If a patient tells you that their eyesight has improved, would you always believe that their eye has improved ?
59 year old man walked into my clinic with a surprisingly positive complaint
"Doctor, I think my eyes have become better"
So, he had just come for a routine eye checkup. Prior to this, his vision was checked using the Snellen's chart. In fact, he had noticed something that made him quite happy at the very moment.
He could read the chart as well as his phone without the reading glasses !
He was dependent on a glass of power+1.5D for past several years. It was over 8-10 months that something strange was happening to his eyes. His glasses were becoming unnecessary. He could read text, messages on his phone, read the newspaper. At present moment, refraction revealed more myopic but he had been mildly hyperopic for several years
He could even thread a needle easily without the aid of glasses
Basically, he thought "My eyesight is improving with age". However, he has only one problem. That is, he could read but couldn't see the TV much clearly. Traffic lights, signs were little difficult to recognize and the headlight of the approaching vehicle created more glare than before.
He was puzzled about how his near vision getting better and distance vision getting worse. How could both be happening in the same eye ?
There comes the ophthalmologist weapon to see the eye : SLIT LAMP BIOMICROSCOPE. On examination, there was a progressive nuclear sclerosis of the crystalline lens. Lens had become more denser that had changed his optical power. It was a refractive illusion created by the cataract.
SLIT LAMP EXAMINATION
Clear view of progressive nuclear sclerosis
SECOND SIGHT PHENOMENON
As cataract (Nuclear Sclerosis) progresses, refractive index of lens nucleus also increases. This can overall increase the eye's overall refractive power.
Science behind his eyesight improvement is due to shift towards myopia. Previously presbyopia patient may temporarily improve uncorrected near vision. Cataract hasn't restored his accommodation. Simply has changed his refractive state. This phenomenon is called Second Sight Phenomenon.
As the lens protein and compounds changes, the structure of the lens changes. Lens becomes harder in the central part called as nuclear sclerosis.
Nuclear Sclerosis compensating for accommodation [Source]
Higher refractive index lens bends the light more and focuses on retina without the need of lens to change its shape.
A very two different perception :
Him: "I am seeing better" - experience improvement
Me : "Your cataract is progressing" - eye is actually deteriorating
So, this is not permanent. Lens opacity increases whereas glare, optical aberrations and distance vision decreases. Even the clarity; contrast sensitivity decreases.
This patient taught me an important clinical lesson that not every visual function improvement in patient represents the improvement in ocular health.
Other sites to look on for :
- "Second Sight" masking Adult Cataract
- Don't lose permanent treasure for temporary pleasure
- Initial Signs of Cataract
My other blogs to follow :
- A Swollen Disc, A Difficult Decision, A Remarkable Recovery - Papillitis
- Ocular Toxoplasmosis - When Standard Treatment Wasn't Enough
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