Patient-reported vision-related quality of life after laser in situ keratomileusis, surface ablation, and phakic intraocular lens: The 5.5-year follow-up study.

To evaluate the long-term efficacy of refractive surgery of all cases in a single center via the use of a patient-reported outcome (PRO) refractive status questionnaire using descriptive statistics. This study was prospective, single-center, cohort study that involved 1422 patients who underwent refractive surgery (laser in situ keratomileusis, surface ablation, and phakic intraocular lens) at Baptist Eye Institute, Kyoto, Japan. The patients were asked to answer the Refractive Status and Vision Profile (RSVP) questionnaire before the surgery after 6 months (n = 1133 patients) and after 5.5 years (n = 232 patients). During the same period, examination by slit-lamp biomicroscopy and visual acuity tests were performed. Moreover, the patients were asked to rate their satisfaction with the surgery 6 months and 5.5 years after it. We examined overall RSVP scale (S), 8 RSVP subscales, rate of satisfaction with surgical outcome, slit-lamp biomicroscopy findings, and refractive error. The mean preoperative S was 36, yet that score significantly improved to 19 at 6 postoperative months postoperatively (P < .01), and basically remained the same (i.e., 20) throughout the 5.5-year postoperative period. During the 5-year follow-up period, mean refractive error became slightly myopic (0.3 D). No change in the rate of satisfaction was observed at both 6 months and 5.5 years postoperative period. The findings of this study help to clarify long-term PRO quality of vision (QOV) postrefractive surgery in a single center, and show that minor change in refractive error during 5 years postoperative period had no influence on the mean RSVP scores among outpatients. Nearly all patients reported short-term improvement of QOV, which continued throughout the long-term follow-up period.

Assessment of pupillary influence in LASIK patients using a digital pupillometer and VQF 25 questionnaire.

PURPOSE: Identify ideal profiles in patients undergoing to photorefractive laser surgery with the aid of an automated pupillometry and psychometric analysis of patients with visual function questionnaire (VQF 25). METHODS: Seventy-seven patients undergoing photorefractive laser surgery laser (LASIK) were analyzed with the aid of an automated digital pupillometer based on an infrared camera coupled to the optical head of a videokeratography system. Patients underwent complete ophthalmic evaluation and documentation of the pupillary behavior under different intensities of illumination, simulating situations of everyday life. Visual quality function questionnaire, translated to Portuguese was assessed. RESULTS: All patients, regardless of pupillary change under varying conditions of illumination (scotopic, mesopic and photopic) showed improvement in all sub-groups of the VQF 25. Pupil diameter was not the primary determinant of patients' visual satisfaction. CONCLUSION: Despite digital pupillometer has proven to be a useful tool in documenting and understanding of pupil behavior, a set of factors such as psycho-social profile, preoperative ametropy and final residual ametropy, contributed decisively to determine the degree of satisfaction of patients undergoing LASIK.

Assessment of pupillary influence in LASIK patients using a digital pupillometer and VQF 25 questionnaire / Avaliação da influência pupilar em pacientes submetidos a LASIK com a utilização de um pupilômetro digital e do questionário VQF 25

PURPOSE: Identify ideal profiles in patients undergoing to photorefractive laser surgery with the aid of an automated pupillometry and psychometric analysis of patients with visual function questionnaire (VQF 25). METHODS: Seventy-seven patients undergoing photorefractive laser surgery laser (LASIK) were analyzed with the aid of an automated digital pupillometer based on an infrared camera coupled to the optical head of a videokeratography system. Patients underwent complete ophthalmic evaluation and documentation of the pupillary behavior under different intensities of illumination, simulating situations of everyday life. Visual quality function questionnaire, translated to Portuguese was assessed. RESULTS: All patients, regardless of pupillary change under varying conditions of illumination (scotopic, mesopic and photopic) showed improvement in all sub-groups of the VQF 25. Pupil diameter was not the primary determinant of patients' visual satisfaction. CONCLUSION: Despite digital pupillometer has proven to be a useful tool in documenting and understanding of pupil behavior, a set of factors such as psycho-social profile, preoperative ametropy and final residual ametropy, contributed decisively to determine the degree of satisfaction of patients undergoing LASIK.

