EFFECTS OF PANRETINAL PHOTOCOAGULATION ON CHOROIDAL THICKNESS AND CHOROIDAL BLOOD FLOW IN PATIENTS WITH SEVERE NONPROLIFERATIVE DIABETIC RETINOPATHY MASAHIRO OKAMOTO, MD, TOYOAKI MATSUURA, MD, NAHOKO OGATA, MD Purpose: To evaluate the choroidal thickness and choroidal blood flow in the subfoveal region quantitatively after panretinal photocoagulation (PRP) in eyes with severe nonproliferative diabetic retinopathy. Methods: This was a prospective comparative study of 24 eyes of 24 patients with type II diabetes and severe nonproliferative diabetic retinopathy with no macula edema. The foveal retinal thickness and choroidal thickness were measured by enhanced depth imaging optical coherence tomography. The subfoveal choroidal blood flow was represented by the mean blur rate obtained by laser speckle flowgraphy. The intraocular pressure, blood pressure, pulse rate, and hemoglobin A1c level (HbA1c) were also measured before and after PRP. Results: The mean foveal retinal thickness did not change significantly during the follow-up period. The mean subfoveal choroidal thickness was reduced significantly from 327.4 mm at the baseline to 286.3 mm at 1 month and 285.0 mm at 3 months after PRP. The mean blur rate ratio decreased significantly to 87.5% at 1 month and 86.0% at 3 months of the baseline values. There was a significant correlation between the subfoveal choroidal thickness and subfoveal choroidal blood flow after PRP. After PRP, the best-corrected visual acuity, intraocular pressure, mean arterial pressure, ocular perfusion pressure, pulse rate, and HbA1c did not change significantly. Conclusion: The success of PRP in treating eyes with severe nonproliferative diabetic retinopathy is probably due to the significant reduction of the subfoveal choroidal thickness and subfoveal choroidal blood flow after PRP. RETINA 36:805–811, 2016
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improves the oxygenation of the ischemic inner retinal layers by destroying some of the metabolically highly active photoreceptor cells which would then lead to a greater flow of oxygen from the choriocapillaris to the inner layers of the retina.3 Indeed, animal studies have shown an increase in the oxygen delivered from the choriocapillaris to the inner retina after photocoagulation.4 The pathophysiology of DR has not been determined definitively, although it is known that the breakdown of the inner blood retinal barrier is a core event.5 In addition, the choroidal vasculature is believed to play an important role6 in the pathophysiology of DR.7–10 A better clinical
iabetic retinopathy (DR) is an important public health concern and is a leading cause of blindness in the working population.1 Panretinal photocoagulation (PRP) is the standard treatment for eyes with DR, and its use has proven to reduce the incidence of severe visual loss.2 It has been proposed that PRP
From the Department of Ophthalmology, Nara Medical University, Kashihara, Japan. None of the authors have any financial/conflicting interests to disclose. Reprint requests: Nahoko Ogata, MD, Department of Ophthalmology, Nara Medical University, 840 Shijo-cho, Kashihara, Nara 634-8522, Japan; e-mail: [email protected]
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understanding of the choroidal circulation would be important for an accurate assessment of diabetic eye diseases although not much attention has been paid to the choroidal vasculature after PRP. One of the problems in assessing the role of the choroid in the pathophysiology of DR is the absence of a technique of measuring the choroidal thickness quantitatively. The recent introduction of enhanced depth imaging by spectral domain optical coherence tomography has allowed clinicians to measure the choroidal thickness quantitatively and noninvasively.11 However, there have been only a few studies that examined the changes of the choroidal thickness in eyes with DR before and after PRP.7,10,12,13 However, the effect of PRP on the choroidal circulation has been studied to some degree. Color Doppler imaging,14 laser interferometry,15 and laser Doppler flowmetry16 have been used to obtain quantitative data on choroidal circulation in eyes with DR before and after PRP. However, the results have been contradictory probably because of the different measuring methods, instruments, measured regions, and stage of the disease processes. To the best of our knowledge, the correlation between the subfoveal choroidal thickness and subfoveal choroidal blood flow has not been reported for eyes with DR before and after PRP. Therefore, the purpose of this study was to assess the effect of PRP on the subfoveal choroidal thickness and subfoveal choroidal blood flow in patients with severe nonproliferative diabetic retinopathy (S-NPDR). Materials and Methods Participants This study was conducted at the Nara Medical University from April 2011 through December 2013. The protocol of this study conformed to the tenets of the Declaration of Helsinki and was approved by the Internal Review Board of the Nara Medical University. The nature of the study was explained to all of the patients, and a signed informed consent was obtained. Twenty-four consecutive patients with type II diabetes and S-NPDR without macular edema were studied. The severity of the retinopathy was graded according to the method set forth by the Global Diabetic Retinopathy Project Group.17 Each subject received a comprehensive ocular examinations to diagnose and stage the DR including measurements of the best-corrected visual acuity, biomicroscopic examinations, intraocular pressure (IOP), indirect ophthalmoscopy, fundus fluorescein angiography (FA), and spectral domain optical coherence tomography (Spectralis, Heidelberg Engineering, Heidel-
berg, Germany). Only one eye from each participant was included in the study. If both eyes met the inclusion criterion, the eye with better visual acuity was included. The exclusion criteria included the presence of refractive errors greater than ±3.0 diopters, amblyopia, significant cataracts, retinal or choroidal pathology, e.g., age-related macular degeneration, choroidal neovascularization, vitreomacular traction, epiretinal membrane, macular hole, any history of eye diseases or any type of ocular surgery or photocoagulation, and systemic diseases other than diabetes. To avoid the effects of pharmacologic agents on the retinal or choroidal vasculature, eyes with any previous treatment, including intravitreal or subtenon injections of triamcinolone or anti–vascular endothelial growth factor, were also excluded. Panretinal Photocoagulation Panretinal photocoagulation was performed in eyes with S-NPDR according to the recommendations of the Early Treatment Diabetic Retinopathy Study group.18 Fluorescein fundus angiography (FA) showed that all patients had avascular retinal areas in three or more quadrants. The PRP was delivered through a widefield contact lens (Ocular Mainster PRP 165; Ocular Instruments, Bellevue, WA) using a slit-lamp adapted photocoagulator (Multicolor Scan Laser Photocoagulator, MC-500 Vixi; NIDEK Co., Gamagouri, Japan) using yellow color according to the Early Treatment Diabetic Retinopathy Study protocol.18 The PRP for each eye was performed in 3 to 5 sessions with an interval of 2 weeks between sessions. For each session, 200 mm spot sizes with pulse duration of 0.2 seconds. Three hundred to 400 spots were made for a total to 1,200 to 2,000 spots for a complete PRP. The power of the laser was individually adjusted to produce yellowishwhite coagulative spots and ranged between 180 mW and 230 mW. Follow-up visits were scheduled for 1 month and 3 months after the last treatment session. A thorough ophthalmologic examination, including the measurement of the best-corrected visual acuity, OCT, choroidal blood flow, and fundus examination, was performed at each visit and FA was performed 3 months after the last treatment. Measurements of Retinal and Choroidal Thicknesses The foveal thickness of the retina was defined as the distance between the inner limiting membrane and the retinal pigment epithelium in the spectral domain optical coherence tomography images (upper white arrow in Figure 1A). This distance was automatically determined by a software embedded in the OCT. The fundus was scanned with 6-mm horizontal and vertical
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Fig. 1. Spectral domain optical coherence tomographic (SDOCT) image and laser speckle flowgraphy (LSFG) map of an eye with severe nonproliferative diabetic retinopathy before panretinal photocoagulation. A. SDOCT of the region shown in (B). The foveal retinal thickness was defined as the distance between the inner limiting membrane and the retinal pigment epithelium (RPE) (upper white arrow). The subfoveal choroidal thickness was manually measured as the distance between the basal edge of the RPE and the chorioscleral border (lower white arrow) on the enhanced depth image (horizontal view) of the optical coherence tomographic image. The choroidal thickness was measured at 5 points; beneath the fovea, and the superior, inferior, temporal, and nasal points of 1 mm from the fovea. The choroidal thickness was measured as the distance between the retinal pigment epithelium and the chorioscleral border. B. Color-coded map of LSFG showing the blood flow of the subfoveal choroid. The blood flow of the subfoveal choroid was measured in the macular avascular region (open circle), and the mean blur rate was extracted by the embedded software tool (LSFG Analyzer, version 3.0.43.0; Softcare Ltd.). Red color indicates high blood flow and blue color indicates low blood flow.
