Int Ophthalmol DOI 10.1007/s10792-014-9939-3
ORIGINAL PAPER
Optic nerve head drusen: a comparative study of 10 MHz and 20 MHz ultrasound probes Sonia Zaouali • Nesrine Abroug • Sana Khochtali Rim Kahloun • Bechir Jelliti • Sonia Attia • Salim Ben Yahia • Moncef Khairallah
•
Received: 13 October 2013 / Accepted: 22 March 2014 Ó Springer Science+Business Media Dordrecht 2014
Abstract The aim of this study was to evaluate and compare 10-MHz and 20-MHz ultrasonography in the assessment of patients with optic nerve head drusen (ONHD). The design of the study was prospective, comparative and cross-sectional. Ultrasonographic examination with a 10 and 20 MHz probe was performed in 45 eyes with suspected ONHD. The 20 MHz probe showed drusen in 43 eyes (95.5 %), while the 10 MHz probe revealed drusen in only 33 eyes (73.3 %, p = 0.0001). The 10 MHz probe showed surface drusen in 10 eyes (22.2 %), while the 20 MHz probe showed surface drusen in 14 eyes (31.1 %) (sensitivity 71.4 %; 95 % CI [47.6– 95.1 %]). The 10 MHz probe showed buried drusen in 23 eyes (23.1 %), while the 20 MHz probe showed buried drusen in 29 eyes (64.4 %) (sensitivity 79.3 %; 95 % CI [56.6–86.2 %]). The sensitivity was 76.7 % with 10 MHz probe compared to a 20 MHz as gold standard. The use of 20 MHz probe increased the sensitivity of buried disc drusen by 1.5 times and surface disc drusen by nearly 2 times. Using the 10 MHz probe alone the false negative error rate was
S. Zaouali N. Abroug S. Khochtali R. Kahloun B. Jelliti S. Attia S. Ben Yahia M. Khairallah (&) Department of Ophthalmology, Fattouma Bourguiba University Hospital, Faculty of Medicine, University of Monastir, 5019 Monastir, Tunisia e-mail: [email protected]
83.3 %. The 20 MHz probe has shown itself to be an excellent method for the diagnosis of ONHD; it is more sensitive and reliable than 10 MHz probe and should be considered in the management of patients with clinical evidence of ONHD. Keywords Optic nerve head drusen Ultrasonography 10 MHz 20 MHz
Introduction Optic nerve head drusen (ONHD) are defined as hyaline bodies that result from calcification of intracellular axonal mitochondria located in the prelaminar portion of optic nerve [1]. They are a common cause of pseudo-papilledema and represent an important differential diagnosis of optic disc swelling [1, 2]. Therefore, several diagnostic methods have been used including preinjection control photography for detection of autofluorescence, B-scan ultrasonography, computed tomography (CT) and recently time and spectral domain optical coherence tomography (OCT) [1–7]. Ultrasonography is a useful technique for diagnosing ONHD [1, 6, 8, 9]. However, when there are surface drusen only, or the calcified areas are small, conventional 10 MHz imaging may overlook these calcifications. The 20 MHz probe gives high resolution images of the posterior ocular segment and may provide very valuable information on the analysis of ONHD [10].
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Int Ophthalmol
The objective of this study was to compare 10 MHz and 20 MHz ultrasonography in the assessment of patients with ONHD.
