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Файл:Ординатура / Хирургия / Библиотека им академика М.И. Перельмана / Книга_145_библиотеки_им_акад_М_И_Перельмана
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Fig. (4). Retinal fundus camera.
Fundus photography can include additional techniques such as fluorescein and
indocyanine green angiography, provided that appropriate filters are used. The
image-forming optics of the fundus camera direct the necessary light to illuminate
the fundus in an axial manner. The optical device of the camera projects a ring of
light from the internal strobe through the dilated pupil, effectively separating
incoming and outgoing illumination. The outer pupil is illuminated by the ring of
light, which reflects off the eye, and the central part of the ring allows light to
pass through the pupil. This light then passes through the lenses of the fundus
camera, creating a film plane view of the fundus [25].
Advantages
●
Images can be captured and stored which can be used at later times.
●
Different filters and dyes are allowed for different types of test.
●
Dilation is not required therefore less invasive.
Disadvantages
●
Problem in observing anomalies as it lacks depth appreciation on images.
●
Unable to produce better three-dimensional images and images are not very
clear.
Fundus Fluorescein Angiography (FFA)
FFA, which stands for Fundus Fluorescein Angiography, is a diagnostic technique
used to study the vasculature of the retina. The name “FFA” can be broken down
as follows: “Fundus” corresponds to the retina, “Fluorescein” corresponds to the
dye (fluorescein solution) used, and “Angiography” refers to the study of blood
vessels. The FFA procedure relies on the principle of injecting a fluorescein
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solution and then photographing the retina to study the contrast report of the blood
vessels [26].
During the FFA procedure, ophthalmologists start by putting eye drops in the
patient's eye to dilate the pupil. Then, a yellow-colored fluorescein dye is injected
into a vein, typically in the arm. After a few seconds, the dye reaches the blood
vessels in the eye, causing them to shine brightly. A digital imaging system is
then used to capture digital pictures of the eye, providing ophthalmologists with
valuable information to manage and monitor eye disorders over time [27]. FFA is
particularly useful in tracking changes in eye diseases and identifying specific
treatment areas.
Advantages
●
The treatments have an almost 100 percent success rate, with only a few patients
out of hundreds of thousands experiencing critical or life-threatening effects.
Fluorescein dye treatment is considered very safe, with a low risk of side effects
such as nausea.
Disadvantages
●
The visualization of choroidal vasculature is challenging due to a limited view,
and the method is invasive as it involves the requirement of an injection.
Heidelberg Retinal Tomography (HRT)
Heidelberg Retinal Tomography (HRT) is a valuable diagnostic technique used
for thorough examination and documentation of the optic nerve head, which plays
a crucial role in diagnosing and treating glaucoma. Essentially, HRT is a
commercial term for confocal scanning laser ophthalmoscopy. By employing a
special laser, HRT captures three-dimensional images of the optic nerve and
surrounding retina. This technology allows for precise measurements of
topography on a pixel-by-pixel basis and the evaluation of various optic disc
parameters in a fast and reproducible manner.
During the HRT procedure, the system captures a series of deeper images until
reaching the desired depth. It acquires three images for each eye, all without the
need for dilating the pupils. A diode laser with a wavelength of 670 nm is utilized
for illumination, and a set of 32 confocal photos with 256 × 256 pixels is obtained
for analysis.
An updated version of HRT, known as HRT II, uses digital transformation to
generate frames of 384 × 384 pixels, further enhancing image resolution and
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diagnostic capabilities. This sophisticated imaging technology continues to be a
valuable tool in the diagnosis and management of glaucoma and other related eye
conditions.
Advantages
●
Pupil dilation is not necessary, as there is an extensive amount of normative data
available.
●
HRT acquires a three-dimensional images of the optic nerve head.
Disadvantages
●
HRT relies on the operator for contour marking and is specifically designed for
the optic nerve head.
●
It should be noted that the appearance of a blood vessel can be misleading in the
process.
Slit-Lamp Photography
Slit-lamp photography involves a specifically designed horizontally mounted
microscope to capture images of the eye’s structures. The microscope’s
illumination can be adjusted, ranging from a wide pattern to a narrow slit of light,
which gives the technique its name. A specific application of slit lamp
photography is Specular Micrograph, used to image the cells comprising the
corneal endothelium on the backside of the cornea. These images assist physicians
in evaluation the condition of the cornea. The technique relies on two types of
illumination systems: The Zeiss slit lamp bio microscope with a bottom-mounted
light source and the Haag Streit slit lamp bio microscope with a top-mounted light
source.
