Category Archives: Ophthalmology (vision and eye diseases)

– How the eye works? : eye anatomy, myopia, hyperopia.
– Presbyopia.
– Glaucoma.

Trabeculectomy

Below is a narrated animation about trabeculectomy procedure for glaucoma. Click here to license this video on Alila Medical Media website.


Trabeculectomy, also called Filtration Surgery, is a surgical procedure performed for treatment of glaucoma. The treatment involves removing part of the trabecular meshwork and creating a new escape route for the aqueous humor. When successful, it allows the aqueous fluid to drain from the eye into an area ( called a bleb) underneath the conjunctiva where it is subsequently absorbed by the body’s circulatory system or filtered into tears.
Trabeculectomy with iridectomy

Fig. 1: Trabeculectomy (on top) compared to normal anatomy (bottom). Click on image to see it on Alila Medical Media website where the image is also available for licensing (together with other related images and videos).

 

 

 

 


In this procedure:

–          A conjunctival pocket is created and maybe treated with Mitomycin or other antimetabolites for a few minutes. These drugs are used to prevent scarring of the operation site. Scarring, if occurs, may clog the new drainage canal, and is therefore the major reason the procedure may fail.

–          A half thickness flap is then made in the sclera and is dissected all the way to the clear cornea. (step 1 in Fig.2)

–          A block of scleral tissue including part of the trabecular meshwork and Schlemm’s canal is then removed to make a hole into the anterior chamber of the eye. (step 2 in Fig. 2)

–          As the iris may plug up this hole from the inside, a piece of the iris maybe removed at this time. This is called iridectomy. (step 2 in Fig. 2)

–          The scleral flap is then sutured loosely back in place (step 3 in Fig. 2). These sutures can be released gradually during a couple of weeks after surgery. This allows adjustment of the aqueous flow in order to achieve target pressure and to avoid the complication of having a too low intraocular pressure.

–          The conjunctiva is sewn back in place to cover the area.
Trabeculectomy with iridectomy front view.

Fig. 2: Steps of Trabeculectomy procedure, anterior view. Click on image to see it on Alila Medical Media website where the image is also available for licensing (together with other related images and videos).

 

 

After surgery, aqueous humor drains into a filtering area called a “bleb” under the conjunctiva. Since the surgery is usually performed near the top of the eye, the bleb can easily be concealed behind the upper eyelid.

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Trabeculoplasty

Below is a narrated animation about ALT and SLT laser trabeculoplasty for glaucoma. Click here to license this video on Alila Medical Media website.

Trabeculoplasty – the Procedure

Trabeculoplasty is a laser treatment for primary open-angle glaucoma. The laser is used to treat the trabecular meshwork, through which the aqueous humor drains. In this procedure:
– The eye is numbed with eye drops.
–  A special laser lens is placed on the eye to help control the direction of the laser beams.
– The laser burns a small area in the trabecular meshwork, opening up the drainage canal.
– About 50 spots over 180 degrees of the meshwork circle are treated in one therapy.
Trabeculoplasty labeled.
Fig. 1: Laser Trabeculoplasty procedure. Click on image to see it on Alila Medical Media website where the image is also available for licensing (together with other related images and videos).

Argon Laser Trabeculoplasty (ALT) and Selective Laser Trabeculoplasty (SLT)

Argon Laser Trabeculoplasty (ALT) : The original laser trabeculoplasty procedure applies argon laser of 514-nm (nano meter) wavelength on half of the meshwork circle in one treatment. Although a second treatment can be performed on the other half of the circle, the procedure is generally not repeatable as it causes extensive scarring of the trabecular meshwork.
The newer technique – Selective Laser Trabeculoplasty or SLT – uses a solid-state (Nd:YAG) laser of 532-nm wavelength. The pulse energy of SLT is about 100 times lower than the traditional argon laser trabeculoplasty. SLT selectively targets pigmented cells while leaving the rest of the trabecular meshwork tissue intact. For this reason, it can be applied to 360 degrees of the meshwork in one treatment and is considered safe to be repeated.

