National Eye Institute (NEI)


For Immediate Release: Thursday, November 3, 2011





Dilated fundus examination (DFE) is a diagnostic procedure that employs the use of mydriatic eye drops (such as tropicamide) to dilate or enlarge the pupil in order to obtain a better view of the fundus of the eye   Once the pupil is dilated, examiners often use specialized equipment such as an ophthalmoscope or fundus camera to view the inner surfaces of the eye. DFE has been found to be a more effective method for evaluation of internal ocular health than non-dilated examination  It is frequently performed by ophthalmologists and optometrists as part of an eye examination.



November 3, 2011  —  Diabetic retinopathy is one of the most common and debilitating complications of diabetes. During National Diabetes Month, the National Eye Institute (NEI), a part of the National Institutes of Health, is encouraging people with diabetes to get annual dilated eye exams and take steps to avoid vision loss.


About 28.5 percent of U.S. adults age 40 and older with diabetes have diabetic retinopathy, a condition that causes blood vessels of the retina to swell and leak fluid. The retina is the light-sensing layer of tissue in the back of the eye. As the disease progresses, blood vessels become blocked and rupture or new vessels grow on the retina, leading to permanent and sometimes profound vision loss.


People with diabetes are at greater risk for cataracts, which cause clouding of the eye lens, and glaucoma, which damages the optic nerve. In the United States, diabetes is the leading cause of blindness among working-age adults.


People with diabetes can take steps to prevent complications of diabetes. In addition to controlling blood glucose and blood pressure through healthy eating, adequate exercise, and medication, people with diabetes should have annual dilated eye exams to identify signs of diabetic retinopathy, which usually has no symptoms until vision loss occurs. Comprehensive

dilated eye exams allow eye care professionals to monitor the eye, including the retina, for signs of disease. Ninety percent of diabetes-related blindness is preventable through early detection, timely treatment, and appropriate follow-up care.


The NEI supports research aimed at understanding, preventing, and treating diabetic retinopathy.


The Action to Control Cardiovascular Risk in Diabetes (ACCORD) Eye Study, sponsored in part by the NEI, showed that intensive control of blood glucose and blood lipids, including cholesterol, slows the progression of diabetic retinopathy.


The NEI Diabetic Retinopathy Clinical Research Network ( is an NEI-sponsored collaboration of more than 300 physicians at more than 100 clinical sites across the United States. Since 2002, has coordinated 18 clinical studies investigating treatments for various diabetes-related conditions, including a condition that causes central vision loss called macular edema.


A recent study of people with diabetic macular edema showed that about 50 percent of participants treated with eye injections of the drug Lucentis combined with conventional laser treatment had dramatic improvements in vision, compared to about 30 percent of participants who received laser treatment alone. This is the first new treatment for diabetic eye disease in 25 years.


The NEI provides resources to health professionals and the public to educate and increase awareness of diabetic eye disease through its National Eye Health Education Program (NEHEP).


During National Diabetes Month, NEHEP is targeting those at increased risk of vision loss from diabetes by raising awareness of the importance of early detection among health providers, who play a crucial role in motivating patients to protect their eyes. According to an NEI survey, 96 percent of adults said they would get a comprehensive dilated eye exam if their health care provider suggested they get one. People at highest risk of vision loss and blindness from diabetes include African Americans, Hispanics, American Indians, and Alaskan Natives.


NEHEP is distributing free diabetic eye disease resources to health professionals and community organizations serving people with diabetes. Resources include teaching tools for community health workers, cards to promote the Medicare benefit available to people with diabetes, and other educational materials. All resources are available in English and Spanish.


The National Eye Institute (NEI), part of the National Institutes of Health, leads the federal government’s research on the visual system and eye diseases. NEI supports basic and clinical science programs that result in the development of sight-saving treatments. For more information, visit <>.


About the National Institutes of Health (NIH): NIH, the nation’s medical research agency, includes 27 Institutes and Centers and is a component of the U.S. Department of Health and Human Services. NIH is the primary federal agency conducting and supporting basic, clinical, and translational medical research, and is investigating the causes, treatments, and cures for both common and rare diseases. For more information about NIH and its programs, visit <>.




National Eye Institute



What is a Comprehensive Dilated Eye Exam?


A comprehensive dilated eye exam is a painless procedure in which an eye care professional examines your eyes to look for common vision problems and eye diseases, many of which have no early warning signs. Regular comprehensive eye exams can help you protect your sight and make sure that you are seeing your best.

What does a comprehensive dilated eye exam include?

A comprehensive eye examination includes: dilation, tonometry, visual field test and visual acuity test.

Dilation: Drops are placed in your eyes to dilate, or widen, the pupils. Your eye care professional uses a special magnifying lens to examine your retina to look for signs of damage and other eye problems, such as diabetic retinopathy or age-related macular degeneration. A dilated eye exam also allows your doctor to check for damage to the optic nerve that occurs when a person has glaucoma. After the examination, your close-up vision may remain blurred for several hours.