lines centered on the fovea. The location of the fovea was determined by the fundus photographs, and the patients were limited to those who could fixate the fixation point of the OCT steadily. Cross-sectional images were obtained by the same experienced examiner, and each examination was repeated until highly reproducible scans were recorded. The subfoveal choroidal thickness, which was measured manually as the distance between the basal edge of the retinal pigment epithelium and the chorioscleral border, was measured on the images obtained by enhanced depth imaging by spectral domain optical coherence tomography from all patients. It was measured at 5 points: directly beneath the fovea, and the superior, inferior, temporal, and nasal points of 1 mm from the fovea (lower white arrow in Figure 1A). All measurements were performed between 13:00 to 15:00 hours to avoid diurnal variations.19,20 All images were recorded by an experienced ophthalmologist or by one of the authors, and the measurements were made by two experienced examiners (M.O., T.M.) who were masked to the choroidal blood flow findings. If the measurements by the 2 examiners differed by more than 15%, the examiners repeated the measurements together. Measurement of Blood Flow by Laser Speckle Flowgraphy The subfoveal choroidal blood flow was measured with a laser speckle flowgraphy instrument (LSFGNAVI; NIDEK CO., LTD., Gamagouri, Japan) from the laser speckle images.21 The offline analysis software (LSFG Analyzer, version 3.0.43.0; Softcare Ltd.,
Fukutsu, Japan) combined all images over a 4-second recording period into color-coded maps with each pixel assigned a computed mean blur rate (MBR). The MBR is the squared ratio of the mean intensity divided by the standard deviation of the changes in the light intensity which varies temporally and spatially according to the velocity of the erythrocytes.21 Thus, the MBR is a quantitative index of the relative blood flow velocity.21 In the color-coded maps, a red color indicates high blood flow velocities and blue color indicates low blood flow velocities.21 Laser speckle flowgraphy was used to determine the blood flow velocity (MBR) of the subfoveal choroid quantitatively.22 The MBR of the subfoveal choroid was measured in the avascular region of the macular area (open circle, Figure 1B), and it was determined for all eyes before, 1 month, and 3 months after PRP. To evaluate the changes in MBR, the changes in the MBR relative to that at the baseline were used because the MBR is a quantitative index of the “relative” blood flow velocity. Systemic Hemodynamics The systolic blood pressure (SBP) and diastolic blood pressure (DBP) were measured at the upper arm by an automated oscillometric device. The mean arterial pressure (MAP) was calculated by the following equation: MAP = DBP + 1/3 (SBP − DBP). The ocular perfusion pressure (OPP) was calculated to be: OPP = 2/ 3 (MAP − IOP). The pulse rate was automatically recorded by a finger pulse-oxymeter (HP-CMS Patient Monitor; Hewlett Packard, Palo Alto, CA) before,
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1 month, and 3 months after PRP. The hemoglobin A1c levels (HbA1c) were also measured before, 1 month, and 3 months after PRP. Statistical Analyses The outcome measures taken at 1 month and 3 months after PRP were compared with that of the baseline data using paired sample t - test. The data are presented as the means ± SDs. To examine the relationship between the choroidal thickness and choroidal blood flow in the subfoveal region after PRP, the Pearson’s correlation test was performed. A P-value ,0.05 was considered to be significant. Statistical analysis was performed using licensed statistical software (SPSS version 21.0; SPSS Inc., Chicago, IL). Results Twenty-four eyes from 24 patients with type II diabetes and S-NPDR with no macula edema were studied prospectively. There were 14 men and 10 women whose mean age was 62.3 ± 10.2 years, and the mean duration of the diabetes was 17.1 years with a range of 10 to 25 years. The total number of photocoagulation burns was 1,855 ± 381 per eye. None of the patients developed any adverse effects related to the PRP. Each subject recognized no progress of DR on FA findings measured 3 months after PRP. The blood vessel dilation and vascular permeability was improved and also decreased those indicating that PRP was successfully achieved. The differences in the best-corrected visual acuity before the pretreatment and that at 1 and 3 months after PRP were not significant (P . 0.05; Table 1). None of the eyes had a worsening of the best-corrected visual acuity. Retinal and Choroidal Thicknesses The mean foveal retinal thickness was 184.0 ± 25.0 mm at the baseline, and the thickness did not change
significantly during the follow-up period (186.1 ± 27.9 mm at 1 month and 191.3 ± 25.2 mm at 3 months; P = 0.49 and P = 0.44, respectively). In contrast, the subfoveal choroidal thickness was significantly decreased at both 1 and 3 months after PRP (from 327.4 ± 54.4 mm at the base line to 286.3 ± 50.6 mm at 1 month, 285.0 ± 49.2 mm at 3 months; P = 0.002 and P = 0.002, respectively, Table 2). The mean choroidal thickness at perimacular (superior, inferior, temporal, nasal) also significantly decreased at 1 month and 3 months after PRP (Table 2). The interobserver reproducibility was excellent (intraclass correlation coefficient = 0.98). Choroidal Blood Flow The relative MBR was calculated relative to the pretreatment value (base line) which was expressed as 100%. The relative MBR values significantly decreased to 87.5 ± 10.3% at 1 month and to 86.0 ± 12.7% at 3 months after PRP (P = 0.0007 and P = 0.0005; Figure 2). Correlation Between Choroidal Thickness and Choroidal Blood Flow We calculated the correlation between the subfoveal choroidal thickness and subfoveal choroidal blood flow. We found that there was a significant positive correlation between the changes in the subfoveal choroidal thickness and subfoveal choroidal blood flow during the 3-month follow-up period (r = 0.71, P , 0.001, Figure 3). Systemic Hemodynamics The IOP, MAP, OPP, basal pulse rate (in beats per minute), and HbA1c level (in mg/dL) at the baseline were not significantly different at 1 and 3 months after the PRP (P . 0.05 for all, Table 1).
