Добавил:
Sekretar
kiopkiopkiop18@yandex.ru
t.me/Prokururor I Вовсе не секретарь, но почту проверяю
Опубликованный материал нарушает ваши авторские права? Сообщите нам.
Вуз:
Предмет:
Файл:Ординатура / Хирургия / Библиотека им академика М.И. Перельмана / Книга_103_библиотеки_им_акад_М_И_Перельмана
.pdf
354
ab
https://t.me/med1917
Fig. 27.10 Images of the retina captured under blue light and Sodium uorescein injected into blood (a) without and
(b) with a barrier lter into the imaging path
S. Pal
is presented by a continuous blue line in
Fig. 27.9a. It is ltered further with a low-pass
contrast, it is required that the boundaries of the
excitation and barrier lters are well separated.
lter, known as an excitation lter, with a cut-on
wavelength of around 500nm (blue dotted line in
Fig.27.9a). Some system uses an excitation lter
27.4.5 Image Sensors
in conjunction with a powerful white light source,
such as a halogen lamp, to produce the necessary
blue light beam for FA.Light scattered back from
the retina is ltered just before the sensor with a
long-pass lter, commonly known as a barrier lter, with a cut-off wavelength near 515 nm. A
bandpass lter can alternatively be used for this
purpose. Once illuminated with blue light, all
parts of the retina reect blue light towards imaging optics. Only the parts of the retina containing
blood (blood vessels or areas of blood spillage)
absorb blue and emit in the green region. Without
a barrier lter, the camera detects both green and
blue light returning from all parts of the retina
and captures a picture like Fig. 27.10a.
Fluorescein angiograph (Fig.27.10b) is then captured by blocking blue rays with a barrier lter.
Edmund Optics [34] offers a pair of excitation
and barrier lters, where an excitation lter has a
cut-on wavelength at 506nm, and a barrier lter
(a bandpass lter) has a lower cut-off at 513nm.
To prevent spillover, which could reduce image
The image sensor is the last but not the least
important part of the retinal camera. Two types of
sensors are commonly used; (1) charged couple
device (CCD) and (2) complementary metaloxide semiconductor (CMOS). Until the rst
decade of this century, CCDs were the preferred
digital sensor for retinal imaging and many other
scientic experiments. CCDs are generally sensors having larger pixel sizes, excellent sensitivity, higher dynamic range, and low noise
characteristics [35]. Higher sensitivity with lower
noise allows imaging at a lower light level suitable for fundus imaging. More importantly,
higher dynamic range facilitates imaging of the
bright optic disc and comparatively darker
peripheral region simultaneously with satisfactory details.
CMOS sensors remained far behind CCDs in
three qualities, as mentioned earlier, for many
years [36]. In the previous decade, COMOS was
increasingly recognized and used in many imag-
27 Paediatric Wide-Field Retinal Imaging
https://t.me/med1917
355
ing products, including medical devices and scientic experiments. (For example, in 2015,
SONY decided to discontinue CCD manufacturing and focus on CMOS technology).
Recent developments in the semiconductor
industry helped signicantly to improve the sensitivity, noise quality, and dynamic range of
CMOS sensors, which are now at par with
CCD. Additionally, CMOS consumes much
lower power than a CCD, which makes it suitable
for handheld, portable, and battery-operated systems. In CMOS, a pixel size of a few degrees
smaller than that of CCDs can be achieved, and
therefore a much higher megapixel sensor can be
produced in smaller sized devices. But one must
be careful about selecting cameras with very
small pixel sizes as this can increase the risk of
crosstalk. The possibility of erecting an ON-chip
processing unit with CMOS technology makes
the overall size of CMOS cameras much smaller
than a CCD camera. It also facilitates high-speed
readout and, subsequently faster frame rate.
The performance of any camera system
depends mainly on the judicial selection of the
sensor. A frame rate of at least 15 frames per second (FPS) is essential for handheld imaging of the
paediatric subject. A dynamic range close to
70 dB or more is suitable for capturing bright
optic disc and darker periphery with useful details.
Cameras with a signal-to-noise ratio (SNR) higher
than 40dB are desirable. Compared to colour fundus imaging, FA requires greater quantum efciency to capture generally weak uorescence.
