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NR 1-3/2009
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Refraction and the
axial length of the eyeball in patients with the optic disc
drusen
Refrakcja i długość gałki
ocznej u pacjentów z druzami tarczy nerwu wzrokowego
Obuchowska Iwona, Mariak Zofia
Department of Ophthalmology, Medical University of Bialystok
Head: Professor Mariak Zofia, MD, PhD |
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| Summary: |
Purpose: The aim of
the study was to demonstrate the relationship between
the optic disc drusen (ODD) and the axial length of the
eyeball as well as refractive error.
Material and methods: We examined prospectively
40 patients with ODD, 18 men and 22 women, age range
from 34 to 69 years. All subjects underwent full
ophthalmic examination, visual field testing and
color-coded duplex sonography of the ocular vessels.
Refraction was determined with an autorefractometer (Topcon
RM-8000B) and further refined subjectively. Spherical
equivalent refraction was calculated as the spherical
dioptre plus one half of the cylindrical dioptre. Axial
lengths were measured with a Sonomed ultrasound scanner
model E-Z Scan AB5500.
Results: Clinical signs were observed in 65% of
the eyes with drusen, among them, 38% had symptoms of
visual acuity loss and all had visual fields defects.
There were 21 eyes (18 eyes with and 3 without drusen),
with a recorded refractive error. Significant
differences in hyperopia were observed between the eyes
with and without drusen (p = 0.048). The rate of
occurrence of myopia did not differ significantly
between affected and unaffected eyes (p = 0.06).
The mean spherical equivalent refraction and axial
dimensions of the eye differed significantly among the
groups of eyes with and without drusen (p<0.05).
Significant differences in mean values of peak-systolic
and end-diastolic velocities (p<0.001) as well as in the
resistivity index (p = 0.047) were observed between eyes
with and without drusen.
Conclusions: The optic disc drusen are often
associated with shorter and hyperopic eyes. This
anatomical conditions and vascular factors may
contribute to pathogenesis of drusen. |
| Słowa kluczowe: |
optic disc drusen,
refractive error, axial length. |
| Key words: |
druzy nerwu wzrokowego,
wady refrakcji, długość osiowa. |
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Introduction
Optic disc drusen (ODD) are hyaline-like deposits localized in
the prelaminar part of the optic nerve. They occur in
approximately 2% of the population and are transmitted as an
autosomal dominant trait (1).
Even though the pathogenesis of ODD remains unknown, the most
accepted theories suggest an alteration in ganglion cell
axoplasmatic transport (2,3). Disturbed axon metabolism can lead
to gradual calcification of their cellular mitochondria and thus
axon membranes rupture and mitochondria pass into the
extracellular space, where they undergo further calcification
and fuse into larger complexes that form drusen. The narrow
scleral canal, which is more frequently observed in eyes with
optic disc drusen, is considered an additional risk factor in
pathogenesis of ODD (4). According to this theory, a small
scleral canal physically compresses the optic nerve, blocking
axoplasmatic flow, leading to ganglion cell axonal damage and
ganglion cell death.
Many other clinical aspects, such as the visual field (5,6), the
thickness of the retinal nerve fibre layer (7,8) or visual
evoked potential (9) have been reported in patients with drusen.
In this study, we assessed the other clinical characteristics,
such as the axial length of the eye and refractive error, which
have not hitherto been reported in patients with ODD. We
attempted to determined whether there are any differences in
biometric and refractive characteristics of eyes with drusen and
unaffected fellow eyes.
Material and methods
We examined prospectively all patients with ODD admitted to the
Department of Ophthalmology of the Medical University in
Bialystok, between 2002 and 2008. The study was approved by the
University Institutional Review Board (according to the
guidelines of the Helsinki Declaration),and all patients gave
written consent for the use of their clinical material for
publication.
Our study group included 40 patients, 18 men and 22 women, age
range from 34 to 69 years (mean 49.92 years). All subjects were
examined by one ophthalmologist.
We recorded the following data: age, sex, visual acuity (VA),
refractive error, color perception, intraocular pressure (IOP),
presence of an afferent pupillary defect, appearance of the
optic disc, and axial dimensions of the eye. Refraction was
determined with an autorefractometer (Topcon RM-8000B), and
further refined subjectively. Myopia was defined as a spherical
equivalent refraction ≤ -0.75 D; hyperopia – spherical
equivalent refraction
≥ +0.75 D, and emmetropia – spherical equivalent refraction
> -0.75 D and < +0.75 D. Spherical equivalent refraction was
calculated as the spherical dioptre plus one half of the
cylindrical dioptre. Axial lengths (AL) were measured with a
Sonomed ultrasound scanner model E-Z Scan AB5500 after pupil
dilatation.
