|Year : 2013 | Volume
| Issue : 3 | Page : 153-158
Evaluation of retinal nerve fiber layer thickness in diabetic retinopathy by optical coherence tomography after full scatter panretinal argon laser photocoagulation
Faried M Wagdy, Hoda M El Sobky, Abd El-Rahman E Sarhan, Mohammed A Hafez
Department of Ophthalmology, Menofia University, Shebin El Kom, Egypt
|Date of Submission||15-May-2013|
|Date of Acceptance||21-May-2013|
|Date of Web Publication||28-Feb-2014|
Faried M Wagdy
Asem Hema Street, Shebin El Kom
Source of Support: None, Conflict of Interest: None
The aim of this study was to evaluate the retinal nerve fiber layer (RNFL) thickness after full scatter panretinal argon laser photocoagulation in diabetic patients using optical coherence tomography.
Patients and methods
This study was carried out on 40 eyes of 22 patients with the clinical diagnosis of severe nonproliferative and proliferative diabetic retinopathy treated by full scatter panretinal photocoagulation at the ophthalmic diagnostic laser unit, Menoufiya University Hospital.
Follow-up up to 6 months indicated that the percentage reduction in the average RNFL thickness after 6 months of laser treatment was 28.9%, which was statistically significant (P = 0.041). This reduction in the RNFL thickness varied from one retinal quadrant to another, with the most significant change taking place in both the nasal and the inferior quadrants.
In the treatment of diabetic retinopathy, maximal effect with lowering number of shots as much as is necessary to avoid decrease RNFL thickness to great degree and so avoiding the optic disc pallor and optic atrophy.
Keywords: Optical; photocoagulation; tomography
|How to cite this article:|
Wagdy FM, El Sobky HM, Sarhan ARE, Hafez MA. Evaluation of retinal nerve fiber layer thickness in diabetic retinopathy by optical coherence tomography after full scatter panretinal argon laser photocoagulation. J Egypt Ophthalmol Soc 2013;106:153-8
|How to cite this URL:|
Wagdy FM, El Sobky HM, Sarhan ARE, Hafez MA. Evaluation of retinal nerve fiber layer thickness in diabetic retinopathy by optical coherence tomography after full scatter panretinal argon laser photocoagulation. J Egypt Ophthalmol Soc [serial online] 2013 [cited 2019 Aug 25];106:153-8. Available from: http://www.jeos.eg.net/text.asp?2013/106/3/153/127365
| Introduction|| |
Retinal nerve fiber layer (RNFL) measurements using optical coherence tomography (OCT) programs for nerve head indicate that the highest degree of variability can be attributed to interpatient differences. The recently developed OCT provides the ophthalmologist with the opportunity to customize scans and to tailor a single scan circle to examine RNFL thickness. Custom scans can be useful to help the ophthalmologist differentiate normal from early glaucomatous peripapillary RNFL . The use of laser photocoagulation in the treatment of diabetic retinopathy is one of the best examples in which laser energy has revolutionized the treatment of a serious disease . Although pan-retinal photocoagulation (PRP) has been proven to be an effective treatment strategy for severe diabetic retinopathy, the laser intensity utilized is decided by the physician. Most physicians agree that laser intensity that causes damage to the entire retinal layer should be avoided. It has been reported that a high-intensity laser beam can cause destruction of the entire retinal layer, including ganglion cells. Damage to ganglion cells results in loss of the RNFL and a sequential decrease in the peripapillary nerve fiber layer thickness .
| Patients and methods|| |
This study was carried out on 40 eyes of 22 patients with a clinical diagnosis of severe nonproliferative diabetic retinopathy (non-PDR) and PDR treated by light scatter treatment for severe non-PDR and full scatter panretinal photocoagulation for PDR at the ophthalmic diagnostic laser unit, Menoufiya University Hospital.
Patients with PDR (not high risk or advanced) and severe non-PDR were defined by early treatment diabetic retinopathy study (ETDRS) by the presence of one of the following criteria between 40 and 60 years of age:
- Severe intraretinal hemorrhages in four quadrants.
- Venous beading in at least two quadrants.
- Moderate to severe intraretinal microangiopathy in at least one quadrant.
- Capillary dropouts in more than one quadrant.
The following patients were excluded from the study:
- Patients with densely opaque media (as cataract or vitreous hemorrhage).
- Glaucomatous patients.
- Hypertensive patients.
- Patients with any other associated retinopathies.
- Patients with any other retinal disease.
After assessment of medical and family history, the following were performed:
- Refraction and best-corrected visual acuity before laser treatment.
- Anterior segment examination using the binocular silt-lamp biomicroscopy.