Table 1. Systemic Hemodynamics and Ophthalmological Data Before and After PRP Pretreatment BCVA (logMAR) IOP (mmHg) Foveal retinal thickness (mm) MAP (mmHg) OPP (mmHg) PR (bpm) HbA1c (mg/dL)
0.03 14.6 184.0 95.5 54.6 65.0 6.7
± ± ± ± ± ± ±
0.12 4.0 25.0 11.2 9.0 8.4 1.3
1 Month After PRP 0.04 15.3 186.1 92.8 51.1 63.6 6.5
± ± ± ± ± ± ±
0.10 3.7 27.9 10.8 9.3 7.5 1.5
3 Months After PRP 0.04 14.2 191.3 94.1 53.6 65.0 6.4
± ± ± ± ± ± ±
0.14 3.2 25.2 10.6 9.7 9.8 1.1
Values are expressed as mean ± SD. BCVA, best-corrected visual acuity; HbA1c, Hemoglobin A1c; IOP, intraocular pressure; MAP, mean arterial pressure; OPP, ocular perfusion pressure; PR, pulse rate.
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PANRETINAL PHOTOCOAGULATION ON CHOROID OKAMOTO ET AL Table 2. Changes of Choroidal Thickness Pretreatment (mm) 1 Month After PRP (mm) Subfoveal choroidal thickness Superior 1 mm Inferior 1 mm Temporal 1 mm Nasal 1 mm
327.4 306.1 306.9 310.5 294.9
± ± ± ± ±
54.4 52.0 48.3 44.0 54.3
286.3 261.9 267.8 277.2 258.0
± ± ± ± ±
50.6 51.6 44.5 52.3 51.8
P 0.002 0.001 0.005 0.01 0.005
3 Months After PRP (mm) 285.0 260.0 268.8 273.2 252.2
± ± ± ± ±
49.2 75.9 82.0 59.5 69.2
P 0.002 0.001 0.005 0.009 0.003
Values are expressed as mean ± SD.
Our results showed that PRP on eyes with S-NPDR significantly reduced the subfoveal choroidal thickness and also reduced the relative subfoveal choroidal blood flow velocity. Earlier studies reported a significant thinner choroid after PRP on eyes with S-NPDR compared with that of untreated eyes with S-NPDR.7,10,12,13 However, there was a report that the subfoveal choroidal thickness increased significantly at 1 week after PRP.23 The investigators suggested that choroidal effusion after PRP might have contributed an increase of the choroidal thickness, although it has been reported that ciliochoroidal effusion after PRP was completely absorbed in 2 weeks.24 It has also been reported that the choroidal blood flow was significantly slower in PRP-treated eyes compared with that of untreated eyes as measured by laser interferometry and Color Doppler imaging.15,25,26 However, some studies showed that the choroidal blood flow velocity in the foveal region was not changed significantly compared with that of untreated eyes as measured by laser Doppler flowmetry.16 The measuring methods, instruments, measured regions, and disease processes were different in each
study, and this may contribute to the variability of the results. If PRP led to an increase of oxygenation, this should lower the expression levels of vascular endothelial growth factor and vascular endothelial growth factor receptors.27,28 Vascular endothelial growth factor induces blood vessel dilation and increase the ocular blood flow because of an increase in nitric oxide production.29,30 Vascular endothelial growth factor also increases the vascular permeability in eyes with DR.31 We performed fundus fluorescein angiography 3 months after PRP and confirmed that the dilation of the blood vessels and the vascular permeability were decreased indicating that PRP was successfully achieved. We assumed that successful PRP reduced the vascular endothelial growth factor production and resulted in a reduction of the blood vessel dilation and vascular permeability. We suggest that the significant reduction of the subfoveal choroidal thickness and subfoveal choroidal blood flow after PRP would also indicate the reduced levels of vascular endothelial growth factor. The optimal amount of PRP treatment and the end point for laser treatment have not been determined because the reaction to PRP is unpredictable for each individual. Fujio et al32 suggested that retinal blood flow
Fig. 2. The relative mean blur rates (MBRs) of the subfoveal choroid after panretinal photocoagulation (PRP). The relative MBR values are calculated relative to the baseline value (100%). The relative MBR values significantly decreased to 87.5% at 1 month and 86.0% at 3 months after PRP (*P , 0.05 vs. pretreatment).
Fig. 3. Correlation between the subfoveal choroidal thickness and subfoveal choroidal blood flow. There was a significant positive correlation between the subfoveal choroidal thickness and subfoveal choroidal blood flow at 3 months after panretinal photocoagulation (r = 0.71, P , 0.05).