Advantages
●
●
Slit lamps are gaining popularity in the field of optometry. These systems
provide opthalmologists with a close and detailed view of the eyeball, enabling
them to identify subtle changes in corneal conditions, such as infections or
edema.
With the help of a slit lamp camera, eye care professionals can capture specific
photographs and videos using a high-resolution digital camera, allowing them to
closely monitor the eye’s condition. This capability encourages clinicians to
document parts or the entirety of the examination, as well as preserve still
photographs as visual records of their findings.
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Disadvantages
●
As the magnification increases, the depth of focus reduces, potentially causing
the image to become out of focus.
●
Capturing the best retina image while holding the lens by hand is challenging.
●
Taking fundus photographs on a slit-lamp without adapters can be very difficult.
The following Table 2 gives the details of various imaging equipment.
Table 2. Description of imaging equipment [49].
Machine/
Eye Imaging
Equipment
Digital retinal cameras
OCT
Scanning laser
ophthalmoscope
Photo slit-lamp
micrography
Corneal topography Orbscan 2
Optic nerve
head analyzer
External photography
Rostock corneal
module
Lenses/
System
Required
Topcon and
Zeiss
OCT Zeiss
Stratus, Cirrus
HRA2 from
Heidelberg
Engineering
Natural
crystalline lens
HRT3,
Heidelberg
Engineering
digital Nikon
SLR)
HRT Keratitis, Dry Eye
Features Application
Macular degeneration,
choroid disturbances,
and diabetic retinopathy,
lesions, hard and soft
exudates.
Age Macular
Degeneration,
Diabetic Retinopathy
Structural changes in
Glaucoma,
Dense Cataract
Cornea and anterior eye
assessment
Corneal diseases,
Irregular astigmatism,
Postoperative cataract
extraction
Glaucoma
Eye external structures
like cornea, lashes,
conjunctiva, eyelids, and
FFA, color fundus photography
Allows for cross-sectional imaging.
Macular and optic nerve head imaging
is the common application.
For fundus autofluorescence, FFA, and
ICG angiography.
The cornea, iris, conjunctiva, and lens
are examples of anterior eye structures
that can be photographed.
The cornea's thickness, refractive
power, and shape are all measured.
For accurate imaging of the optic nerve
head. People suffering from glaucoma
or those suspected of having glaucoma
should use this medication.
Eyelids and other facial structures can
be photographed using this technique.
sclera
All corneal layers are magnified at high
magnification. Allows for the counting
of endothelial cells.
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EYE DISEASES
Various sorts of eye disorders like Diabetic Retinopathy, Diabetic Macular
Edema, Age-Related Macular Degeneration, glaucoma, and cataract are taken into
consideration along with their symptoms and risk factors (Table 3). Additionally,
a review of the relevant literature is conducted to understand the timely detection
of abnormalities and determine which techniques yield more effective results.
Table 3. Description of different eye diseases along with their causes risk and symptoms.
Diseases
Types
Cataract
Glaucoma
Retinal
Detachment
Diabetic
Retinopathy
(DR)
Causes
Malformation
Congenital factors
Aging
Inflammation
Trauma
Overuse of steroids
dilating eye drops.
Poor or reduced blood
flow to your optic
nerve.
Shrinkage of vitreous
Inflammatory
disorder
Prolonged high
blood glucose
levels
Microaneurysms
“floaters,” or spots
that appear across
your field of vision.
Darker area of
vision.
Symptoms and
Signs
Reduces visual acuity
Blurring of vision
Photosensitivity
Mild bilateral
discomfort (tired
eyes, foggy
vision)
Progressive loss of
visual field
Halos may be present
around
Light.
Redness in eye
Floaters shadow over
field
of vision blur
Obscure vision spots
in the eye
Aniseikonia
Ocular pain
Diagnosis
Direct and indirect
ophthalmoscopy
Penlight of slit
lamps
Ophthalmic
Examination
Tonometry
Optic nerve head
analyzer using
HRT3 machine
Ultrasound imaging
Retinal examination
Fluorescein
angiography
Optical coherence
tomography
Risk factors
– Diarrhoea
– Smoking
– Diabetes
– Smoking
– Drinking
– Alcohol
– Having high
internal eye
pressure (intraocular
pressure)
– Experiencing a
– glaucoma-related
family history.
– Diabetes, heart
disease, and high BP
are symptoms.
