alta miopía y donación de sangre ¿por qué no se permite?

Title: High Myopia and Blood Donation: Why Is It Not Allowed? Author: [not provided] Reviewer: [not provided] Commissioner: [not provided] Organization: [not provided] In blood donation vehicles or blood centers, staff often ask, 'What is your degree of myopia?' If the answer exceeds 600 degrees, individuals are often courteously rejected.

Many people do not understand this: my blood quality is completely normal, and I even feel very well, so why do I lose my eligibility to donate blood just for wearing thick glasses? In fact, this regulation is not due to a disregard for blood quality but rather to protect the medical safety of the donor. Its central logic lies in avoiding the potential risk of retinal detachment.

I. Fundamentals of Anatomy: The Fragile Structure of the Retina.

In medicine, high myopia is defined as having a myopia degree greater than 600 degrees (-6.00D).

The ocular axis of a normal adult measures approximately 24 millimeters. In patients with high myopia, the ocular axis often increases significantly, exceeding 26 millimeters or more. The wall of the eyeball consists, from the outside to the inside, of the sclera, choroid, and retina. As the ocular axis elongates, the wall of the eyeball is forced to expand. Since the elasticity of the retina is much lower than that of the sclera, this expansion can lead to excessive stretching and thinning of the retina.

This thinning mainly occurs in the periphery of the retina, facilitating the occurrence of degenerative changes such as lattice degeneration, cystoid degeneration, and even retinal tears. This results in the eye structure of patients with high myopia being in an extremely unstable 'sub-health' state, with a significantly lower tolerance to fluctuations in blood pressure and changes in intraocular pressure compared to normal individuals.

Second, Triggering Mechanisms: Blood Flow Dynamics and Fluctuations in Intraocular Pressure.

Although blood donation itself (typically between 200 and 400 milliliters) has minimal impact on the circulatory system of healthy individuals, there are two potential risks for patients with high myopia:

Fluctuations in intraocular pressure: During the blood donation process, some donors may experience stress reactions due to tension, pain, or the sight of blood, leading to excitement of the sympathetic nervous system and a temporary increase in blood pressure. This fluctuation in blood pressure can be transmitted to the ocular vessels, causing a temporary increase in intraocular pressure (IOP). In patients whose retina is already degenerated and thin, sudden changes in ocular pressure can tension the retina and cause tears or detachment.

Hemodynamic changes: Blood extraction within a short time may cause a decrease in circulating blood volume throughout the body. Although the body can compensate quickly, the perfusion of vessels in the choroid and retina can experience small fluctuations. In patients with pathological myopia (accompanied by lesions in the fundus), these changes in microcirculation can trigger spasms or bleeding in the retinal vessels, which may threaten vision.

Three, Industry Standards and Risk Mitigation.

One misconception that needs correction is that national standards do not absolutely prohibit blood donation for high myopia.

According to the latest 'Health Examination Requirements for Blood Donors' in China (GB 18467-2011), it is not clearly specified that 'high myopia' is a reason for permanent exclusion, but it is stated that those 'who suffer from high myopia with retinal changes' cannot donate blood temporarily.

However, in practice, blood stations and donation points often apply stricter criteria, often directly rejecting individuals with a myopia level exceeding 600. The reason is as follows:

Cost of evaluation: The blood donation vehicle does not have the necessary conditions to conduct a pupil dilation examination and a detailed fundus examination. Staff cannot determine if a person with high myopia has developed tears or degenerations in the retina.

Defensive medicine: To maximize the safety of blood donors and avoid severe medical complications such as retinal detachment, blood collection institutions tend to adopt all-or-nothing exclusion strategies.

Fourth, Conclusion.

Hospitals or blood banks that reject donors with high myopia are essentially taking risk control measures.

Although from a statistical standpoint, the probability of blood donation causing retinal detachment is very low, for patients with high myopia, who have an extremely long ocular axis and a very thin retina, any activity that may induce drastic fluctuations in ocular pressure or changes in hemodynamics (such as intense exercise, bungee jumping, heavy physical work, or blood donation) is considered a risk factor. Due to the delicate state of such a thin retina, this precaution is entirely necessary.