- Measurement of the intraocular pressure by Goldmann applanation tonometry before treatment and at follow-up visits.
- Posterior segment examination using a binocular indirect ophthalmoscope as well as binocular slit-lamp biomicroscopy with the +90 D lens for examination of the macula, optic disc, retinal vessels, retinal background, and RNFL.
- Colored fundus photography before laser treatment.
- Fundus fluorescein angiography before laser treatment.
- OCT circle scan of 3.4 mm diameter scanning the peripapillary area before laser treatment.
OCT scanning was performed using the OCT scanner (Humphrey-Zeiss Stratus OCT; Germany; [Figure 1]). The signal source was a super luminescent diode, with a wavelength of 850 nm. It had a longitudinal resolution of 10-20 μm, the field of view was 30 × 24°, and the scan time was 1 s. The OCT scanner has several predefined scan scripts performing two basic scans: a linear scan and a circle scan. In this study, we used a circle peripapillary scan of 3.4 mm diameter. OCT scanning was performed for all the patients before laser treatment and 1 and 6 months after laser treatment, respectively [Figure 2],[Figure 3] and [Figure 4].
OCT scanning was performed as follows: the patient data were entered into the computer including name, birth date, identification number, and the spherical equivalent of the patient refraction. The patient is positioned comfortably on the head rest. The fundus viewing unit and the condensing lens are positioned along the optical axis of the eye. The entire unit is brought forward until the imaging lens is about 1 cm from the eye, placing an image of the transverse scanning mirrors into the patient's pupillary plane. The position of the condensing lens is then adjusted along the optical axis until the image of the fundus is brought into focus. The circle scan of 3.4 mm in diameter is positioned around the optic nerve head so that the optic nerve head is centralized in the center of the circle. To allow precise positioning on the retina, a fixation spot is generated under computer control by the OCT probe beam that is visualized simultaneously with the scanning pattern on the retina of the eye being imaged (internal fixation target). Fine positioning of the OCT scan is achieved by directly adjusting the position of the scan probe beam.
All patients were treated with argon laser full scatter panretinal photocoagulation as follows:
Pupillary dilatation was performed using mydrapid 1% before laser treatment. Benoxinate hydrochloride 0.4%, a local anesthetic eye drop, was administered before starting laser treatment. Treatment was performed using an argon laser instrument.
Mainster wide-field contact lens (Ocular Instruments Group, SanFrancisco, California, USA) was applied to the eye with the aid of methylcellulose; this lens has the advantage of allowing a field of view of 125° of the entire posterior retina so that the posterior pole and mid-periphery is visible with one field of view and the fovea and the disc are readily visualized. Then, the retinal surface was carefully focused initially with the rays of light from the silt-lamp directed perpendicular to the surface of the lens, and then the rays were directed more tangentially to avoid the reflection from the surface of the lens.
Once the retinal surface was visualized and the location of the landmarks of the retina were easily recognized, full scatter panretinal photocoagulation with 200 μm spot size and 0.1 s duration was performed starting at ∼200 mW of power, slowly increasing or decreasing the power by 25-50 mW increments to achieve a moderately white burn.
The Mainster wide-field contact lens allows a magnification effect of about 0.68, thus yielding an actual burn size of 320 μm for a spot size set at 200 μm.
The temporal foveal border of the panretinal photocoagulation was delineated with three to four rows of laser burns placed in an arcuate manner at least two disc diameters from the fovea. Throughout the course of treatment, the optic disc and fovea were visualized repeatedly. Laser spots were placed approximately one burn width apart.
In general, the full scatter panretinal photocoagulation was divided into two sessions. In the first session, the inferior half of the retina was treated with 800-1000 burns so that if significant vitreous hemorrhage were to occur between the two sessions, the hemorrhage would then settle more inferiorly with the gravity, enabling treatment of the superior portion of the retina. Laser burns were brought up to one disc diameter from the optic disc; new vessels at disc (NVDs) were not treated directly. Elevated new vessels elsewhere (NVEs) were not treated. In the second session, patients were scheduled to return within 2 weeks for completion of the full scatter panretinal photocoagulation (superior half). In this session, the superior half of the retina was treated with another series of 800-1000 burns. Application of treatment to major vessels or chorioretinal scars and areas of preretinal hemorrhage was avoided. Fluorescein angiography was performed at the 1-month follow-up visit after completion of the laser treatment to ensure regression of NVDs and/or NVEs; if a patient showed minimal to no regression of his/her retinopathy or had new NVDs or NVEs, reinforcement treatment was performed. Reinforcement full scatter panretinal laser photocoagulation was performed by filling in the spaces of untreated retina between the older photocoagulation scars using a Mainster wide-field contact lens with 200 μm spot size and 0.1 s duration. Starting at ∼200 mW of power, the power was slowly increased or decreased by 25-50 mW increments to achieve a moderately white burn.