27.5 Imaging Technique
Primary challenges in premature/infant screening
are accessibility, poor cooperation, and a shorter
time window for imaging. It is practically impossible to image a baby’s eyes in a supine position
with conventional tabletop devices. Conversely,
it is too early to make the newborn sit upright and
place the chin over the chinrest. A portable hand-
held device is very much necessary for paediatric
screening. A contact base operation is preferable
for non-cooperative subjects, despite potential
health risks like contamination or cornea scarring
on rare occasions. Moreover, a wide-angle camera facilitates capturing a larger portion of the
retina in a single image, reducing the screening
time. This section will mainly focus on imaging
techniques associated with the devices presented
in Table27.1.
Contact devices use sterile lubricant gel
between the contact lens and cornea to ensure
smooth movement while manoeuvring the
probe during the operation. Eye gel also creates
a continuous medium of refractive index close
to 1.4, which is between the corneal refractive
index of 1.33 and the refractive index of a glass,
commonly 1.5. It reduces Snell’s reection of
light at the corneal surface, which can create
glare/artefact on the nal image. A uniform
contact of the imager with the cornea ensures
continuity in the medium, reducing the risk of
air pocket formation and unwanted artefacts
due to reection.
It is comparatively easier to capture a maculacentric image. The main challenge is to capture
ora serrata that needs a tilt even with the device
having FoV as large as 150°. In imaging premature babies, it is advisable to use an eyelid speculum to create space for easy manoeuvring of the
imaging device, and occasionally, a depressor is
used to improve the visibility of the peripheral
region further (Fig.27.11).
Proper dilation of the pupil is essential for a
uniformly illuminated retinal image. An inappropriate dilation can lead to a central shadow on the
captured image by blocking the light rays near
the outer edge of the ring light (Fig.27.12).
FA is an invasive procedure and demands special attention. It is highly advisable to perform
FA near a life support system to tackle the rare
adverse effect of NaFl on the human body. Before
starting the procedure for FA, a colour fundus
image is generally taken to set an appropriate
356
ab
https://t.me/med1917
S. Pal
Fig. 27.11 (a)
Speculum (b) depressor
occasionally used for
ROP screening
ab
Fig. 27.12 Possible image artefacts in ROP images; (a) shadow due to undilated pupil and (b) reection observed due
to formation of air pockets inside lubricant gel (white arrow; images captured with the 3nethra neo-HD FA)
abc
Fig. 27.13 Progress dye into the blood after (a) 8.7 s, (b) 10.5 s, and (c) 14.3s after injecting the dye. (Camera: 3nethra
neo-HD FA)
focus for the subject. A 10% solution of Sodium
uorescein dye at 0.1ml per kg of baby’s weight
is generally injected intravenously, followed by
an isotonic saline ush [31]. In some situations,
oral NaFl dosing is used as an alternative. A timer
is started at the time of injection of the dye.
Software associated with the device attaches a
time stamp from the timer running at the time of
27 Paediatric Wide-Field Retinal Imaging
https://t.me/med1917
357
the image capture and saves it with the image.
Time stamps carry vital information as the contrast and characteristic of the image primarily
depends on the offset from the time of the shot.
The image in Fig. 27.13a is captured when the
dye reaches retinal blood vessels, and as a result,
arteries are lighter compared to other parts of the
retina. As time progresses, dye reaches other capillaries, and an image similar to Fig. 27.13c is
captured.
27.6 Clinical Application
Wide-eld imaging in the paediatric sector is
predominantly used for ROP screening. The
retina is imaged up to 100–130° in a single
click. The FoV can also be increased by montaging the images or using ultra-wide eld
imaging system. These help in documentation,
compare the retinopathy status between different follow-up visits, monitor the response to
treatment, training, and telescreening. Besides
better parental understanding of the disease’s
progression and consequently better cooperation, image-based counselling allows parents to
make decisions about their course of treatment
and supports that course of action in the event of
a medicolegal dispute. The imaging devices can
pick of subtle vascular changes which a busy
practitioner might miss while screening a large
number of patients with indirect ophthalmoscope. Image of mature retina without any signature of ROP are presented in Panel-1(a, b) of
Fig. 27.15. Whereas as mild tortuosity in the
blood vessels is noticed on the image presented
in Panel-1(c) of Fig.27.14, as an indication of
plus disease. Figure 27.14 also describes the
various states of ROP [8].
Stage-1 ROP (Fig. 27.14, Panel 2a). A thin
demarcation, relatively at, at the junction of vascular and avascular regions is seen.
