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Saturday
Jul022011

cone dystrophy

Due to her concerns never being met, this particular patient had been bouncing around from doc to doc, with generalized vision complaints, i.e. not seeing well, etc.  She was in her mid to late fifties when symptoms began.  

As can be common with cone dystrophy, dilated fundus evaluation tends to look perfectly normal.  Upon my examination of her, there were enough other "scapegoats" to blame slightly decreased and fluctuating vision on.  The patient had extremely dry eyes and had a surgical history for radial keratotomy.  Fundus evaluations always looked great.  We tried several refractive solutions, rigid gas permeable contact lenses for example, that would work for awhile, and then not.

In spite of me never truly having an answer for her chief complaint, this patient stuck with me over several visits.  Ultimately, due to her own research, we decided to send her on for further testing with a retinologist.  The diagnosis was again missed, due to all findings appearing "normal."  She then went to another retinologist in another state where the diagnosis was eventually confirmed.  

What's interesting here is that I did receive a spectral domain OCT in office during this time.  And when I did get a chance to examine her again, not long after her 2nd retinologist visit, I decided to run a macular grid scan.  The results were astounding.

As a control, below are 2 scans of a normal patient that was actually referenced in an earlier blog entry as a "normal patient" video.

One in b & w, normal patient:

and one in color, normal patient:

 

These are 5 separate HD macular scans that image the entire macula from our patient with cone dystrophy.  These patient scans can be enlarged by clicking on the image, they will open in a new window.

scan 1:  (click image to enlarge)

 

scan 2:  (click image to enlarge)

 

scan 3:  (click image to enlarge)

 

scan 4:  (click image to enlarge)

 

scan 5:  (click image to enlarge)

Some commentary.  Note the scans are scanning sections of the macula.  The fovea, or most central part of the macula, is the middle scan or scan #3.  This is undeniably the most important anatomical point of the macula.  This contains the fovea, within the foveal pit, and has the most dense packing of cone cells.  This is where our 20/20 or better, visual acuity comes from.  

Scan 1:  You can see some disruption of the lower layers of the retina, but this is subtle, and could easily be missed by a technician, or attributed to a "low signal" scan.  

Scan 2:  Enlarge this scan by clicking on the picture above, and you will see more lower retinal layer "disruption,"  still somewhat subtle.

scan 3:  central macula.  At this point, one can plainly see something is amiss.  The lowest, hyper reflective layer in the scan is the RPE layer.  It is intact.  That is where normal anatomy ends.  In cone dystrophy, the outer nuclear layer of the cones can completely disappear.  

For this scan, one could say that the photoreceptor outer segment and RPE complex are gone in areas.  There are some areas where it is still there, but mottled or inconsistent.  There is an anatomical feature in the scan that runs directly above this portion that is called the inner segment/outer segment photoreceptor junction.  It has also been referred to in peer reviewed journals as the PIL, or photoreceptor integrity layer.  It is missing in some areas, and "beat up" in others.  There is also something called the PIL hump, where the cone cells are actually more highly developed and "longer" in the foveal area: this is normal and is a good sign.  Check the normal scan above to see this.  The hump is diminished, if not present at all, in this cone dystrophy scan.

scan 4:  extensive photoreceptor integrity loss, though less than that of scan 3.

scan 5:  looks like relatively normal retina.

Here's the graphical overlay map of her macular thickness.  It's colored blue due to the unit determining that her macular thickness is far below others her age, when compared to the normative database.

 Here is a look at the 3D manipulation tool the Cirrus offers, of this cone dystrophy patient:

 

 

 

 This scan is part of the advanced imaging tools.  Skip ahead to about the 38 second mark.  (The defect actually starts at the :57 second mark.)  You can actually see the cone outer segment defect as the scanning line passes through the area.  It is a remarkable view of the macula in a top down view.

Keep in mind all of the above data was achieved with a single scan that took around 3 seconds.

 

Just for kicks, have a look at how the older imagers used to look.  Many of these are still in use today, due to the large price tag of the newer units.

 

These older scans are no fun to view, due to the low rez, but do still have some clinical usefulness.

Cone dystrophy is difficult for general eyecare practitioners to diagnose, but HD or spectral domain OCT can sort it out rather quickly.  Ultimately, all retinologists would prefer to have an ERG as well as a fluorescein angiography to have a definitive diagnosis.  Although, I'm confident OCT imaging will have a much larger role in detection of this rare disorder.  

Family history, color vision testing, and genetic research (family history) can aid in this diagnosis as well.


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