Tonometry: This test helps to detect glaucoma by measuring eye pressure. Your eye care professional may direct a quick puff of air onto the eye, or gently apply a pressure-sensitive tip near or against the eye. Numbing drops may be applied to your eye for this test. Elevated pressure is a possible sign of glaucoma.

Visual field test: This test measures your side (peripheral) vision. It helps your eye care professional find out if you have lost side vision, a sign of glaucoma.

Visual acuity test: This eye chart test measures how well you see at various distances.


Eye dilation: Necessary with every eye exam?

Eye dilation is inconvenient for me. Is it necessary to have my eyes dilated during every eye exam?


from Dennis Robertson, M.D., Mayo Clinic

Whether eye dilation is necessary for every eye exam depends on the reason for your eye exam, your overall health and your risk of eye diseases.

During an eye exam, your doctor uses special eyedrops to cause eye dilation. The drops cause the black portion at the center of your eye (iris) to widen, allowing your doctor a good view of the back of your eye. Eye dilation can help your doctor diagnose many diseases and conditions, such as:

  • Diabetes
  • Eye tumors
  • High blood pressure
  • Infectious diseases
  • Macular degeneration
  • Retinal detachment
  • Vasculitis

Many diseases and conditions can be detected at their earliest stages during an eye exam. For this reason, most eye doctors recommend eye dilation as part of your routine eye exam schedule.

Still, eye dilation can be inconvenient, since it makes it difficult to focus on close objects. This can interfere with your ability to drive or work for a few hours after your eye exam. Eye dilation also makes your eyes more sensitive to bright light. If eye dilation is a great inconvenience, ask your doctor about other tests to examine the back of your eye. Alternative tests are available, but none is proven as effective as an exam that involves eye dilation.

In determining whether eye dilation is necessary for you, your eye doctor may consider:

  • Your age. The risk of eye diseases increases with age.
  • Your eye health. If you have a history of eye diseases that affect the back of the eye, such as retinal detachment, you may have an increased risk of future eye problems.
  • Your overall health. Certain diseases, such as diabetes, increase the risk of eye disease.
  • Your reason for an exam. If you’re seeking an eye exam because you have new, worrisome eye symptoms or vision problems, then eye dilation may be necessary to make a diagnosis.
  • Results of previous eye exams. If recent eye exams have included eye dilation with no unusual findings, it may be possible to skip the eye-dilation portion of your next exam. If this is your first eye exam, it’s a good idea to have the eye-dilation portion of the exam. Discuss this with your eye doctor.



Comprehensive Dilated Eye Exam



Fundus (eye)


An ophthalmogram, showing the optic disc as a bright area on the right where blood vessels converge. The spot to the left of the centre is the macula. The grey, more diffuse spot in the centre is a shadow artifact.



Fundus of human eye



Fundus of human eye



The fundus of the eye is the interior surface of the eye, opposite the lens, and includes the retina, optic disc, macula and fovea, and posterior pole. The fundus can be viewed with an ophthalmoscope. The term may also be inclusive of Bruch’s membrane and the choroid.

The color of the fundus varies both between and within species. In one studyof primates the retina is blue, green, yellow, orange, and red; only the human fundus (from a lightly pigmented blond person) is red. The major differences noted among the “higher” primate specieswere size and regularity of the border of macular area, size and shape of the optic disc, apparent ‘texturing’ of retina, and pigmentation of retina.

The eye’s fundus is the only part of the human body where the microcirculation can be observed directly. The diameter of the blood vessels around the optic disc is about 150 μm, and an ophthalmoscope allows observation of blood vessels with diameters as small as 10 μm

Medical signs that can be detected from observation of eye fundus (generally by funduscopy) include hemorrhages, exudates, cotton wool spots, blood vessel abnormalities (tortuosity, pulsation and new vessels) and pigmentation. Arteriolar constriction, seen as `silver wiring` and vascular tortuosities are seen in hypertensive retinopathy.




Schematic Diagrams of the Human Eye


The Limbus of the Human Eye





The Sclera


The sclera (from the Greek skleros, meaning hard), also known as the white or white of the eye, is the opaque (usually white, though certain animals, such as horses and lizards, can have black sclera), fibrous, protective, outer layer of the eye containing collagen and elastic fiber.  In the development of the embryo, the sclera is derived from the neural crest.  In children, it is thinner and shows some of the underlying pigment, appearing slightly blue. In the elderly, fatty deposits on the sclera can make it appear slightly yellow.

Human eyes are somewhat distinctive in the animal kingdom in that the sclera is very plainly visible whenever the eye is open. This is not just due to the white color of the human sclera, which many other species share, but also to the fact that the human iris is relatively small and comprises a significantly smaller portion of the exposed eye surface compared to other animals. It is theorized that this adaptation evolved because of our social nature as the eye became a useful communication tool in addition to a sensory organ. It is believed that the conspicuous sclera of the human eye makes it easier for one individual to infer where another individual is looking, increasing the efficacy of this particular form of nonverbal communication. Animal researchers have also found that, in the course of their domestication, dogs have also developed the ability to pick up visual cues from the eyes of humans, making them one of only two species known to seek visual cues from another individual’s eyes. Dogs do not seem to use this form of communication with one another and only look for visual information from the eyes of humans.