– Aging
– Extreme near-
sightedness Previous
eye surgery
– Diabetes lifetime - no
matter how long the
diabetes is, the more
likely you are to
acquire DR.
– High blood pressure.
– High cholesterol.
– Tobacco use.
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(Table 3) co nt.....
Diseases
Types
Diabetic
Macular
Edema
Age-Related
Macular
Degeneration
Causes
Blood sugar isn't
well-controlled
weakens the blood
vessels in the eyes.
Drusen- the
impression of tiny
yellow particles that
develop beneath the
retina
Symptoms and
Signs
Straight lines that
look wavy Blind
spots or patches
Loss of color
perception
Loss of detail of
the vision.
Visual distortions
Reduced either or
both eyes have
central vision
decreased colour
intensity or
sharpness
Face recognition
problem
metamorphopsia
Diagnosis
Fluorescein
angiography
Optical coherence
tomography
Fundus
Photography
Fluorescein
angiography
Optical coherence
tomography
Risk factors
– Hypertension
– Smoking
– Fluid Retention
– Hyperlipidemia
– Hypoalbuminemia
– Smoking.
– Overweight.
– Age
– Family history and
genetics
– Cardiovascular
disease
– Hypertension
Diabetic Retinopathy
Diabetic Retinopathy (DR) is a prevalent retinal disease and a leading cause of
vision loss among the global working-age population [28]. It is a condition that
affects the eyes due to untreated diabetes over an extended period. DR impacts
over 290 million individuals worldwide, including 69.2 million in India, and this
number is expected to rise significantly in the coming years. The condition arises
when blood vessels in the retina become swollen, leaky, or close off completely
[29]. Clinical features of DR include hemorrhages, microaneurysms (MA), and
exudates. Microaneurysms are seen in the inner nuclear and outer plexiform layers
and serve as an initial sign of DR, appearing as microscopic red dots. Intraretinal
haemorrhage occurs when these microaneurysms or capillaries become weakened
or ruptured [30]. Haemorrhages may take the form of dot and blot haemorrhages,
where dots are bright red and blots represent larger lesions. Another sign of DR is
the presence of exudates, which are classified as hard or soft exudates. Hard
exudates appear as yellow lipid deposits filled within the outer plexiform and
inner nuclear layers. Cotton wool spots or soft exudates are fluffy lesions in the
nerve fibre layer caused by capillary occlusion at the nerve fiber layer due to
infraction [31].
Diabetic retinopathy is categorized into two types: non-proliferative DR (NPDR)
and proliferative DR (PDR). NPDR is the initial stage characterized by swelling
of tiny blood vessels in the retina. NPDR is further classified into different levels
of severity, including mild (hard exudates), moderate (mild NPDR and cotton
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wool spots), severe (moderate NPDR with specific criteria), and very severe (a
combination of all features). On the other hand, PDR is a more advanced stage of
DR caused by neovascularization, where new blood vessels grow on the retina.
PDR is more serious and can cause significant damage to central and peripheral
vision, especially when new blood vessels form on the disc or elsewhere. Various
techniques are employed for the detection of diabetic retinopathy, and the
distinction between normal and diabetic retinopathy can be observed in Fig. (5).
Fig. (5). Comparison of normal retina with diabetic retinopathy retina [44].
Age-Related Macular Degeneration
Age-Related Macular Degeneration (AMD) is a condition that weakens the retina
and causes a blur in the central vision, significantly impacting daily activities such
as driving and reading. AMD primarily affects individuals aged 50 years or older,
and it specifically targets the macula, a crucial part of the eye [5]. AMD can be
classified into two types: dry AMD and wet AMD. Dry AMD occurs when areas
of the macula thin out with age, and small clumps of a protein called drusen
accumulate (this form is not curable). In contrast, wet AMD involves the growth
of abnormal blood vessels under the macula, which leads to fluid leakage through
the retina [32]. Fig. (6) depicts images of normal retinas, dry AMD, and wet
AMD, respectively.
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Fig. (6). (a) Normal Retina (b) Dry AMD (c) Wet AMD.
A notable study has indicated that the intake of certain vitamins and nutrients like
vitamins C and E, lutein, zeaxanthin, zinc, and copper, under the guidance of a
medical professional, could help slow down the progression of dry AMD [33].