OBJETIVO: Identificar perfis ideais em pacientes submetidos à cirurgia fotorrefrativa a laser com o auxílio de um pupilômetro automatizado e análise psicométrica de pacientes com o questionário de função visual (VQF 25). MÉTODOS: Setenta e sete pacientes submetidos à cirurgia fotorrefrativa a laser (LASIK) foram analisados com o auxílio de um pupilômetro digital automatizado baseado em uma câmera de infravermelho acoplado à cabeça óptica de um sistema de videoceratografia. Os pacientes foram submetidos à avaliação oftalmológica completa e documentação do comportamento pupilar em diferentes intensidades de iluminação, simulando situações da vida cotidiana. O questionário de qualidade da função visual, traduzido para o Português, foi avaliado. RESULTADOS: Todos os pacientes, independentemente da mudança pupilar em diferentes condições de iluminação (escotópica, mesópica e fotópica) apresentaram melhora em todos os subgrupos do VQF 25. O diâmetro pupilar não foi o principal determinante da satisfação visual dos pacientes. CONCLUSÃO: Apesar do pupilômetro digital ter provado ser uma ferramenta útil na documentação e compreensão do comportamento da pupila, um conjunto de fatores, tais como o perfil psicossocial, ametropia pré-operatória e ametropia residual final, contribuiu de forma decisiva para determinar o grau de satisfação dos pacientes submetidos a LASIK.

Visual and non-visual factors associated with patient satisfaction and quality of life in LASIK.

PURPOSE: The aim of this study was to determine how laser in situ keratomileusis (LASIK) affects quality of life (QOL) and to identify factors that may affect satisfaction after LASIK. METHODS: A total of 104 patients with a mean age of 29±6, treated with LASIK for myopia and astigmatism, were enrolled in a prospective study. High (90%) and low (10%) contrast visual acuity (CVA) were measured under photopic and scotopic conditions before surgery and at 3 months later. A multidimensional QOL scale (Institute for Eye Research multidimensional QOL scale), which assesses psychological characteristics, personality traits, cosmesis, frequency, and tolerance to disturbing visual and ocular symptoms, and overall satisfaction with vision correction, was also used. Paired rank tests were used to compare preoperative and postoperative vision and QOL scores. Correlations and a multiple linear regression were used to describe the relationship between CVA, QOL, and satisfaction after LASIK. RESULTS: Significant postoperative changes included increased satisfaction following LASIK (P<0.001), reduced frequency of visual and ocular symptoms (P<0.001), and change in psychological characteristics (P=0.033). The change in satisfaction with LASIK can be predicted by a combination of preoperative satisfaction, postoperative frequency of disturbing visual and ocular symptoms, postoperative mean spherical equivalent, and postoperative scotopic high CVA (R (2)=0.725, P<0.05). CONCLUSIONS: Satisfaction with LASIK is related to visual function, preoperative expectations, psychological characteristics, and uncorrected CVA achieved. An increased sense of subjective well-being, adaptability, and self-efficacy was evident after LASIK. Patients reported a more optimistic attitude to life and increase perceived QOL after surgery.

[Quality of life after Lasik: part I. Validation of the French translation of the NEI-RQL-42 scale]. / Qualité de vie après Lasik : partie I. Validation de la traduction française de l'échelle NEI-RQL-42.

INTRODUCTION: The objective of this study was to bring some validation elements to a French adaptation of an American refraction-related quality of life scale, as applied to a population of Lasik patients. METHODS: The NEI-RQL-42 scale was developed in 2003 in the United States. It comprises 42 questions and 13 scores exploring quality of vision, functional symptoms, influence of refraction on daily activities and psychological impact. The authors propose here a French adaptation and elements for its validation (internal consistency, discriminating validity and external validity). These were assessed through an observational cross-sectional study, performed in one center on all patients consecutively treated with Lasik between January and March 2008. RESULTS: The study sample (307 patients) has the expected characteristics of Lasik-treated patients. The French adaptation of the NEI-RQL-42 has a good internal consistency with Cronbach's coefficients greater or equal to 0.7 for 10 scores out of 12. The discriminating validity of the scale was shown though the reference groups techniques: quality of life is generally lower in severe hyperopes compared with non-severe myopes. The scale's external validity is confirmed by the comparison of its results to those of a satisfaction questionnaire that was simultaneously sent to patients. CONCLUSION: The results obtained are favorable arguments for the validity of the proposed French adaptation of the NEI-RQL-42. This is the first scale available in French to assess refraction-related quality of life.