The appearance of the optic disc was determined using indirect
slit-lamp biomicroscopy with Volk lens and indirect
ophthalmoscopy. If the optic disc appeared abnormal, the eye was
evaluated with B-scan ultrasonography (Sonomed E-Z scan AB5500),
and fluorescein angiography was performed (Kowa VX-10 Fundus
Camera). In order to exclude neurological cases of optic nerve
edema, a CT scan of the head and orbits was performed. A
diagnosis of ODD was made with the aid of ophthalmoscopic and
angiographic examinations, orbital ultrasonography, or computed
tomographic scanning. ODD were classified on the basis of the
appearance of the optic disc, as visible and buried drusen.
Patients with a history or evidence on examination of other
ocular disease and past intraocular surgery or laser treatment
were excluded from the study.
All subjects underwent visual field testing, performed using the
Medmont Automated Perimeter and Color Doppler sonography of the
ophthalmic artery (OA), the central retinal artery (CRA), and
the posterior ciliary arteries (PCA). The blood flow examination
was performed using a Siemens Elegra (Germany) unit with 7.5 MHz
linear probe. Peak-systolic velocity (PSV), end-diastolic
velocity (EDV), and the resistivity index (RI) were measured
during the study. The data were compared with age norms
established in our ultrasonographic laboratory.
The statistical analysis was performed by SPSS (version 8, PL).
Numerical data are shown as mean ± standard deviation (SD).
Unpaired t-test was used to compare mean values between the
studied groups. Categorical data were analyzed using the Fisher
exact test. The difference was considered statistically
significant at p value less than 0.05.
Results
Our study group included 28 patients (56 affected eyes) with
bilateral drusen and 12 patients (12 affected and 12 unaffected
eyes) with unilateral drusen. Of the 68 affected eyes, 38 (56%)
were visible and 30 (44%) were buried drusen.
Clinical signs were observed in 44 (65%) eyes with drusen. More
than one visual symptom was revealed in 17 eyes. All eyes
without drusen had normal visual acuity (≥ 1.0). The symptoms
are listed in Table I.
There were 21 eyes, including 18 eyes with drusen and 3 without
drusen, with a recorded refractive error. Myopia in the range
0.75-3.0 D was present in 7 out of 80 eyes and hyperopia in the
range 0.75-4.5 D was detected in 14 out of 80 eyes (Table II).
Significant differences in hyperopia were observed between the
eyes with and without drusen (p = 0.048). The rate of occurrence
of myopia did not differ significantly between the eyes with and
without drusen (p = 0.06). There were no significant differences
in the occurrence of the refractive error between visible and
buried drusen (hyperopia p = 0.156; myopia p = 0.774).
The mean spherical equivalent refraction and axial dimensions of
the eye differed significantly among the groups of affected and
unaffected eyes. No significant differences were found in eyes
with visible and buried drusen in terms of axial length.
Although the mean spherical equivalent refraction in eyes with
visible drusen was greater than in eyes with buried drusen, the
differences were not significant (Table III).
The mean intraocular pressure by applanation examination was
15.51 ± 2.34 mmHg. We did not observe differences between the
IOP height in eyes with and without drusen. Of the 68 affected
eyes, only 2 (3%) had colour-deficiency and 3 (4.5%) eyes had an
afferent pupillary defect.
The largest blood flow disturbances were found in the central
retinal artery. Mean values of peak-systolic and end-diastolic
velocities as well as the resistivity index compared between
eyes with and without drusen differed statistically (Table IV).
We did not observe any statistically significant differences
between blood flow Doppler parameters in the ophthalmic artery
and short posterior ciliary arteries. Mean values of blood flow
parameters in all the examined arteries in the eyes with visible
and buried drusen did not differ significantly.
Discussion
In the present study we characterized symptoms and signs
associated with optic disc drusen, paid the special attention to
biometric and refractive characteristics. We found very
interesting dependences in this clinical aspects.
It is commonly known that the refractive error is strongly
correlated with the axial length of the eyeball (10). We found
that drusen were more frequently associated with hyperopia and
smaller eyeballs.
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However, the literature does not
allow these questions to be resolved unequivocally, as the
eyeball length in eyes with drusen has not hitherto been
examined. Although there are some reports concerning the
association between drusen and hyperopia (11), the opinion
commonly prevails that the refractive error distribution in eyes
with ODD parallels that in the general population (1,12). On the
other hand, it has been shown that in patients with drusen, the
size of the optic disc and the width of the scleral canal are
much smaller as compared to subjects without drusen (4,13,14).
