Aims: The aim of this study was to determine the impact of diabetic macular oedema (DME) on the quality of life (QOL) in patients with type 2 diabetes mellitus.
Methods: The study was a prospective, consecutive, non-comparative case series. An observational study evaluated the quality of vision and vision-specific QOL using the 25-item National Eye Institute Visual Function Questionnaire (NEI VFQ-25). Mean VFQ-25 subscale scores in type 2 diabetic study patients were compared with mean VFQ-25 subscale score in groups of patients with type 1 diabetic retinopathy (T1DR) and varying degrees of age-related macular degeneration (ARMD), glaucoma and cataracts and in reference populations.
Results: Thirty-three patients completed the NEI VFQ-25. The mean age of the study population was 64 years. When performing a comparison of those patients with DME versus those with isolated T1DR we found that for the general health subscale, the DME versus T1DR group means were 42±4.4 versus 61±1.0 respectively. The DME versus T1DR quality of vision categorical mean scores were 69±4.1 versus 93±3.9. The DME versus T1DR VR-QOL categorical mean scores were 62±5.0 versus 93±1.0. The DME group was significantly worse in each of these three categories compared with the T1DR group (p<0.01). An additional analysis was performed to examine the differences in VR-QOL in the DME group versus varying common ocular diseases, including age-related macular degeneration (ARMD), glaucoma, cataracts and disease-free reference groups. The mean values of VFQ-25 subscale in the DME group were significantly lower then the glaucoma group in ten of 12 subscales, the cataract group in 11 of 12 subscales, and the reference group in 12 of 12 subscales. However, the mean values of VFQ-25 subscale in the DME group were only significantly different from the ARMD group in three of 12 subscales.
Conclusions: Type 2 diabetes patients with macular oedema experience a decreased VR-QOL compared with type 1 diabetic patients with diabetic retinopathy, glaucoma or cataracts. However, VR-QOL in type 2 diabetic patients with macular oedema was similar to those individuals with ARMD.
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More than 15 million people in the USA have diabetes.1 Diabetic retinopathy is the leading cause of blindness and visual loss among working adults.2 Diabetic macular oedema (DME) is a common complication of diabetic retinopathy. Evidence from the Wisconsin Epidemiologic Study of Diabetic Retinopathy (WESDR) found that 20% of patients with type 1 diabetes and 25% of those with type 2 diabetes will develop DME.3 Clinically objective measures of vision, such as visual acuity, are the traditional indicators used in the clinic. However, recent findings suggest that patient-perceived vision-related quality of life (VR-QOL) in conjunction with traditional measures of vision should be the new standard of care.4–10
The 25-item Visual Function Questionnaire (VFQ-25), created by the National Eye Institute (NEI), measures the self-reported vision-targeted health status that is most important to persons who have chronic eye diseases.4 11 The survey measures the influence of visual disability and visual symptoms on general health domains such as emotional well-being and social functioning, in addition to daily visual function. The extent to which the eye disease affects a patient’s ability to live without pain, work productively and interact with family and friends, all measurements of VR-QOL, are interpreted with the VFQ-25.11
Individuals free of eye disease and patients with eye diseases such as age-related macular degeneration (ARMD), cataracts and glaucoma have been evaluated with the VFQ-25.4 12 Although the 25-item NEI-VFQ has been administered to patients with diabetic retinopathy, little information exists on the VR-QOL of patients suffering from DME.6 13 The purpose of this study is to administer the VFQ-25 to patients treated for macular oedema in order to better characterise the VR-QOL for this population, as well as to compare the self-reported VR-QOL in DME patients with the VR-QOL of patients with other ocular disease. This study helps to characterise the VR-QOL of patients suffering from DME, and may allow us to tailor the standard of care treatment for patients with this disease.
A prospective, consecutive, non-comparative case series was carried out with the approval of the University of Chicago School of Medicine Institutional Review Board. From January 2006 to March 2006, 33 patients with clinically significant DME, who were currently under the care of the University of Chicago Department of Ophthalmology Vitreoretinal Service and met eligibility criteria, were invited to participate in this study. Participants had to be at least 16 years of age or older, English-speaking, have type 2 diabetes, and be diagnosed with clinically significant DME (optical coherence tomography centre involvement with thickening greater than 250 μm was a mandatory inclusion criterion). Exclusion criteria included diagnosis of ocular disease other than diabetic retinopathy that may alter visual acuity measurements (e.g. vascular occlusion, glaucoma, amblyopia, subfoveal lipid and macular degeneration). Oral consent was obtained from each participant. All interviews were conducted on the telephone, and the VFQ-25 was administered. Following the interview, a retrospective chart analysis was conducted to obtain Snellen visual acuity measurements at the time of last visit. For statistical analysis, Snellen visual acuity measurements were converted to a logarithm of the minimum angle of resolution (logMAR) units.14 15
All VFQ-25 interviews were conducted by a single trained interviewer (L Miller). Data recorded during the interview included patient age, sex and duration of diabetes. Data obtained from the retrospective chart review included Snellen visual acuity for each eye and presence of macular oedema.
