An estimated minimum of 4.9 million people globally are blind because of corneal disease.1,2 This is one of the leading causes of blindness.3,4 Frequently occurring corneal diseases are pseudophakic bullous keratopathy, keratoconus, trauma, keratitis, endothelial dysfunction, and corneal stromal dystrophies. In some cases, corneal blindness or visual impairment is preventable or treatable with medication. However, for advanced corneal disease, when the outcomes of other strategies are insufficient, surgical treatments such as corneal transplantation are most effective.2,4 A successful transplant might result in partial or full recovery of vision.
Worldwide, corneal transplantation is the most frequent type of transplant. A global survey, which included data from 148 countries representing 95% of the world's population, found that one third had satisfactory access to corneal transplantation, whereas more than half had no access.5 This study also showed that the ratio between the number of people benefiting from transplantation and people waiting for it is about 1:70. Approximately 12.7 million people are on a waiting list, with a median waiting time of 6.5 months. In 2012, 184,576 corneal transplantations were performed in 116 countries, of which 55% were performed in the United States, India, and Brazil.5
Most studies on the effect of corneal transplantation have focused on clinical outcomes, such as visual acuity, refractive error,6–8 endothelial cell loss, complications,7,8 and graft survival.6,8,9 Although penetrating keratoplasty might result in improved visual acuity, it has possible drawbacks such as astigmatism and endothelial cell loss. Moreover, there is a risk of adverse events, such as primary graft failure, graft rejection, graft dislocation, elevated intraocular pressure, and suture-related problems.10
In addition to clinical outcomes, patient-reported outcome measures (PROMs) are increasingly being used in health care as an important indicator of quality of care. A recent qualitative study showed that corneal disease and transplantation affect several life domains related to activities and participation, such as playing sports, driving a car, and reading, but also seeing functions, energy level, the use of contact lenses and glasses, and adapting to the condition.11 However, apart from 1 meta-analysis of subjective visual outcomes, patient satisfaction and preferences of 27 patients in 3 studies,12 patient-reported outcomes such as quality of life have not been investigated in the available literature reviews.13,14
To further increase understanding of the effect of corneal transplantation on a patient's daily life, a thorough analysis of the literature seems warranted. Therefore, the aim of this study was to systematically review the literature on the effect of transplantation on patient-reported outcomes, such as quality of life and mental health, and to investigate potential predictors of positive outcomes. Knowledge about the predictors of beneficial short- and long-term effects might help to improve treatment effectiveness in several life domains.
MATERIALS AND METHODS
A comprehensive search was performed until October 21, 2019, in the literature databases PubMed, Embase, and PsycINFO, in collaboration with an experienced clinical librarian. Terms referring to corneal transplantation, also defined as corneal graft or keratoplasty, were combined with terms referring to quality of life and other related patient-reported outcomes, such as patient satisfaction, activities of daily living, health status, mental health, and participation. Supplemental Digital Content 1 (http://links.lww.com/ICO/B52) shows the full search strategy. After deduplication, articles were screened by title, abstract, and full text. Reference lists of included articles were screened by hand to identify possible other relevant studies.
Articles were included when: (1) the original research was published in English, (2) a longitudinal study design was used, with at least 1 preoperative and 1 postoperative measurement, that is, a randomized controlled trial (RCT), controlled clinical trial (CCT), cohort study (CS), or before–after study (BA), (3) the study population underwent corneal transplantation, and (4) patient-reported outcomes were reported as primary or secondary outcome measures. Studies were excluded when there was no full text available (ie, only reported as abstract).
The characteristics of the extracted studies were as follows: (1) author, year of publication, and country, (2) sample size (initial consent), participant characteristics at baseline (ie, mean age and sex), and dropout, (3) diagnosis/indications for corneal transplantation and severity of visual impairment, (4) outcome measures and follow-up period, and (5) intervention(s) and control condition (if applicable).
As recommended in the Preferred Reporting Items for Systematic reviews and Meta-Analyses (PRISMA) statement,15 a guideline for reporting systematic reviews, the quality of all studies was assessed using a standard approach with defined criteria. The Quality Assessment Tool for Quantitative Studies,16 developed by the Effective Public Health Practice Project, was used. This includes 8 methodological quality components: (1) selection bias, (2) study design, (3) confounders, (4) blinding, (5) data collection methods, (6) withdrawals and dropouts, (7) intervention integrity, and (8) analyses. Components 1 to 6 were rated as strong, moderate, or weak, leading to an overall rating. Components 7 and 8 were left out of the overall rating but were assessed by describing, for example, treatment fidelity, intention-to-treat, or sample size issues of the included studies. The rating procedure was performed for each study independently by 2 researchers. Any uncertainties or discrepancies between ratings were resolved by discussion and a joint decision.