Mullie et al. (4) found that these differences could be as much
as 20-33%. There are also reports demonstrating that the length
of the eyeball is closely associated with the size of the optic
disc and the number of fibres in the optic nerve (15,16). With
regard to our study, it can be assumed that shorter eyeballs in
eyes with drusen are likely to be associated with smaller optic
discs and narrower scleral canals. Thus, our results confirm the
theory that a narrow scleral canal is one of the risk factors
for the development of drusen. Thus, the optic fibres are
gathered on a smaller surface and are mechanically compressed,
leading to axoplasm transport inhibition and atrophy of retinal
ganglionic cell axons (2,3). This theory was challenged by Floyd
et al. (17), who did not report any differences between the size
of the scleral canal in eyes with and without drusen. However,
the authors considered that their results could be connected
with distension of the optic nerve by drusen and circumferential
displacement of the retinal pigment epithelium and Bruch’s
membrane. It has also been alleged that the authors did not take
into account the race of the subjects examined in their study
(18) and as their paper comes from the USA it should be
remembered that African-American patients have larger disc areas
than Caucasian ones (19).
Lee et al. (20) made the interesting observation that the
diameter of retinal vessels was smaller in smaller eyes and
smaller optic discs. This results in the blood flow velocity in
those vessels, as compared to the retinal central artery and
vein of eyes with larger sizes of optic nerve discs. Thus, it is
possible that in patients with drusen, whose optic disc size is
smaller, blood flow in the retinal vessels may be reduced.
However, it should be stressed that disorders of the blood
supply to the optic nerve are considered to be one of the
pathogenetic mechanisms for the development of visual field
defects and reduction of visual acuity in eyes with ODD. Thus,
our result of blood flow in the CRA may confirm this theory.
Thought we can not confirm the primary role of biometric and
refractive factors in the pathogenesis of ODD, we have
demonstrated that some anatomical conditions may contribute to
drusen development.
References:
1. Auw-Haedrich C, Staubach F, Witschel H: Optic disc drusen.
Surv Ophthalmol 2002, 47, 515-532.
2. Spencer WH: Drusen of the optic disc and aberrant
axoplasmatic transport. The XXXIV Edward Jackson Memorial
Lecture. Am J Ophthalmol 1978, 85, 1-12.
3. Tso MO: Pathology and pathogenesis of drusen of the optic
nerve head. Ophthalmology 1981, 88, 1066-1080.
4. Mullie MA, Sanders MD: Scleral canal size and optic nerve
head drusen. Am J Ophthalmol 1985, 99, 356-359.
5. Lee AG, Zimmerman MB: The rate of visual field loss in optic
nerve head drusen. Am J Ophthalmol 2005, 139, 1062-1066.
6. Gonzalez CC, Bueso SE, Valle DD, Frutos RJ, Carretero MM, del
Castillo BJM, Sanchez GJ: Optic nerve drusen and deep visual
fields defects. Arch Soc Esp Oftalmol 2006, 81, 269-274.
7. Bednarczyk-Meller J, Wasilewicz R, Pecold-Stepniewska H,
Wasiewicz-Rager J: OCT and PVEP examination in eyes with visible
optic disc drusen. Klin Monatsbl Augenheilkd 2006, 223, 993-996.
8. Katz BJ, Pomeranz HD: Visual field defects and retinal nerve
fiber layer defects in eyes with buried optic nerve drusen. Am J
Ophthalmol 2006, 141, 248-253.
9. Scholl GB, Song HS, Windkler DE, Wray SH: The pattern visual
evoked potential and pattern electroretinogram in drusen
associated optic neuropathy. Arch Ophthalmol 1992, 110, 75-81.
10. Touzeau O, Allouch C, Borderie V, Kopito R, Laroche L:
Correlation between refraction and ocular biometry. J Fr
Ophthalmol 2003, 26, 355-363.
11. Strassman J, Silverston B, Seelenfreund M, Landau L, Scher
A, Berson D: Optic disc drusen and hypermetropia. Metab Pediatr
Syst Ophthalmol 1991, 14, 59-61.
12. Rosenberg MA, Savino PJ, Glaser JS: A clinical analysis of
pseudopapilledema. I. Population, laterality, acuity, refractive
error, ophthalmoscopic characteristics, and coincident disease.
Arch Ophthalmol 1979, 97, 65-70.
13. Jonas JB, Gusek GC, Guggenmoos-Holzmann I, Naumann GO: Optic
nerve head drusen associated with abnormally small optic disc.
Int Ophthalmol 1987, 11, 79-82.
14. Jonas JB: Biomorphometrie des nervus opticus. Bücherei des
Augenarztes, Enke-Verlag 1989, Stuttgart.