Diabetic Macular Edema
Diabetic Macular Edema (DME) refers to the accumulation of fluid in the macula,
the region responsible for our most precise vision, and is caused by leaky blood
vessels [34]. DME typically develops as a complication of diabetic retinopathy
[35]. It can occur at any stage of diabetic retinopathy and may be triggered by any
condition that affects the blood vessels in the retina [37]. Additionally, Macular
Edema (ME) can also arise following eye surgery or as a consequence of
inflammatory eye diseases. Medical professionals use various diagnostic methods,
including a dilated eye exam and visual acuity tests, along with advanced imaging
techniques like Optical Coherence Tomography (OCT) and Fluorescein
Angiography (FA) to facilitate early detection and monitor the healing process of
the eye [22, 26].
Glaucoma
Glaucoma is an eye condition that primarily affects the optic nerve, also known as
the second cranial nerve, responsible for transmitting visual information from the
retina to the brain's vision centers through electrical impulses [37].
Embryologically, the optic nerve is derived from the forebrain outgrowth, making
it a part of the central nervous system (CNS) and consisting of CNS fiber tracts
[38]. Damage to the optic nerve typically occurs due to elevated intraocular
pressure, a condition known as high eye pressure.
Glaucoma is one of the leading causes of vision loss in individuals aged 60 and
above. Early detection of glaucoma is crucial as it can lead to blindness if left
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untreated. Employing proper detection techniques is essential for timely diagnosis
and appropriate treatment, which can help preserve the patient's vision. Various
techniques for glaucoma detection are illustrated in Fig. (7), while Fig. (8)
displays images of normal and glaucomatous retinas from the DRISHTI eye
dataset, with the region of interest (ROI) encircled. The outer dashed lines
indicate the optic disc and the inner dashed lines represent the optic cup.
Optic Disc Evaluation
Glaucoma
Diagnosis
Intraocular Pressure
Field Defects
Fig. (7). Different ways to diagnose.
Fig. (8). Images of Normal and Glaucomatous Retina respectively.
Glaucoma can be classified into several types, including primary open-angle
glaucoma, normal-tension glaucoma, closed-angle glaucoma, congenital
glaucoma, and secondary glaucoma [39]. A brief overview of these glaucoma
types is provided to enhance understanding.
According to the National Eye Institute (NEI) [40], open-angle glaucoma [41] is
the most prevalent type of glaucoma. It is a slow process in which the eye fails to
drain fluid properly, leading to an increase in eye pressure and subsequent damage
to the optic nerve. At its initial stages, open-angle glaucoma is painless and does
not cause noticeable changes in vision [42].
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Normal-tension glaucoma (NTG), also known as low-tension glaucoma, occurs
when the optic nerve is damaged despite the eye pressure remaining within the
normal range of 12-22 mm Hg. In this type of glaucoma, extreme sensitivity or
insufficient blood supply to the optic nerve can contribute to the condition.
Closed-angle glaucoma, also referred to as angle closure, narrow-angle, or acute
glaucoma, occurs when the iris is positioned very close to the drainage angle of
the eye, potentially obstructing it. This condition may present symptoms such as
severe eye pain, blurred vision, and nausea [39].
Congenital glaucoma results from poor eye development, leading to an increase in
intraocular pressure. It is caused by a genetic abnormality in the eye's angle
growth. Primary congenital glaucoma (PCG) is a critical condition that requires
immediate treatment. It typically affects infants, with parents often noticing
symptoms like photophobia (sensitivity to light), watery eyes (epiphora), and eye
closure (blepharospasm). This condition occurs in about one out of every 10,000
babies, and untreated cases can lead to childhood blindness.
Secondary glaucoma is often a consequence of other eye problems, negligence, or
the use of certain medications like corticosteroids. It can also be a rare side effect
of eye surgery.
Glaucoma is often referred to as “The Silent Thief of Sight” due to its
characteristic of causing no pain or symptoms, making it challenging to detect
without proper screening. Glaucoma computer-aided diagnosis is an emerging
area of medical imaging research [43].
Cataract
A cataract is a condition characterized by the development of a cloudy and thick
region in the eye's lens. This occurs when proteins in the eye clump together,
leading to the lens being unable to transmit clear images to the retina. The retina
plays a crucial role in converting the incoming light through the lens into signals,
which are then sent to the optic nerve and further transmitted to the brain. In a
clear lens, a cataract appears as an opaque or cloudy patch [44]. Depending on its
size and location, a cataract can obstruct normal vision.
The majority of cataracts are age-related, resulting from natural changes in the
eyes as a person ages [45]. The treatment for cataracts, regardless of their type,
involves surgery. Fig. (9) classifies retinal images as non-cataract, mild, moderate,
and severe cataract, respectively, providing a visual representation of the
condition's progression.
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