Synthesis of Outcomes
A narrative method was used to synthesize the outcomes of the included studies. If possible, effect sizes (standardized mean differences) were calculated between the baseline and follow-up measurement using Review Manager software, version 5.3.17 Cohen's d method was used to interpret the effect sizes, with 0.20 to 0.49 representing a small effect, 0.50 to 0.79 a medium effect, and ≥0.80 a large effect.18 For each outcome, the number of participants, mean score at baseline and follow-up, and SDs were extracted for each intervention group. However, not all effect sizes [and/or 95% confidence intervals (CIs)] could be calculated for each outcome because some studies reported medians19,20 or SDs were not available.21–24 In these cases, the authors were contacted twice by email and asked to provide their data. If they did not respond or no longer had any data available, the means and SDs were estimated. For 2 studies,23,24 estimation methods were used as reported in the Cochrane Handbook for Systematic Reviews of Interventions,25 and for 2 studies19,20 that reported medians, methods to estimate means and SDs were used as reported in the publication of Wan et al.26 For 1 study,21 the SD could not be estimated, so the effect size could not be calculated. Results and effect sizes were extracted for the 12-month follow-up measurement. Other follow-up time points were extracted if the 12-month follow-up measurement was not available or if longer follow-up time points were also available in addition to the 12-month follow-up measurement.
Database Search and Study Characteristics
The search strategy identified a total of 2140 publications and is outlined in Figure 1. In the 14 included studies of various designs, a total of 2692 participants were included after initially consenting to participate (Table 1). Sample sizes ranged from 18 patients19 to 1544 patients.24 The mean age ranged from 32 years19 to 74 years,27 and the proportion of women, if reported, ranged from 33%19 to 78%.27 The most often reported diagnoses were Fuchs endothelial dystrophy (9 studies)20,21,23,27–32 and keratoconus (7 studies).19–22,28,33,34 Corneal surgeons used various transplantation techniques in the studies: penetrating keratoplasty (8 studies),19,20,22,24,27–29,33 Descemet stripping automated endothelial keratoplasty (4 studies),30–32,35 anterior lamellar keratoplasty (2 studies),20,24 deep anterior lamellar keratoplasty (2 studies),22,34 femtosecond laser–assisted Descemet stripping endothelial keratoplasty (2 studies),29,35 ultrathin Descemet stripping automated endothelial keratoplasty (2 studies),23,30 deep lamellar endothelial keratoplasty (1 study),27 Descemet membrane endothelial keratoplasty (1 study),23 Descemet stripping endothelial keratoplasty (1 study),27 and posterior lamellar keratoplasty (1 study).20 Nine studies were performed in Europe,19,20,22,24,29–32,34 3 in the United States,23,27,33 and 2 in Canada.21,28 Follow-up periods ranged from 4 months20 to 3 years.27
Researchers used PROMs that measured the constructs health-related quality of life,24,30 vision-related quality of life,20,22,23,27,30–32,34,35 visual functioning,19,21,28,33 subjective visual symptoms,21,28,29 mental health,20 and patient satisfaction20,24,28,33 (Table 1). They used the Health Utilities Index Mark 330 and 12-item Short-Form Health Survey24 to measure health-related quality of life, the National Eye Institute Visual Function Questionnaire (NEI VFQ-2520,22,27,30,32,34,35/NEI VFQ-39)23 and Catquest-9SF31 for vision-related quality of life, the Visual Function Index19,28 (modified version)21,33 for visual functioning, the Visual Symptom Score28,29 for subjective visual symptoms, and the Beck Depression Inventory and Hamilton Anxiety Rating Scale20 for mental functioning. In some studies, researchers asked questions about satisfaction with vision/graft outcomes and general appreciation of the graft, expectations about the impact of surgery and complications, and willingness to undergo surgery again, from the patient's perspective.