Stage-2 ROP (Fig. 27.14, Panel 2b). The
demarcation line changes into a wider elevated
ridge. Isolated tufts of neovascular tissue on the
retinal surface, commonly known as popcorn,
may be seen posterior to the ridge in Stage-2
(white arrow, Panel 2c).
Stage-3 ROP (Fig. 27.14, Panel 3a). Extraretinal neovascular proliferation extends from the
ridge into the vitreous and is continuous, with the
posterior aspect of the ridge producing a ragged
appearance as proliferation progresses.
Stage-4 ROP (Fig.27.14, Panel 3b and c). It is
characterized by a partial retinal detachment that
spares or includes the fovea. Clinical signs of
retinal detachment include loss of ne detail in
the choroidal vasculature or the granular pigment
epithelium, a ground glass appearance compared
to the neighbouring connected retina, or both
(Fig.27.14, Panel 4a).
Stage-5 ROP (Fig.27.14, Panel 4b). A total
detachment is a rule.
Field of view is sometime extended beyond
the limit set by the imaging system by stitching
multiple images together, as presented in
Fig. 27.15. Figure 27.15a shows a montage of
four different colour fundus images having area
of overlapping. Three angiographs, with similar
time stamp, are stitched together and presented in
Fig.27.15b.
Besides ROP screening, wide-angle imaging
is also used to study retinoblastoma in infants
(Fig.27.16).
358
abc
https://t.me/med1917
abc
abc
S. Pal
ab
Fig. 27.14 Panel 1. (a)†, (b) Mature retina without ROP;
dichotomously branching of retinal blood vessels seen up
to the end of the retina imaged, and (c) plus disease, showing tortuosity in the blood vessels in Zone-II.Panel 2. (a)
Stage-1 with thin demarcation line in Zone-III. (b)†
Stage-2 Zone-II ROP showing a ridge, hyperacutely
branching retinal blood vessels, mild dilatation, and tortuosity. (c) Stage-2 ROP shows a thick and elevated demarcation line in Zone-III with popcorn lesion. Panel 3. (a)†
The right eye shows Stage-3 Zone-II ROP with plus; note
the nger like extensions from the posterior aspect of the
ridge representative of extra-retinal brovascular proliferation. (b)† The left eye showing Stage-4A with plus and
narrowing of the angle between the temporal retinal vascular arcades. There was a fractional retinal detachment
along the brovascular proliferation temporally, and (b)
Stage-4A in Zone-III on the temporal side of the left eye
with loss of choroidal detail on the extreme right of the
image. Panel 4. (a)† The left eye Stage-4B Cicatricle ROP
showing a retinal fold extending temporally from the optic
disc. The macula and temporal vascular arcades are
dragged within the retinal fold. (b)† Stage-5 ROP with
total closed funnel retinal detachment. †Captured at LV
Prasad Eye Institute, Bhubaneswar, India. (© Tapas R
Padhi, MD, with permission)
ab
ab
27 Paediatric Wide-Field Retinal Imaging
https://t.me/med1917
Fig. 27.15 Montage of
(a) colour fundus images
and (b) uorescein
angiographs. (a) shows
structure created by
photocoagulation at the
top of the image
Fig. 27.16 (a) Colour
fundus image (b)
angiograph of a subject
suffering from
retinoblastoma
359
27.7 Conclusion
Wide-angle cameras with trans-pupillary illumination are the preferred tools for paediatric screening.
The study on trans-pars-planar illumination will
continue to search for a potential alternative which
frees the pupil for imaging and helps extend FoV
beyond the current standard. Trans-pars-planar
illumination, as far as the author is aware, has not
yet been demonstrated for FA and may be an area
to explore. However, it may encounter difculties
due to the shorter penetration depth of blue light. A
transition from trans-pupillary lighting to a transpars-planar illumination system may occur soon,
whereas the imaging system may continue with its
current structure. The use of CMOS sensors for
retinal imaging is expected to increase after the
recent advancement in the respective eld.
Funding Nil.
Disclosure Forus Employee.
References
1. Owens WC, Owens EU. Retrolental broplasia in
premature infants. Am J Ophthalmol. 1949;32:1–21.
2. Reese AB, King MJ, Owens WC. Classication
of retrolental broplasia. Am J Ophthalmol.
1953;36(10):1333–5.
3. Patz A. Retrolental broplasia. Surv Ophthalmol.
1969;14(1):1–29.
4. Flynn JT, O’Grady GE, Herrera J, etal. Retrolental
broplasia: I.Clinical observations. Arch Ophthalmol.
