0.31 ± 0.17 (P < .001). For all parameters studied, statistically significant differences were found between the preoperative and postoperatively values, with no differences between the results 1, 3, and 6 months after surgery (P > .05). CONCLUSIONS: Biaxial microincision cataract surgery provided optimum clinical outcomes. The optical quality and visual performance improved significantly 1 month after surgery, with the results remaining stable at 6 months. The postoperative visual function was similar to that in subjects of the same age with healthy eyes. FINANCIAL DISCLOSURE: None of the authors has a financial or proprietary interest in any material or method mentioned.

Theoretical analysis for spherical aberration induction with low-order correction in refractive surgery: comment.

In this paper, we reply to post-surgical corneal asphericity conclusions made by Dai [Appl. Opt.51, 3966 (2012)]. We deduced, after a theoretical analysis, that the conclusions derived from this analysis are not theoretically or experimentally sound, because the author considers only the Munnerlyn formula for ablation algorithms and not the paraxial Munnerlyn formula, which is widespread in refractive surgery [J. Cataract Refract. Surg.14, 46 (1988)]. We refer to a previous paper published by Jiménez et al. [J. Opt. Soc. Am. A21, 98 (2004)] for a complete analysis on this matter that clarifies some points of confusion in Dai's paper.

Designing multifocal corneal models to correct presbyopia by laser ablation.

Two multifocal corneal models and an aspheric model designed to correct presbyopia by corneal photoablation were evaluated. The design of each model was optimized to achieve the best visual quality possible for both near and distance vision. In addition, we evaluated the effect of myosis and pupil decentration on visual quality. The corrected model with the central zone for near vision provides better results since it requires less ablated corneal surface area, permits higher addition values, presents stabler visual quality with pupil-size variations and lower high-order aberrations.

Theoretical analysis of the effect of pupil size, initial myopic level, and optical zone on quality of vision after corneal refractive surgery.

PURPOSE: To analyze the theoretical effect that pupil size, optical zone, and initial myopic level have on the final retinal image after corneal refractive surgery. METHODS: A schematic myopic eye model corrected by the Munnerlyn formula was used to analyze the optical quality of the final retinal image. Root-mean-square radius spot and modulation transfer function were cal- culated by ray tracing to evaluate retinal image quality. RESULTS: Pupil size had a negative effect on the retinal image only when it was greater than the diameter of the optical zone. In addition, the greater the initial myopic level, the more the pupil size affected image quality. Thus, a clear dependence exists between the initial myopic level and effect that the pupil size can have on the retinal image after laser refractive surgery. CONCLUSIONS: Pupil size may be a risk factor for night vision disturbances, but only when it is larger than the theoretical optical zones utilized in this study. Its effect depends not only on the optical zone size, but also on the initial "myopic level. Therefore, this relationship should be taken into account during patient selection for refractive surgery

Optical quality and visual discrimination capacity after myopic LASIK with a standard and aspheric ablation profile.

PURPOSE: To determine whether the eye's optical quality is correlated to the visual discrimination capacity of patients treated with LASIK using two different ablation algorithms. METHODS: Visual discrimination was evaluated by the disturbance index under low illumination (Halo v1.0 software, Laboratory of Vision Sciences and Applications) in two groups of patients who underwent LASIK with two different ablation algorithms using the Allegretto Wave Eye-Q 400 Hz laser (WaveLight AG). In the first group (standard group; 30 eyes), corneal ablations were performed with the standard algorithm (preoperative spherical equivalent refraction -3.20±1.70 diopters [D]). In the second group (Q-optimized group; 38 eyes; spherical equivalent refraction -3.40±1.90 D), the ablations were made with the Q-optimized (F-CAT) algorithm. Optical quality of the eye was calculated by the Strehl ratio measured with a double-pass device (OQAS, Visiometrics SL). RESULTS: After LASIK, both the Strehl ratio as well as visual discrimination capacity diminished in both groups, although the changes were significantly greater in the standard group than in the Q-optimized group. CONCLUSIONS: A high correlation was found between the Strehl ratio and the disturbance index in patients who underwent LASIK, regardless of the ablation algorithm applied. Optical and visual deterioration were greater after standard ablation.

Characterizing corneal shape after LASIK using a reference system intrinsic to the cornea.

The reliability of using a reference system intrinsic to the cornea has been evaluated in order to characterize corneas of subjects after refractive surgery. Data on 90 eyes operated on by LASIK to correct myopia and astigmatism were considered. The corneal parameters (curvature radii and corneal asphericity) found with respect to this reference system are compared with the parameters provided directly by the corneal topographer. The corneal parameters referenced to the intrinsic main axes of the cornea allow a better characterization of the corneal geometry, showing lower variability and diminishing the dissimilarities between the different eyes. The use of these parameters reduces the discrepancies between the real experimental and the theoretically predicted values (21% mean relative error using intrinsic data versus 81% using the topographer data). To understand and reduce these differences is essential in refractive surgery.