[Quality of life after LASIK: part II. Quality of life and satisfaction of a population of patients treated with LASIK]. / Qualité de vie après LASIK : partie II. Qualité de vie et satisfaction d'une population de patients opérée par LASIK.

INTRODUCTION: The objective of this study was to assess the refraction-related quality of life and patients' satisfaction in a LASIK-treated sample. METHODS: The French adaptation of the NEI-RQL-42 scale and a satisfaction questionnaire were sent to all patients consecutively treated with LASIK (all ages, all indications) in a same center between January and March 2008. The 13 scores of the NEI-RQL-42 were described. The scores "satisfaction with correction" and "glare" have been further analyzed using multivariate logistic regression. Answers to the satisfaction questionnaire were also described. RESULTS: The study sample (307 patients) has the expected characteristics of LASIK-treated patients. Quality of life scores are generally high (>70/100), except for the "glare" (65/100) and "expectations" (42/100) scores. Most of the scores are higher in myopes than in hyperopes. A lower "satisfaction with correction" score was associated with hyperopia (P<0.001) and with a lower "glare" score. A lower "glare" score was associated with ametropia severity (P=0.002), secondary surgery (P=0.02) and to the use of a non-customized treatment (P=0.047). Satisfaction rate was 95%. CONCLUSIONS: Quality of life scores and satisfaction rate are high in this sample, and suggesting how the refractive results impact patients' lives. They also show the importance of glare and other visual symptoms.

Measuring patient's expectation and the perception of quality in LASIK services.

BACKGROUND: LASIK is the use of excimer lasers to treat therapeutic and refractive visual disorders, ranging from superficial scars to nearsightedness (myopia), and from astigmatism to farsightedness (hyperopia). The purposes of this study are to checking the applicability and psychometric properties of the SERVQUAL on Lasik surgery population. Second, use SEM methods to investigate the loyalty, perceptions and expectations relationship on LASIK surgery. METHODS: The method with which this study was conducted was questionnaire development. A total of 463 consecutive patients, attending LASIK surgery affiliated with Chung Shan Medical University Eye Center, enrolled in this study. All participants were asked to complete revised SERVQUAL questionnaires. Student t test, correlation test, and ANOVA and factor analyses were used to identify the characters and factors of service quality. Paired t test were used to test the gap between expectation and perception scores and structural equation modeling was used to examine relationships among satisfaction components. RESULTS: The effective response rate was 97.3%. Validity was verified by several methods and internal reliability Cronbach's alpha was > 0.958. The results from patient's scores were very high with an overall score of 6.41(0.66), expectations at 6.68(0.47), and perceptions at 6.51(0.57). The gap between expectations and perceptions was significant, however, (t = 6.08). Furthermore, there were significant differences in the expectation scores among the different jobs. Also, the results showed that the higher the education of the patient, the lower their perception score (r = -0.10). The factor loading results of factor analysis showed 5 factors of the 22 items of the SERVQUAL model. The 5 factors of perception explained 72.94% of the total variance there; and on expectations it explained 77.12% of the total variance of satisfaction scores.The goodness-of-fit summary, of structure equation modeling, showed trends in concept on expectations, perceptions, and loyalty. CONCLUSION: The results of this research appear to show that the SERVQUAL instrument is a useful measurement tool in assessing and monitoring service quality in LASIK service, and enabling staff to identify where improvements are needed, from the patients' perspective. There were service quality gaps in the reliability, assurance, and empathy. This study suggested that physicians should increase their discussions with patients; which has, of course, already been proven to be an effective way to increase patient's satisfaction with medical care, regardless of the procedure received.

[The impact of photorefractive excimer laser keratectomy (PRK) and laser in situ keratomileusis (LASIK) on visual quality and life in patients with ametropias]. / O impacto da cirurgia de ceratectomia fotorrefrativa (PRK) e ceratomileuse assistida por excimer laser in situ (LASIK) na qualidade visual e de vida em pacientes com ametropias.

