Pellucid Marginal Corneal Degeneration or Keratoconus – That is the question

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.    

 

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Importance of Screening & Early Diagnosis

We have been talking about how cross linking can help patients suffering from Keratoconus. We may’ve a bigger issue to confront. What about before cross linking, what about the diagnosis and screening of Keratoconus. It is important for patients with Keratoconus to be screened as early as possible. The best results with corneal cross linking eye procedure are obtained when the disorder is arrested early. As the disease progresses the loss of visual acuity increases dramatically, and the earlier it is detected the easier and higher possibility that full visual acuity returns. You may want to read some frequently asked questions on keratoconus and cross linking.

Some symptoms of Keratoconus are blurry vision, increased light sensitivity, eye strain, headaches/general eye pain, eye irritation/excessive eye rubbing. A caution should be noted that these symptoms can also be indications of other eye problems. That is why it i important to see a keratoconus expert. The doc in conjunction with measurement of the curvature of the cornea, a depth map and examining the eyes can identify the disease more early and accurately.

From a doctor’s perspective, as they physically examine the eye with a microscope, the signs they  would be looking for are corneal thinning, Fleischer’s ring, Vogt’s striae, and apical scarring. The measuring of the corneal curvature can be done three different ways: first would be keratometry, second is corneal tomography, and third is a corneal OCT. Though all three should performed for increasing the accuracy of the measurement.     

Now that you have a basic understanding of importance of early detection try our quiz on keratoconus.

CXL Post-Op Care

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.