Discussion
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and the vessel diameter could be studied as potential markers for the response to laser photocoagulation. Grunwald et al33 suggested using the restored response to the hyperoxic challenge was a tool to gauge the success of laser photocoagulation. In addition, Kotoula et al34 studied the clinical responses to PRP by the glycemic control index. Compared with well-controlled diabetics, they found that poorly controlled diabetics had suboptimal responses to PRP. We found that there was a significant positive correlation between the decrease of the subfoveal choroidal thickness and subfoveal choroidal blood flow after PRP with no deterioration of visual performance and HbA1c level. Thus, we suggest that these may be useful parameters to determine whether the treatment with PRP was successful. The limitations of this study are the relatively short follow-up period and small sample size. In addition, this was a prospective study with no control group. Although the effect of systemic medication should be considered, it should not interfere in choroidal thickness and choroidal blood flow because no major complications were found in our patients. In conclusion, PRP significantly reduced the subfoveal choroidal thickness and subfoveal choroidal blood flow in eyes with S-NPDR. The effects and possible mechanism of PRP in eyes with S-NPDR may be related to the effects of the decreases of choroidal blood flow. Our results suggest that these changes may be helpful in assessing the effectiveness of the treatment with PRP in eyes with S-NPDR. Key words: laser speckle flowgraphy, diabetic retinopathy, panretinal photocoagulation, choroidal thickness, choroidal blood flow. References 1. Ruta LM, Magliano DJ, Lemesurier R, et al. Prevalence of diabetic retinopathy in type 2 diabetes in developing and developed countries. Diabet Med 2013;30:387–398. 2. Early photocoagulation for diabetic retinopathy. ETDRS report number 9. Early Treatment Diabetic Retinopathy Study Research Group. Ophthalmology 1991;98:766–785. 3. Stefánsson E. Ocular oxygenation and the treatment of diabetic retinopathy. Surv Ophthalmol 2006;51:364–380. 4. Budzynski E, Smith JH, Bryar P, et al. Effects of photocoagulation on intraretinal PO2 in cat. Invest Ophthalmol Vis Sci 2008;49:380–389. 5. Cunha-Vaz J, Faria de Abreu JR, Campos AJ. Early breakdown of the blood-retinal barrier in diabetes. Br J Ophthalmol 1975;59: 649–656. 6. Cao J, McLeod S, Merges CA, Lutty GA. Choriocapillaris degeneration and related pathologic changes in human diabetic eyes. Arch Ophthalmol 1998;116:589–597. 7. Querques G, Lattanzio R, Querques L, et al. Enhanced depth imaging optical coherence tomography in type 2 diabetes. Invest Ophthalmol Vis Sci 2012;53:6017–6024.
8. Esmaeelpour M, Považay B, Hermann B, et al. Mapping choroidal and retinal thickness variation in type 2 diabetes using three-dimensional 1060-nm optical coherence tomography. Invest Ophthalmol Vis Sci 2011;52:5311–5316. 9. Vujosevic S, Martini F, Cavarzeran F, et al. Macular and peripapillary choroidal thickness in diabetic patients. Retina 2012;32:1781–1790. 10. Regatieri CV, Branchini L, Carmody J, et al. Choroidal thickness in patients with diabetic retinopathy analyzed by spectral-domain optical coherence tomography. Retina 2012;32:563–568. 11. Spaide RF, Koizumi H, Pozzoni MC. Enhanced depth imaging spectral-domain optical coherence tomography. Am J Ophthalmol 2008;146:496–500. 12. Kim JT, Lee DH, Joe SG, et al. Changes in choroidal thickness in relation to the severity of retinopathy and macular edema in type 2 diabetic patients. Invest Ophthalmol Vis Sci 2013;54:3378–3384. 13. Esmaeelpour M, Brunner S, Ansari-Shahrezaei S, et al. Choroidal thinning in diabetes type 1 detected by 3-dimensional 1060 nm optical coherence tomography. Invest Ophthalmol Vis Sci 2012;53:6803–6809. 14. Mendivil A. Ocular blood flow velocities in patients with proliferative diabetic retinopathy after panretinal photocoagulation. Surv Ophthalmol 1997;42:S89–S95. 15. Savage HI, Hendrix JW, Peterson DC, et al. Differences in pulsatile ocular blood flow among three classifications of diabetic retinopathy. Invest Ophthalmol Vis Sci 2004;45:4504–4509. 16. Takahashi A, Nagaoka T, Sato E, Yoshida A. Effect of panretinal photocoagulation on choroidal circulation in the foveal region in patients with severe diabetic retinopathy. Br J Ophthalmol 2008;92:1369–1373. 17. Wilkinson CP, Ferris FL III, Klein RE, et al; Global Diabetic Retinopathy Project Group. Proposed international clinical diabetic retinopathy and diabetic macular edema disease severity scales. Ophthalmogy 2003;110:1677–1682. 18. Early Treatment Diabetic Retinopathy Study Group. Techniques for scatter and local photocoagulation treatment of diabetic retinopathy: early treatment diabetic retinopathy study report number 3. Int Ophthalmol Clin 1987;27:254–264. 19. Brown JS, Flitcroft DI, Ying GS, et al. In vivo human choroidal thickness measurements: evidence for diurnal fluctuations. Invest Ophthalmol Vis Sci 2009;50:5–12. 20. Tan CS, Ouyang Y, Ruiz H, Sadda SR. Diurnal variation of choroidal thickness in normal, healthy subjects measured by spectral domain optical coherence tomography. Invest Ophthalmol Vis Sci 2012;53:261–266. 21. Sugiyama T, Araie M, Riva CE, et al. Use of laser speckle flowgraphy in ocular blood flow research. Acta Ophthalmol 2010;88:723–729. 22. Saito M, Saito W, Hashimoto Y, et al. Macular choroidal blood flow velocity decreases with regression of acute central serous chorioretinopathy. Br J Ophthalmol 2013;97:775–780. 23. Cho GE, Cho HY, Kim YT. Change in subfoveal choroidal thickness after argon laser panretinal photocoagulation. Int J Ophthalmol 2013;6:505–509. 24. Yuki T, Kimura Y, Nanbu S, et al. Ciliary body and choroidal detachment after laser photocoagulation for diabetic retinopathy. A high-frequency ultrasound study. Ophthalmology 1997; 104:1259–1264. 25. Bressler NM, Beck RW, Ferris FL III. Panretinal photocoagulation for proliferative diabetic retinopathy. N Engl J Med 2011;365: 1520–1526. 26. Geyer O, Neudorfer M, Snir T, et al. Pulsatile ocular blood flow in diabetic retinopathy. Acta Ophthalmol Scand 1999;77: 522–525.
PANRETINAL PHOTOCOAGULATION ON CHOROID OKAMOTO ET AL 27. Ogata N, Ando A, Uyama M, Matsumura M. Expression of cytokines and transcription factors in photocoagulated human retinal pigment epithelial cells. Graefes Arch Clin Exp Ophthalmol 2001;239:87–95. 28. Ogata N, Nishikawa M, Nishimura T, et al. Unbalanced vitreous levels of pigment epithelium-derived factor and vascular endothelial growth factor in diabetic retinopathy. Am J Ophthalmol 2002;134:348–353. 29. Tilton RG, Chang KC, LeJeune WS, et al. Role for nitric oxide in the hyperpermeability and hemodynamic changes induced by intravenous VEGF. Invest Ophthal Vis Sci 1999;40:689–696. 30. Ku DD, Zaleski JK, Liu S, Brock TA. Vascular endothelial growth factor induces EDRF-dependent relaxation in coronary arteries. Am J Physiol 1993;265:H586–H592.
