Tag: Peripheral vision

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Macular Degeneration Treatments

Implantable Telescope Treats Macular Degeneration

A new implantable intraocular telescope is now available for patients with endstage macular degeneration.  Patients with severe, bilateral (both eyes), loss of central vision caused by macular degeneration may now benefit from this tiny visual prosthesis.  The company, VisionCare, received FDA approval for CentraSight just last week.

How Does CentraSight Work?

The CentraSight implantable telescope is designed to be placed inside only one of your eyes.  This  “telescope,” a very strong intraocular lens, will magnify your central vision and project your central vision on a larger corresponding area of your retina.  The operative eye (the eye receiving the implant) will give you central vision.

Your other eye (not receiving the implant, but has lousy central vision) will remain the same, but give you peripheral vision.  You’ll have one eye for central and the other eye for peripheral vision.

The CentraSight Program

There are four steps;  Diagnosis, Screening, Implantation and Visual Training.

Diagnosis of Macular Degeneration

You must suffer from end-stage macular degeneration.  This can be either wet  or dry.  This must be confirmed by a retina specialist.  You must be stable and are no longer treatable with any medications such as anti-VEGF.

Candidate Screening

In addition to suffering from macular degeneration, other criteria include;

  • you are legally blind from macular degeneration
  • vision improves with external telescope simulator
  • your disease is irreversible, and no longer needing drug treatment
  • you have not had cataract surgery in the eye receiving the implant
  • you meet age, vision, eye and health requirements

Surgical Implantation

Once you are determined to be an excellent candidate, surgery will be performed very similar to cataract surgery.  It will be performed as an outpatient.  There are risks of eye surgery, but none too different than other intraocular surgery.

Visual Rehabilitation

After surgery, you’ll work with eye doctors and other low vision professionals to teach you to use your new intraocular telescope.

What Does This Mean? This is not a cure for the disease, but seems to be an excellent choice for those that have profound, permanent, visual loss.  This may potentially return visual function to those suffering from permanent loss of their central vision.  This could transform disability to impairment (another topic of discussion).

This means there is hope despite a pretty bleak path for those that have suffered significant loss of vision so far.

This means we should be watchful for more news as it develops and mindful that this is brand new.

It is exciting.

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Retinal Detachments

Retinal Detachments Can Blind

The natural history of a retinal detachment is blindness.  “Natural history” of a disease is the same as the usual outcome.  So, the usual outcome of a retinal detachment is complete blindness if eye surgery is not performed.

Retinal Detachments Only Become Larger

Retinal tears and holes cause a retinal detachment.  A small amount of fluid goes through the tear and gets underneath the retina causing the detachment.  With time the amount of fluid increases underneath the retina, and so, too, the size of the retinal detachment enlarges.

Always Lose Side Vision First

Because all tears and holes occur  in the peripheral retina (the portion of the retina giving us peripheral, or side, vision), you always lose your side, or peripheral vision, first.  As the detachment grows, the macula becomes detached and central vision will eventually be lost.  The initial goal of retinal detachment surgery is to fix the detachment before the central eyesight is affected.  By doing so, you minimize the risk of permanent loss of your central.

We usually try to operate within days.

When the macula (central portion of the retina responsible for reading, etc.) detaches, there can be permanent loss of eyesight despite successful surgery.

Rods and Cones

The retina is a laminated tissue.  It has several layers.  The rods and cones are underneath the top layer.  Loss of vision from a detachment is due to the physical separation of the rods and cones (aka photoreceptors) from the layer beneath them.

Retinal Detachment Surgery Prevents Blindness

There are several ways to fix a retinal detachment.  These are outlined in the overview of retinal detachments.  The goal of any retinal detachment surgery is to prevent blindness by reattaching the retina and, if possible, fix the eye before central vision is affected.

Longstanding Retinal Detachments

Chronic, or longstanding, retinal detachments are those unfortunate eyes that were never diagnosed or operated upon.  In general, eye surgery doesn’t always work to restore sight in these cases.  Permanent damage to the rods and cones occurs with time, and, despite success in reattaching the retina, vision does not return.

By chronic, I’d say conditions lasting months to years.

Losing the Eye Can Happen

In extreme cases of retinal detachments that never get repaired, the eye can start to die and shrink.  This condition, phthisis bulbi, occurs when the retina has not been attached for years (generally).  While it doesn’t always occur, it can be extremely disfiguring and can be a psychological nightmare.

What Does This Mean? Because the outcome of a retinal detachment is so grim, surgery is almost always recommended.  If the natural history is blindness, that is, the chance of going blind is 100%.  Though there are risks of eye surgery (blindness), the chances are small.  Thus, there really isn’t much to lose by operating.

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Retina

Your Retina Sees Backwards

Images on your retina are reversed.  Your retina “sees” everything backwards.  Your brain reorients you.  This image reversal is an adaptive advantage providing us with tremendous peripheral vision and the ability to view objects much larger than just a few millimeters.

Image Becomes Reversed

Everything is Upside Down…and Reversed

The simplest illustration of how your retina sees is shown above.  If you look at the eye chart, it gets turned upside down and reversed on the retina.

The image the retina “sees” is completely reversed.

The brain has to then reorient the image to allow you to see things “right side up” (and re-reversed).

Keyholes are Actually Pupils

Imagine you were looking through a keyhole trying to spy on someone inside a room.  As you are scanning the room, looking at the right side of the room to the left side of the room, you really need to move your head/body in the opposite direction.  This is the only way you can “see” the entire room.

The important point is that you can see the entire room through a very tiny hole.  In the eye, the analogous part is the pupil.

Images need to be reversed so we can see objects much larger than the size of our pupil and so that we may have peripheral vision.

The Washington Monument is Upside Down

Using an example of the Washington Monument may help a bit.  The image of the top of the monument must travel through your pupil and is focused on the inferior, or bottom, portion of your retina.  The image of the base of the monument is focused (along with all the flags) on the superior, or top, portion of your retina.

Light Rays Converge and Cross

What Does This Mean?

By reversing the image, we are able to visualize objects much larger than our eye.  If you look at the light rays, colored in blue (see above), you will notice that the distance between the light rays emanating from the top and the bottom of the chart get closer together as they approach the eye. At some point, they actually cross and reverse.

The image of the eye chart is getting smaller, too.  The light rays get smaller allowing the entire image to fit through the pupil and form a complete image on the retina, albeit upside down and reversed.

Without this reversal, we would have a very limited view of our world.  It would be similar to viewing the world through a drinking straw.

(Note:  For those of you who have had retinal detachment surgery involving gas injection, or macular hole surgery with gas or an intravitreal injection with an air bubble, this explains why the “gas/air” appears toward the bottom of your vision when looking straight ahead.  With your head erect, the gas rises to the top of your eye, giving you the impression that the gas is on the floor,)

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