- Refraction and best-corrected visual acuity after 1 and 6 months of laser treatment.
- Anterior segment examination using binocular silt-lamp biomicroscopy.
- Measurement of intraocular pressure by Goldmann applanation tonometry at follow-up visits.
- Posterior segment examination was performed using a binocular indirect ophthalmoscope as well as binocular slit-lamp biomicroscopy with a +90 D lens for examination of the macula, optic disc, retinal vessels, retinal background, and RNFL.
- Fluorescein angiography was performed after 1 and 6 months of follow-up.
- OCT circle scan of 3.4 mm diameter was performed scanning the peripapillary area after 1 and 6 months of laser treatment.
Image processing and data analysis of retinal nerve fiber layer thickness (optical coherence tomography interpretation)
The image was corrected for artifacts because of involuntary patient motion during data acquisition. An image processing computer program was developed to quantify RNFL thickness for the OCT sections obtained by scanning a circle of 3.4 mm diameter around the optic nerve head. RNFL thickness was determined by a computer; it is assumed to be correlated with the extent of the red, highly reflective layer at the vitreoretinal interface. The thickness was reported individually for each scan as averages for each quadrant (superior, inferior, temporal, and nasal), as averages for each clock hour, or as an average over the entire cylindrical section. The RNFL is the thickest in the peripapillary region and the thinnest in the peripheral retina, correlating with the distribution of the ganglion cells. The mean superior, inferior, nasal, and temporal RNFL thickness at the disc margin was 136, 142, 88, and 70 mm, respectively. Some difficulties were encountered in the practical use of OCT in this study: patient cooperation was a major difficulty encountered during this study as OCT scans need proper fixation. In patients with fixation problems, scan acquisition was difficult and the scan failed. Patients with dry eye syndrome were also problematic; thus, in these patients, methylcellulose eye drops were very useful during the scan procedure and also failure of pupillary dilatation in some patients affected the quality of the scan quality.
OCT was used to examine 40 eyes of 22 patients with a clinical diagnosis of severe non-PDR and PDR before and 1 and 6 months after scatter panretinal photocoagulation (cases with macular edema were treated first before PRP by either focal or grid laser treatment). After completion of laser treatment, the patients were divided into two groups: the first group, which did not require supplemental laser session, included 24 eyes of 12 patients who received total less than 2000 laser shots (group A). The second group of patients, who required a supplemental laser session, included 16 eyes of 10 patients who received a total of more than 2000 laser shots (group B).
| Results|| |
Although there was a reduction in the average RNFL thickness after 1 month of laser treatment, it was statistically insignificant, but after 6 months of laser treatment, there was a further reduction in the average RNFL thickness that became statistically significant (P = 0.041) as can be seen in [Table 1].
|Table 1: Reduction difference (μm) in the average retinal nerve fiber layer thickness in all quadrants in group A (<2000 shots)|
Click here to view
Although there was a reduction in the average RNFL thickness after 1 month of laser treatment, it was statistically insignificant, but after 6 months of laser treatment, it was statistically significant and there was a statistically significant reduction in the average RNFL thickness between 1 and 6 months as can be seen in [Table 2].
|Table 2: Reduction difference (mm) in the average retinal nerve fiber layer thickness in all quadrants in group B (>2000 shots)|
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Comparison between group A and group B
There was a significant reduction in RNFL thickness in all quadrants in group A and group B, but there was greater reduction in RNFL thickness in group B, which received more than 2000 laser shots.
| Discussion|| |
Although PRP has been proven to be an effective treatment strategy for severe diabetic retinopathy, the laser intensity utilized is decided by the ophthalmologist. Most ophthalmologists agree that laser intensity that causes damage to the entire retinal layer should be avoided. It has been reported that a high-intensity laser beam can cause destruction of the entire retinal layer, including ganglion cells .
Damage to ganglion cells results in loss of RNFL and a sequential decrease in the peripapillary nerve fiber layer thickness . Changes in the RNFL are difficult to judge clinically and require an experienced observer. Computerized quantitative RNFL analysis provides a more reliable assessment of early changes in RNFL thickness .
