What is Pellucid Marginal Corneal Degeneration (PMD)? In short it is an eye disease very similar to Keratoconus in that it also causes thinning of the corneas. The difference between Keratoconus and Pellucid Marginal Corneal Degeneration is that PMD causes a crescent shaped band of thinning in the lower region of the eye, while the central cornea is usually of a normal thickness; as well as the cornea appearing transparent in PMD . There is a third disease called Keratoglobus that like the previous two also causes corneal thinning (more about this disease will be discussed in a future post).
Now you may ask if there is an actual difference between Keratoconus and PMD and Keratoglobus or if the three diseases are the same. The answer is that doctors are not sure either. They do not know if the three eye diseases are different diseases, or just different phenotypic (expression) variations of one disease.
Some of the different signs of PMD may include drastically reduced uncorrected visual acuity that usually cannot be improved with glasses (usually for astigmatism), roughly normal pinhole visual acuity, and refraction/keratometry that shows against the rule astigmatism (where the astigmatism on a corneal topography is seen horizontally).
Patients are also commonly asymptomatic except for the gradual worsening of vision that is unaided by glasses. The clinical diagnosis for PMD is the same as Keratoconus where the patient is examined by doctor on a slit lamp microscope and checked with patient’s history and supported by corneal topography & pachymetry.
We talked last time about getting screened for Keratoconus and the importance of early diagnosis. Today let’s talk about what to expect after the cross linking procedure has finished. Immediately after the UV-A light part of the surgery is over, a bandage contact lens will be put in the eye. This is done in order to protect the eye from dust,wind, et cetera. The second important reason is that it prevents the lid from rubbing the abraded cornea. If it is not put or falls off the lid like a windshield wiper can sweep healing cells and irritate the corneal nerves. A topical antibiotic, a non-steroidal anti-inflammatory (NSAID), 4 times a day for the first week.
A steroid will be prescribed once the epithelium has healed completely.The steroid being usually continued for another 1-3 weeks.
The Keratoconus surgeon will usually follow up with an appointment with in 24 to 48 hours as well as the week following surgery to make sure the eye is healing properly. If needed, after the epithelium is intact, the doctor would send the patient’s back to co-managing doctors for the remainder of their follow up care.
We all have to be careful during the post period to avoid touching or rubbing the eye. Some discomfort and watering of the eye is to be expected. If you develop sever pain or discharge contact doc immidiately.
New Scleral contacts or old soft lens may continued under the watchful eyes of the keratoconus doctor.
I am amazed when doctors claim that they have invented a procedure even though it has existed for years before. For example a surgeon claiming they invented cornea cross linking even though it was being performed in Europe for many years.
What gets me peeved is that some doctors use unproven technology and convince patients its the best. Snake oil sellers are an amusement till patients are harmed. So I decided to list some truths about keratoconous eye disease and cornea collagen cross linking.
The 10 Golden Truths about Cornea Cross Linking By Rajesh Khanna, MD a Keratoconus specialist.
- Keratoconus is a sight threatening disease. It involves the thinning and bulging of the cornea.
- Recent data suggests it may be more prevalent than 1 in 2000 people
- Cornea Collagen Cross Linking (CXL) is a proven and effective way to halt the progression of progressive keratoconus eye disease.
- CXL may be used to stabilize post lasik ectasia.
- Epithelium off Cornea cross linking is more effective than epi on cross linking.
- Conventional cornea cross linking – 3 mw for 30 minutes is the gold standard.
- Conventional cross linking is more effective than accelerated cross linking (18 mw or 30 mw). No other power setting is better.
- No studies have shown epi on cross linking to be more effective than conventional epi off cross linking.
- FDA has only approved Avedro KXL system/Photrexa for treatment of progressive keratoconus. No other system nor riboflavin compound has passed that litmus test.
- Avedro KXL/ Photrexa which treats at 3mw is currently safer and more effective than other currently available epi on choices in Los Angeles
I would invite comments by optometrists, ophthalmologists and peers especially keratoeonus experts.
Avedro KXL system in the hands of an experienced Keratoconus surgeon following FDA protocols would be safer than an unproven experimental epi on technology. We therefore offer Avedro cornea collagen cross linking with the FDA approved protocol.
We have been talking about the advantages of epithelium off cross linking. This from of cross linking has shown to work in numerous studies across the world.
But are all delivery methods the same? Certain machines hope the patient keeps looking at the UV light. Have you tried staring at something for 30 minutes. As a kid you may have played the stare off game. Its tough to do it especially in Los Angeles with the dry weather.
The solution in this fight against keratoconus is to involve a pupil tracker. In the above video you will see it in action. If the eye moves away from the light, the UV delivery and timer will stop. You can set how much movement you are willing to allow.
This increases the safety. One can definitely know that 30 minutes was delivered. It can avoid a situation where a fidgety patients moves and receives only 20 minutes of the radiation. Increasing safety also relaxes the patients. Most of the people requiring this intervention against Keratoconus eye disease are teenagers. Pupil tracking rocks.
Keratoconus progression can be halted by corneal collagen cross linking has been established. We thank all our patients who believed and participated in the trials. Now the hot question is which is better- to remove epithelium or to leave it alone.The debate has recently become intense. Various specialists have filed trade marks, patents or invested in a particular technology. Sometimes their opinions seem biased. So where do we turn to if we want to know the true answer?
How about the FDA? They are experts at looking at the data and known for they unbiased opinion. They have the interest of American patients in mind.
They analyzed lot of safety data. Here is what they have approved in USA
Epi off cornea cross linking
So that means so far Epi off is better than epi on or it’s variations like c3R
The epithelium interferes in the seepage of riboflavin i the cornea. It also hinders the uniform transmission of uvA . Therefore it a good idea to remove it
Some may disagree and say FDA process is tedious and hence Epi on is still stuck somewhere. We can than turn to peer reviewed journals. No published study has ever shown that Epi on crosslinking is better than Epi off.
Multiple studies have shown that Epi on Cross linking is the current Gold Stsndard.
So we rest our case
Epi off cross linking is the procedure Keratoconus specialists recommend
Yes what we had been waiting for finally happened. Another arrow in fight against keratoconus . FDA looked at the safety and efficacy of riboflavin activated by uv A radiation in detail. They looked at the data submitted by Avedro. FDA said epithelium removed or epi off is a good option.
This means if you have been waiting to make your cornea stronger the time has arrived. It may also mean your insurance may cover part of the cost. So send your insurance card to our keratoconus center. You may also qualify for no interest 36 monthly payment plan.
Unfortunately they have not approved epi on or c3r and other variants. So invest your money in the technique FDA considers more safe and result oriented.
Come to our Beverley Hills center for keratoconus treatment and get an unbiased opinion.
In this study done in Ibaraki, Japan, keratoconus and cornea researchers wanted to see whether three-dimensional (3D) corneal and anterior segment optical coherence tomography (CAS-OCT) or a rotating Scheimpflug camera combined with a Placido topography system (Scheimpflug camera with topography) was better to study the cornea. They wanted to see how it would be best to detect the signs of early keratoconus disease. Their goal was to asses if normal eyes and forme fruste keratoconus could be separated based on that criteria. They found out that both systems worked equally good. Our own Los Angeles Keratoconus Expert feels an early cornea topography works equally good in the hands of an experienced keratoconus expert.