15. Jonas JB, Schmidt AM, Müller-Bergh JA, Schlötzer-Schrehardt
UM, Naumann GOH: Human optic nerve fiber count and optic disc
size. Invest Ophthalmol Vis Sci 1992, 33, 2012-2018.
16. Papastathopoulos KI, Jonas JB, Panda-Jonas S: Large optic
discs in large eyes, small optic discs in small eyes. Exp Eye
Res 1995, 60, 459-462.
17. Floyd MS, Katz BJ, Digre KB: Measurement of the scleral
canal using optical coherent tomography in patients with optic
nerve drusen. Am J Ophthalmol 2005, 139, 664-669.
18. Lee MS: Scleral canal size in patients with optic disc
drusen. Correspondence. Am J Ophthalmol 2005, 140, 1168-1169.
19. Girkin CA, McGwin G, Xie A, Deleon-Ortega J: Differences in
optic disc topography between black and white normal subject.
Ophthalmology 2005, 112, 33-39.
20. Lee KE, Eden Kobrin Klein B, Klein R Meuer SM: Association
of retinal vessel caliber to optic disc and cup diameters.
Invest Ophthalmol Vis Sci 2007, 48, 63-67.
The study was originally received 15.12.2008 (1087)/
Praca wpłynęła do Redakcji 15.12.2008 r. (1087)
Accepted for publication 20.01.2009/
Zakwalifikowano do druku 20.01.2009 r.Adres do
korespondecji (Reprint requests to):
dr n. med. Iwona Obuchowska
ul. Gruntowa 6c m 19
15-706 Białystok
iwonaobu@wp.pl
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Affected eyes (n=68) |
| Asymptomatic |
24 (35%) |
Visual acuity loss
0.9 – 0.7
0.6 – 0.4
0.3 – 0.2
0.1
0.05 |
17 (25%)
6 (35%)
6 (35%)
3 (18%)
1 (6%)
1 (6%) |
Visual field loss
Enlargement blind spot
Nerve fibre bundle
Generalized constriction |
44 (65%)
19 (43%)
15 (34%)
10 (23%) |
Tab. I. Visual symptoms in patients with
optic disc drusen.
Tab. I. Objawy oczne u pacjentów z druzami nerwu wzrokowego.
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Emmetropia |
Myopia |
Hyperopia |
| Unaffected eyes (n = 12) |
9 |
3 |
0 |
Affected eyes (n = 68)
(visible/buried) |
50
(26/24) |
4
(2/2) |
14
(10/4) |
| total |
59 |
7 |
14 |
Tab. II. Refractive error in affected and
unaffected fellow eyes in patients with optic disc drusen.
Tab. II. Wada refrakcji u pacjentów w oczach z druzami i drugim
oku bez druz na tarczy nerwu wzrokowego.
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Affected eyes
(n = 68)
(visible/ buried) |
Unaffected
eyes
(n = 12) |
P values |
Spherical equ-
ivalent refraction
(dioptre) |
+0.34 ± 1.03
+0.49 ± 1.24/
+0.15 ± 0.65 |
-0.46
± 0.89 |
P = 0.014
P = 0.163 |
| Axial length (mm) |
22.80 ± 0.59
22.76 ± 0.69/
22.89 ± 0.44 |
23.36
± 0.90 |
P = 0.003
P = 0.515 |
Tab. III. Comparison of differences in mean
values of spherical equivalent refraction and axial length of
affected and unaffected fellow eyes in patients with optic disc
drusen.
Tab. III. Porównanie różnic średniej wartości sferycznego
ekwiwalentu refrakcji i długości osiowej u pacjentów w oczach z
druzami i drugim oku bez druz na tarczy nerwu wzrokowego.
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Affected eyes
(n = 68) |
Unaffected eyes
(n = 12) |
P values |
| PSV (cm/ s) |
7.6 ± 1.8
(4.0-10.3) |
10.4 ± 1.9
(7.8-14.5) |
P<0.001 |
| EDV (cm/ s) |
2.3 ± 1.1 (0-3.9) |
3.4 ± 0.8 (2.3-5.5) |
P<0.001 |
| RI |
0.71 ± 0.11
(0.58-1.0) |
0.64 ± 0.06
(0.54-0.74) |
P = 0.047 |
Tab. IV. Blood flow Doppler parameters
in the central retinal artery in affected and unaffected fellow
eyes in patients with optic disc drusen.
Tab. IV. Dopplerowskie parametry przepływu w tętnicy środkowej
siatkówki u pacjentów w oczach z druzami i drugim oku bez druz
na tarczy nerwu wzrokowego.
PSV – peak systolic velocity; EDV –
end systolic velocity; RI – resistivity index
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