Developing a contact probe for rodent fundus imaging in a
confocal scanning laser ophthalmoscope
Xiaoyun Jiang (江晓芸)
1
, Yichen Ding (丁翼晨)
1
, Wenyao Wang (王文耀)
2
,
Zhiyu Huang (黄智宇)
1
, Zhiru Wang (王志茹)
3,4
, Elie de Lestrange Anginieur
1
,
Yue Yu (俞 玥)
1
, Jun Li (李 军)
3
, Mingliang Pu (濮鸣亮)
2
, Qiushi Ren (任秋实)
1
,
and Changhui Li (李长辉)
1,
*
1
Department of Biomedical Engineering, Peking University, Beijing 100871, China
2
Department of Anatomy, School of Basic Medical Sciences, Peking University, Beijing 100191, Chi na
3
Laboratory Animal Center, Peking University, Beijing 100871, China
4
School of Public Health, Jilin University, Changchun 130012, China
*Corresponding author: chli@pku.edu.cn
Received November 15, 2015; accepted January 8, 2016; posted online February 22, 2016
Since significant ocular differences in both anatomical structure and optical properties exist between rodents and
humans, clinical imaging devices for human use are not suitable for use on rodents. In this study, we develop a
contact probe with a flexible surface that can closely fit the rodent cornea for fundus imaging with a confocal
scanning laser ophthalmoscope. Both Zemax simulation and in vivo fundus imaging demonstrate that this con-
tact probe can significantly improve both the imaging quality and the operational convenience.
OCIS codes: 170.0170, 170.4460, 170.5755, 170.2520.
doi: 10.3788/COL201614.031701.
Rodent animals, including rats and mice, are commonly
used in the study of fundus diseases
[1–6]
. As part of the
brain, the retina offers a unique opportunity for directly
visualizing vascular alterations associated with neurode-
generative disorders. Although ex vivo retinal histopathol-
ogy plays an important role in the study of the rodent
retina, it lacks important in vivo longitudinal observation
of the same animal. Therefore, high-resolution, noninva-
sive, and in vivo fundus imaging gains increasing atten-
tion. To date, several noninvasive fundus imaging
methods have been developed to image fundus blood
circulation and visual nerves
[7–11]
.
Among those noninvasive fundus imaging methods,
the confocal scanning laser ophthalmoscope (CSLO) is
a powerful tool
[12]
. By raster scanning a laser spot and
detecting backscattered or fluorescence light through a
pinhole
[13–15]
, it produces video rate, high-resolution, and
high-contrast retinal images. Over decades of develop-
ment several clinical CSLO products have been developed
such as the Zeiss scanning laser ophthalmoscope (SLO)
[16]
,
the Optos SLO
[17]
, and the Heidelberg Engineering Heidel-
berg Retina Tomograph (HRT), as well as the Heidelberg
Retina Angiography (HRA)
[18]
. The CSLO is now widely
adapted in the clinical diagnosis of various ocular diseases,
such as diabetic retinopathy (DR)
[10]
, age-related macular
degeneration (AMD)
[11]
, and glaucoma
[19]
.
However, those clinical CSLOs cannot be directly used
for rodent fundus imaging due to the large differences in
the ocular structure and optical properties between ro-
dents and humans. As shown in Table
1, rodent eyes have
shorter axial lengths, higher optical powers, larger refrac-
tive errors, and larger numerical apertures (NAs). In order
to image the fundus of rodents, two methods have been
implemented. One is to use additional lenses and a
customized contact lens [such as the rigid gas permeable
contact lens (RGPCL)
[20]
] for the aforementioned clinical
CSLO instruments
[12]
. The other is to cover the cornea
with a plano–concave glass lens and image the eye under
the confocal microscope
[21]
. However, neither of these
methods is convenient for the imaging of small rodents’
eyes by using either of these two methods. Unlike humans,
who can observe a guiding light to temporally fix the eye
position, rats or mice under anesthesia will automatically
move their eyes during imaging, making it difficult to
maintain good alignment in a clinical CSLO system. In
addition, it is challen ging to fix small contact lenses on
small rodent eyes, especially for small mouse eyes. For
the second method, the very limited working space in a
commercial confocal microscope also increases the diffi-
culty of operation. In this study, we developed a flexible
contact probe. This contact probe not only helps to fix the
eye to maintain the alignment in the CSLO system, but
also significantly reduces optical aberrations, leading to
high-quality fundus images.
Table 1. Ocular Parameters for Human, Rat, and Mouse
Eyes
[22]
Average
axial length
(mm)
Total
power
(D)
Average
refractive
error (D) NA
Human ∼23.5–24 ∼60 ∼0toþ1 ∼0.20
Rat ∼6.1 ∼300 þ5toþ15 ∼0.43
Mouse ∼3.3 ∼560 þ7toþ15 ∼0.49
COL 14(3), 031701(2016) CHINESE OPTICS LETTERS March 10, 2016
1671-7694/2016/031701(4) 031701-1 © 2016 Chinese Optics Letters