The assessments of each methodological quality component for each of the included studies are presented in Figure 2. The study by Trousdale et al27 was assessed twice for both study designs. Selection bias was rated as moderate for all 15 studies,19–24,27–34 which indicates some issues with representativeness of the target population and/or the response rate. The confounding component was assessed as weak for the most BAs19–21,24,28,32,34 because adjustment procedures were performed for less than 60% of relevant confounders. Most studies20–24,27–34 performed moderately on blinding procedures, and 1 study19 was rated as weak after the author informed us that neither assessors nor participants were masked. Data collection methods were rated as strong in all studies19–24,27–34 because questionnaires were both valid and reliable. The withdrawals and dropouts component was rated as weak for 2 studies,21,27 where less than 60% of the participants completed the study. Global rating was strong for 4 RCTs,22,23,29,30 1 CCT,27 1 CS,31 and 1 BA,33 reflecting at least moderate ratings on all 6 methodological quality components. Concerning intervention integrity, treatment fidelity was maintained in 2 studies19,32 but deviated22,23,27,29–31 or unclear20,21,24,27,28,33,34 in all others. Finally, 5 studies22,23,30–32 performed an intention-to-treat analysis, which is considered appropriate for RCTs, but 3 studies22–24 had an insufficient sample size.
Synthesis of Outcomes
The effect sizes in Table 1 are standardized mean differences between baseline and follow-up and are reported per intervention or control group.
Heath-Related Quality of Life
Corneal patients improved on health-related quality of life 12 months postoperatively, with large effect sizes,30 whereas no effects were also found,24 depending on study design (Table 1). Their mental health improved, but their physical health remained unchanged 12 months after surgery.24 However, a difference was found between the physical health of men and women: it remained unchanged in men (effect size 0.02, 95% CI, −0.09 to 0.12), whereas it deteriorated in women (effect size 0.18, 95% CI, 0.06 to 0.30) 12 months after surgery.24
Vision-Related Quality of Life, Visual Functioning, and Subjective Visual Symptoms
Corneal patients improved on vision-related quality of life 12 months postoperatively, with medium22 and large23,27,30–32,34,35 effect sizes, and on other follow-up time points with medium20 and large27 effect sizes as well (Table 1). Clinical factors such as better postoperative visual acuity23 in the worse (grafted) eye20,27 and in both eyes together,34 lower astigmatism,27 and lower disability glare27 were associated with higher vision-related quality of life, whereas higher postoperative astigmatism34 and higher doses of prednisone20 were associated with lower vision-related quality of life.
Corneal patients improved on visual functioning 12 months postoperatively,21,28,33 with medium effect sizes, and on other follow-up time points as well, with small28 and large19 effect sizes (Table 1). Clinical factors such as lower preoperative visual acuity in the grafted eye28 and in the best (usually the fellow) eye,33 better postoperative visual acuity in the grafted eye19 and in the best eye,28 better visual field in both eyes together,19 stereoacuity,19 postoperative contact lens use,33 and highest priority for surgery (shortest waiting time)21 were associated with higher visual functioning, whereas lower priority for surgery (longer waiting time)21 was associated with lower visual functioning. Lower preoperative visual functioning21,28 was also associated with higher postoperative visual functioning. Furthermore, younger age was associated with higher visual functioning.33
Corneal patients improved on subjective visual symptoms 12 months postoperatively,21,28,29 such as blurry vision,28,29 glare, halos,29 and pain,21,28 with small to large effect sizes depending on study design, and at 24 months as well, with a small effect size28 (Table 1).
Corneal patients improved on depression 4 months postoperatively, as was shown by a small effect size. However, they remained stable on anxiety 4 months postoperatively20 (Table 1). Postoperative visual acuity in the worse (grafted) eye and prednisone were associated with severity of depression and anxiety, whereas better postoperative visual acuity in the worse (grafted) eye was associated with lower depression and anxiety after 4 months. Furthermore, higher doses of prednisone were associated with more severe symptoms of depression and anxiety after 4 months.20
Corneal patients were often satisfied 12 months postoperatively20,24,28,33 and at 24 months as well, with large effect sizes28 (Table 1). Approximately 78% were satisfied with their vision28,33 and the subjective outcomes of the graft,24 92% would choose to have the surgery again if needed33 12 months after surgery, and 75% were still satisfied with their vision after 24 months.28 Lower postoperative visual acuity and adverse reactions/complications were associated with lower patient satisfaction.24 Furthermore, no correlation was found between sex and patient satisfaction.24
To our knowledge, this is the first literature review on the effect of corneal transplantation on patient-reported outcomes. PROMs, next to clinical outcomes, are increasingly used as an indicator for assessing the quality of health care.