Methods Between January 2011 and January 2012, 25 patients were referred to the department of Ophthalmology, Fattouma Bourguiba University Hospital of Monastir, Tunisia for further evaluation of suspected ONHD. All patients underwent a complete ophthalmic examination, including measurement of Snellen best-corrected visual acuity, slit-lamp examination, tonometry and dilated fundus examination. B-scan ultrasonography, with a 10 and 20 MHz probes, was performed in all patients. Among the 50 eyes examined, the diagnosis of clinically definite or suspected ONHD was made, independently by two senior physicians (MK and SBY) in 45 eyes. The ultrasonographic examination was performed by the same senior physician (SZ). We used the Quantel Medical ‘Cinescan’ (Quantel Medical Inc.) B-scan, with a 10 and 20 MHz probes. B-scans were performed with the patients placed supine on a reclining chair. We used coupling gel and all scans were performed with the probe placed directly on the eyelid. All settings and examination methods except the decibel (dB) gain were identical when comparing 10 and 20 MHz images. The dB gain was adjusted when using each probe to give the optimal images of the ocular or orbital structure of interest. While viewing the ultrasound B images, three of us (SZ, SA and BJ) assigned the diagnosis of ONHD and classified the drusen in two groups: –
–
Definite; which appears as highly reflective round structures with acoustic shadowing in the mediumgain scan. Questionable; when the ultrasonography showed elevated optic disc with no obvious echogenic lesion.
Statistical analyses were performed using SAS version 9.1 statistical software. The accuracy of ultrasonography in diagnosing ONHD was estimated by measuring and comparing the sensitivity of 10 and 20 MHz probes.
123
Results The mean age of our patients was 31.4 years (range of 11–57 years). There were 16 female and 9 male patients. Among the 45 eyes with suspected ONHD, the 20 MHz probe showed drusen in 43 eyes (95.5 %), while the 10 MHz probe revealed drusen in only 33 eyes (73.3 %, p = 0.0001) (Table 1). The 10 MHz probe showed surface drusen in 10 eyes (22.2 %), while the 20 MHz probe showed surface drusen in 14 eyes (31.1 %), i.e. the 10 MHz probe sensitivity was 71.4 %. (95 % CI [47.6–95.1 %]) (Fig. 1A, B). However, the 10 MHz probe showed buried drusen in 23 eyes (23.1 %), while the 20 MHz probe showed buried drusen in 29 eyes (64.4 %). (sensitivity 79.3 %; 95 % CI [56.6–86.2 %]) (Fig. 2A, B). The 10 MHz probe showed definite surface drusen in 6 eyes (13.3 %) and questionable in 4 eyes (8.8 %), definite buried drusen in 18 eyes (40 %) and questionable in 5 eyes (11.1 %). The sensitivity was 76.7 % with 10 MHz probe compared to a 20 MHz as gold standard. The use of 20 MHz probe increased the sensitivity of buried disc drusen by 1.5 times and surface disc drusen by nearly 2 times. Using the 10 MHz probe alone the false negative error rate was 83.3 %. Two eyes (4.4 %) were found to have no drusen with 10 and 20 MHz examinations and were, therefore, diagnosed as papilledema. Further investigations including CT scan and magnetic resonance angiography were performed to rule out an intracranial mass or cavernous sinus thrombosis. A lumbar puncture was performed showing high cerebrospinal fluid pressure, and the diagnosis of idiopathic intracranial hypertension was established.
Table 1 Ultrasonographic findings of patients 10 MHz probe Eyes = 33
20 MHz probe %
Eyes = 43
%
Surface drusen Definite
6
13.3
14
31.1
Questionable
4
8.8
0
0
18 5
40 11.1
29 0
64.4 0
Buried drusen Definite Questionable
Int Ophthalmol
Fig. 1 A The 10 MHz probe showed elevated optic disc (arrow). B The 20 MHz probe showed superficial drusen present as small ovoid highly reflective structures (arrow) with acoustic shadowing (white arrowheads)
Discussion Histopathologically, ONHD are calcified, intracellular mitochondria of optic nerve axons [1]. They are present clinically in 0.3 % of individuals and histopathologically in 2 % of individuals [11, 12]. They appear clinically as a globular bodies protruding anteriorly from the disc, giving rise to an irregular, indistinct disc margin [1]. Superficial drusen of the optic nerve head are usually easily identified on ophthalmoscopy by the characteristic glowing yellow light they reflect [8]. However, deeply situated buried drusen may be difficult to differentiate from true optic disc oedema by ophthalmoscopic appearance alone [8]. B-scan ultrasonography is an invaluable, versatile, non-invasive tool in ophthalmology [10]. It is a
Fig. 2 A The 10 MHz probe showed elevated optic disc (arrow). B The 20 MHz probe showed buried drusen present as highly reflective round structures (arrowhead)
reliable method for confirming the presence of optic disc drusen, which present as highly reflective round structures with acoustic shadowing in the mediumgain scan. Characteristically they can still be detected in low-gain scans due to their calcium content [1, 6, 8, 13]. The advantage of this method as compared to other diagnostic techniques is that the entire area of the disc can be scanned by a sweeping movement of the ultrasound probe [1, 9, 14]. B-scan ultrasonography has shown to be the most reliable method in drusen detection [1, 8, 13]. This view was supported by a comparative study in 82 eyes with suspected buried drusen, where B-scan showed drusen in 39 eyes as compared to 15 positive eyes in preinjection photography (p \ 0.001). None of the cases diagnosed by either preinjection photography or CT as harbouring drusen were missed by B-scan ultrasonography [8].