1977;95(2):217–23.
5. Kushner BJ, Essner D, Cohen IJ, Flynn JT.Retrolental
broplasia. II. Pathologic correlation. Arch
Ophthalmol. 1977;95(1):29–38.
6. Kingham JD. Acute retrolental broplasia. Arch
Ophthalmol. 1977;95(1):39–47.
7. The Committee for the Classication of Retinopathy
of Prematurity. An international classication of
retinopathy of prematurity. Arch Ophthalmol.
1984;102(8):1130–4.
8. The Committee for the Classication of Retinopathy
of Prematurity. An international classication of
retinopathy of prematurity, Third edition. Arch
Ophthalmol. 2021;128(10):51–68.
9. Wang SK, Korot E, Zaidi M, etal. Modeling absolute zone size in retinopathy of prematurity in relation
360
https://t.me/med1917
S. Pal
to axial length. Sci Rep. 2022;12:4717. https://doi.
org/10.1038/s41598- 022- 08680- 5.
10. Toslak D, Chau F, Erol MK, etal. Trans-pars-planar
illumination enables a 200° ultra-wide eld pediatric
fundus camera for easy examination of the retina.
Biomed Opt Express. 2020;11:68–76.
11. Atkinson A, Mazo C. Imaged area of the retina.
https://www.freelists.org/archives/optimal/02- 2017/
pdf91WmMGLh6Q.pdf.
12. Prakalapakorn SG, Wallace DK, Freedman SF.Retinal
imaging in premature infants using the Pictor noncontact digital camera. J AAPOS. 2014;18(4):321–6.
13. Davitt BV, Wallace DK. Plus disease. Surv
Ophthalmol. 2009;54(6):663–70.
14. Vinekar A, Gilbert C, Dogra M, etal. The KIDROP
model of combining strategies for providing retinopathy of prematurity screening in underserved areas in
India using wide-eld imaging, tele-medicine, nonphysician graders and smart phone reporting. Indian
J Ophthalmol. 2014;62(1):41–9.
15. Vinekar A, Jayadev C, Mangalesh S, et al. Role of
tele-medicine in retinopathy of prematurity screening
in rural outreach centers in India—a report of 20,214
imaging sessions in the KIDROP program. Semin
Fetal Neonatal Med. 2015;20(5):335–45.
16. Ji MH, Zaidi M, Bodnar Z, etal. Effective eld of
view of wide-eld fundus photography in the Stanford
University Network for Diagnosis of Retinopathy of
Prematurity (SUNDROP). Sci Rep. 2022;12:19276.
https://doi.org/10.1038/s41598- 022- 22964- w.
17. Harris WF.Nodes and nodal points and lines in eyes
and other optical systems. Ophthalmic Physiol Opt.
2009;30(1):24–42.
18. Yao X, Toslak D, Son T, Ma J. Understanding the
relationship between visual-angle and eye-angle for
reliable determination of the eld-of-view in ultrawide eld fundus photography. Biomed Opt Express.
2021;12:6651–9.
19. DeHoog E, Schwiegerling J.Fundus camera systems:
a comparative analysis. Appl Opt. 2009;48:221–8.
20. Gullstrand A. New methods of reexless ophthalmoscopy. Berichte Deutsche Ophthalmologische
Gesellschaft. 1910;36:326.
21. Keeler R, Singh AD, Dua HS.Reecting on reections: Gullstrand’s large reex-free ophthalmoscope.
Br J Ophthalmol. 2010;94:826.
22. Kaschke M, Kaschke KH, Rill MS.Optical devices
in ophthalmology and optometry. Wiley-VCH; 2013.
23. Toslak D, Thapa D, Chen Y, et al. Trans-palpebral
illumination: an approach for wide-angle fundus photography without the need for pupil dilation. Opt Lett.
2016;41(12):2688–91.
24. Toslak D, Thapa D, Chen Y, etal. Wide-eld fundus
imaging with trans-palpebral illumination. Proc SPIE
Int Soc Opt Eng. 2017;10045:100451X. https://doi.
org/10.1117/12.2252491.
25. Wang B, Toslak D, Alam MN, et al. Contact-free
trans-pars-planar illumination enables snapshot fundus camera for nonmydriatic wide eld photography. Sci Rep. 2018;8:8768. https://doi.org/10.1038/
s41598- 018- 27112- x.
