What is the difference between lens opacity and vitreous opacity?

　　The differences between lens opacities and vitreous opacities generally include the site of onset, symptom presentation, causes, impact on vision, and common affected populations. A detailed analysis is as follows:

　　1. Site of Onset: Lens opacities occur in the crystalline lens within the eye, which lies between the iris and the vitreous body and is an important part of the refractive system. Vitreous opacities occur in the vitreous body located behind the lens; the vitreous is a transparent, gel-like substance that fills the posterior portion of the eyeball.

　　2. Symptom Presentation: Lens opacities primarily manifest as progressive decline in vision, blurred vision, and may be accompanied by reduced contrast sensitivity and altered color perception. Vitreous opacities typically present as floating dark spots in the visual field—appearing as dots, lines, or絮状 (floccular) shapes—that move with eye movements.

　　3. Causes: Lens opacities are mainly associated with aging. Other contributing factors include ultraviolet radiation, diabetes, and malnutrition. They result from aging or damage to the lens. Vitreous opacities are mostly caused by degenerative changes in the vitreous, but can also result from vitreous inflammation or hemorrhage.

　　4. Impact on Vision: Lens opacities directly affect light refraction. As the opacity worsens, vision gradually deteriorates and may eventually lead to blindness. If the retina is not involved, vitreous opacities have minimal impact on vision in early stages, mainly affecting visual comfort. However, if there is vitreous traction on the retina, vision may be impaired.

　　5. Common Affected Populations: Lens opacities are most commonly seen in middle-aged and elderly individuals, with incidence increasing gradually after age 40 and higher prevalence with advancing age. Vitreous opacities are more common in people with high myopia and older adults, although some younger individuals may also experience symptoms due to excessive eye strain or premature vitreous liquefaction.

　　If vision declines or there is an increase in floaters, prompt ophthalmologic evaluation is recommended. Diagnostic tools such as slit-lamp examination and fundoscopy can help determine the type of opacity. Daily eye protection, avoiding eye strain, and regular vision check-ups are essential for early detection and intervention of ocular conditions.