How effective is it?

In term of efficiency, the two techniques return similar results in lowering intraocular pressure. Laser trabeculoplasty treatment is effective in about 75% of patients. The effect may take a few weeks to kick in and can last for several years. Along with pharmaceutical treatments, laser therapy is offered as first-line options for newly diagnosed primary open-angle glaucoma.

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Cataract and Cataract Surgery

Below is a narrated animation about cataract and surgical treatment. Click here to license this video on Alila Medical Media website.

What is Cataract?

A cataract is a clouding of the lens in the eye that affects vision.
The lens is a clear biconvex structure located behind the pupil and helps to focus light on the retina. The lens must be clear to let the light through for sharp vision.
Clouding of the lens reduces the amount of light that reaches the retina, causing blurred vision. The color of the lens also changes, adding a brownish tint to the image.
Eye disease - Cataract

Fig. 1: Clouding of the lens in cataract. Click on image to see it on Alila Medical Media website where the image is also available for licensing (together with other related images and videos).

Causes

– Aging : Cataract is most commonly related to aging. With time, proteins of the lens denature and clump together forming patches on the lens. These patches grow larger over time.

– Secondary cataracts develop as a result of other eye diseases such as glaucoma, or other health conditions such as diabetes.

– Radiation: Radiation such as X-rays or ultraviolet light, especially UVB (in the sunlight), can increase the risks of developing cataracts.

– Genetic: genetic make-up plays a significant role.

– Congenital cataracts: (rare) babies are born with cataracts, or develop them in early childhood, often in both eyes. This usually happens as part of a particular syndrome, or as a result of certain type of infection during pregnancy.

How Cataract is Treated?

Surgery is the most effective treatment for cataract. Surgery involves removing the cloudy lens and replacing it with an artificial lens. Cataract surgery is relatively simple and highly successful.
There are two main types of surgeries for cataract removal:

Phacoemulsification, or phaco is the most commonly performed. In this procedure:
– A small incision is made on the side of the cornea.
– An ultrasound probe is used to emulsify the cloudy lens which is then removed by suction.
– A plastic foldable lens, called an intraocular lens or IOL, is inserted to replace the natural lens.
Cataract surgery

Fig. 2: Phacoemulsification. Click on image to see it on Alila Medical Media website where the image is also available for licensing (together with other related images and videos).

 

 

 

Extracapsular cataract extraction: this procedure is performed for harder cataracts that cannot be readily emulsified. In this procedure, a larger incision is made and the cloudy lens is removed in one piece. After placement of the artificial lens, sutures will be required to close the incision.

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Glaucoma

Below is a narrated animation about glaucoma development and types of glaucoma. Click here to license this video and/or other eye and vision related videos on Alila Medical Media website.

Glaucoma is a group of eye diseases in which the optic nerve is damaged leading to irreversible loss of vision. In most cases, this damage is due to an increased pressure within the eye – elevated intraocular pressure.

How glaucoma develops


The eye produces a fluid called aqueous humor which is secreted by the ciliary body into the posterior chamber, a space between the iris and the lens. It then flows through the pupil into the anterior chamber between the iris and the cornea. From here, it is drained through a sponge-like structure located at the base of the iris called the trabecular meshwork and leaves the eye. In a healthy eye, the rate of secretion balances the rate of drainage.

In people with glaucoma, this drainage canal is partially or completely blocked. Fluid builds up in the chambers and this increases pressure within the eye. The pressure drives the lens back and presses on the vitreous body which in turn compresses and damages the blood vessels and nerve fibers running at the back of the eye. These damaged fibers result in patches of vision loss and if left untreated may lead to total blindness.

For eye anatomy basics click here.