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31. Ferrara N. Vascular endothelial growth factor: molecular and biological aspects. Curr Top Microbiol Immunol 1999;237: 1–30. 32. Fujio N, Feke GT, Goger DG, McMeel JW. Regional retinal blood flow reduction following half fundus photocoagulation treatment. Br J Ophthalmol 1994;78:335–338. 33. Grunwald JE, Brucker AJ, Petrig BL, Riva CE. Retinal blood flow regulation and the clinical response to panretinal photocoagulation in proliferative diabetic retinopathy. Ophthalmology 1989;96:1518–1522. 34. Kotoula MG, Koukoulis GN, Zintzaras E, et al. Metabolic control of diabetes is associated with an improved response of diabetic retinopathy to panretinal photocoagulation. Diabetes Care 2005;28:2454–2457.
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improves the oxygenation of the ischemic inner retinal layers by destroying some of the metabolically highly active photoreceptor cells which would then lead to a greater flow of oxygen from the choriocapillaris to the inner layers of the retina.3 Indeed, animal studies have shown an increase in the oxygen delivered from the choriocapillaris to the inner retina after photocoagulation.4 The pathophysiology of DR has not been determined definitively, although it is known that the breakdown of the inner blood retinal barrier is a core event.5 In addition, the choroidal vasculature is believed to play an important role6 in the pathophysiology of DR.7–10 A better clinical
iabetic retinopathy (DR) is an important public health concern and is a leading cause of blindness in the working population.1 Panretinal photocoagulation (PRP) is the standard treatment for eyes with DR, and its use has proven to reduce the incidence of severe visual loss.2 It has been proposed that PRP
From the Department of Ophthalmology, Nara Medical University, Kashihara, Japan. None of the authors have any financial/conflicting interests to disclose. Reprint requests: Nahoko Ogata, MD, Department of Ophthalmology, Nara Medical University, 840 Shijo-cho, Kashihara, Nara 634-8522, Japan; e-mail: [email protected]
805
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understanding of the choroidal circulation would be important for an accurate assessment of diabetic eye diseases although not much attention has been paid to the choroidal vasculature after PRP. One of the problems in assessing the role of the choroid in the pathophysiology of DR is the absence of a technique of measuring the choroidal thickness quantitatively. The recent introduction of enhanced depth imaging by spectral domain optical coherence tomography has allowed clinicians to measure the choroidal thickness quantitatively and noninvasively.11 However, there have been only a few studies that examined the changes of the choroidal thickness in eyes with DR before and after PRP.7,10,12,13 However, the effect of PRP on the choroidal circulation has been studied to some degree. Color Doppler imaging,14 laser interferometry,15 and laser Doppler flowmetry16 have been used to obtain quantitative data on choroidal circulation in eyes with DR before and after PRP. However, the results have been contradictory probably because of the different measuring methods, instruments, measured regions, and stage of the disease processes. To the best of our knowledge, the correlation between the subfoveal choroidal thickness and subfoveal choroidal blood flow has not been reported for eyes with DR before and after PRP. Therefore, the purpose of this study was to assess the effect of PRP on the subfoveal choroidal thickness and subfoveal choroidal blood flow in patients with severe nonproliferative diabetic retinopathy (S-NPDR). Materials and Methods Participants This study was conducted at the Nara Medical University from April 2011 through December 2013. The protocol of this study conformed to the tenets of the Declaration of Helsinki and was approved by the Internal Review Board of the Nara Medical University. The nature of the study was explained to all of the patients, and a signed informed consent was obtained. Twenty-four consecutive patients with type II diabetes and S-NPDR without macular edema were studied. The severity of the retinopathy was graded according to the method set forth by the Global Diabetic Retinopathy Project Group.17 Each subject received a comprehensive ocular examinations to diagnose and stage the DR including measurements of the best-corrected visual acuity, biomicroscopic examinations, intraocular pressure (IOP), indirect ophthalmoscopy, fundus fluorescein angiography (FA), and spectral domain optical coherence tomography (Spectralis, Heidelberg Engineering, Heidel-
berg, Germany). Only one eye from each participant was included in the study. If both eyes met the inclusion criterion, the eye with better visual acuity was included. The exclusion criteria included the presence of refractive errors greater than ±3.0 diopters, amblyopia, significant cataracts, retinal or choroidal pathology, e.g., age-related macular degeneration, choroidal neovascularization, vitreomacular traction, epiretinal membrane, macular hole, any history of eye diseases or any type of ocular surgery or photocoagulation, and systemic diseases other than diabetes. To avoid the effects of pharmacologic agents on the retinal or choroidal vasculature, eyes with any previous treatment, including intravitreal or subtenon injections of triamcinolone or anti–vascular endothelial growth factor, were also excluded. Panretinal Photocoagulation Panretinal photocoagulation was performed in eyes with S-NPDR according to the recommendations of the Early Treatment Diabetic Retinopathy Study group.18 Fluorescein fundus angiography (FA) showed that all patients had avascular retinal areas in three or more quadrants. The PRP was delivered through a widefield contact lens (Ocular Mainster PRP 165; Ocular Instruments, Bellevue, WA) using a slit-lamp adapted photocoagulator (Multicolor Scan Laser Photocoagulator, MC-500 Vixi; NIDEK Co., Gamagouri, Japan) using yellow color according to the Early Treatment Diabetic Retinopathy Study protocol.18 The PRP for each eye was performed in 3 to 5 sessions with an interval of 2 weeks between sessions. For each session, 200 mm spot sizes with pulse duration of 0.2 seconds. Three hundred to 400 spots were made for a total to 1,200 to 2,000 spots for a complete PRP. The power of the laser was individually adjusted to produce yellowishwhite coagulative spots and ranged between 180 mW and 230 mW. Follow-up visits were scheduled for 1 month and 3 months after the last treatment session. A thorough ophthalmologic examination, including the measurement of the best-corrected visual acuity, OCT, choroidal blood flow, and fundus examination, was performed at each visit and FA was performed 3 months after the last treatment. Measurements of Retinal and Choroidal Thicknesses The foveal thickness of the retina was defined as the distance between the inner limiting membrane and the retinal pigment epithelium in the spectral domain optical coherence tomography images (upper white arrow in Figure 1A). This distance was automatically determined by a software embedded in the OCT. The fundus was scanned with 6-mm horizontal and vertical
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Fig. 1. Spectral domain optical coherence tomographic (SDOCT) image and laser speckle flowgraphy (LSFG) map of an eye with severe nonproliferative diabetic retinopathy before panretinal photocoagulation. A. SDOCT of the region shown in (B). The foveal retinal thickness was defined as the distance between the inner limiting membrane and the retinal pigment epithelium (RPE) (upper white arrow). The subfoveal choroidal thickness was manually measured as the distance between the basal edge of the RPE and the chorioscleral border (lower white arrow) on the enhanced depth image (horizontal view) of the optical coherence tomographic image. The choroidal thickness was measured at 5 points; beneath the fovea, and the superior, inferior, temporal, and nasal points of 1 mm from the fovea. The choroidal thickness was measured as the distance between the retinal pigment epithelium and the chorioscleral border. B. Color-coded map of LSFG showing the blood flow of the subfoveal choroid. The blood flow of the subfoveal choroid was measured in the macular avascular region (open circle), and the mean blur rate was extracted by the embedded software tool (LSFG Analyzer, version 3.0.43.0; Softcare Ltd.). Red color indicates high blood flow and blue color indicates low blood flow.