Testing a model for excimer laser-ablation rates on corneal shape after refractive surgery.

We have tested whether a recent model [Appl. Phys. Lett.95, 174105 (2009)APPLAB0003-695110.1063/1.3254236] that considers the angular dependence of laser-ablation rates, including reflection losses and geometrical dependence of incident fluence, and the effect of plume absorption can have significant effects for refractive surgery patients. We have developed a mathematical procedure and deduced equations that show that this model can significantly influence postsurgical corneal parameters (radius and asphericity) and, thus, should be considered in ablation algorithms in order to achieve a better emmetropization and an effective correction of eye aberrations.

Visual performance after LASIK for a Q-optimized and a standard ablation algorithm.

We test visual performance after LASIK (laser in situ keratomileusis) for a Q-optimized ablation algorithm and one based on the Munnerlyn formula. The visual functions tested include aberrometry, monocular and binocular contrast sensitivity function (CSF), and a discrimination test under low-illumination conditions. This test is useful to quantify night-vision disturbances. A total of 102 patients took part in the experiments, and visual data were taken before (with best correction) and after LASIK. Results show a deterioration in aberrometry, CSF, binocular summation, and discrimination index for the two algorithms tested, although this deterioration is significantly lower for the Q-optimized algorithm.

Effect of LASIK and contact lens corneal refractive therapy on higher order aberrations and contrast sensitivity function.

PURPOSE: Corneal and total higher order eye aberrations and their effects on visual function were compared in two groups subjected to different emmetropization techniques-refractive surgery (LASIK) and corneal refractive therapy (CRT). METHODS: Twenty eyes of 11 patients and 22 eyes of 13 patients were examined in the CRT and LASIK groups, respectively. Mesopic contrast sensitivity function (CSF) was studied monocularly and binocularly in the two groups of patients undergoing CRT and LASIK who had approximately the same mean refractive error. Corneal asphericity and corneal and total aberrations were calculated, and the differences were analyzed between groups. Visual acuity, corneal and total ocular aberrations, corneal asphericity, and mesopic CSF were determined before and 3 months after treatment. RESULTS: In both groups, corneal and total higher order aberrations increased after treatment, and the change in some Zernike coefficients was significant. Mesopic CSF diminished after treatment under monocular as well as binocular conditions, with the greatest decline being found in the CRT group under binocular conditions. Corneal asphericity also increased significantly in both groups, which was more accentuated in the CRT group. CONCLUSIONS: Both emmetropization techniques increased higher order ocular aberrations, implying a decline in the mesopic CSF. The increase in aberrations and the consequent deterioration in visual function was more marked in the CRT group.

Technical note: Pre-surgical anisometropia influences post-LASIK binocular mesopic contrast sensitivity function.

PURPOSE: To investigate if pre-surgical anisometropia influences the post-LASIK binocular mesopic contrast sensitivity function (CSF). METHODS: Pre- and post-surgical binocular CSF was measured for 54 patients under mesopic conditions. Data on visual acuity and corneal topography were also obtained. RESULTS: The binocular contrast sensitivity declined significantly (r = 0.86; p < 0.001) with increasing pre-surgical anisometropia. Post-surgical interocular differences in corneal asphericity were also associated with increasing pre-surgical anisometropia. CONCLUSIONS: Pre-surgical anisometropia may be indicative of a possible significant deterioration of post-surgical mesopic binocular CSF, and therefore should be taken into account before surgery in analysing the possible disadvantages and limitations of refractive surgery.

Experiment on PMMA models to predict the impact of corneal refractive surgery on corneal shape: Comment.

Recently, two papers "Dorronsoro et al., Experiment on PMMA models to predict the impact of corneal refractive surgery on corneal shape, Opt. Express 14, 6142 (2006)" and "JR Jiménez et al., Deviations of Lambert-Beer's law affect corneal refractive parameters after refractive surgery, Opt. Express 14, 5411 (2006)" have been published on an important question in corneal refractive surgery: to explain the differences between post-surgical corneal elevation maps and those predicted after theoretical ablation. An analysis of Dorronsoro et al. data demonstrates that the failures in Lambert-Beer's law could be in the origin of shape discrepancies. New models and experimental data on deviations of Lambert-Beer's law might help to minimize post-surgical corneal discrepancies and thus optimise eye emmetropization.