The sclera forms the posterior five-sixths of the connective tissue coat of the globe. It is continuous with the dura mater and the cornea, and maintains the shape of the globe, offering resistance to internal and external forces, and provides an attachment for the extraocular muscle insertions. The sclera is perforated by many nerves and vessels passing through the posterior scleral foramen, the hole that is formed by the optic nerve. At the optic disc the outer two-thirds of the sclera continues with the dura mater (outer coat of the brain) via the dural sheath of the optic nerve. The inner third joins with some choroidal tissue to form a plate (lamina cribrosa) across the optic nerve with perforations through which the optic fibers (fasciculi) pass. The thickness of the sclera varies from 1mm at the posterior pole to 0.3 mm just behind the rectus muscle insertions. The sclera’s blood vessels are mainly on the surface. Along with the vessels of the conjunctiva (which is a thin layer covering the sclera), those in the episclera render the inflamed eye bright red.

In many vertebrates, the sclera is reinforced with plates of cartilage or bone, together forming a circular structure called the scleral ring. In primitive fish, this ring consists of four plates, but the number is lower in many living ray-finned fishes, and much higher in lobe-finned fishes, various reptiles, and birds. The ring has disappeared in many groups, including living amphibians, some reptiles and fish, and all mammals.

The eyes of all non-human primates are dark with small, barely visible sclera.

The collagen of the sclera is continuous with the cornea. From outer to innermost, the four layers of the sclera are:

The sclera is opaque due to the irregularity of the collagen fibers, as opposed to the near-uniform thickness and parallel arrangement of the corneal collagen. Moreover, the cornea bears more mucopolysaccharide (a carbohydrate that has among its repeating units a nitrogenous sugar, hexosamine) to embed the fibrils.

The cornea, unlike the sclera, has 5 layers. The middle, thickest layer is also called the stroma. The sclera, like the cornea, contains a basal endothelium, above which there is the lamina fusca, containing a high count of pigment cells.

Sometimes, very small gray-blue spots can appear on the sclera, a harmless condition called scleral melanocytosis.




Cooperative Eye Hypothesis



Human eye

The cooperative eye hypothesis is a proposed explanation for the appearance of the human eye. It suggests that the eye’s distinctive visible characteristics evolved to make it easier for humans to follow another’s gaze while communicating or while working together on tasks.

Differences in primate eyes

Unlike other primates, human beings have eyes with a distinct colour contrast between the white sclera, the coloured iris, and the black pupil. This is due to a lack of pigment in the sclera. Other primates have pigmented sclera that are brown or dark in colour. There is also a higher contrast between human skin, sclera, and irises. Human eyes are also larger in proportion to body size, and are longer horizontally. Among primates, humans are the only ones where the outline of the eye and the position of the iris can be clearly seen.



Bonobo with dark sclera



The cooperative eye hypothesis was tested at the Max Planck Institute for Evolutionary Anthropology in Germany. Researchers examined the effect of head and eye movement on changing gaze direction in humans and great apes. A human experimenter, observed by either a human infant, a gorilla, a bonobo, or a chimpanzee, did one of four actions:

  • Tilted his head up while closing his eyes
  • Looked at the ceiling with his eyes while keeping his head stationary
  • Looked at the ceiling with his head and his eyes
  • Looked straight ahead without moving his head or his eyes

The apes were most likely to follow the gaze of the experimenter when only his head moved. The infants followed the gaze more often when only the eyes moved.

The results suggest that humans depend more on eye movements than head movements when trying to follow the gaze of another. Anthropologists not involved in the study have called the hypothesis plausible, noting that “human infants and children both infer cooperative intentions in others and display cooperative intentions themselves.”[

Why did it evolve?

Studies of great ape behavior show that they are good at cooperating in situations where there is no potential of deception, but behave egoistic in situations where there is motifs for deception, suggesting that their “lack of cooperativeness” are not a lack of a cognitive ability at all, but rather a necessary adaptation to a society full of deception.  This suggests that human cooperativeness began when proto-humans began to successfully avoid competition, which is also supported by the fact that the oldest evidence of care for the long-term sick and disabled are from shortly after the first emigration of hominids out of Africa about 1.8 million years ago.

Other hypotheses

The cooperative eye hypothesis is not the only one that has been proposed to explain the appearance of the human eye. Other hypotheses include the proposal that white sclera are a sign of good health, useful in mate selection, or that eye visibility promotes altruistic behaviour by letting people know they are being watched. The Planck institute study noted that “these hypotheses are not mutually exclusive, and highly visible eyes may serve all of these functions.”