Retinoscope

Everything there is to know about a retinoscope

Typically, ophthalmologists use the retinoscope to diagnose vision issues, such as myopia and hyperopia, and determine the precise measurements to correct the condition. In this article, we will dissect the basic concepts of retinoscopy, how physicians use a retinoscope, its indications, and the companies that lead this market.

History of retinoscopy

The first physician to analyze the shadow effect was Sir William Bowman, who paved the way to develop retinoscopy. While using a Helmholtz ophthalmoscope, he noticed an unusual shadow in 1859, which is the basic principle behind the retinoscope's mechanism of action. In 1873, a French ophthalmologist named Ferdinand Cuignet experimented on individuals known to have different refractive errors, using a simple ophthalmoscope.

At the time, Cuignet believed that the cornea was responsible for his observations, which led him to name the technique keratoscopy. Five years later, Cuignet's pupil, M. Mengin, released a paper where he explained that the retina is the source of the reflex seen during retinoscopy. So far, all the techniques used were qualitative. In other words, they do not give measurements of the refractive errors, but rather establish them. In 1880, H. Parent was the first scientist to introduce the quantitative refraction test, using lenses. H. Parent was also the first person to call the technique retinoscopy, the French term for retinoscopy. 

How a retinoscope works

A retinoscope is a simple instrument that emits a light that reaches the retina and is reflected as a bright, red spot. Using the reflex's characteristics, the ophthalmologist will determine whether there is a refractive error or not, as well as the degree of that error if present. While the principle behind this instrument is simple, it is based on multiple physical and anatomical properties of the lens, retina, light transmission, and reflective patterns.

Generally speaking, retinoscopy is performed by optometrists, ophthalmologists, and any medical professional who received the appropriate training to use this device and interpret the results. With the patient's eyes open, the retinoscope is swiped in both directions, and the light reflex is monitored. Depending on the direction of the bright, red spot and its size, the physician will determine the presence and degree of the refractive error.

Indications to use a retinoscope

Retinoscopy is a commonly performed procedure during annual systemic checkups. The physician will use a retinoscope to evaluate the reflex emitted by the retina in an attempt to objectify any refractive errors that require a corrective lens.

Here are the common indications for a retinoscope:

Astigmatism

Astigmatism is the most common refractive error worldwide.

The primary abnormality in this condition is the shape of the lens, which has two refractive surfaces that lead to blurry vision. Before the optician can design glasses that correct this issue, he/she will need a full report of the refractive error measurements calculated by the retinoscope to create the appropriate lenses for the patient.

Hyperopia

Hyperopia, or farsightedness, is an ophthalmological condition where patients can see distant objects clearly but have trouble visualizing near objects. Whenever we open our eyes, the light reflected on the environment enters the cornea. A fundamental structure for vision called the crystallin lens changes its dimensions to focalize the light on the retina. These changes are mediated by the intraocular muscles that ensure the lens is just in the right position to reflect the light onto the retina to get translated into a clear picture. For some patients, this accommodation is impaired, and the light is focused behind the retina, which leads to hyperopia.

As a result, when an object is far away, the patient can see it since the intraocular muscles do not need a lot of power to focus the light on the retina. Conversely, if the object is near, the muscles will forcefully contract to correct the reflective focus, leading to a common symptom seen in hyperopic patients –pain–. If the patient puts the object close, the muscles are no longer able to accommodate, and the vision becomes completely blurry. The retinoscope's light will act as a virtual object to see how well the muscles accommodate. However, to evaluate the reflective error, the physician will use eye drops of a cycloplegic drug to relax the muscles.

Myopia

Similar to hyperopia, myopic patients have problems focusing the light on the retina. However, the light will be targeted ahead of the retina this time, leading to shortsightedness.

Presbyopia

In this condition, the main pathological finding is the age-related decrease in lens performance. Consequently, the lens will no longer focus light correctly, which leads to vision issues.

Macular degeneration

Macular degeneration is common among the elderly, leading to blurry or lost vision in the center of the visual field. This disease has several risk factors, including smoking, prolonged sun exposure, family history, and obesity. There are a few FDA-approved treatment options for macular degeneration, but the most commonly prescribed treatment is anti-VEGF therapy.

Retinal vessel occlusion

As the name implies, retinal vessel occlusion is the result of obstructed small blood vessels in the retina, leading to abnormal test results of retinoscopy.

Retinal detachment

Retinal detachment is a severe surgical emergency that results from the retinal layer detachment from the rest of the eye.

Contraindications and side effects of using a retinoscope

The medical literature does not cite any absolute or relative contraindications to using a retinoscope, as it is a little light emitted by a device. Patients may complain of having an afterimage of the light later on, but it should disappear within a few minutes to a few hours.

The most commonly discussed side effects of retinoscopy are related to the eye drops used to paralyze the ocular muscles. 

These include:

  • Dry mouth
  • Flushing
  • Dizziness
  • Nausea and vomiting
  • Narrow-angle glaucoma

Market-leading brands of retinoscopes

All market research companies agree that the demand for retinoscopes will steeply increase as more cases of glaucoma, lens-focusing abnormalities, and macular degeneration cases are reported every year.

According to one report, the growth of the retinoscope market between 2018 and 2022 is estimated to surpass 70 million dollars, with more than 38% of this growth occurring in the Americas. The top institutions that use these devices are ophthalmology clinics, followed by hospitals and ambulatory surgery centers (ASCs).

Here are the market-leading brands when it comes to retinoscopes:

  • Welch Allyn
  • HEINE USA Ltd
  • Keeler Ltd
  • Us Ophthalmic
  • Rudolf Riester GmbH
  • Holtex
  • Carl Zeiss Meditec AG
  • GlobalMed
  • Albert Waeschle Ltd
  • Zumax Medical Co. Ltd
  • Invotech Excel Fzco
  • Spengler

General specifications of a retinoscope

Here are the general specifications of the Heine Beta 200 AV LED Ophthalmoscope, a commonly used device in ophthalmology clinics and hospitals:

  • LED with continuous brightness control
  • Aluminum frame system
  • 27 single lenses (ranging from -35D to +40D)
  • No pinhole macula aperture
  • Recessed windows prevent stray light from escaping to minimize distractions
  • One-handed control for ease of use
  • Able to examine small and constricted pupils.
  • Eliminates corneal reflex
  • Ideal for small pupils
  • Dustproof

Conclusion

Retinoscopes, or ophthalmoscopes, are essential instruments for evaluating refractive errors and other pathologies of the eye. These devices offer a non-invasive procedure that precisely measures the intraocular muscle accommodation deficiency and aids the optician to design accurate contact lenses or eyeglasses for patients. Hopefully, this article helped you appreciate the benefits of retinoscopes and the potential market growth in the near future.

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