|Year : 2014 | Volume
| Issue : 2 | Page : 49-54
Quantitative assessment of optic disc edema using spectral domain optical coherence tomography
Ahmed Mohamed Kamal Elshafei, Raafat Mohyeldeen Abdelrahman, Heba Radi AttaAllah
Department of Ophthalmology, Faculty of Medicine, El Minia University, El Minia, Egypt
|Date of Submission||10-Jan-2014|
|Date of Acceptance||07-Apr-2014|
|Date of Web Publication||12-Sep-2014|
Heba Radi AttaAllah
32 Adnan El Maleky street, Ard Sultan, El Minia
Source of Support: None, Conflict of Interest: None
Optic disc edema (ODE) can be caused by a variety of conditions including pseudotumor cerebri, hypertension, diabetes, uveitis, anemia, lymphoma, and papillitis. Improvement in the quality of optical coherence tomography (OCT) can support the diagnosis and management of ODE. OCT may help in this diagnosis by showing peripapillary retinal nerve fiber layer (RNFL) thickening.
Aim of the work
To evaluate quantitative assessment of optic disc edema by measuring peripapillary nerve fiber layer (RNFL) thickness, and peripapillary maximum neurosensory retinal (MNSR) thickness in the four quadrants using spectral domain OCT.
Patients and methods
The study was done in El-Minya Investigation Eye Center between May 2012 and May 2013. The study included 21 eyes of 16 patients with optic disc edema and 20 eyes of 11 normal control persons. Both patients and normal control were examined by spectral domain OCT, two sets of measurements were evaluated and compared:
Peripapillary RNFL thickness measurement in four quadrants using the standard optic disc cube 200 × 200 acquisition protocol, spectral domain OCT, Peripapillary maximum neurosensory retinal thickness (MNSR) in four quadrants using high definition 5 line images.
In ODE group, 21 eyes of 16 patients were evaluated. The control group included 20 eyes of 11 normal subjects. The Mean average peripapillary RNFL was 93.1 ± 8.2 in control group 132.3 ± 46 µ in mild ODE, 139.4 ± 29.2 µ in moderate ODE and 264.2 ± 116.9 µ in severe ODE. The mean average peripapillary MNSR in the four quadrants was 350.1 ± 36.3 µm in control group, 458.7 ± 37.3 µm in mild ODE, 634.4 ± 35.01 µm in moderate ODE and 968.3 ± 245 µm in severe ODE.
There was a statistically significant increase in mean RNFL thickness and mean MNSR in four quadrants in all grades of ODE group compared with the control group (P = 0.001). There was a strong positive correlation (r = 0.89, P = 0.001) between the mean MNSR and the mean RNFL in eyes with ODE.
Keywords: disc swelling, optical coherence tomography, optic disc edema, papilledema
|How to cite this article:|
Kamal Elshafei AM, Abdelrahman RM, AttaAllah HR. Quantitative assessment of optic disc edema using spectral domain optical coherence tomography. J Egypt Ophthalmol Soc 2014;107:49-54
|How to cite this URL:|
Kamal Elshafei AM, Abdelrahman RM, AttaAllah HR. Quantitative assessment of optic disc edema using spectral domain optical coherence tomography. J Egypt Ophthalmol Soc [serial online] 2014 [cited 2017 Aug 21];107:49-54. Available from: http://www.jeos.eg.net/text.asp?2014/107/2/49/140626
| Introduction|| |
Optic disc edema (ODE) can be caused by a variety of conditions including pseudotumor cerebri, hypertension, diabetes, uveitis, anemia, lymphoma, and papillitis . Papilledema is an optic disc swelling secondary to axoplasmic flow stasis in the optic nerve head, which results from raised intracranial pressure transmitted to the optic nerves by the cerebrospinal fluid . Pseudopapilledema can be defined as any disc appearance that can be confused with papilledema. The distinction is obviously important because of the profound implications associated with papilledema. The most frequently encountered causes of pseudopapilledema include optic disc drusen, hyperopia, hyaloid remnants, and congenital disc elevations. Until a few years ago, diagnosis of papilledema relied solely on fundus examination and retinal angiography. Differential diagnosis between ODE and optic disc pseudoedema may be a clinical challenge even for well-trained ophthalmologists .
Improvement in the quality of optical coherence tomography (OCT) can support the diagnosis and management of ODE . OCT may help in this diagnosis by showing peripapillary retinal nerve fiber layer (RNFL) thickening. Fixed standard 3.4-mm-diameter circular scans centered on the optic nerve head are commonly used to measure the peripapillary RNFL thickness. Measurement of RNFL thickness is a sensitive and specific discriminator of atrophic diseases of the optic nerve . Measurement of RNFL thickness has also demonstrated its usefulness in the diagnosis of optic disc swelling. However, OCT RNFL thickness measurements does not appear to differentiate between individuals with congenitally crowded optic nerves and those with mild papilledema .
