Year : 2005 | Volume
: 53 | Issue : 2 | Page : 93--99
Visual outcomes of pan-retinal photocoagulation in diabetic retinopathy at one-year follow-up and associated risk factors
Mohan Rema, Purushothaman Sujatha, Rajendra Pradeepa
Madras Diabetes Research Foundation, Dr. Mohans' M. V. Diabetes Specialities Centre, Chennai, India
Dr. M Rema, Madras Diabetes Research Foundation, 4, Conran Smith Road, Gopalapuram, Chennai - 600 086. India
Purpose: To assess the visual outcomes at one-year follow-up after pan-retinal photocoagulation (PRP) in type 2 diabetes mellitus subjects with proliferative diabetic retinopathy (PDR) and associated risk factors.
Materials and Methods: A retrospective study, using data from medical records of 5000 Type 2 diabetic patients who underwent a retinal examination between 1995 and 1999 at a diabetic centre. Ocular, clinical and biochemical parameters were assessed at baseline and at one-year follow-up after PRP. Diabetic retinopathy (DR) was documented by colour photography and PRP was performed according to the ETDRS criteria.
Results : PRP was done in 413 eyes, of which 261 eyes of 160 subjects were eligible for the study. One hundred and forty eyes (73%) of 191 eyes with good visual acuity (6/9) at baseline maintained the same vision at one-year follow-up. Of the 53 eyes with visual acuity of 6/12-6/36 at baseline, 58.5% (31 eyes) maintained same vision and 18.9% (10 eyes) improved their vision at one-year follow-up. Of the 17 eyes with visual acuity �6/60 at baseline, 12 maintained the same vision and the remaining 5 improved their vision. The causes of visual loss included vitreous haemorrhage in 20 subjects (31.7%), progression of cataract in 19 (30%), chronic macular oedema in 15 (23.8%), pre-retinal haemorrhage in the macula in 6 (9.5%) and pre-retinal fibrosis in the macula in 3 (4.7%) subjects. On multiple logistic regression analysis, diastolic blood pressure ( P =0.03), duration of diabetes ( P =0.006), fasting blood glucose ( P =0.02) and nephropathy ( P =0.01) were associated with decreased vision after PRP. Glycated haemoglobin (HbA1c) ( P <0.001), serum creatinine ( P =0.03), HDL cholesterol ( P =0.05), diabetic neuropathy ( P <0.001), hypertension ( P =0.01) and diabetic nephropathy ( P <0.001) showed a significant association with PDR.
Conclusion: Visual acuity at baseline, the duration of diabetes and proteinuria played a significant role in determining the post-PRP visual acuity.
|How to cite this article:|
Rema M, Sujatha P, Pradeepa R. Visual outcomes of pan-retinal photocoagulation in diabetic retinopathy at one-year follow-up and associated risk factors.Indian J Ophthalmol 2005;53:93-99
|How to cite this URL:|
Rema M, Sujatha P, Pradeepa R. Visual outcomes of pan-retinal photocoagulation in diabetic retinopathy at one-year follow-up and associated risk factors. Indian J Ophthalmol [serial online] 2005 [cited 2023 May 29 ];53:93-99
Available from: https://journals.lww.com/ijo/pages/default.aspx/text.asp?2005/53/2/93/16171
Photocoagulation was first performed by Meyer-Schwickerath  and still remains the most effective treatment for proliferative diabetic retinopathy.  The beneficial effects of pan-retinal photocoagulation (PRP) for diabetic retinopathy and its effectiveness in decreasing the incidence of blindness were established almost 20 years ago by a multicentric study, the Diabetic Retinopathy Study (DRS).  Both DRS and the Early Treatment Diabetic Retinopathy Study (ETDRS) provided data to establish the guidelines for detection and effective treatment of proliferative diabetic retinopathy (PDR) and diabetic macular oedema.  While the DRS findings demonstrated that PRP reduces the risk of severe visual loss in patients with high-risk PDR by 50-60%,  ETDRS reported the effectiveness of using photocoagulation to treat diabetic macular oedema and recommended that documented pan-retinal photocoagulation should be initiated early to be most effective in the management of PDR. 
Few studies have reported on the visual outcomes after PRP. The beneficial effect of PRP on visual outcome is directly related to the concomitant treatment of retinopathy risk factors.  Thus identifying the risk factors of PDR and the visual outcomes after PRP in diabetic patients would result in effective treatment of the patient as a whole, thereby reducing failure rates. The aim of the present study was to assess the visual outcomes one year after pan-retinal photocoagulation for proliferative diabetic retinopathy in type 2 diabetic patients attending a specialised diabetic eye care centre.