26. Laforest T, Künzi M, Kowalczuk L, etal. Transscleral
optical phase imaging of the human retina. Nat
Photonics. 2020;14(7):439–45.
27. Lingenfelder C, Koch F, Koelbl P, etal. Transscleral
LED illumination pen. Biomed Eng Lett.
2017;7:311–5.
28. Kölbl PS, Lindner C, Lingenfelder C, etal. An extraocular non-invasive transscleral LED-endoilluminator
for eye speculum integration. Graefes Arch Clin Exp
Ophthalmol. 2015;253:1529–35.
29. Pomerantzeff O, Govignon J.Design of wide-angle
ophthalmoscope. Arch Ophthalmol. 1971;80:420–4.
30. Pomerantzeff O. Equator-plus camera. Invest
Ophthalmol Vis Sc. 1975;14:401–6.
31. Lepore D, Molle F, Pagliara MM, etal. Atlas of uorescein angiographic ndings in eyes undergoing
laser for retinopathy of prematurity. Ophthalmology.
2011;118(1):168–75.
32. Chopdar A.Fundus uorescein angiography. Elsevier
Health Service; 1996.
33. Doughty MJ. pH dependent spectral properties of
sodium uorescein ophthalmic solutions revisited.
Ophthalmic Physiol Opt. 2010;30:167. https://doi.
org/10.1111/j.1475- 1313.2009.00703.x.
34. Fluorescence Filter Set. https://www.edmundoptics.
in/p/uorescence- lter- set- for- tc- uorescein/21528/.
35. Durini D.High performance silicon imaging: fundamentals and applications of CMOS and CCD sensors.
Elsevier Science; 2019.
36. Bigas M, Cabruja E, Forest J, Salvi J. Review of
CMOS imagers. Microelectron J. 2006;37(5):433–51.
Optical Coherence Tomography
https://t.me/med1917
andOptical Coherence
Tomography-Angiography
NirojKumarSahoo , PriyaR.Chandrasekaran ,
NinanJacob , andGemmyCheung
28
28.1 Introduction
28.1.1 Principles ofOptical
Coherence Tomography (OCT)
The fundamental principle behind OCT imaging
is light interference. The basic mechanism of an
OCT can be described with the help of a Michelson
interferometer, as described below. The light from
a low coherence (high bandwidth) source is split
into two paths by a coupler, directing it along two
separate arms of the interferometer, the sample
arm, and the reference arm. As the light exits
either arm, it is passed through lenses and mirrors to control its shape, depth of focus, intensity,
etc. A reference mirror reects the light back into
the reference arm, and it returns along the same
path it came on, whereas the light in the sample
arm is backscattered by the sample of interest.
The returning light from both arms recombines at
the coupler and generates an interference pattern
recorded by the detector. The sample beam has to
N. K. Sahoo
Kode Venkatadri Chowdary Campus, LV Prasad Eye
Institute, Vijayawada, India
P. R. Chandrasekaran · G. Cheung (*)
Singapore National Eye Centre, Singapore Eye
Research Institute, Singapore, Singapore
e-mail: Gemmy.cheung.c.m@singhealth.com.sg
N. Jacob
Anant Bajaj Retina Institute, Kode Venkatadri
Chowdary Campus, L V Prasad Eye Institute,
Vijayawada, India
be moved across the sample to record an A scan at
each point, which can be combined to generate an
OCT image or a B scan. For a given wavelength,
the axial resolution is based on the bandwidth,
whereas the lateral resolution is limited by the
diffraction caused by the pupil and the minimum
spot size of the focused probing beam. [1].
28.1.2 OCT Systems (Table28.1)
The early time-domain (TD)-OCT technology is
based on scanning reference delay. This setup is limited by the time constraints and mechanical inertia
imposed by the moving reference mirror, limiting
the number of A scans to a few thousand per second.
Most systems in clinical use now are Fourier-domain
(FD)-OCT [Fig. 28.1]. The key difference between
the two is that the FD-OCT uses a static reference
mirror, which facilitates higher data acquisition
speeds. By performing an inverse Fourier transform,
the acquired wavenumber- dependent data is transformed into axial scan information. FD-OCT imaging includes spectral-domain OCT (SD-OCT) and
swept-source OCT (SS-OCT). [1].