Vartin et al.  compared peripapillary total retinal (PTR) thickness measurement using the macular cube 512 × 128 acquisition protocol centered on the optic nerve head with conventional RNFL measurement. We adapted a new measuring protocol for ODE using spectral domain OCT, which depends on measurement of peripapillary maximum neurosensory retinal (MNSR) thickness in four quadrants.
| Objective|| |
The aim of the study was to evaluate quantitative assessment of ODE by measuring peripapillary nerve fiber layer thickness and peripapillary MNSR thickness in the four quadrants using spectral domain OCT.
| Patients and methods|| |
The study was conducted in El-Minya Investigation Eye Center between May 2012 and May 2013 and was approved by ethical committee board of El-Minya University. The study included 21 eyes of 16 patients with ODE and 20 eyes of 11 normal control persons.
There were seven male patients and nine female patients with age range from 19 to 82 years, whereas the normal controls included three male individuals and eight female individuals with age range from 18 to 56 years.
Exclusion criteria for both patients and normal individuals were eyes with high ametropia (refractive error >5 D equivalent sphere or 3 D of astigmatism refraction), cases with media opacities (cataract, corneal opacities) that may interfere with proper clinical evaluation and degrade the quality of OCT images, and the presence of any optic disc changes (glaucoma, congenital anomalies, disc tumors, and optic disc drusen).
All patients were subjected to the following:
(1) Ophthalmic and medical history taking.
(2) Slit-lamp examination of the anterior segment.
(3) Dilated fundus examination using slit-lamp biomicroscopy with +78 D lens.
Three masked observers were asked to classify each optic disc as being normal or showing ODE, then to grade ODE according to the Modified Frisιn Scale with a key feature (*) for each grade .
Grade 0 (normal optic disc):
(1) Prominence of the RNFL at the nasal, superior, and inferior poles in inverse proportion to disc diameter.
(2) Radial nerve fiber layer striations, without tortuosity.
Grade 1 (minimal degree of edema):
(1) C-shaped halo that is subtle and grayish with a temporal gap: obscures underlying retinal details*.
(2) Disruption of normal radial nerve fiber layer arrangement striations.
(3) Temporal disc margin normal.
Grade 2 (low degree of edema):
(1) Circumferential halo*.
(2) Elevation (nasal border).
(3) No major vessel obscuration.
Grade 3 (moderate degree of edema):
(1) Obscuration of at least one segment of major blood vessels leaving disc*.
(2) Circumferential halo.
(3) Elevation (all borders).
(4) Halo (irregular outer fringe with finger-like extensions).
Grade 4 (marked degree of edema):
(1) Total obstruction on the disc of a segment of a major blood vessel on the disc*.
(2) Elevation (whole nerve head, including the cup).
(3) Border obstruction (complete).
(4) Halo (complete).
Grade 5 (severe degree of edema):
(1) Obstruction of all vessels on the disc and leaving the disc*.
For analysis, we considered the grade accepted by two examiners, and then patients with ODE were classified into those with mild edema including grades 1 and 2, those with moderate edema including grade 3, and those with severe edema including grades 4-5.
All patients and controls were subjected to spectral domain OCT scanning (Cirrus HD-OCT, software version 18.104.22.168; Carl Zeiss Meditec Inc., Dublin, USA) after pupillary dilation. During the examination, the patient had to fixate on an internal fixation target. A real-time OCT fundus image allowed the examiner to observe the patient's fixation and to target the circle scan on the optic disc. The scan with the strongest signal and the best centration on the nerve head was chosen with signal strength not less than 8/10.
Two sets of measurements were evaluated and compared ():
(1) Peripapillary RNFL thickness measurement was performed in four quadrants using the standard optic disc cube 200×200 acquisition protocol. From the disc shape, the geometric centre is found and the A-scans forming a 3.4 mm-diameter circle that centre is selected to form a RNFL circular B-scan. Values for RNFL thickness obtained from each A-scan were averaged to find the overall average thickness as well as the average thickness for each of the quadrants (temporal, inferior, nasal, and superior) ([Figure 1]).
|Figure 1: Retinal nerve fi ber layer (RNFL) thickness analysis of patient's left eye: optic disc cube 200×200 showing that the average RNFL is increased (121 μm), and it is increased in the nasal, inferior, and temporal quadrants.|
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(2) Peripapillary MNSR thickness was measured in four quadrants using high-definition five line images with length of 6 mm and spacing of 0.25 mm and scan angles of 90° for superior and inferior peripapillary areas and 0° for temporal and nasal peripapillary areas.
Images with the highest peripapillary retinal elevation were chosen for each quadrant, and measurements were taken from the highest point of retinal elevation perpendicular to a line extended tangentially to the upper surface of the retinal pigment epithelium ([Figure 2] and [Figure 3]).
|Figure 2: Nasal and temporal peripapillary maximum neurosensory retinal thickness in a case of moderate optic disc edema.|
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|Figure 3: Superior and inferior peripapillary maximum neurosensory retinal thickness in a case of moderate optic disc edema.|
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Data were analyzed using SPSS for Windows, version 11 (University of Durham Information Technology Service, North England, UK). Descriptive statistics were used to examine the characteristics of the participants. The χ2 -test was used to compare proportions, and the t-test and one-way ANOVA were used to compare means. The accepted level of significance was 0.05 or less.
| Results|| |
In the ODE group, 21 eyes of 16 patients were evaluated. There were seven male patients (43.7%) and nine female patients (56.3%) with age range from 19 to 82 years and mean age of 42.8±17.9. The right eye was evaluated in nine patients, the left eye in two patients, and both eyes in five patients.
