Eye Dork - Eye Have the Answer

Vision is a very complex task that begins in the eye and ends in visual cortex located in the back end of the brain. For visual information to get to the back of the head it must take a long and complex course. If there is an obstruction along the way, a scotoma results. A scotoma is a missing piece of the visual puzzle. Based on the size, shape and location of the missing vision we can predict the location of abnormal brain function. Normal peripheral vision consists of a 150 degree view for an individual eye and 180 degrees for both eyes working together. Peripheral vision can be roughly estimated by counting fingers at the edge of the visual field (confrontations) or more precisely with a small beam of light at random spots in the visual field (automated visual field testing. Different structures in the eye can influence peripheral vision testing. Cataracts or a corneal condition can dim vision and only allow patients to see brighter test points. Retinal defects produce a scotom...

The pupil is the hole that allows images to enter the eye and determines the level of brightness inside the eye. The pupil can sharpen vision by constricting and blocking out peripheral image rays that cause a larger blur circle. This can be demonstrated by looking through a pinhole (1 to 1.5mm hole). During the day or in a bright environment the pupil constricts (miosis). At night, the pupil dilates to let more light into the eye. A larger pupil is the cause for most patients night driving problems. A larger pupil allows more peripheral image rays into the eye. A larger surface area of the cornea is required to focus images which exaggerates nearsightedness or astigmatism present. If cataracts are present, a larger pupil leads to more image ray scattering and bluriness. Pupil size can be affected by factors other than light. When reading up close the pupil constricts. The pupil is closely tied to the focusing system. This link is located anatomically at the ciliary ganglion. The c...

Headaches are a common problem patients encounter. Sometimes a new glasses prescription can fix the problem; other times the problem can be more severe or complex. When headaches are located in the forehead, temples and/or around the eyes the headaches are likely due to changes in prescription. Focusing issues from excess computer use and/or reading can also cause headaches in this area. Anti-reflective coating and polarized sunglasses can prevent headaches caused by glare. Eye alignment should also be evaluated. Cluster headaches are felt in or behind the eye. These headaches can be caused by caffeine, stress, nitroglycerin and/or tobacco use. For some patients the headaches are caused by narrow drainage strucures within the eye which require laser treatment to open the drainage structures. For those with normal drainage, the source of pain can be ovetaction of the trigeminal nerve or hypothalamus. Prescription headache medications are often required for patients with normal drain...

Double vision should be considered an ocular emergency. Double vision is assessed by the Eye Doctor with extraocular muscle (EOM) testing, cover test and phoria testing. During EOM testing the Eye Doctor moves a target up, down, and side to side. This test assesses the function of cranial nerves (3, 4, and 6) and the muscles they control. These are the muscles that move the eye in various directions. The cover test is useful for testing eye alignment by measuring the phoria and tropia. A phoria or heterophoria is the natural position of eye alignment. If the eyes are naturally misaligned horizontally or vertically the EOMs can strain to some degree to correct this and keep vision single. If double vision is present, then a tropia is present. For a tropia, eye misalignment is to large to be compensated for. Tropia is known as a strabismus or eye turn. For a new tropia or strabismus double vision results. The brain really dislikes double images and attempts to prevent double visio...

We don't know whether the question has been asked for hundreds or thousands of years. We do know that it creates unneccesary anxiety for many patients. Luckily, there is new technology attempting to eliminate the need for this question. This article will discuss the process of refraction (1 or 2 test), how it can be simplified to reduce anxiety, and how new technology measures up in its attempt to make it easier and more accurate. Using the traditional methods of refraction I say "is 1 or 2 better" 150 to 600 times per day. Needless to say, I've put a lot of thought into making the test easier for patients and my vocal cords. I will compare the old fashioned methods with new technology available today. The traditional (old) process of refraction begins with gathering data. A lensometer is used to measure to correction in the current spectacle prescription. Visual acuity with the spectacles on can be used to estimate how far the prescription is off. Keratometry can...

Hopefully your eye exam will find your vision to be 20/20, but what does that mean and how does it compare to everyone else out there? In the US, the ability to see visual detail (visual acuity) is described in a fraction. The first number indicates the distance to the visual target. This is 20 feet for the standard in the US and 6 meters for most other countries. Most exams rooms are not 20'. This is why it's common to see mirrors which lengthen the target distance in smaller exam rooms. The second number is the size of the target letter. For 20/20, the target letter is 8.87mm (0.35") tall by 8.87mm wide. Therefore, 20/20 is the ability to identify an 8.87mm character at 20'. Of course some letters are easier to identify than others. Letters with straight lines, such as an "E" are more readily recognized than circular letters "O". Straight lines provide more clues to the brain as it is putting the visual picture together. Some patients may no...