Materials and Methods
This is a retrospective analysis of medical records of 5000 type 2 diabetic patients who underwent retinal examination between 1995 and 1999 at the Dr. Mohans' M.V. Diabetes Specialities Centre, Chennai, India. Four hundred and thirteen eyes of 288 type 2 diabetes mellitus patients with PDR underwent PRP during that period. A list of patients diagnosed with PDR was obtained from a computerised registry of diagnostic codes maintained by the diabetic retinopathy unit at the centre. Of these, 261 eyes of 160 subjects were eligible for the study (defined as those subjects who had at least one eye treated with PRP and were followed up for at least one year). Subjects for whom the biochemical and clinical parameters were not available at baseline and subjects who did not have a follow-up for a year were excluded. Age, gender, and duration-matched 160 type 2 diabetic subjects without diabetic retinopathy served as controls for risk factor analysis.
Data collected from the patients' records included patients' age, gender, duration of diabetes mellitus, age at onset of diabetes mellitus, presence or absence of hypertension, body mass index, use of insulin or oral hypoglycaemic agents, presence of other systemic diabetic complications and other general illnesses.
Ocular parameters were assessed at baseline and at one-year follow-up by recording the best-corrected visual acuity, intraocular pressure, slitlamp examination, retinal examination, stereo colour fundus photographs and fundus fluorescein angiography (FFA). Best-corrected visual acuity was recorded by Snellen's visual acuity chart and analysis performed using the Snellen's reciprocal.  If the visual acuity was / or ST segment changes (Minnesota codes 1-1-1 to 1-1-7) and/or T wave changes (Minnesota codes 5-1 to 5-3) in electrocardiography (ECG). 
The diagnostic criteria for macroproteinuria (nephropathy) was an estimated 24-hour protein excretion of �500 mg/day and for microproteinuria was protein excretion of 150-499 mg/day as previously described.  Biothesiometry was performed to assess the vibration perception thresholds. Neuropathy was diagnosed if the vibratory perception threshold (VPT) of the great toe exceeded 25 Volts. 
Visual acuity was defined 'stable' when vision at baseline was maintained after PRP; 'decreased' when the baseline vision decreased by��2 lines; and 'improved' when the baseline vision improved by �2 lines after PRP at the end of one year.
All the data were computed on FoxPro database and statistical analyses were done using SPSS PC windows version 10 (Chicago, IL). The students' "t" test was used to compare continuous variables between groups and the paired 't' test was used to compare continuous variables within the group. P values P =0.011), HbA1c levels ( P P =0.006), serum creatinine levels ( P =0.001), systolic and diastolic blood pressure ( P =0.001 and P =0.002 respectively) and macroproteinuria ( P P =0.028), postprandial blood glucose ( P =0.009) and HbA1c levels ( P P =0.002) levels were lower compared to the one-year follow-up.
In these patients NVE was observed in 77.8% (203 eyes), NVD in 33.3% (87 eyes) and tractional retinal detachment was present in only 1.2% (3 eyes) at baseline among the 261 eyes. Vitreous haemorrhage and pre-retinal haemorrhage was observed in 21 (13.0%) and 22 (13.8%) study subjects at baseline respectively.
Of the 261 eyes, 28 eyes (10.7%) had undergone cataract surgery, none of these received YAG capsulotomy during the period of follow-up. Prior to PRP, nerve palsy was reported in 3 eyes, and 2 subjects were on therapy for open angle glaucoma. Retinal vein occlusion (2 eyes), corneal degeneration (1 eye) and heterochromia iridis (1 eye) were other eye disorders documented.
Intraocular pressure both at baseline and at one-year follow-up after PRP did not influence the visual outcome in this cohort. At baseline, 191 (73.2%) eyes had visual acuity of 6/9 or better, 53 (20.3%) eyes had visual acuity of 6/12-6/36 and 17 (6.5%) eyes had visual acuity of �6/60. The odds ratio (OR) was computed for visual acuity taking �6/12 as the reference category. The analysis suggested that patients with PDR had a 4-fold risk for decline in vision ( P P =0.028) following PRP at one year. Among the eyes with vision �6/9 at baseline and duration of �10 years of diabetes, only 2 eyes (2%) developed poor visual acuity (�6/60) at the end of one year, whereas 9 eyes (22%) of patients with duration of >20 years developed poor visual acuity (�6/60) at one year. This is consistent with the guidelines shown in the ETDRS that when PRP is initiated early visual prognosis is better.
At baseline, the risk factors which had a positive association with decreased vision compared to the individuals with normal vision at one-year follow-up on multiple logistic regression model analysis, were duration of diabetes (OR-1.2, CI-1.1-1.3, P =0.006), diastolic blood pressure (OR-1.1, CI-1.0-1.12, P =0.03), fasting blood glucose (OR-1.0, CI-1.0-1.01, P =0.02) and macroproteinuria (nephropathy) (OR-7.6, CI-1.6-35.8, P =0.01).