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In last few years, the 20 MHz probe has been introduced which gives high resolution images of posterior segment [10]. The resolution of the 20 MHz probe should be twice as good as that achieved by the 10 MHz probe [10]. However, as the frequency of ultrasound increases, the attenuation by tissue also increases, while exploration area is reduced. Ultrasonographic examination is indeed very quickly limited by noise if the gain is increased. Hewick et al. [10] showed that the 20 MHz probe has a superior resolution and can be used to better detect details at the posterior pole and in the orbit, while the 10 MHz probe has superior sensitivity and can be used to examine low intensity scatterers, such as those in the vitreous. To the best of our knowledge this is the first report comparing 10 MHz and 20 MHz ultrasound in the assessment of patients with ONHD. In this study, the use of 20 MHz probe increased the sensitivity of buried disc drusen by 1.5 times and surface disc drusen by nearly 2 times. Using the 10 MHz probe alone the false negative error rate was 83.3 %. The 20 MHz probe has a superior resolution and can be used to better detect details of the optic nerve. In our study, the 20 MHz has shown itself to be an excellent method for the diagnosis of optic nerve drusen; it is more sensitive and reliable than 10 MHz probe. More recently, studies reported results using time domain [2] and spectral domain OCT [3, 7]. Johnson et al. [2] have documented that qualitative and quantitative parameters on OCT can aid in differentiating optic disc oedema due to papilledema or other optic neuropathies from ONHD. Merchant et al. [7] have assessed the value of enhanced depth imaging OCT (EDI-OCT) in diagnosing ONHD compared with conventional diagnostic methods including B-scan ultrasonography. EDI-OCT had a significantly higher ONHD detection rate than ultrasound B-scan in all eyes (p \ 0.001). In summary, optic nerve head drusen are typically classified as benign conditions and must be differentiated from optic disc oedema. This distinction is crucial because of the expensive and invasive investigations used in the latter condition. Optic disc drusen are diagnosed most reliably with B-scan ultrasonography. The 20 MHz probe has superior resolution than 10 MHz probe and should be considered in the management of patients with clinical evidence of optic nerve head drusen. Additional prospective
123
comparative studies are required to establish the accuracy of spectral domain OCT, autofluorescence imaging and 20 MHZ B-scan ultrasonography in diagnosing ONHD. Acknowledgments This work has been supported by the Ministry of Higher Education and Scientific Research of Tunisia. Conflict of interest The authors report no conflicts of interest. The authors alone are responsible for the content and writing of the paper.
