Thursday, March 30, 2006

Where is the ciliary ganglion?

The ciliary ganglion (arrow 4) is an important anatomic structure in the posterior orbit because sensory innervation to the anterior eye, parasympathetic axons for the iris to control pupil constriction, and sympathetic fibers pass that innervate the iris dilators and blood vessels. Located about 1 cm in front of the annulus of Zinn, the ciliary ganglion lies interposed between the optic nerve (shown in gray in the image) and lateral rectus (arrow 9) at the lateral aspect of the ophthalmic artery with its attendant innervation from the abducens nerve. Only the parasympathetic fibers are thought to synapse in the ganglion. The input to the ciliary ganglion includes the nasociliary nerve (arrowhead 6), sympathetic fibers from the internal carotid (arrow 7), and a motor root from the inferior division of the 3rd nerve (3 in the image) that eventually innervates the inferior oblique muscle (arrow 5). The superior division of the 3rd nerve (2 in the image) supplies the superior rectus and then courses around its medial border (arrow 10 shows the course of the nerve) to supply the levator palpebrae. The inferior division of the 3rd nerve also supplies the inferior rectus (arrow 11). The ciliary ganglion provides short ciliary nerves that travel on both sides of the optic nerve (arrow 8). Despite this maze of inputs, only parasympathetic fibers synapse in the ciliary ganglion. A low power photomicrograph of a section of a dissected ciliary ganglion (number 1) shows the nerve trunks (arrows 2 that emanate from the ganglion. At higher magnification one can see ganglion cells with central nuclei (arrow 3) and prominent nucleoli.

Tuesday, March 21, 2006

What are the landmarks of the limbus?

The limbus is a transition zone where the cornea meets with elements of the sclera; both contribute. The transition zone begins at a line (the green arrow in the figure) designated by the termination of Bowman's layer and Descemet's membrane. The transition ends at a line (the red line in the figure)designated by the scleral spur drawn perpendicular to the ocular surface. The transition zone with these limits is then a donut that is about 1.5 mm in width. The surgical limbus has been stated in many books to have clear landmarks that include Bowman's layer. Since Bowman's layer is not readily visible in the slit lamp consider the limbus as the blue region overlying clear cornea and extending back to the scleral spur. The limbus is an important landmark for surgical procedures for cataract extraction, glaucoma filtration surgery etc. . Because the trabecular meshwork is encompassed in this region, the limbus has implications in the laser treatment for glaucoma.

Saturday, March 04, 2006

What is the SQ5R method of studying?

Human memory has an intrinsic decay rate that is staggeringly exponential. Retention of learned material from reading drops to about 20-30% after 1 hour for most people The SQ5R, SQ4RW, SQ3R are all study methods that if used properly with textbooks and readings can increase your retention to 80% on a long term basis. The basis of the method is that you are engaged in active processing of material driven by 'curiosity', the most powerful stimulus for learning.
Here is the method:
SURVEY - Before reading the actual chapter, read the introduction and summary (if given). Skim through the chapter paying attention to topic headings, bold-faced words, pictures, charts, and graphs. These can give you an idea of the general structure and content before you begin reading. This should stimulate curiosity for the material and questions will begin to arise. You might also simply jot down everything you know about the subject before you start reading and then ask what you would think is important to learn that you don't know.
QUESTION - Set a purpose for your reading by developing questions about the material. Use the topic and heading information you gathered in the survey step to create questions to be answered. Begin asking yourself who, what, where, when, why, and how questions. Questions are most beneficial when they are general, covering main topics and important points. However, remember that the purpose of the questions is to stimulate curiosity.
READ - Read to answer your questions. Some say divide the reading material into sections that will take about 20 minutes to read (often the chapter is already broken into sections which will work just fine). Read the material section by section. Look for answers to your questions, key concepts, and supporting details. Study charts, graphs, tables, and pictures. These can serve to present new information as well as tie together concepts from the reading.
RECITE - Ask your question and try to recite the answer incorporating key information and ideas. Put the material in your own words and go back and re-read until you feel comfortable with it. This may be frustrating at first, but it will lead to better understanding and save you review time in the long run. (Do this after each section.)
RECORD (WRITE) - Here I would strongly recommend putting your questions on the computer or writing them in a notebook. Then in a brief note format with abbreviations you develop, write the answers without looking at the material. Check it after to make sure it is right. Chances are this process will lead to other questions and you may wish to jot those down as well and try to answer them.
REVIEW - After completing each section review the prior sections simply by answering your questions. You will be amazed how much you retain compared to just reading a chapter or underlining. An hour later review your notes again. Review will need to be done again in one day and then in a week to maintain your 80% retention.

We have tried to promote this method in the material presented in anatomy here by asking you questions that you search for the answers in links. We have purposely added more material than the answer to be complete. The material is redundant in areas to encourage review.

For ophthalmology residents, putting the notes on your laptop is a great resource for clinic. You can link your answers to photographs that you take later, or ones available on the web. You can link to original articles and to medrounds for the diagrams and answers. Take your laptop everywhere so you can continually organize and review the material. Material that you don't wish to memorize such as specific drug therapy for relatively rare problems can be found in your notes. You can add to your information and update it at rounds and conferences. You can also keep patient photographs and information organized so you can show specialists later to help you with the diagnosis as you follow their case.