PURPOSE: To evaluate the quality of life, vision and stress before and after refractive surgery. METHODS: This is a longitudinal, observational study, where 100 patients were evaluated; 54 espectacles wearers, 21 contact lens users before surgery and 25 controls wearers spectacles or contact lenses, who did not want to undergo refractive surgery during one year despite refractive error. The applied questionnaires were Self Reporting Questionnaires SRQ-20 of quality of life and vision and National Eye Institute Visual Function Questionnaire NEI VFQ-25 for the assessment of mental health. The intervention group answered the questionnaires before surgery, three, six and twelve months after follow-up and the control group answered the questionnaires at six and twelve months after the baseline. The questionnaires of the intervention group were applied by an independent person. RESULTS: In the intervention group (54 spectacle wearers), 39 were treated by photorefractive excimer laserkeratectomy (PRK) and 15 by laser in situ keratomileusis (LASIK), of the 21 contact lens users: 12 received photorefractive excimer laser keratectomy and nine were treated by laser in situ keratomileusis (LASIK). The control group remained stable during the study. After three months of follow-up the intervention group showed improvement in quality of life, vision and reduction of stress. After one year of follow-up the assessments of quality of life and mental health were similar to the control group. After three months there was a significant reduction of psychiatric symptomatology in the intervention group. CONCLUSION: Patients operated for correction of ametropia showed a significant improvement in quality of life and mental health assessments.

O impacto da cirurgia de ceratectomia fotorrefrativa (PRK) e ceratomileuse assistida por excimer laser in situ (LASIK) na qualidade visual e de vida em pacientes com ametropias / The impact of photorefractive excimer laser keratectomy (PRK) and laser in situ keratomileusis (LASIK) on visual quality and life in patients with ametropias

OBJETIVO: Avaliar a qualidade de vida e de visão e o estresse de pacientes portadores de ametropias submetidos a procedimentos cirúrgicos. MÉTODOS: Estudo longitudinal observacional em que foram estudados 100 pacientes; 54 usuários de óculos, 21 usuários de lentes de contato interessados no procedimento cirúrgico e 25 controles usuários de óculos ou lentes de contato, mas que não desejavam ser operados no período de um ano. Os questionários aplicados foram o National Eye Institute Visual Function Questionnaire (NEI-VFQ-25) de qualidade de vida e o Self Reporting Questionnaire - SRQ-20 para avaliação da saúde mental. Os pacientes que se submeteram à cirurgia responderam aos questionários aplicados por uma observadora antes da mesma, três, seis e doze meses após a intervenção. O grupo controle respondeu de forma auto-aplicada no início do estudo, seis e doze meses após a primeira avaliação. RESULTADOS: No grupo da cirugia dos 54 pacientes que usavam óculos 39 fizeram cirurgia de ceratectomia fotorrefrativa por excimer laser(PRK) e 15 fizeram ceratomileuse assistida por excimer laserin situ (LASIK) e dos 21 que usavam lentes de contato 12 fizeram cirurgia de ceratectomia fotorrefrativa e nove fizeram ceratomileuse assistida por excimer laser in situ (LASIK). O grupo controle esteve estável durante os 12 meses em relação aos instrumentos aplicados. Três meses após a cirurgia o grupo da cirurgia apresentou melhora significante da qualidade de vida e de visão em relação ao pré-operatório independentemente do tipo de cirurgia realizada. Um ano após a cirurgia os índices de qualidade de vida e de saúde mental, foram semelhantes aos do grupo controle. O Self Reporting Questionnaire - SRQ 20 mostrou diminuição significante do índice de sintomas a partir dos três meses de pós-operatório. A qualidade de visão e de vida dos pacientes submetidos à cirurgia de correção de ametropia mudou significantemente para melhor em relação ao préoperatório, com redução substancial do estresse psicológico.

PURPOSE: To evaluate the quality of life, vision and stress before and after refractive surgery. METHODS: This is a longitudinal, observational study, where 100 patients were evaluated; 54 espectacles wearers, 21 contact lens users before surgery and 25 controls wearers spectacles or contact lenses, who did not want to undergo refractive surgery during one year despite refractive error. The applied questionnaires were Self Reporting Questionnaires SRQ-20 of quality of life and vision and National Eye Institute Visual Function Questionnaire NEI VFQ-25 for the assessment of mental health. The intervention group answered the questionnaires before surgery, three, six and twelve months after follow-up and the control group answered the questionnaires at six and twelve months after the baseline. The questionnaires of the intervention group were applied by an independent person. RESULTS: In the intervention group (54 spectacle wearers), 39 were treated by photorefractive excimer laserkeratectomy (PRK) and 15 by laser in situ keratomileusis (LASIK), of the 21 contact lens users: 12 received photorefractive excimer laser keratectomy and nine were treated by laser in situ keratomileusis (LASIK). The control group remained stable during the study. After three months of follow-up the intervention group showed improvement in quality of life, vision and reduction of stress. After one year of follow-up the assessments of quality of life and mental health were similar to the control group. After three months there was a significant reduction of psychiatric symptomatology in the intervention group. CONCLUSION: Patients operated for correction of ametropia showed a significant improvement in quality of life and mental health assessments.