References 1. Claudia A-H, Flemming S, Heinrich W (2002) Optic Disc Drusen. Surv ophthalmol 47:515–532 2. Johnson LN, Diehl ML, Hamm CW, Sommerville DN, Petroski GF (2009) Differentiating optic disc edema from optic nerve head drusen on optical coherence tomography. Arch Ophthalmol 127:45–49 3. Sato T, Mrejen S, Spaide RF (2013) Multimodal imaging of optic disc drusen. Am J Ophthalmol 156:275–282 4. Friedman AH, Beckerman B, Gold DH, Walsh JB, Gartner S (1977) Drusen of the optic disc. Surv Ophthalmol 21:373–390 5. Mustonen E, Nieminen H (1982) Optic disc drusen- a photographic study: autofluorescence pictures and fluorescein angiography. Acta Ophthalmol (Copenh) 60:849–858 6. McNicholas MM, Power WJ, Griffin JF (1994) Sonography in optic disk drusen: imaging findings and role in diagnosis when funduscopic findings are normal. AJR Am J Roentgenol 162:161–163 7. Merchant KY, Su D, Park SC, Qayum S, Banik R, Liebmann JM, Ritch R (2013) Enhanced depth imaging optical coherence tomography of optic nerve head drusen. Ophthalmology 120:1409–1414 8. Kurz-Levin MM, Landau K (1999) A comparison of imaging techniques for diagnosing drusen of the optic nerve head. Arch Ophthalmol 117:1045–1049 9. Boldt HC, Byrne SF, DiBernardo C (1991) Echographic evaluation of optic disc drusen. J Clin Neuroophthalmol 11:85–91 10. Hewick SA, Fairhead AC, Culy JC, Atta HR (2004) A comparison of 10 MHz and 20 MHz ultrasound probes in imaging the eye and orbit. Br J Ophthalmol 88:551–555 11. Lorentzen SE (1966) Drusen of the optic disk: a clinical and genetic study. Acta Ophthalmol (Copenh) Suppl 90:1–180 12. Friedman AH, Gartner S, Modi SS (1975) Drusen of the optic disc. A retrospective study in cadaver eyes. Br J Ophthalmol 59:413–421 13. Atta HR (1988) Imaging of the optic nerve with standardised echography. Eye (Lond) 2:358–366 14. Kheterpal S, Good PA, Beale DJ, Kritzinger EE (1995) Imaging of optic disc drusen: a comparative study. Eye (Lond) 9:67–69
ORIGINAL PAPER
Optic nerve head drusen: a comparative study of 10 MHz and 20 MHz ultrasound probes Sonia Zaouali • Nesrine Abroug • Sana Khochtali Rim Kahloun • Bechir Jelliti • Sonia Attia • Salim Ben Yahia • Moncef Khairallah
•
Received: 13 October 2013 / Accepted: 22 March 2014 Ó Springer Science+Business Media Dordrecht 2014
Abstract The aim of this study was to evaluate and compare 10-MHz and 20-MHz ultrasonography in the assessment of patients with optic nerve head drusen (ONHD). The design of the study was prospective, comparative and cross-sectional. Ultrasonographic examination with a 10 and 20 MHz probe was performed in 45 eyes with suspected ONHD. The 20 MHz probe showed drusen in 43 eyes (95.5 %), while the 10 MHz probe revealed drusen in only 33 eyes (73.3 %, p = 0.0001). The 10 MHz probe showed surface drusen in 10 eyes (22.2 %), while the 20 MHz probe showed surface drusen in 14 eyes (31.1 %) (sensitivity 71.4 %; 95 % CI [47.6– 95.1 %]). The 10 MHz probe showed buried drusen in 23 eyes (23.1 %), while the 20 MHz probe showed buried drusen in 29 eyes (64.4 %) (sensitivity 79.3 %; 95 % CI [56.6–86.2 %]). The sensitivity was 76.7 % with 10 MHz probe compared to a 20 MHz as gold standard. The use of 20 MHz probe increased the sensitivity of buried disc drusen by 1.5 times and surface disc drusen by nearly 2 times. Using the 10 MHz probe alone the false negative error rate was
S. Zaouali N. Abroug S. Khochtali R. Kahloun B. Jelliti S. Attia S. Ben Yahia M. Khairallah (&) Department of Ophthalmology, Fattouma Bourguiba University Hospital, Faculty of Medicine, University of Monastir, 5019 Monastir, Tunisia e-mail: [email protected]
83.3 %. The 20 MHz probe has shown itself to be an excellent method for the diagnosis of ONHD; it is more sensitive and reliable than 10 MHz probe and should be considered in the management of patients with clinical evidence of ONHD. Keywords Optic nerve head drusen Ultrasonography 10 MHz 20 MHz
Introduction Optic nerve head drusen (ONHD) are defined as hyaline bodies that result from calcification of intracellular axonal mitochondria located in the prelaminar portion of optic nerve [1]. They are a common cause of pseudo-papilledema and represent an important differential diagnosis of optic disc swelling [1, 2]. Therefore, several diagnostic methods have been used including preinjection control photography for detection of autofluorescence, B-scan ultrasonography, computed tomography (CT) and recently time and spectral domain optical coherence tomography (OCT) [1–7]. Ultrasonography is a useful technique for diagnosing ONHD [1, 6, 8, 9]. However, when there are surface drusen only, or the calcified areas are small, conventional 10 MHz imaging may overlook these calcifications. The 20 MHz probe gives high resolution images of the posterior ocular segment and may provide very valuable information on the analysis of ONHD [10].