The VFQ-25 contains 25 questions and addresses three main categories as perceived by the patient. These categories include the general health of the subject, the subject’s quality of vision, and the vision-related quality of life (VR-QOL) for the subject.11 Within these three main categories there are a total of 12 subscales. These subscales include: General Vision, Difficulty with Distance, Difficulty with Near Tasks, Colour Vision Difficulty, Dependency on Others, Role Limitation, Mental Health, Social Function, Driving, and Ocular Pain. For each question, the answer is converted into a 100-point scale, with 100 being the optimum score and 0 being the worst score. There are one or more questions specific to each subscale, and therefore the subscale score is the average of one or more questions specific to that subscale.11
In order to determine how our sample population VFQ-25 subscale scores compared with those with type 1 diabetes, DME VFQ-25 subscale scores from this study were compared with previously reported NEI VFQ-25 subscales in patients with long-term type 1 diabetes.6 To investigate the relationship between the DME VFQ-25 subscale scores from this study and those with other ocular diseases, we compared the subscale scores from four groups in the previously reported NEI VFQ-25 field test sample.11 These four groups include a reference group (without ocular disease), a group with ARMD, a glaucoma group and a cataract group. Specific criteria for each of these groups have been described previously.4
Criteria for clinically significant macular oedema included any one of the following findings: retinal thickening at or within 500 μm of the centre of the macula; hard exudates at or within 500 μm of the centre of the macula if associated with thickening of the adjacent retina; zone or zones of retinal thickening 1 disc area in size, at least part of which was within 1 disc diameter of the centre.16
Diabetes type was assessed through patients’ reporting of whether they were diagnosed with type 1 or type 2 diabetes. Duration of diabetes was calculated by patients’ reports of when they were originally diagnosed with diabetes.
Statistical analysis was performed using SPSS. Significant differences between VFQ-subscale scores of study patients and the comparison groups was assessed using a two-sample t test (p<0.05). All data are presented as mean ± standard error.
Study sample characteristics (DME)
Thirty-three patients were enrolled in the study. The ratio of men to women was 12:21. The average age was 64 years old (±2.1). The average duration of type 2 diabetes was 16±1.7 years. The mean visual acuity score for the better eye was 0.35±0.05 logMAR.
DME versus type 1 diabetic retinopathy sample
We first compared our DME group to a well characterised type 1 diabetic group with diabetic retinopathy (T1DR).6 The body of research that concerns VR-QOL in diabetic patients has focused primarily on type 1 diabetic patients.2 5 6 13 17 18 Therefore, we investigated the relationship between the VR-QOL of our DME group and that of a well characterised type 1 diabetic population. It is important to note that Klein’s study was a cross-sectional study and the 25 item NEI-VFQ seemed to be strongly associated with vision, independent of severity of retinopathy and other complications associated with type 1 diabetes. However, Klein’s univariate analyses revealed that the total NEI-VFQ-25 score was lower in persons who were older, had a longer duration of diabetes, higher glycosylated haemoglobin, were in renal failure, had a history of cardiovascular disease, hypertension, or amputation of a lower limb, had poorer visual acuity, more severe diabetic retinopathy, macular oedema, glaucoma, cataract, abnormalities in tactile sensation or temperature sensitivity, smoked more total pack-years, led a more sedentary lifestyle and had poor peak expiratory flow. Table 1 shows the data for the study sample and those of the type 1 diabetic retinopathy sample (T1DR).6 The mean age of the DME population versus T1DR was significantly higher (64±2.1 vs. 41±0.4). The duration of diabetes in the DME group was significantly than in the T1DR group (p<0.001). We found that for each mean VFQ-25 subscale score, except ocular pain, the DME group reported significantly worse scores than the T1DR group (table 2). Although the VFQ-25 has 12 different subscales, these 12 subscales can be divided into three common themes. Categorising the VFQ-25 subscales into common themes allows for easier interpretation of VR-QOL based on General Health, Quality of Vision or Vision-Related Quality of Life. The VFQ-25 subscales were subsequently grouped into three categories: (1) General Health; (2) Quality of Vision (subscales: General Vision, Near Activities, Distance Activities, Peripheral Vision and Colour Vision); (3) Vision-Related Quality of Life (subscales: Driving, Ocular Pain, Role Difficulties, Dependency, Social Functioning and Mental Health). Figure 1 illustrates the General Health, Quality of Vision and Vision-Related Quality of Life (VR-QOL) reported by both the DME and T1DR groups. For the general health subscale, the DME versus T1DR group means were 42±4.4 versus 61±1.0 respectively. The DME versus T1DR quality of vision categorical mean scores were 69±4.1 versus 93±3.9. The DME versus T1DR VR-QOL categorical mean scores were 62±5.0 versus 93±1.0. The DME group was significantly worse in each of these three categories compared with the T1DR group (p<0.01).