Etiology of ODE included papilledema due to benign increased intracranial pressure in 12 patients (15 eyes) and due to space occupying lesion in four patients (six eyes).
Three eyes had mild ODE (14.3%), nine eyes had moderate ODE (42.85%), and nine eyes had severe ODE (42.85%).
The control group included 20 eyes of 11 normal individuals, three male individuals (27.3%) and eight female individuals (72.7%) with age range from 18 to 56 years and mean age of 38.0±12.4. The left eye was evaluated in two normal individuals and both eyes in nine individuals.
The peripapillary retinal nerve fibers thickness (RNFL) in four quadrants in both control and ODE groups is shown in [Table 1].
The peripapillary MNSR thickness in four quadrants in both control and ODE groups is shown in [Table 2].
|Table 1 The peripapillary retinal nerve fi bers thickness in four quadrants in both control and optic disc edema groups (¦Ìm)|
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|Table 2 The peripapillary maximum neurosensory retinal thickness in four quadrants in ¦Ìm|
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There was a statistically significant increase in both the mean MNSR and RNFL thickness in four quadrants in all grades of the ODE group compared with the control group (P = 0.001).
[Table 3] and [Table 4] show the quadrants of maximum RNFL thickness and MNSR, respectively.
The mean average peripapillary RNFL was 93.1 ± 8.2 μm in the control group, 132.3 ± 46 μm in mild ODE, 139.4 ± 29.2 μm in moderate ODE, and 264.2 ± 116.9 μm in severe ODE. The mean average peripapillary MNSR in the four quadrants was 350.1 ± 36.3 μm in the control group, 458.7 ± 37.3 μm in mild ODE, 634.4 ± 35.01 μm in moderate ODE, and 968.3 ± 245 μm in severe ODE [Table 5].
|Table 5 Mean average maximum neurosensory retinal and retinal nerve fi ber layer in eyes with optic disc edema|
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There was a strong positive correlation (r = 0.89, P = 0.001) between the mean MNSR and the mean RNFL in eyes with ODE ([Figure 4]).
|Figure 4: The correlation between the mean maximum neurosensory retinal (MNSR) and the mean retinal nerve fi ber layer (RNFL) in eyes with optic disc edema.|
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| Conclusion|| |
In the current study, quantitative assessment of ODE using OCT was studied through two methods of measurements. The first is measurement of the RNFL thickness in four quadrants. There was a statistically significant increase in mean RNFL thickness in four quadrants in all grades of the ODE group compared with the control group (P = 0.001).
Rebolleda et al.  studied OCT measurement of peripapillary RNFL thickness in patients with mild papilledema associated with idiopathic intracranial hypertension. They found a greater average RNFL thickness in all four quadrants in eyes with papilledema compared with controls (P = 0.000).
El-Dairi et al.  reported a thicker average RNFL in eyes of children with pseudotumor cerebri compared with controls, but the RNFL differences were not significant in all quadrants.
Karam and Hedges  used OCT to evaluate RNFL in patients with congenital crowding of the optic nerve and in patients with mild papilledema. They found that both groups had OCT measurements of RNFL thickness higher than control individual eyes. However, the distinction between these two entities was not possible by OCT alone.
The second method of measurement in this study is the measurement of the MNSR thickness in four quadrants from the highest point of retinal elevation perpendicular to a line extended tangentially to the upper surface of the retinal pigment epithelium. This method takes into account edema of all of neurosensory retinal layers and subretinal fluid accumulation that may occur in cases of ODE. To the best of our knowledge, this is the first study using this technique for evaluation of ODE.
There was a statistically significant increase in the mean MNSR in four quadrants in all grades of the ODE group compared with the control group (P = 0.001). There was a strong positive correlation (r = 0.89, P = 0.001) between the mean MNSR and the mean RNFL in eyes with ODE.
Vartin et al.  used RNFL thickness measurements using the standard optic disc cube 200×200 acquisition protocol and PTR thickness measurements using the macular cube 512 × 128 acquisition protocol centered on the optic disc inside the 3.0-mm-diameter circle area for detection of cases of mild papilledema. They found that PTR thickness measurement increases the sensitivity of detection of mild papilledema compared with conventional RNFL measurement. The two techniques were equivalent to document moderate to severe papilledema.
Although the PTR measurement using the macular cube protocol takes into account subretinal fluid accumulation, it could be affected by the size of the optic disc.
One limitation in our study is limited number of patients with mild papilledema. Another limitation is that the MNSR thickness measurements were obtained with a manual caliper directly from the computer screen, and this method of measurement is prone to errors in variability. This potential for error would be reduced if OCT manufacturers make an internal caliper for MNSR thickness measurement.
| Acknowledgements|| |
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[Figure 1], [Figure 2], [Figure 3], [Figure 4]
[Table 1], [Table 2], [Table 3], [Table 4], [Table 5]