123
Int Ophthalmol
The objective of this study was to compare 10 MHz and 20 MHz ultrasonography in the assessment of patients with ONHD.
Methods Between January 2011 and January 2012, 25 patients were referred to the department of Ophthalmology, Fattouma Bourguiba University Hospital of Monastir, Tunisia for further evaluation of suspected ONHD. All patients underwent a complete ophthalmic examination, including measurement of Snellen best-corrected visual acuity, slit-lamp examination, tonometry and dilated fundus examination. B-scan ultrasonography, with a 10 and 20 MHz probes, was performed in all patients. Among the 50 eyes examined, the diagnosis of clinically definite or suspected ONHD was made, independently by two senior physicians (MK and SBY) in 45 eyes. The ultrasonographic examination was performed by the same senior physician (SZ). We used the Quantel Medical ‘Cinescan’ (Quantel Medical Inc.) B-scan, with a 10 and 20 MHz probes. B-scans were performed with the patients placed supine on a reclining chair. We used coupling gel and all scans were performed with the probe placed directly on the eyelid. All settings and examination methods except the decibel (dB) gain were identical when comparing 10 and 20 MHz images. The dB gain was adjusted when using each probe to give the optimal images of the ocular or orbital structure of interest. While viewing the ultrasound B images, three of us (SZ, SA and BJ) assigned the diagnosis of ONHD and classified the drusen in two groups: –
–
Definite; which appears as highly reflective round structures with acoustic shadowing in the mediumgain scan. Questionable; when the ultrasonography showed elevated optic disc with no obvious echogenic lesion.
Statistical analyses were performed using SAS version 9.1 statistical software. The accuracy of ultrasonography in diagnosing ONHD was estimated by measuring and comparing the sensitivity of 10 and 20 MHz probes.
123
Results The mean age of our patients was 31.4 years (range of 11–57 years). There were 16 female and 9 male patients. Among the 45 eyes with suspected ONHD, the 20 MHz probe showed drusen in 43 eyes (95.5 %), while the 10 MHz probe revealed drusen in only 33 eyes (73.3 %, p = 0.0001) (Table 1). The 10 MHz probe showed surface drusen in 10 eyes (22.2 %), while the 20 MHz probe showed surface drusen in 14 eyes (31.1 %), i.e. the 10 MHz probe sensitivity was 71.4 %. (95 % CI [47.6–95.1 %]) (Fig. 1A, B). However, the 10 MHz probe showed buried drusen in 23 eyes (23.1 %), while the 20 MHz probe showed buried drusen in 29 eyes (64.4 %). (sensitivity 79.3 %; 95 % CI [56.6–86.2 %]) (Fig. 2A, B). The 10 MHz probe showed definite surface drusen in 6 eyes (13.3 %) and questionable in 4 eyes (8.8 %), definite buried drusen in 18 eyes (40 %) and questionable in 5 eyes (11.1 %). The sensitivity was 76.7 % with 10 MHz probe compared to a 20 MHz as gold standard. The use of 20 MHz probe increased the sensitivity of buried disc drusen by 1.5 times and surface disc drusen by nearly 2 times. Using the 10 MHz probe alone the false negative error rate was 83.3 %. Two eyes (4.4 %) were found to have no drusen with 10 and 20 MHz examinations and were, therefore, diagnosed as papilledema. Further investigations including CT scan and magnetic resonance angiography were performed to rule out an intracranial mass or cavernous sinus thrombosis. A lumbar puncture was performed showing high cerebrospinal fluid pressure, and the diagnosis of idiopathic intracranial hypertension was established.
