The Hypodermic Needle and Molecular Surgery

Palo Alto, CA — Most people today, including many physicians, see the hypodermic needle as a mundane instrument that isn’t worth a second thought. This is not so for eye surgeons. The hypodermic needle is one of their most important surgical instruments with a fascinating history.

Organic materials like hollow reeds, geese quills, and animal bladders were used in early medicine to drain urine, puss, worms, and other abnormalities from the body. These primitive instruments worked passively or by gravity, since syringes could only inject liquids into the body. Urgent care, often on the battlefield, prompted people to use their mouths as medical instruments, sucking out foreign bodies, blood clots, and poisons. 

It wasn’t until the 19th Century that the hypodermic needle revolutionized medicine. In Edinburgh in 1853, Alexander Wood designed the first modern hypodermic needle, modeled off of a bee’s stinger, and injected morphine into patients. For the first time, physicians could both inject and draw liquids from the body. Except for removable parts, the design of the hypodermic needle has remained much the same and has become universally used since the 1950s when plastic allowed for disposable syringes and needles.

Vinit Mahajan M.D., Ph.D., professor at Stanford and director of the Molecular Surgery Program, said, “In ophthalmology we think of a needle as a precision surgical instrument. The size, length, diameter, tip-shape, and strength of the needle are very carefully thought out.”

Mahajan added, “We can bend the tip of the needle and use it as a cystotome to start a capsulorhexis for cataract surgery, or we can use it to help peel an epiretinal membrane from the surface of the retina. We commonly use it to inject drugs inside the eye or to remove fluid from the eye. Needles are used to dislodge microscopic foreign bodies from the surface of the eye after trauma, or to precisecly cut microscopic sutures.” 

Molecular surgery, a groundbreaking field pushing the boundaries of precision medicine, still depends on the hypodermic needle.

Mahajan said, “Perhaps the most exciting current use of the hypodermic needle is for human gene therapy. I use a 41- gauge needle with a bore size of only 100-microns to inject viruses carrying healthy genes into the subretinal space. Our margin of error is only a few microns. The injection was typically done as a manual push of the syringe by the assistant. Now we connect the syringe to a machine adaptor that gives the surgeon foot pedal control over air pressure that drives the injection. We can also use optical coherence tomography built into the surgical microscope to live-image the injection as the virus spreads underneath the retina. These innovations follow years of highly precise surgical application and development."

As a researcher, it is what the needle can pull out of the eye that excites Mahajan the most. Mahajan and his team created an ophthalmology biobank that archives eye fluid collected during surgeries. The careful and immediate preservation of this fluid in the operating room ensures that these liquid biopsies are available for future translational research aimed at discovering biomarkers for curing blindness.

Mahajan said, “This seemingly simple instrument allows us to collect eye fluid that holds the clues to the origin, progression, and treatment of both common and rare eye diseases. The proteins in dieseased fluid are a map for researchers to find new biomarkers that may lead to new drugs.”

He added, “The hypodermic needle should not be underestimated, and I think there remain opportunities for advanced engineering and new applications.”