Click here to see an animation of glaucoma progression on Alila Medical Media website where the video is also available for licensing.
Stages of glaucoma, a common eye disease
Fig. 1 : Development of glaucoma. Click on image to see a larger version on Alila Medical Media website where the image is also available for licensing.

 

 

 

 

 

 

 

Open-Angle Glaucoma vs. Angle-Closure Glaucoma


These are the two main types of glaucoma. The “angle” here refers to the corner between the cornea and the iris where the trabecular meshwork is located.

Primary Open-Angle or Chronic Open-Angle Glaucoma is the most common form of glaucoma accounting for about 90% of cases. This is caused by partial blockage of the drainage canal. The angle is “open”, meaning the entrance to the drain is clear, but the flow of aqueous humor is somewhat slow. The pressure builds up gradually in the eye over a long period of time. There is no pain and visual loss appears gradually, starting from peripheral vision, and may go on unnoticed until the central vision is affected. Progression of glaucoma can be stopped with medical treatments, but part of vision that is already lost can not be restored. This is why it’s very important to detect signs of glaucoma early with regular eye exams.

Closed-angle or Acute angle-closure glaucoma (AACG) is less common. This type of glaucoma is caused by a sudden and complete blockage of aqueous humor drainage. The pressure within the eye rises rapidly and may lead to total vision loss quickly. This is a medical emergency and requires immediate attention. Symptoms to watch out for: sudden severe pain inside and around the eye, redness, blurry vision, seeing halos around a light, some people may also feel headache, nausea.

Certain anatomical features of the eye make it easier for AACG to happen. These include: narrow drainage angle, shallow anterior chamber, thin and droopy iris, lens sitting too much forward. These features are often inherited and so AACG incidents are likely to run in the family.

Glaucoma closed angle vs open angle

Fig. 2 : Open angle vs closed angle glaucoma. Click on image to see a larger version on Alila Medical Media website where the image is also available for licensing.

 

 

 

 

Typically, this is what happens in AACG : the pupil is dilated (e.g. when looking in the dark) and the lens is stick to the back of the iris. This prevents the aqueous humor from flowing through the pupil into the anterior chamber (primary block). As the fluid accumulates in the posterior chamber it presses on the iris causing it to bulge outward and block the drainage angle (secondary block).

Other types of Glaucoma

Normal pressure glaucoma – Some people can get glaucoma (vision loss due to damaged optic nerve) without elevated intraocular pressure. This may be due to poor blood supply (e.g. damaged blood vessels in diseases such as diabetes) to the nerve fibers.

Secondary glaucoma – glaucoma develops as a result of trauma after eye injuries.

Congenital glaucoma – glaucoma that is present at birth.

Treatments

Progression of glaucoma can be halted or slowed down with medical treatments, but part of vision that is already lost can not be recovered. This is why it’s very important to detect signs of glaucoma early with regular eye exams.

– Eye drops that lower intraocular pressure and/or reduce fluid production.

– Laser treatments : Laser is used to burn part of the trabecular meshwork to improve fluid flow – laser trabeculoplasty. It can also be used to remove part of the ciliary body to reduce fluid secretion. For acute glaucoma, small holes can be made in the iris to relieve the primary block – laser iridotomy.

– Eye surgeries: a procedure called trabeculectomy is used to create a channel –  an alternative route – for aqueous fluid drainage. For acute glaucoma a procedure called  iridectomy may be performed to drill a hole in the iris. Canaloplasty is a newer, less invasive surgical procedure performed for treatment of open angle glaucoma. This procedure involves enlargement of the eye’s natural drainage canal.

In people with AACG, laser and surgical treatments may be performed for the other, still healthy eye as well to prevent future development of glaucoma.

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Presbyopia

Below is a narrated animation of the Near Vision of the Eye. Click here to license this video and other similar images/videos on Alila Medical Media website.

Presbyopia is a very common age-associated condition in which the eye loses the ability to adjust to near vision.