lines centered on the fovea. The location of the fovea was determined by the fundus photographs, and the patients were limited to those who could fixate the fixation point of the OCT steadily. Cross-sectional images were obtained by the same experienced examiner, and each examination was repeated until highly reproducible scans were recorded. The subfoveal choroidal thickness, which was measured manually as the distance between the basal edge of the retinal pigment epithelium and the chorioscleral border, was measured on the images obtained by enhanced depth imaging by spectral domain optical coherence tomography from all patients. It was measured at 5 points: directly beneath the fovea, and the superior, inferior, temporal, and nasal points of 1 mm from the fovea (lower white arrow in Figure 1A). All measurements were performed between 13:00 to 15:00 hours to avoid diurnal variations.19,20 All images were recorded by an experienced ophthalmologist or by one of the authors, and the measurements were made by two experienced examiners (M.O., T.M.) who were masked to the choroidal blood flow findings. If the measurements by the 2 examiners differed by more than 15%, the examiners repeated the measurements together. Measurement of Blood Flow by Laser Speckle Flowgraphy The subfoveal choroidal blood flow was measured with a laser speckle flowgraphy instrument (LSFGNAVI; NIDEK CO., LTD., Gamagouri, Japan) from the laser speckle images.21 The offline analysis software (LSFG Analyzer, version 3.0.43.0; Softcare Ltd.,
Fukutsu, Japan) combined all images over a 4-second recording period into color-coded maps with each pixel assigned a computed mean blur rate (MBR). The MBR is the squared ratio of the mean intensity divided by the standard deviation of the changes in the light intensity which varies temporally and spatially according to the velocity of the erythrocytes.21 Thus, the MBR is a quantitative index of the relative blood flow velocity.21 In the color-coded maps, a red color indicates high blood flow velocities and blue color indicates low blood flow velocities.21 Laser speckle flowgraphy was used to determine the blood flow velocity (MBR) of the subfoveal choroid quantitatively.22 The MBR of the subfoveal choroid was measured in the avascular region of the macular area (open circle, Figure 1B), and it was determined for all eyes before, 1 month, and 3 months after PRP. To evaluate the changes in MBR, the changes in the MBR relative to that at the baseline were used because the MBR is a quantitative index of the “relative” blood flow velocity. Systemic Hemodynamics The systolic blood pressure (SBP) and diastolic blood pressure (DBP) were measured at the upper arm by an automated oscillometric device. The mean arterial pressure (MAP) was calculated by the following equation: MAP = DBP + 1/3 (SBP − DBP). The ocular perfusion pressure (OPP) was calculated to be: OPP = 2/ 3 (MAP − IOP). The pulse rate was automatically recorded by a finger pulse-oxymeter (HP-CMS Patient Monitor; Hewlett Packard, Palo Alto, CA) before,
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1 month, and 3 months after PRP. The hemoglobin A1c levels (HbA1c) were also measured before, 1 month, and 3 months after PRP. Statistical Analyses The outcome measures taken at 1 month and 3 months after PRP were compared with that of the baseline data using paired sample t - test. The data are presented as the means ± SDs. To examine the relationship between the choroidal thickness and choroidal blood flow in the subfoveal region after PRP, the Pearson’s correlation test was performed. A P-value ,0.05 was considered to be significant. Statistical analysis was performed using licensed statistical software (SPSS version 21.0; SPSS Inc., Chicago, IL). Results Twenty-four eyes from 24 patients with type II diabetes and S-NPDR with no macula edema were studied prospectively. There were 14 men and 10 women whose mean age was 62.3 ± 10.2 years, and the mean duration of the diabetes was 17.1 years with a range of 10 to 25 years. The total number of photocoagulation burns was 1,855 ± 381 per eye. None of the patients developed any adverse effects related to the PRP. Each subject recognized no progress of DR on FA findings measured 3 months after PRP. The blood vessel dilation and vascular permeability was improved and also decreased those indicating that PRP was successfully achieved. The differences in the best-corrected visual acuity before the pretreatment and that at 1 and 3 months after PRP were not significant (P . 0.05; Table 1). None of the eyes had a worsening of the best-corrected visual acuity. Retinal and Choroidal Thicknesses The mean foveal retinal thickness was 184.0 ± 25.0 mm at the baseline, and the thickness did not change
significantly during the follow-up period (186.1 ± 27.9 mm at 1 month and 191.3 ± 25.2 mm at 3 months; P = 0.49 and P = 0.44, respectively). In contrast, the subfoveal choroidal thickness was significantly decreased at both 1 and 3 months after PRP (from 327.4 ± 54.4 mm at the base line to 286.3 ± 50.6 mm at 1 month, 285.0 ± 49.2 mm at 3 months; P = 0.002 and P = 0.002, respectively, Table 2). The mean choroidal thickness at perimacular (superior, inferior, temporal, nasal) also significantly decreased at 1 month and 3 months after PRP (Table 2). The interobserver reproducibility was excellent (intraclass correlation coefficient = 0.98). Choroidal Blood Flow The relative MBR was calculated relative to the pretreatment value (base line) which was expressed as 100%. The relative MBR values significantly decreased to 87.5 ± 10.3% at 1 month and to 86.0 ± 12.7% at 3 months after PRP (P = 0.0007 and P = 0.0005; Figure 2). Correlation Between Choroidal Thickness and Choroidal Blood Flow We calculated the correlation between the subfoveal choroidal thickness and subfoveal choroidal blood flow. We found that there was a significant positive correlation between the changes in the subfoveal choroidal thickness and subfoveal choroidal blood flow during the 3-month follow-up period (r = 0.71, P , 0.001, Figure 3). Systemic Hemodynamics The IOP, MAP, OPP, basal pulse rate (in beats per minute), and HbA1c level (in mg/dL) at the baseline were not significantly different at 1 and 3 months after the PRP (P . 0.05 for all, Table 1).