In this literature review, 14 longitudinal studies, described in 16 publications and including 15 study designs (4 RCTs, 1 CCT, 1 CS, and 9 BAs) ranging from strong to weak quality, showed that corneal transplantation had overall beneficial effects on patient-reported outcomes. Patient satisfaction was high. For health-related quality of life, the improvement varied between no effects and large effects 12 months after transplantation. For vision-related quality of life, effect sizes were mainly large; for visual functioning, they were medium; and for subjective visual symptoms, they were small to large 12 months after transplantation. However, there were limited effects for mental health, as shown by 1 study where patients slightly improved on depression symptoms but remained stable on anxiety symptoms 4 months after transplantation. Potential predictors of positive patient-reported outcomes, if investigated, were clinical factors such as lower preoperative visual acuity and better postoperative visual factors. When patient characteristics were considered, different results were found for sex: women showed slightly lower health-related quality of life as an effect of transplantation than men, whereas no sex differences were found for patient satisfaction. Moreover, younger age was associated with better visual functioning. For patient-reported factors, lower preoperative visual functioning was associated with better postoperative visual functioning.
Frost et al13 have shown that there are relatively few long-term studies on quality of life in addition to clinical outcomes as an effect of transplantation. This literature review found only 14 longitudinal studies, and 3 studies included longer follow-up times. One possible explanation for these low numbers is the limited availability of corneal disease-specific PROMs in ophthalmic research and clinical practice,36 compared with macular degeneration, glaucoma, or cataract. The qualitative study of Vreijsen et al11 also showed the impact of corneal disease and transplantation on several life domains, such as vision-related activities. There was only 1 study in which researchers investigated mental health, and none examined labor participation.
The strengths of the studies included in this literature review are that all used validated questionnaires and that almost half received a favorable quality assessment, which was reflected by good-quality RCTs and a CCT. Their limitations are methodological, related to selection bias and lack of blinding procedures regarding assessors and participants. Other methodological limitations were intervention infidelity, less favorable study designs, confounding, dropouts, and inadequate power in some of the studies. In addition, only 3 studies included follow-up times longer than 12 months. The time between surgery and complete suture removal is usually more than 12 months, whereafter visual outcomes such as visual acuity and astigmatism might still change.37,38 Studies with longer follow-up measurements to evaluate the long-term effect of transplantation on patient-reported outcomes therefore seem warranted. Because only 1 study included mental health as one of the outcomes, 2 studies included health-related quality of life, and none took labor participation into account, more research into these topics seems necessary.
The limitations of this literature review are that the number of useful publications was quite small, and the effect sizes were calculated with estimated data for 4 studies and could not be calculated for 1 study. In addition, we limited the review to a more narrative synthesis of the outcomes. We could not include a meta-analysis because treatment and/or control groups were not comparable. A synthesis of pre–post data was optional; however, Cuijpers et al39 have argued that a meta-analysis using pre–post effect sizes should be avoided because of the probable risk of biased results due to dependence of baseline and follow-up data. Finally, the studies showed heterogeneity in lengths for both the intermediate and final postoperative follow-up measurements, which varied from 4 to 36 months.
The results of this literature review describing the effects of corneal transplantation on patient-reported outcomes and predictors might be valuable for clinical practice in several ways. First, PROMs can be applied to assess the effect of corneal transplantation from the patient's perspective.40 Second, they can also be used to involve patients in therapeutic decisions, which facilitates shared decision making. Administering PROMs both before and after corneal transplantation provides the ophthalmologist with additional information on patient preferences.36 Third, the outcomes of PROMs can be used to adjust patient-centered information and formulate realistic expectations of the experienced outcomes of corneal transplantation. This will facilitate patient–doctor communication.40,41 Fourth, ophthalmologists might be able to refer patients to other care providers based on PROM data, such as rehabilitation centers for visually impaired people or social workers.41 Finally, by facilitating PROMs, patients might feel a greater sense of involvement by ophthalmologists and health care professionals in general, which will stimulate patient-centered care and patient satisfaction.40
When taking the global impact of corneal transplantation into account, it can be concluded that research regarding the effect of transplantation on patient-reported outcomes is far from achieving its full potential. This systematic review implies that more high-quality studies are warranted to gain a better understanding of the effects of transplantation from the patient's perspective and its important predictors. Future studies should focus on not only health- and vision-related quality of life but also mental health and labor participation using longitudinal study designs.
The authors thank Linda J. Schoonmade, clinical librarian from Amsterdam UMC, for her help in building the search strategy used in this literature review.
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