For information on eye anatomy other common defects click here.

How near vision is achieved?


When the eye is focused on a faraway object, light rays coming from the object are almost parallel and have no difficulty to converge on the retina (Fig. 1, upper panel).

When looking at a nearby object, light rays coming from the object are too divergent to come into focus on the retina without any help. In order to see nearby objects clearly, the eye has to make the following adjustments:

– Convergence of the two eyes – this is to make sure the object is focused on the same area of both retinas of the two eyes. Failure of doing so (e.g. when eye muscles are weak) would result in double vision.

– Constriction of pupil – this is to reduce spherical aberration. Spherical aberration occurs when light rays strike on the edge of a lens and produce blurriness. Constricted pupil allows light rays to enter the lens only at the center where they are best refracted.

– Accommodation of the lens – ciliary muscles contracted to make the lens thicker, more convex. This increases the optical power of the lens, it now can converge the light rays on the retina (Fig. 1, lower panel).

The near response of the eye
Fig. 1: The near response of the eye. Click on image to see a larger version on Alila Medical Media website where the image is also available for licensing.

 

 

 

 

 

Presbyopia and correction

With age, the lens loses its flexibility and becomes stiff. It can no longer change its shape to accommodate near vision. This results in prebyopia – inability to see nearby objects.

Prebyopia is corrected with convex lenses that converge the light rays slightly before they enter the eye (Fig. 2). However, as this is needed only for looking at close-range objects, bifocal lenses are usually recommended.
Eye condition :presbyopia
Fig. 2: Presbyopia and correction lenses. Click on image to see a larger version on Alila Medical Media website where the image is also available for licensing.

 

 

 

Presbyopia is not to be confused with hyperopia, a condition in which the eyeball is too short.

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How the eye works

Anatomy of the eye

Below is a narrated animation of eye anatomy and common defects. Click here  to license this video (and other related videos) on Alila Medical Media website.


The eyeball is roughly a sphere of about one inch in diameter. The main components of the eye include:

– The cornea – the transparent front part of the eye. The cornea refracts light and accounts for about two-thirds of the eye’s total focusing power.

– The iris – the pigmented part of the eye that makes up the eye color. The iris regulates the amount of light that enters the eye by adjusting the size of the pupil – an opening in the center of the iris.

– The crystalline lens – a clear biconvex structure located behind the pupil and helps to focus light further. The lens is capable of changing its shape to accommodate near vision.  

Eye anatomy labeled diagram
Fig. 1 : Anatomy of human eye. Click on image to see a larger version on Alila Medical Media website where the image is also available for licensing.

 

 

 

 

Light refracted by the cornea and the lens creates an image of the visual object on the retina. The retina is a light-sensitive tissue lining the inner surface of the eye. Within the retina, optical information is converted into neural action potentials which are then transmitted to the visual cortex of the brain through the optic nerve.

– The fovea (fovea centralis) is the (small) central area of the retina where the sharpest central vision is achievable.

Common eye defects

In the normal eye, light rays converge right on the retina. This results in sharp vision.
Myopia and hyperopia

Fig. 2 : Light focusing in normal vision (upper panel), hyperopia (middle panel) and myopia (lower panel). Click on image to see a larger version on Alila Medical Media website where the image is also available for licensing.

 

 

 

 

In myopia, or nearsightedness, a condition in which the eyeball is too long, light rays converge before they reach the retina. The focal plane is located in front of the retina resulting in blurry vision. This happens when the person is looking at faraway objects. Myopia is corrected with concave lenses which diverge the light rays slightly before they enter the eye (Fig. 2). 

In hyperopia, or farsightedness, a condition in which the eyeball is too short, light rays have not yet converged when they reach the retina. The focal plane is located behind the retina resulting in blurry vision. This happens when the person is looking at nearby objects. Hyperopia is corrected with convex lenses which converge the light rays slightly before they enter the eye (Fig.2).

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