Table 1. Systemic Hemodynamics and Ophthalmological Data Before and After PRP Pretreatment BCVA (logMAR) IOP (mmHg) Foveal retinal thickness (mm) MAP (mmHg) OPP (mmHg) PR (bpm) HbA1c (mg/dL)
0.03 14.6 184.0 95.5 54.6 65.0 6.7
± ± ± ± ± ± ±
0.12 4.0 25.0 11.2 9.0 8.4 1.3
1 Month After PRP 0.04 15.3 186.1 92.8 51.1 63.6 6.5
± ± ± ± ± ± ±
0.10 3.7 27.9 10.8 9.3 7.5 1.5
3 Months After PRP 0.04 14.2 191.3 94.1 53.6 65.0 6.4
± ± ± ± ± ± ±
0.14 3.2 25.2 10.6 9.7 9.8 1.1
Values are expressed as mean ± SD. BCVA, best-corrected visual acuity; HbA1c, Hemoglobin A1c; IOP, intraocular pressure; MAP, mean arterial pressure; OPP, ocular perfusion pressure; PR, pulse rate.
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PANRETINAL PHOTOCOAGULATION ON CHOROID OKAMOTO ET AL Table 2. Changes of Choroidal Thickness Pretreatment (mm) 1 Month After PRP (mm) Subfoveal choroidal thickness Superior 1 mm Inferior 1 mm Temporal 1 mm Nasal 1 mm
327.4 306.1 306.9 310.5 294.9
± ± ± ± ±
54.4 52.0 48.3 44.0 54.3
286.3 261.9 267.8 277.2 258.0
± ± ± ± ±
50.6 51.6 44.5 52.3 51.8
P 0.002 0.001 0.005 0.01 0.005
3 Months After PRP (mm) 285.0 260.0 268.8 273.2 252.2
± ± ± ± ±
49.2 75.9 82.0 59.5 69.2
P 0.002 0.001 0.005 0.009 0.003
Values are expressed as mean ± SD.
Our results showed that PRP on eyes with S-NPDR significantly reduced the subfoveal choroidal thickness and also reduced the relative subfoveal choroidal blood flow velocity. Earlier studies reported a significant thinner choroid after PRP on eyes with S-NPDR compared with that of untreated eyes with S-NPDR.7,10,12,13 However, there was a report that the subfoveal choroidal thickness increased significantly at 1 week after PRP.23 The investigators suggested that choroidal effusion after PRP might have contributed an increase of the choroidal thickness, although it has been reported that ciliochoroidal effusion after PRP was completely absorbed in 2 weeks.24 It has also been reported that the choroidal blood flow was significantly slower in PRP-treated eyes compared with that of untreated eyes as measured by laser interferometry and Color Doppler imaging.15,25,26 However, some studies showed that the choroidal blood flow velocity in the foveal region was not changed significantly compared with that of untreated eyes as measured by laser Doppler flowmetry.16 The measuring methods, instruments, measured regions, and disease processes were different in each
study, and this may contribute to the variability of the results. If PRP led to an increase of oxygenation, this should lower the expression levels of vascular endothelial growth factor and vascular endothelial growth factor receptors.27,28 Vascular endothelial growth factor induces blood vessel dilation and increase the ocular blood flow because of an increase in nitric oxide production.29,30 Vascular endothelial growth factor also increases the vascular permeability in eyes with DR.31 We performed fundus fluorescein angiography 3 months after PRP and confirmed that the dilation of the blood vessels and the vascular permeability were decreased indicating that PRP was successfully achieved. We assumed that successful PRP reduced the vascular endothelial growth factor production and resulted in a reduction of the blood vessel dilation and vascular permeability. We suggest that the significant reduction of the subfoveal choroidal thickness and subfoveal choroidal blood flow after PRP would also indicate the reduced levels of vascular endothelial growth factor. The optimal amount of PRP treatment and the end point for laser treatment have not been determined because the reaction to PRP is unpredictable for each individual. Fujio et al32 suggested that retinal blood flow
Fig. 2. The relative mean blur rates (MBRs) of the subfoveal choroid after panretinal photocoagulation (PRP). The relative MBR values are calculated relative to the baseline value (100%). The relative MBR values significantly decreased to 87.5% at 1 month and 86.0% at 3 months after PRP (*P , 0.05 vs. pretreatment).
Fig. 3. Correlation between the subfoveal choroidal thickness and subfoveal choroidal blood flow. There was a significant positive correlation between the subfoveal choroidal thickness and subfoveal choroidal blood flow at 3 months after panretinal photocoagulation (r = 0.71, P , 0.05).
Discussion
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and the vessel diameter could be studied as potential markers for the response to laser photocoagulation. Grunwald et al33 suggested using the restored response to the hyperoxic challenge was a tool to gauge the success of laser photocoagulation. In addition, Kotoula et al34 studied the clinical responses to PRP by the glycemic control index. Compared with well-controlled diabetics, they found that poorly controlled diabetics had suboptimal responses to PRP. We found that there was a significant positive correlation between the decrease of the subfoveal choroidal thickness and subfoveal choroidal blood flow after PRP with no deterioration of visual performance and HbA1c level. Thus, we suggest that these may be useful parameters to determine whether the treatment with PRP was successful. The limitations of this study are the relatively short follow-up period and small sample size. In addition, this was a prospective study with no control group. Although the effect of systemic medication should be considered, it should not interfere in choroidal thickness and choroidal blood flow because no major complications were found in our patients. In conclusion, PRP significantly reduced the subfoveal choroidal thickness and subfoveal choroidal blood flow in eyes with S-NPDR. The effects and possible mechanism of PRP in eyes with S-NPDR may be related to the effects of the decreases of choroidal blood flow. Our results suggest that these changes may be helpful in assessing the effectiveness of the treatment with PRP in eyes with S-NPDR. Key words: laser speckle flowgraphy, diabetic retinopathy, panretinal photocoagulation, choroidal thickness, choroidal blood flow. References 1. Ruta LM, Magliano DJ, Lemesurier R, et al. Prevalence of diabetic retinopathy in type 2 diabetes in developing and developed countries. Diabet Med 2013;30:387–398. 2. Early photocoagulation for diabetic retinopathy. ETDRS report number 9. Early Treatment Diabetic Retinopathy Study Research Group. Ophthalmology 1991;98:766–785. 3. Stefánsson E. Ocular oxygenation and the treatment of diabetic retinopathy. Surv Ophthalmol 2006;51:364–380. 4. Budzynski E, Smith JH, Bryar P, et al. Effects of photocoagulation on intraretinal PO2 in cat. Invest Ophthalmol Vis Sci 2008;49:380–389. 5. Cunha-Vaz J, Faria de Abreu JR, Campos AJ. Early breakdown of the blood-retinal barrier in diabetes. Br J Ophthalmol 1975;59: 649–656. 6. Cao J, McLeod S, Merges CA, Lutty GA. Choriocapillaris degeneration and related pathologic changes in human diabetic eyes. Arch Ophthalmol 1998;116:589–597. 7. Querques G, Lattanzio R, Querques L, et al. Enhanced depth imaging optical coherence tomography in type 2 diabetes. Invest Ophthalmol Vis Sci 2012;53:6017–6024.