Patient motivation for laser in situ keratomileusis in the State of Bihar.

PURPOSE: To evaluate the main reasons for seeking laser in situ keratomileusis (LASIK) and patient satisfaction after surgery in the socioeconomically underdeveloped eastern state of Bihar, India. METHODS: This retrospective study evaluated results of the first 100 consecutive patients (169 eyes) who had LASIK at our center from July 2002 to September 2003. RESULTS: Of the 100 patients, 65% were male and 35% were female. Ninety percent of male patients were between 18 and 24 years old; they sought LASIK to achieve an uncorrected visual acuity of 6/6 to 6/9-the basic qualifying criterion for jobs in the railway and defense services. Eighty-six percent of female patients were of marrying age. At 1 month after LASIK, 93% of patients achieved an UCVA of 6/6, 4% had UCVA between 6/9 to 6/12, and only 1% had <6/60. CONCLUSION: In the socioeconomically poor state of Bihar, the main reason for males in our study to seek LASIK was to enhance their job prospects. In females, the main reason was to improve facial appearance in order to enhance marriage prospects.

[Lasik, PRK and quality of vision: a study of prognostic factors and a satisfaction survey]. / Lasik, photokéractectomie réfractive et qualité de vision: étude des facteurs pronostiques et enquête de satisfaction.

PURPOSE: To confirm the clinical interest of pupillary diameter measurement for selecting indications and determining surgical protocols, to look for clinical factors predisposing to night vision symptoms, and to the assess patient satisfaction level for photoablation techniques not based on aberrometry. METHODS: This retrospective study was conducted on 111 consecutive myopic patients (219 eyes, with a mean spherical equivalent of -4.25+/-1.84 D); they underwent Lasik (91.3% of cases) or photorefractive keratectomy, after having their pupillary diameter measured by the Colvard pupillometer. Clinical data were collected from medical files, and an anonymous questionnaire was sent in order to assess quality of vision and postoperative satisfaction. RESULTS: Preoperative aims were reached (r=0.41, p<0.0001). The response rate for the questionnaire was 81.1%. Daytime vision was the same or better for 91.1% of the patients, but 25.6% had worse night vision than before. Night vision symptoms were mentioned by 46.7% of the patients, and the most frequent complaint was halos. However, 97.8% of the patients declared themselves as satisfied and would recommend such surgery to their family and friends. A preoperative myopia greater than 4.50D (RR=1.52, p<0.05) and a postoperative keratometry greater than 8.44 mm (RR=1.62, p<0.05) were risk factors for having night vision symptoms, but pupillary diameter was not a risk factor. CONCLUSION: This survey gives an indirect confirmation of the interest of scotopic pupillary diameter measurement and taking it into account in photoablation protocols. However, night vision symptoms remain frequent but do not influence patient satisfaction. Knowledge of risk factors and technical progress should provide a better quality of vision after Lasik.

[Predictors of quality of life in refractive surgery]. / Les prédicteurs de qualité de vie en chirurgie réfractive.