OCT measurements of the RNFL thickness showed a statistically significant reduction in the mean RNFL thickness 6 months after laser treatment compared with a statistically nonsignificant reduction in the mean RNFL thickness 1 month after laser treatment, indicating that the major reduction in RNFL thickness occurs at the time interval between 1 and 6 months following laser treatment. This reduction in the RNFL thickness varied from one retinal quadrant to another, with the most significant change taking place in both the nasal and the inferior quadrants. The temporal and superior quadrants were less affected and the change in the RNFL was found to be statistically nonsignificant. The very mild reduction in RNFL thickness in the temporal quadrant can be attributed to the sparing of the papillomacular bundle during application of laser treatment.
In addition, the results of this study showed that the percentage reduction in the average RNFL thickness after 6 months of laser treatment was 28.9%, which was statistically significant (P = 0.041). In agreement with Lim and colleagues, who studied 94 eyes of 48 healthy individuals, 89 eyes of 55 diabetic patients who did not undergo PRP and 37 eyes of 24 patients with diabetes who underwent PRP were included in this study. Eyes that had been treated with PRP had thinner peripapillary RNFL compared with the other groups; this was statistically significantly different in the inferior (P = 0.004) and nasal (P = 0.003) regions. Moreover, there was a statistically significant difference in RNFL thickness in the inferior and nasal peripapillary regions among the three groups when adjusted for study center, age, and race compared with normal eyes; those that had received PRP treatment had statistically significantly thinner RNFL measurements in the inferior (P = 0.001) and the nasal quadrant (P = 0.002). Thus, there was a significant reduction in RNFL thickness in the period between 1 and 6 months more than after 1 month after panretinal photocoagulation .
Also, Soliman and colleagues studied 50 eyes with severe non-PDR and PDR that had received argon laser full scatter panretinal photocoagulation with a 7082 Zeiss instrument, Germany with a total of 1500-2500 laser shots with 50-100 μm spot size and 0.1 s duration to compare the average RNFL thickness and the mean RNFL thickness in four different quadrants 6 months after laser treatment with the normal values of the average RNFL thickness and RNFL thickness of each quadrant [evaluation of RNFL thickness was carried out of the same age group using an OCT 2000 instrument (Humphrey-Zeiss Stratus OCT) using a peripapillary circle scan of 3.4 mm diameter].
They found that there was a 19.4% reduction in the average RNFL thickness in all quadrants after 6 months of laser treatment compared with normal values of the same age group.
Also, there was a 22.8% reduction in the RNFL thickness in the superior quadrant after 6 months of laser treatment compared with normal values of the same age group. In addition, they reported that there was a 24.2% reduction in the RNFL thickness in the inferior quadrant after 6 months of laser treatment compared with normal values of the same age group. They also reported that there was a reduction in the RNFL thickness in the temporal quadrant and this reduction was the least between all quadrants, 14.5%, after 6 months of laser treatment compared with normal values of the same age group. Finally, they reported that the reduction in the RNFL thickness in the nasal quadrant was the most severe between all quadrants, 32.5%, after 6 months of laser treatment compared with normal v alues of the same age group .
Also, Parikh et al.  reported that the RNFL becomes thinner (0.16 μm/year). Many researchers, such as Lopes de Faria et al.  and Takahashi et al. , have suggested a relationship between diabetes and RNFL loss. Özdek et al.  also suggested a strong relationship between diabetic retinopathy and RNFL loss. A study by Takahashi et al.  reported that RNFL thinning in diabetes increases with worsening disease severity and did not find a statistically significant difference in RNFL measurements among diabetic eyes without PRP with varying severity of retinopathy. However, Kim and Cho suggested that the peripapillary RNFL thickness decreased in both the treatment and the control groups and the difference between the two groups was not statistically significant. Therefore, it is difficult to conclude that the change in thickness was because of the laser treatment. In their study, retinal laser photocoagulation was used, which can cause laser burns, but does not necessarily damage the RNFL if the laser burn is only of a moderate degree. However, the results are limited to 6 months of follow-up. There was no relationship between laser burn frequency and peripapillary RNFL thickness change in the treatment group. This indicates that an adequate intensity of retinal laser photocoagulation does not alter retinal function in patients with diabetic retinopathy. In their study, they also confirmed that the thickness of the peripapillary RNFL decreased 0.93 ± 4.24 μm over 6 months in the treatment group.
| Conclusion|| |
RNFL thickness study by OCT indicated that when performing panretinal photocoagulation, it is very important to have the maximal effect with lower number of shots and burns to avoid decreasing RNFL thickness to a huge degree and to avoid optic disc pallor and optic atrophy.
| Acknowledgements|| |
Conflicts of interest
There are no conflicts of interest.
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[Figure 1], [Figure 2], [Figure 3], [Figure 4]
[Table 1], [Table 2]