Abisha S, B.Optom
Aravind Fellowship in Optometry, Aravind Eye Care System, Chennai, India
Has anyone heard about the term “second sight”?
The phenomenon of ‘second sight’ is quite interesting, as it appears to the patients to be a ‘magical’ restoration of vision after the vision becomes poor. After several years of using glasses to have a clear vision for near work, the patient starts seeing well again without glasses. Most of the time, they attribute it to supernatural power or their prayers. But this phenomenon occurs due to some changes in the natural lens of the eyes which can be scientifically explained, how the vision improves after years of dependence on glasses.
The Aging Process of Eyes
Age-related changes in the crystalline lens led to two major lens pathologies, cataracts, and presbyopia.(1) Cataracts, defined as any lens opacity, are the leading cause of reversible blindness in the world, whereas presbyopia is caused by a reduction in the lens’ ability to change shape during focusing (accommodation).(1)
How does it happen
This second sight changes occur because the proteins and other compounds that make up the lens begin to change its structure. As the lens becomes harder, especially in the central part called as nuclear sclerosis, its refractive index increases.(2) This higher refractive index of the lens, causes more bending of light to focus the light rays on the retina without the need for the lens to change its shape (i.e., without the accommodation of the lens).(1) This is the stage when the patient does not need glasses to see near objects clearly because the higher refractive index of the lens (nuclear sclerosis) compensates for the loss of accommodation of the lens.
Figure 1: Schematic diagram of Normal presbyopic lens (top) vs. Lens with nuclear sclerosis (bottom)
Consequences of mature cataract
Mature cataracts, if left untreated, may lead to certain complications. Firstly, it becomes difficult to remove surgically. It may also result in patients developing phacomorphic or phacolytic glaucoma, typically in the sixth decade. Phacolytic glaucoma is the sudden onset of open-angle glaucoma while phacomorphic glaucoma is secondary angle-closure glaucoma due to lens intumescence. Cataract surgery in those with phacomorphic glaucoma poses challenges due to high intraocular pressure (IOP), risk of expulsive haemorrhage, positive pressure, and zonular dialysis.(3)
How to conserve your permanent treasure
When a second sight occurs, it makes us near sighted (myopic shift). Smaller amounts of near-sightedness can make the near vision better while causing distance vision blurrier.(3) Thus, if you notice any of your parents or grandparents reading better without their glasses on, it is high time to consult an optometrist or ophthalmologist. If their near vision is suddenly better than ever, chances are that their distance vision may be worse.
To conclude, early diagnosis through a comprehensive eye evaluation and timely surgical intervention are crucial in the management of cataract.(4) Timely cataract surgery helps in recovering both the distance and near vision completely. Public health education and awareness are important and eye care professionals should encourage patients with cataracts to seek early treatment for better prognosis.(3,4)
References:
- Pierscionek B, Bahrami M, Hoshino M, Uesugi K, Regini J, Yagi N. The eye lens: age-related trends and individual variations in refractive index and shape parameters. Oncotarget. 2015 Oct 13;6(31):30532.
- Schmitt C, Hockwin O. The mechanisms of cataract formation. Journal of inherited metabolic disease. 1990 Jul;13(4):501-8.
- Fotedar R, Mitchell P, Burlutsky G, Wang JJ. Relationship of 10-year change in refraction to nuclear cataract and axial length: findings from an older population. Ophthalmology. 2008 Aug 1;115(8):1273-8.
- Azhany Y, Hemalatha C, Nani D, Rosediani M, Liza-Sharmini AT. Sequelae of neglected senile cataract. Malaysian family physician: the official journal of the Academy of Family Physicians of Malaysia. 2013;8(1):33.
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