DME versus ARMD, glaucoma, cataract and reference groups
Following comparison of the DME group with the T1DR group, we sought to examine the differences in VR-QOL in the DME group versus varying common ocular diseases including ARMD, glaucoma, cataracts and a disease-free reference group.11 Figure 2 shows the average logMAR visual acuity in the better eye for the DME, ARMD, glaucoma and reference groups, with the reference group (logMAR = 0.0) having the best visual acuity and the ARMD group (logMAR = 0.5) having the worst visual acuity. The DME group logMAR visual acuity was 0.35±0.05. Since we were unable to obtain the standard deviation in the logMAR scores of the ARMD, glaucoma, cataract and reference groups, we were unable to apply statistical testing to variation in visual acuity between these groups and our study sample. However, the graphical representation of the mean logMAR visual acuity still provides insight into the variation in visual ability between all groups. In order to determine differences in VR-QOL, we compared the glaucoma, cataract and reference groups’ VFQ-25 mean subscale scores with the DME group. The mean VFQ-25 subscale values for the DME group were significantly lower then the glaucoma group in ten of 12 subscales, the cataract group in 11 out of 12 subscales, and the reference group in 12 out of 12 subscales. However, the mean VFQ-25 subscale values in the DME group were only significantly different from the ARMD group in three of 12 subscales (table 3). These results suggest that the VR-QOL in type 2 diabetic patients with macular oedema is similar to those with ARMD and significantly different from those with glaucoma and cataracts.
Diabetic eye disease is the leading cause of vision loss in the USA.19 DME, a common complication of diabetic retinopathy, can compromise visual function. Recently clinicians have begun to investigate the effects of ocular disease on the quality of patients’ lives.8–10 20 21 The NEI VFQ-25 is a valid and reliable vision-specific quality of life assessment tool used for such investigation.11 In this study, we researched the vision-related quality of life (VR-QOL) in type 2 diabetic patients with DME using the VFQ-25. The results of our study imply that type 2 diabetic patients with macular oedema report a VR-QOL to be significantly poorer in 11 out of 12 subscale scores compared with type 1 diabetic patients with diabetic retinopathy. Furthermore, after comparison of the DME group with previously reported findings11 on patients with ARMD, glaucoma, cataracts and a reference group, we determined that the DME group’s VR-QOL was most similar to the ARMD group. Our results from this study contribute meaningful information regarding the extent to which VR-QOL is diminished in type 2 diabetic patients with macular oedema.
Previous studies have researched the VR-QOL in patients with diabetic retinopathy.6 13 These studies have determined that diabetic retinopathy leads to diminished VR-QOL compared with those without the disease. In addition, these studies have found a strong correlation between visual acuity and VR-QOL. The data presented in our study further confirm the fact that diabetic retinopathy decreases VR-QOL compared with those without ocular disease. To our knowledge, we are the first to suggest that type 2 diabetic patients with macular oedema experience a decreased VR-QOL compared with type 1 diabetic patients with diabetic retinopathy, patients with glaucoma and patients with cataracts.
Mangione et al11 developed the VFQ-25 using a field test sample that included reference, cataract, glaucoma and ARMD groups. The ARMD group reported a lower VR-QOL in all of the VFQ-25 subscale scores compared with the other groups. In our study, the DME group VR-QOL was most similar to that of the ARMD group. Out of 12 subscales, only three were significantly different between the ARMD and DME groups. These findings demonstrate the actual problems that type 2 diabetic patients with macular oedema have when performing daily activities dependent on vision, such as reading newspapers, picking out items on a crowded shelf and being able to leave their home. In addition, the isolating effect of this disease can be seen in the DME group’s low mean subscale scores for mental health, social limitation and dependency.
A potential limitation of this study includes the relatively small sample size in the DME groups compared with the sample sizes of the comparison groups. Although we were able to determine statistically significant differences in mean subscale scores, our sample size was not large enough to allow us to generalise our findings to a larger population. This study is also limited in its generalisability due to not utilising our own control and comparison groups. Variation in methodology between our researchers and those who participated in the other studies used for comparison increases the likelihood of error. A study directly comparing, within the same study, the effects of macular oedema in type 2 diabetic patients with those with other ocular diseases may be warranted.
In conclusion, our observations suggest that the VR-QOL in type 2 diabetic patients with macular oedema is diminished compared with other common ocular diseases such as diabetic retinopathy, glaucoma and cataracts. These findings suggest the need for increased attention to the VR-QOL for those with DME. Patient-reported outcomes may play an important role in treatment choice for clinicians in the future. Therefore, it is important to understand the degree to which DME effects VR-QOL. Additional studies are needed to investigate the effectiveness of treatment choices on the VR-QOL in this specific population.
Funding: Funding support received by the Research to Prevent Blindness Organization, New York, New York.
Competing interests: None.
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