28.1.2.1 SD-OCT
Spectrometer-based FD-OCT uses a diffraction
grating element to spatially separate the different
wavelength contributions into a line image
recorded by a high-speed charge-coupled device
(CCD) line camera. A Fourier transform is
© The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd. 2024
T. Das, P. Satgunam (eds.), Ophthalmic Diagnostics, https://doi.org/10.1007/978-981-97-0138-4_28
361
362
ac
https://t.me/med1917
Table 28.1 Comparison of various OCT systems
TD-OCT SD-OCT SS-OCT
Fixed reference mirror
Features
Wavelength 810nm 840nm 1052nm
A scan/s 512 scans/s 50,000 scans/s 100,000 scans/s
Axial resolution
Lateral resolution
Artifacts More Less Less
Length of line scan 6mm Up to 9mm Up to 12mm
Range of imaging Vitreoretinal interface to
Movable reference mirror
10μm 8μm 6μm
20μm 20μm 20μm
retinal pigment epithelium
Spectrometer Tunable laser light source
Posterior cortical vitreous to
sclera using enhanced depth
imaging mode
Posterior cortical vitreous
to sclera
N. K. Sahoo et al.
b
Fig. 28.1 Fourier-domain optical coherence tomography
(OCT). (a) Schematic diagram of a spectral-domain
OCT.It uses a spectrometer for the detection of interference signals. (b) Schematic diagram of a swept-source
OCT.It uses a rapid wavelength-swept light source and
performed on the spectrally resolved interference
pattern detected by the camera array to obtain the
A scan [1, 2].
balanced detection to detect interference signals. (c)
Example of signal detection for the three partial reectors.
Fourier transformation results in the production of three
images corresponding to the reectors. [CCD charge-
coupled device]
over a broad range of wavelengths [1, 2]. In
contrast to SD-OCT, SS-OCT uses a high-speed
complementary metal oxide semiconductor
(CMOS) camera and two parallel photodetectors.
28.1.2.2 SS-OCT
The broadband light source is replaced by a tunable laser rapidly sweeping a narrow line width
A long imaging range of nearly 7.5mm allows a
better view of the vitreoretinal interface and the
choroid in a single frame [1, 2].
28 Optical Coherence Tomography andOptical Coherence Tomography-Angiography
https://t.me/med1917
363
28.1.3 Scanning Protocols
andQuantitative Measures:
(Tables 28.2 and28.3)
Various pre-set acquisition protocols are available on most commercial OCT instruments.
These differ in the area covered, the distance
between adjacent scans, the number of scans
averaged at each location, and the orientation of
scans. Understanding these will ensure that the
most appropriate protocol is used for the pathology being evaluated. Most commercial instru-
Table 28.2 OCT scanning protocols and measurements
1. Macular cube scan
A macular cube scan or a three-dimensional (3D) scan
consists of a number of horizontal line scans
composed of a 6mm x 6mm, 7mm x 7mm square
grid, or a 12mm x 9mm rectangular grid. It generates
a 3D view of the image, which can be subject to
complex analysis
2. Radial scan
The radial scan consists of 6–12 line scans arranged at
equal angles with a common axis. By coinciding with
the common axis with the fovea, the relationship of
the lesion with the fovea can be ascertained
ments also provide the user with basic software
which supports retinal layer segmentation and
quantitative assessments such as retinal thickness. Since the boundaries used for quantication
differ between instruments, quantitative values
such as central retinal thickness must be converted before comparing the instruments. As scan
speed increases, dense volume scans can be
acquired, which can, in turn, be used to generate
en face images. In enhanced depth imaging
(EDI)-mode, the instrument is purposefully displaced to image the deeper layers. Since the
3. Raster scan
A raster scan consists of a series of parallel line scans
that can be oriented at any angle and has a high
resolution. The length, angle, and spacing between the
lines can be adjusted to acquire the best view of the
area of interest
Center point The intersection of the six radial scans of the fast macular
thickness protocol of the OCT
Central subeld Circular area of diameter 1mm centered around the
center point. A total of 128 thickness measurements are
made in this circular area in the fast macula protocol
Center point thickness The average thickness values for the six radial scans at
their point of intersection
Central subeld mean thickness The mean value of the 128 thickness values obtained in
the central subeld
Retinal thickness
Subfoveal choroidal thickness
Value in μm of the distance between the OCT layers
assumed to be the RPE and the internal limiting
membrane
Value in μm of the distance from the outer edge of the
hyperreective line corresponding to the retinal pigment
epithelium to the inner surface of the sclera
Соседние файлы в папке Библиотека им академика М.И. Перельмана