PURPOSE: To investigate predictors of quality of life in refractive surgery: psychological status, quality of vision, visual acuity, and patient satisfaction. METHODS: In a prospective study, 143 patients were evaluated preoperatively and after the third postoperative month using the same questionnaire. Quality of vision, visual acuity, well-being, self-esteem, coping, and patient satisfaction were analyzed with 47 parameters. Refractive procedures included PRK, LASIK, and phakic IOL. Four groups of low (G1), medium (G2), and high myopia (G3) and hyperopia (G4) were individualized to compare the results. RESULTS: We noted a mean postoperative best corrected visual acuity (BCVA) of 20/25 or more for the G1, G2, and G4 groups. For the G3 group, the mean BCVA was increased, with a gain of two Snellen Lines from 20/50 to 20/32. Postoperative patient satisfaction improved, with a significant difference (p<0.05) in all groups. We noted no significant difference in all myopic groups in well-being and no significant decrease in G4. Concerning self-esteem and coping, scores improved, with a significant difference in G3 group (p<0.05). Quality of vision was directly correlated with improvement of quality of life (psychological status), satisfaction scores, and BCVA preoperatively and postoperatively in all patients, but no correlation was noted between visual acuity and patient satisfaction. CONCLUSION: In spite of good refractive results, modification of patient satisfaction depends on quality of vision and quality of life (psychological status) scores. These results give us a new tool that provides useful additional information in refractive surgery.

Defining the content of patient questionnaires: reasons for seeking laser in situ keratomileusis for myopia.

PURPOSE: To determine the relative importance of patients' motives for having laser in situ keratomileusis (LASIK) for myopia. SETTING: The Corneal Diseases and Excimer Laser Research Unit, University of Dundee, Ninewells Hospital and Medical School, Dundee, Scotland. METHODS: Twenty-one cards printed with potential reasons for having LASIK and 3 blank cards for respondents to include additional motives were posted to 71 patients who had myopic LASIK. The cards were ranked by each respondent in order of personal importance and returned for analysis. RESULTS: The response rate was 77.5%. The mean age of the 19 male and 37 female respondents was 41.7 years +/- 9.3 (SD) and the mean preoperative spherical equivalent, -9.26 +/- 4.58 diopters. The primary reasons for seeking treatment (percentage of respondents ranking topic within the top 5) were improvement of unaided social vision (69.1%), intolerance to spectacles/contact lenses (65.5%), and freedom from spectacles/contact lenses (61.8%). Almost 70% of respondents ranked 1 of these reasons as the most important. General inconvenience of spectacles/contact lenses and the desire to pursue sports and leisure activities also ranked high (52.7% and 36.4%, respectively). CONCLUSIONS: Consistent with previous work, better unaided vision, combined with the inconvenience of or intolerance to spectacles or contact lenses, provided the main incentives to have LASIK for myopia, while improved cosmesis was relatively unimportant (29.1%). The results of this study will allow the design of satisfaction questionnaires that are better directed toward establishing satisfaction of specific, relevant functional and psychological aspects of refractive surgery that are important to patients.

Functional, psychological, and satisfaction outcomes of laser in situ keratomileusis for high myopia.

PURPOSE: To identify factors that motivate patients to seek laser in situ keratomileusis (LASIK) treatment for myopia and establish subjective levels of functional improvement and satisfaction across a range of indices after LASIK surgery. SETTING: The Corneal Diseases and Excimer Laser Research Unit, University of Dundee, Ninewells Hospital and Medical School, Dundee, Scotland. METHODS: In this questionnaire-based, cross-sectional study, an anonymous 34-item questionnaire was forwarded to 50 consecutive patients in a prospective study who had had LASIK for high myopia by a single surgeon at a single center. The questionnaire used visual analog scales, anchored at each end by an adjectival descriptor. The mean preoperative myopia was -10.7 diopters +/- 4.4 (SD). Seventy-six percent of eyes (83% of patients) achieved post-LASIK uncorrected visual acuity (UCVA) of 6/12 or better; 1 eye lost 2 lines of corrected Snellen visual acuity. RESULTS: A 98% reply rate was achieved. The most common motivating factor for pursuing LASIK was to improve UCVA (88%); only 21% rated improved cosmesis as an important motive. Most patients (81% to 100%) reported functional improvement across the spectrum of visual tasks assessed, although 8.8% reported difficulty with nighttime driving. Ninety-six percent felt their UCVA was as good as anticipated, 97.9% were satisfied with the speed of visual improvement, 93.8% achieved the goals for which they had surgery, 97.9% reported an improved quality of life, and 97.9% were satisfied with the overall outcome of LASIK. CONCLUSIONS: Using an anonymous, wide-ranging questionnaire, high levels of functional improvement and satisfaction with the speed of visual recovery and outcome were reported by patients after LASIK for high myopia. Nighttime driving symptoms of variable severity were, however, noted by 8.8% of patients, despite high levels of satisfaction with other aspects of visual function.