Prevalence of hypertension (61.9% [n=99], P <0.001) was significantly higher in the study group compared to controls. Significant independent predictors of PDR, determined by multivariate logistic regression model with stepwise analysis were higher fractions of HbA1c, serum creatinine, neuropathy, hypertension, nephropathy and lower levels of HDL cholesterol [Table 2].
The present study attempted to evaluate the visual outcomes of PRP and its associated risk factors. In the ETDRS, vitreous or pre-retinal haemorrhage was the major cause of visual loss and this is an important indicator for serious intraocular disease.  In a long-term study (10 years) on the visual outcome of PRP for PDR, progression of lens opacities, chronic macular oedema, vitreous haemorrhage, macular traction, and neovascular glaucoma were the main causes of visual loss.  In our study, vitreous haemorrhage and progression of lens opacities were the most common causes of severe visual loss followed by chronic macular oedema, pre-retinal haemorrhage and pre-retinal fibrosis at the macula.
In our study, duration of diabetes was an important determinant of the post PRP vision at one-year follow-up. This was shown by the fact that 41% of eyes in patients with more than 20 years of diabetes had decreased vision as compared to only 20% of eyes in those with less than 20 years of duration, at one-year follow-up. Poor vision at baseline was an important risk for visual prognosis at one year after PRP. 73.2% of patients who had 6/9 or better vision at presentation maintained it at the one-year follow-up compared to 14.3% patients who had visual acuity less than 6/9 at baseline.
In the WHO Multinational Study of vascular disease in diabetes, positive odds ratios for PDR were obtained for age, duration, insulin treatment, cholesterol, proteinuria and fasting glycaemia.  The results of our study are consistent with this study. HbA1c, HDL cholesterol, duration, neuropathy, hypertension and nephropathy were significant risk factors for PDR subjects who received PRP. We also found an association with declining visual acuity and PDR. We did not find an association with insulin treatment in this cohort.
Proteinuria was one of the six risk factors identified for severe visual loss despite PRP, during the first 5 years after randomisation in the DRS.  Multiple logistic regression analysis in our study also revealed that macroproteinuria (nephropathy) was a significant risk factor for decreased vision compared to the individuals with normal vision at one-year follow-up.
It has been elegantly demonstrated in both the ETDRS and the Wisconsin Epidemiologic Study of Diabetic Retinopathy (WESDR) that dyslipidemia, independent of glycaemia, is also associated with an increased risk of developing retinopathy although the results have not been consistent. -  In another clinic-based study, it was noted that type 2 diabetic subjects, had an increase in the lipid peroxidation in plasma; this is accentuated in patients with diabetic complications. ,  In our study PDR was not associated with serum cholesterol, triglyceride and LDL cholesterol but showed a strong association with decreased serum HDL cholesterol levels.
Data from the United Kingdom Prospective Diabetes Study (UKPDS) and other epidemiological studies have shown that progression of retinopathy was associated with older age, male gender and glycaemia (as evidenced by higher HbA1c). ,, In this study HbA1c levels were positively associated with PDR, however there was lack of correlation with fasting and postprandial blood glucose levels, possibly due to the fact that the patients were on intensive insulin therapy or oral hypoglycaemic drugs after PDR was diagnosed.
Hypertension has often been shown as a risk factor in the development of retinopathy , ,, and a 34% reduction in the progression of retinopathy (by two steps on the early detection of diabetic retinopathy study chart) was demonstrated in the UKPDS in those treated intensively for hypertension.  This is consistent with our study, where we found a strong correlation of PDR with hypertension in subjects who received PRP.
As reported in Korean  and Japanese  type 2 diabetic subjects with PDR, presence of nephropathy had a statistically significant association with PDR in the current study. Similar observations were also found in our clinic-based study. This suggests a need for concurrent management of retinopathy integrated with the treatment of co-morbidities.
One of the limitations of the current study was the retrospective nature. Only prospective longitudinal studies can give a true estimate of risk factors for PDR.
In conclusion, in this retrospective study, visual acuity at baseline (OR 4.4 for vision �6/12), duration of diabetes (OR 1.2) and proteinuria (OR 7.6) played a significant role in determining the post PRP visual acuity. The predictive risk factors associated with PDR are hypertension (OR 2.6), nephropathy (OR 11.5) and neuropathy along with increased HbA1c (OR 1.4), serum creatinine (OR 2.8) and decreased HDL cholesterol (OR 1.0). This strongly suggests that concomitant treatment of the co-existing conditions with diabetic retinopathy will result in better visual prognosis after PRP.
We acknowledge the help rendered by Mr. V. S. Prem Kumar, Optometrist and Chief photographer, Mr. A. K. Mathai for statistical advice and Mr. C. Premanand, Research Fellow for data entry
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