Table 1 Ultrasonographic findings of patients 10 MHz probe Eyes = 33
20 MHz probe %
Eyes = 43
%
Surface drusen Definite
6
13.3
14
31.1
Questionable
4
8.8
0
0
18 5
40 11.1
29 0
64.4 0
Buried drusen Definite Questionable
Int Ophthalmol
Fig. 1 A The 10 MHz probe showed elevated optic disc (arrow). B The 20 MHz probe showed superficial drusen present as small ovoid highly reflective structures (arrow) with acoustic shadowing (white arrowheads)
Discussion Histopathologically, ONHD are calcified, intracellular mitochondria of optic nerve axons [1]. They are present clinically in 0.3 % of individuals and histopathologically in 2 % of individuals [11, 12]. They appear clinically as a globular bodies protruding anteriorly from the disc, giving rise to an irregular, indistinct disc margin [1]. Superficial drusen of the optic nerve head are usually easily identified on ophthalmoscopy by the characteristic glowing yellow light they reflect [8]. However, deeply situated buried drusen may be difficult to differentiate from true optic disc oedema by ophthalmoscopic appearance alone [8]. B-scan ultrasonography is an invaluable, versatile, non-invasive tool in ophthalmology [10]. It is a
Fig. 2 A The 10 MHz probe showed elevated optic disc (arrow). B The 20 MHz probe showed buried drusen present as highly reflective round structures (arrowhead)
reliable method for confirming the presence of optic disc drusen, which present as highly reflective round structures with acoustic shadowing in the mediumgain scan. Characteristically they can still be detected in low-gain scans due to their calcium content [1, 6, 8, 13]. The advantage of this method as compared to other diagnostic techniques is that the entire area of the disc can be scanned by a sweeping movement of the ultrasound probe [1, 9, 14]. B-scan ultrasonography has shown to be the most reliable method in drusen detection [1, 8, 13]. This view was supported by a comparative study in 82 eyes with suspected buried drusen, where B-scan showed drusen in 39 eyes as compared to 15 positive eyes in preinjection photography (p \ 0.001). None of the cases diagnosed by either preinjection photography or CT as harbouring drusen were missed by B-scan ultrasonography [8].
