Everything there is to know about an a-scan
A-scan, also known as A-scan ultrasound biometry, is one of the most routine diagnostic procedures used in ophthalmology and optometry. During that procedure, a sound beam with a frequency of approximately 10 MHz is released from a specific sensor and then bounced back when it gets to every interface. A-scan is short for amplitude scan.
It usually measures the length of an eye and can be used to diagnose various eye diseases. A-scanning also very often uses different eye surgeries to get a more accurate view of the inner structures of that organ. Nowadays, there exist a few types of apparatuses which combine B- and A-scan technologies.
History of a-scanning
First ideas about using the ultrasound beams for diagnostic and treatment purposes showed right after discovering those beams as a phenomenon. But, as they firstly learned by Lazzaro Spallanzani in 1794, and the technical progress of those times was not steady enough for inventions of that kind, more than 150 passed before the first ultrasound scan machines were founded.
The first ultrasound machines showed up in 1956 and were used mostly for various clinical purposes, but mostly in obstetrics and gynecology. The inventors from Glasgow: engineer Tom Brown and obstetrician Ian Donald invented the first apparatus based on the unique tool for detecting technical flaws in shipbuilding. It was common among the Glasgow hospital doctors to use that method by the end of the 1950s.
The first attempt to use ultrasound for different eye disease diagnostic purposes was reported in 1956 by Mundt and Hughes. Those two ophthalmologists and scientists used industrial apparatuses for A-scanning, adapted them a bit to the size of a human eye, and performed the first examination in-vitro. That day is officially called the day of birth of the A-scan.
Indication to use an a-scan
As mentioned above, the primary types of various pathologies we can diagnose using those apparatuses connect with the eyes. The main, but not the only purpose of that diagnostic method is to obtain valuable information about the length of an eye globe, which can help in calculating the corrective lens power for prescribed glasses of eye lenses.
Among the other conditions that method can efficiently diagnose are various tumors, lens dislocations, and lens transpositions, different types of detections of retinal detachment, and much more. Here are a few examples of other pathological conditions easily determined by observing the posterior eye with this technology:
- Dense cataract
- Corneal opacity
- Vitreous hemorrhage
There are also various types of pathologies that doctors can find only after performing that diagnostic method, often accompanied by different pathologies that form structures obscured by opaque substances. Among those substances are fibrosis or tumor masses, blood, and additional protein inclusions. And those pathologies are:
- Various choroidal lesions: hemangioma, metastases, and melanoma
- Macular lesions: e. g., calcifications, osteoma
- Detachment of retina
- Posterior scleritis
- Optic Disk cupping
- Different choroiditis
- Raptures or dislocations of lens
They are also commonly used during surgical operations on eyes affected by various types of dense cataracts. In such cases, the precise observation of organ structures is complicated, so technology helps obtain a more unobstructed view of an eye's inner spaces.
Benefits of an a-scan
The most significant benefits of an a-scan compared to other visualization techniques, like a CT, MRI, or classic or electric roentgenology, is the full absence of radiological and radiation exposure that can potentially harm vulnerable human tissues and organ structures. But this is not the only benefit granted by that method.
The second notable benefit is obtaining information about organ structures in real-time. We can determine various statistical pathological changes in the anatomy of an organ and see different variations in its physiology and functional statement, which is vital for doctors of multiple specialties, including eye surgeons.
The third massive benefit of using A-scan apparatuses may seem not so crucial for doctors, who do not face financial statistics of the hospital too often. And it's about the cheapness of that method. You do not need a significant amount of electricity or different supplies to make those apparatuses work successfully. And it can potentially save lots of money for the hospital and the whole medical industry in general.
Complications of using A-scan
There is a minimal amount of possible complications of using that technology. The most well researched of those complications is forming the transplanted retina defects after performing a diagnostic procedure, which most commonly occurs at a young age. That is happening due to a lousy congruence of the transplanted retina and native organ tissues, which persists until they reach their 20th year.
There also exists a significant group of complications connected with the inadequate use of apparatuses. For example, when the pressure in an eyeball with the machine's sensor is too high, different traumatic injuries of inner organ tissues may occur. Also, when the apparatuses are misused, the same types of complications may occur as a result.
General specifications of an A-scanning machine
As mentioned above, there are lots of different apparatuses that combine the possibility of performing A-scanning and B-scanning modes together. Generally, almost all of the modern ultrasound scanners are combining those functions. So, it was not so easy to determine the exact specifications for apparatuses of that kind. They appeared to be:
- Fixation Light - included
- Frequency - 10 MHz
- Scan mode - manual and auto
- Patient record - DOB, gender, MRD, Dr's comment, name
- Lens type - Silicon oil, Pseudo, Phakic, Dense Cataract, Aphakic
- IOL configurations - over 200 variations
- Patient record storage - recorded into system hard disk
- Data exporting - Html, pdf, txt, CSV, jpeg, Xls, Xlsx
- Printer - any PC supported
- Axial length measurement - from 12 to 40 mm
- Refraction formulas - SRK-T. Shammas, Rosa, Contact lens, Clinical History Methods
Various types of apparatuses also supported different additional features, e. g., activation of the sensor by pressing the footswitch pedal, or when putting the sensor on the surface of a body or examined organ.
Many different manufacturers already exist in the modern market of these apparatuses. Every day lots of different new companies and resellers are added to this quantity. So it's pretty clear that this list of the products with the highest quality and the most suitable prices will become irrelevant pretty soon, but for now, it looks like this:
- AB Solu
- Eye Cubed;
- Eye One™
- US - 4000
- Axis Nano
- Compact Touch
- MD - 1000A
- ODM - 2100
There are also many different, inexpensive Chinese versions of A-scan machines that often appear in the market. Still, due to their low quality and a small period of an active lifetime, associations of ophthalmologists worldwide do not recommend buying them.
A-scan is a pretty good invention that primarily functions as a diagnostic tool in ophthalmology. It also finds its place before and during performing a few types of ophthalmologic surgeries, e. g., connected with cataracts of various kinds.
This diagnostic tool, which was invented not so long ago and began use for medical purposes less than 70 years ago, may show us many different magnificent properties. For example, it is possible that after a few technical renovations, these apparatuses may replace other techniques of medical visualizations, like CT, MRI, or even PET CT. We never know what the future may bring to us, but we should still wait only for the best!