8. Esmaeelpour M, Považay B, Hermann B, et al. Mapping choroidal and retinal thickness variation in type 2 diabetes using three-dimensional 1060-nm optical coherence tomography. Invest Ophthalmol Vis Sci 2011;52:5311–5316. 9. Vujosevic S, Martini F, Cavarzeran F, et al. Macular and peripapillary choroidal thickness in diabetic patients. Retina 2012;32:1781–1790. 10. Regatieri CV, Branchini L, Carmody J, et al. Choroidal thickness in patients with diabetic retinopathy analyzed by spectral-domain optical coherence tomography. Retina 2012;32:563–568. 11. Spaide RF, Koizumi H, Pozzoni MC. Enhanced depth imaging spectral-domain optical coherence tomography. Am J Ophthalmol 2008;146:496–500. 12. Kim JT, Lee DH, Joe SG, et al. Changes in choroidal thickness in relation to the severity of retinopathy and macular edema in type 2 diabetic patients. Invest Ophthalmol Vis Sci 2013;54:3378–3384. 13. Esmaeelpour M, Brunner S, Ansari-Shahrezaei S, et al. Choroidal thinning in diabetes type 1 detected by 3-dimensional 1060 nm optical coherence tomography. Invest Ophthalmol Vis Sci 2012;53:6803–6809. 14. Mendivil A. Ocular blood flow velocities in patients with proliferative diabetic retinopathy after panretinal photocoagulation. Surv Ophthalmol 1997;42:S89–S95. 15. Savage HI, Hendrix JW, Peterson DC, et al. Differences in pulsatile ocular blood flow among three classifications of diabetic retinopathy. Invest Ophthalmol Vis Sci 2004;45:4504–4509. 16. Takahashi A, Nagaoka T, Sato E, Yoshida A. Effect of panretinal photocoagulation on choroidal circulation in the foveal region in patients with severe diabetic retinopathy. Br J Ophthalmol 2008;92:1369–1373. 17. Wilkinson CP, Ferris FL III, Klein RE, et al; Global Diabetic Retinopathy Project Group. Proposed international clinical diabetic retinopathy and diabetic macular edema disease severity scales. Ophthalmogy 2003;110:1677–1682. 18. Early Treatment Diabetic Retinopathy Study Group. Techniques for scatter and local photocoagulation treatment of diabetic retinopathy: early treatment diabetic retinopathy study report number 3. Int Ophthalmol Clin 1987;27:254–264. 19. Brown JS, Flitcroft DI, Ying GS, et al. In vivo human choroidal thickness measurements: evidence for diurnal fluctuations. Invest Ophthalmol Vis Sci 2009;50:5–12. 20. Tan CS, Ouyang Y, Ruiz H, Sadda SR. Diurnal variation of choroidal thickness in normal, healthy subjects measured by spectral domain optical coherence tomography. Invest Ophthalmol Vis Sci 2012;53:261–266. 21. Sugiyama T, Araie M, Riva CE, et al. Use of laser speckle flowgraphy in ocular blood flow research. Acta Ophthalmol 2010;88:723–729. 22. Saito M, Saito W, Hashimoto Y, et al. Macular choroidal blood flow velocity decreases with regression of acute central serous chorioretinopathy. Br J Ophthalmol 2013;97:775–780. 23. Cho GE, Cho HY, Kim YT. Change in subfoveal choroidal thickness after argon laser panretinal photocoagulation. Int J Ophthalmol 2013;6:505–509. 24. Yuki T, Kimura Y, Nanbu S, et al. Ciliary body and choroidal detachment after laser photocoagulation for diabetic retinopathy. A high-frequency ultrasound study. Ophthalmology 1997; 104:1259–1264. 25. Bressler NM, Beck RW, Ferris FL III. Panretinal photocoagulation for proliferative diabetic retinopathy. N Engl J Med 2011;365: 1520–1526. 26. Geyer O, Neudorfer M, Snir T, et al. Pulsatile ocular blood flow in diabetic retinopathy. Acta Ophthalmol Scand 1999;77: 522–525.
PANRETINAL PHOTOCOAGULATION ON CHOROID OKAMOTO ET AL 27. Ogata N, Ando A, Uyama M, Matsumura M. Expression of cytokines and transcription factors in photocoagulated human retinal pigment epithelial cells. Graefes Arch Clin Exp Ophthalmol 2001;239:87–95. 28. Ogata N, Nishikawa M, Nishimura T, et al. Unbalanced vitreous levels of pigment epithelium-derived factor and vascular endothelial growth factor in diabetic retinopathy. Am J Ophthalmol 2002;134:348–353. 29. Tilton RG, Chang KC, LeJeune WS, et al. Role for nitric oxide in the hyperpermeability and hemodynamic changes induced by intravenous VEGF. Invest Ophthal Vis Sci 1999;40:689–696. 30. Ku DD, Zaleski JK, Liu S, Brock TA. Vascular endothelial growth factor induces EDRF-dependent relaxation in coronary arteries. Am J Physiol 1993;265:H586–H592.
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31. Ferrara N. Vascular endothelial growth factor: molecular and biological aspects. Curr Top Microbiol Immunol 1999;237: 1–30. 32. Fujio N, Feke GT, Goger DG, McMeel JW. Regional retinal blood flow reduction following half fundus photocoagulation treatment. Br J Ophthalmol 1994;78:335–338. 33. Grunwald JE, Brucker AJ, Petrig BL, Riva CE. Retinal blood flow regulation and the clinical response to panretinal photocoagulation in proliferative diabetic retinopathy. Ophthalmology 1989;96:1518–1522. 34. Kotoula MG, Koukoulis GN, Zintzaras E, et al. Metabolic control of diabetes is associated with an improved response of diabetic retinopathy to panretinal photocoagulation. Diabetes Care 2005;28:2454–2457.