123
Int Ophthalmol
In last few years, the 20 MHz probe has been introduced which gives high resolution images of posterior segment [10]. The resolution of the 20 MHz probe should be twice as good as that achieved by the 10 MHz probe [10]. However, as the frequency of ultrasound increases, the attenuation by tissue also increases, while exploration area is reduced. Ultrasonographic examination is indeed very quickly limited by noise if the gain is increased. Hewick et al. [10] showed that the 20 MHz probe has a superior resolution and can be used to better detect details at the posterior pole and in the orbit, while the 10 MHz probe has superior sensitivity and can be used to examine low intensity scatterers, such as those in the vitreous. To the best of our knowledge this is the first report comparing 10 MHz and 20 MHz ultrasound in the assessment of patients with ONHD. In this study, the use of 20 MHz probe increased the sensitivity of buried disc drusen by 1.5 times and surface disc drusen by nearly 2 times. Using the 10 MHz probe alone the false negative error rate was 83.3 %. The 20 MHz probe has a superior resolution and can be used to better detect details of the optic nerve. In our study, the 20 MHz has shown itself to be an excellent method for the diagnosis of optic nerve drusen; it is more sensitive and reliable than 10 MHz probe. More recently, studies reported results using time domain [2] and spectral domain OCT [3, 7]. Johnson et al. [2] have documented that qualitative and quantitative parameters on OCT can aid in differentiating optic disc oedema due to papilledema or other optic neuropathies from ONHD. Merchant et al. [7] have assessed the value of enhanced depth imaging OCT (EDI-OCT) in diagnosing ONHD compared with conventional diagnostic methods including B-scan ultrasonography. EDI-OCT had a significantly higher ONHD detection rate than ultrasound B-scan in all eyes (p \ 0.001). In summary, optic nerve head drusen are typically classified as benign conditions and must be differentiated from optic disc oedema. This distinction is crucial because of the expensive and invasive investigations used in the latter condition. Optic disc drusen are diagnosed most reliably with B-scan ultrasonography. The 20 MHz probe has superior resolution than 10 MHz probe and should be considered in the management of patients with clinical evidence of optic nerve head drusen. Additional prospective
123
comparative studies are required to establish the accuracy of spectral domain OCT, autofluorescence imaging and 20 MHZ B-scan ultrasonography in diagnosing ONHD. Acknowledgments This work has been supported by the Ministry of Higher Education and Scientific Research of Tunisia. Conflict of interest The authors report no conflicts of interest. The authors alone are responsible for the content and writing of the paper.
References 1. Claudia A-H, Flemming S, Heinrich W (2002) Optic Disc Drusen. Surv ophthalmol 47:515–532 2. Johnson LN, Diehl ML, Hamm CW, Sommerville DN, Petroski GF (2009) Differentiating optic disc edema from optic nerve head drusen on optical coherence tomography. Arch Ophthalmol 127:45–49 3. Sato T, Mrejen S, Spaide RF (2013) Multimodal imaging of optic disc drusen. Am J Ophthalmol 156:275–282 4. Friedman AH, Beckerman B, Gold DH, Walsh JB, Gartner S (1977) Drusen of the optic disc. Surv Ophthalmol 21:373–390 5. Mustonen E, Nieminen H (1982) Optic disc drusen- a photographic study: autofluorescence pictures and fluorescein angiography. Acta Ophthalmol (Copenh) 60:849–858 6. McNicholas MM, Power WJ, Griffin JF (1994) Sonography in optic disk drusen: imaging findings and role in diagnosis when funduscopic findings are normal. AJR Am J Roentgenol 162:161–163 7. Merchant KY, Su D, Park SC, Qayum S, Banik R, Liebmann JM, Ritch R (2013) Enhanced depth imaging optical coherence tomography of optic nerve head drusen. Ophthalmology 120:1409–1414 8. Kurz-Levin MM, Landau K (1999) A comparison of imaging techniques for diagnosing drusen of the optic nerve head. Arch Ophthalmol 117:1045–1049 9. Boldt HC, Byrne SF, DiBernardo C (1991) Echographic evaluation of optic disc drusen. J Clin Neuroophthalmol 11:85–91 10. Hewick SA, Fairhead AC, Culy JC, Atta HR (2004) A comparison of 10 MHz and 20 MHz ultrasound probes in imaging the eye and orbit. Br J Ophthalmol 88:551–555 11. Lorentzen SE (1966) Drusen of the optic disk: a clinical and genetic study. Acta Ophthalmol (Copenh) Suppl 90:1–180 12. Friedman AH, Gartner S, Modi SS (1975) Drusen of the optic disc. A retrospective study in cadaver eyes. Br J Ophthalmol 59:413–421 13. Atta HR (1988) Imaging of the optic nerve with standardised echography. Eye (Lond) 2:358–366 14. Kheterpal S, Good PA, Beale DJ, Kritzinger EE (1995) Imaging of optic disc drusen: a comparative study. Eye (Lond) 9:67–69
