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Introduction to Fundoscopy
An integral component of every doctor’s routine physical assessment is an inspection of the eye, a procedure called fundoscopic examination. Fundoscopy is a painless technique that allows the observer to gather a visualization of the patient’s retina. These observations come handy for the medical diagnosis of common medical conditions such as diabetes, hypertension, vascular disease, and lipid disorders. These illnesses typically cause secondary changes in the retina, and their progression can be examined through a quick, 5 to 10-minute check-up of the fundus of the eye. Ophthalmoscopes, the primary tools for this procedure, have, therefore, earned their spot as standard instruments in the doctor’s arsenal, not just for ophthalmologists only.
The Clinical Significance of Fundoscopy
The inspection of these regions can provide significant clues on the probable cause of a simple headache or symptoms of some serious vascular condition. For instance, pathological optic cupping, which is signified by an abnormally large optic cup-to-disc ratio, could be suggestive of glaucoma, an elevated intraocular pressure that can lead to loss of vision or irreversible blindness. Optic disc edema, the swelling of the optic disc due to an increase in fluid, is another ophthalmoscopic condition with serious underlying causes such as increased intracranial pressure or papilledema, infarction, inflammation, or infiltration of cells suggestive of cancer. In patients with severe hypertension, retinal hemorrhages found during fundoscopy signify categorization to accelerated hypertension. Diabetic retinopathy, a condition experienced by people with diabetes wherein high blood sugar levels cause damage to blood vessels in the retina, could be diagnosed early with the recognition of lesions during ophthalmoscopy.
Fundoscopy: The Tool
More than two centuries ago, observers believed in something called the “Black Pupil” phenomenon, wherein eyes of animals appeared to look bright or luminous when they were excited–something that was not observed among humans. Further examination proved that this illumination was due, in fact, to a reflective layer behind the retina, a structure that also existed in human eyes. So why was the human eye not as reflective as the eyes of animals? Simply because the rays of light that were supposed to hit a person’s eyes were often blocked by the head of the observer.
It was only in the middle of the 19th century that scientists were able to procure special circumstances that would adequately illuminate the human eye, wherein the primary light source would be placed adjacent to the eye of the observer, far from but parallel to the eyes of the subject. This discovery is similar to what usually occurs when we take photographs with a flash, and people’s eyes seem to appear red. Thus, this makes up the key concept of how ophthalmoscopes work–the illumination axis and the observer’s viewing axis should be placed as close to each other as possible. Charles Babbage was the first to come up with a basic design for an ophthalmoscope in 1849, using a piece of mirror with a small hole in the center, and a gas flame as the primary light source. This ingenious setup allowed the illumination and viewing axes to be coincident, and the image of the eye is formed on the observer’s retina. Shortly after, in 1851, Hermann von Helmholtz invented what would be the blueprint for today’s modern direct ophthalmoscope.
The Modern Direct Ophthalmoscope
Instead of using a mirror with a hole at the center, modern direct ophthalmoscopes use tilted mirrors beneath and adjacent to the device’s viewing aperture. Combining the light source with the rest of the device became a possibility because of the invention of the electric incandescent lamp. The modern direct ophthalmoscope also comes with parts that allow adjustment of the size, shape, and color of the illumination beam, and adjustment of lens magnification power to allow focus on different eye structures as well as for compensation in cases of myopia or hyperopia in both subject and observer.
Described simply, the standard ophthalmoscope is light with different optical modifications such as filters and lenses of different sizes. For this purpose, the magnifying power of traditional ophthalmoscopes and its many different variations help doctors see patients’ retinas clearly and conveniently. This tool operates by illuminating the retina, the thin layer of tissue lining the eye near the optic nerve, through the hole in the iris, the pupil. The light rays that hit these parts of the eye are then able to form an image of the fundus, the overall area opposite the lens and pupil, magnified for viewing through the lens of the ophthalmoscope.
Given the importance of such a procedure in improving and saving lives, different technological advances have helped update and refine the tool with which doctors can successfully conduct fundoscopic examinations. Aside from direct ophthalmoscopes, some doctors also make use of indirect ophthalmoscopy by shining a light from an instrument worn on the head, viewing the eye through a separate diopter lens held close to the eye. This other procedure gives a wider field of view than direct ophthalmoscopy and produces an inverted image of the back of the eye. Slit-lamp ophthalmoscopy, on the other hand, requires patients to be seated in front of a large, stationary instrument with their head resting and kept in place. These machines are what