Wednesday
Dec012010

Macular holes

A macular hole is a break in the central portion of the human retina.  Significant visual disturbance usually results.  In my experience, observant patients will come in complaining of a "hole" in their vision that they can not see through or around and that moves with gaze changes.  As with most medical conditions, this  can run the gamut as far as presentation and severity. 

Mostly, macular holes develop secondary to vitreal traction of some type.  With the aging process, the vitreous convolutes or degenerates.  As the back part of the vitreous, called the posterior hyaloid face, begins to separate from the retina, that open space facilitates development of something called an epiretinal membrane.  This membrane is a membrane secondary to aging in general and PVD, or posterior vitreal detachment.  An ERM, or epiretinal membrane, is made up of various inflammatory tissue such as proteins and leucocytes.  This is a non-uniform membrane that causes nasty problems for the top layer of the retina and will pull and distort the retina in various ways, invariably causing visual disturbance.

The Cirrus in our office can really show a high level detail for these.  Previously, to pick up on ERM's with "naked eye" examination, all the physician really sees is what appears to be cellophane wrinkling on top of the macula/retina.  It can be quite subtle at times.  But as you can see from the photos below, first a normal HD OCT scan, and 2nd an ERM, retinal distortion is quite obvious.  ERM's really are destructive to the underlying tissue as shown.

 So an ERM ultimately being the cause of a macular hole in most cases, lead to a macular hole staging/naming system.  It's called the Gass classifications.

Stage 1: the foveal pit/depression begins to be more difficult to see, and a small cyst forms below the retinal surface.

Stage 2:  Partial inner retinal breaks can be seen with a lid or operculum adhering to the sides of the hole.

Stage 3:  The lid (operculum) no longer adheres to the retina.  Now is when the physician will start to see retinal edema.

Stage 4:  Hole becomes full thickness. 

Treatment is done by a retinal surgeon and comes in the form of a vitrectomy/membrane peel.  This treatment has much better prognosis now than in the past with improving techniques, although the process is still no fun for the patient.  Vitrectomy is still a quite invasive surgery and should be respected as such.  We will discuss this more on a future post. 

 

Saturday
Oct162010

On plaquenil?

If you are a patient taking plaquenil (hydroxychloroquine) for rheumatoid arthritis, then you should have a dilated eye examination annually at minimum and possibly more frequently based on the duration you have taken the drug and the dosage.  You should be examined by a physician who is familiar with the toxicity that is associated with anti-malarial drugs. 

I recommend a 512 x 128 macular cube scan with the Cirrus HD OCT at my office for all patients undergoing hydroxychloroquine treatment.  Also a visual field test, or automated perimetry, is to be performed with emphasis on the macula.  We perform a threshold 10-2 with a Zeiss Humphrey Matrix perimeter.  Keep in mind smaller people (those with a lean body weight of less than 135 lbs) are more at risk for the toxicity.  The toxicity has a drug to body weight correlation.  So the smaller the stature of the person, the higher the theoretical risk. 

The big issue here is the drug has the potential to cause irreversible retinal damage if allowed to progress.  It is believed that if early macular changes are caught and the drug is discontinued, that the toxicity that has occurred would reverse itself.  (To my knowledge, there are no clinical trials that have demonstrated this to be true.)  Clinicians will see the loss of a foveal light reflex and granular pigmentation of the macular area.  We were taught in school to call this "mottling,"  in the sense of aging metal. 

If left to progress, however, circular zones of RPE disruption, alternating hyper and hypo pigmented areas will form.  Stopping the medication at this point will not have a "reversal" effect.

Luckily, this is not an issue for most patients.  I have seen estimates in the literature anywhere from 1% to 3% of total patients taking the drug ever go on to develop an associated maculopathy.  This can be a scary drug for those of us in the eyecare field due to the "permanence" of the damage if a patient is not compliant with regular care.  I am starting to recommend to patients, who are open to the idea, of being seen every 6 months for evaluation. The new Cirrus imaging unit we have gives a powerful high definition view of the macula, penetrating and imaging all 10 layers of the retina.  This is an invaluable tool for more peace of mind for patient and physician between visits.

However, all of this considered, Plaquenil is a necessary med for physicians looking to manage patient's symptoms associated with Rheumatoid arthritis.  I have had many patients tell me that the drug is the only thing that has helped them re-gain some of their life back from this debilitating disease. 

Other drugs such as Prednisone and certain anti-depressants have been implicated in causing glaucoma or optic nerve damage.  I will highlight some of these on a future post.  Feel free to leave any comments/questions in the comment section.

Sunday
Sep262010

OCT primer

OCT, or ocular coherence tomography, has gone through a few iterations since its inception.  For eye imaging, the mainstay has been the time domain method.  With a high res scan, the time domain method can produce about 1 and 1/2 B scans per second.  This equals around 400 A scans per second.

With spectral domain HD imaging, you go from a peak of 1.5 scans/sec with time domain to almost 500 scans/sec with spectral domain.  This equals around 27,000 A scans per second.  Obviously with the new method, extremely detailed retinal maps can be obtained in a much faster timespan.

SD OCT imaging offers many advantages in terms of patient care.  This imaging technique does not utilize "ionizing radiation" as other medical imaging techniques such as MRI or CT scans.  While not a perfect analogy, this technique is more akin to ultrasound as far as its safety protocol.  No radiation or X-Ray aprons necessary...whew!

Improvements from a technical standpoint (firmware update for the Cirrus HD OCT), have allowed interesting developments in glaucoma management care, and are superior to what has been previously available from other manufacturers. 

To be clear, this is much more than a "fundus photo" that many local eye doctors offer.  This is a high definition imaging device that offers countless advantages over a simple digital camera image. 

more to come...

 

 

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