Roving ring scotoma & Jack-in-the-box phenomenon are few the most confusing aspects of optics in Ophthalmology.
If you have heard about these but couldn't understand them then this is the post for you,I will explain you these concepts in the most easy manner possible with diagrams.
Surgical treatment of cataract by removal of the crystalline lens of the eye results in an aphakic eye which has very different optical properties from the normal or phakic eye.
In particular, after the removal of the crystalline lens which accounts for about one-thirds of the eye's optical power(about 10 -15 Diopters, the patient requires a spectacle lens about +10.00D -+15.00D .
3 main modalities to correct aphakia :
- Aphakic spectacles
- Contact lenses
- Intraocular lens(IOL). (now most widely used)
We are going to stress about few fascinating problems like Roving ring scotoma & Jack-in-the-box phenomenon due to Aphakic spectacles due to which they were replaced by the IOL.
Aphakic Spectacles:
To correct the refractive error in aphakia about 10 dioptre of convex lenses are required for distance vision and about 13 dioptre for near vision. Such high power lenses are associated with numerous physical and optical problems. The most important of these problems are:
- Magnification: Each dioptre of convex power leads to about 3 % magnification of image and a difference of image size between the two eyes of about 7 % is tolerable. Thus 10 dioptre aphakic spectacles lead to about 30 % magnification of the image which give rise to diplopia i.e., two images of one object are seen one small (from normal eye) and other larger (from aphakic eye). Moreover, when the objects appear larger they appear falsely closer than reality, and this leads to physical in-coordination.
- Roving Ring Scotoma: The edge of a convex lens acts as a prism and the higher the power of the convex lens the greater is the prism angle (alpha). The light falling on the prism bends towards its base by an angle alpha/2 , therefore, greater the angle alpha the more will be the bending. In aphakic spectacles, the angle alpha being large, the light falling at the edge of the lens bends towards the center of the lens (base of prism) and does not reach the pupil and is, therefore, not seen. This results in an area of the visual field which is not visible to the patient, or scotoma. And because the edge of the lens is present all around the lens like a ring, so it gives rise to a ring shaped scotoma. The position of this scotoma is not fixed in the visual field because the eye keeps moving (or roving) in relation to the aphakic spectacle. Hence, the result is a roving ring scotoma.
- Jack-in-the-box Phenomenon: The presence of the above scotoma leads to another interesting phenomenon. If an interesting object appears in the periphery of the patients visual field, it appears blurred (because the light is passing from the side of the spectacle frame). The person tends to move his head towards the object in order to see it clearly. But as he turns the head the object comes to lie in the area of scotoma and thus disappears. As he turns his head further so that the object comes to lie in front of the spectacle in the visible area and so reappears again clear and sharp. This sudden disappearance and sharp reappearance of the objects is called jack-in-the-box phenomenon.
- Pin Cushion Effect: The magnification of image is more at the periphery of the lens due to prism effect. Therefore, all the objects appear stretched out at the corners like a pin-cushion.
- Spherical Aberrations: The light converges more near the edge of the lens than at the center so the rays of light falling near the edge are brought to focus in front of the rays falling at the center. This results poor quality of image despite appropriate correction of refractive error.
- Chromatic Aberrations: The shorter the wave-length the more is the refraction a ray of light undergoes. Therefore, in VIBGYOR the violet end undergoes greater refraction than the red end of the spectrum. This causes diffraction of light and makes the edges of white object appear rain-bow colored.
130 comments:
I ve searched for the explatnation of this jack in the box phenomenon in many books and websites but nowhere did i find such an easy and clear explanation. Great job. Thanks a lot. Dr. Munneeb from Pakistan.
Now the phenomenon of jack in the box n roving ring scotoma is very much clear to me thru this explanation. Dr. NOreen from Pakistan.
super dude u are really a jack u rowed me around
great explaination. Dr. Sarita from India
thank you so much.. finally i could understand dis phenomenon! FINALLy. great gob thnk u. dr.zulfeen frm india
thank u so much. i could finally understand dis phenomenon. finally! great job,thank u:) dr. zulfeen frm india
super o super
good explination.outstanding
Very Good Explanation, Thank you
Muhammed Kunzi, india
kindly give reference of your explanation
amazing job......thank you very much:)
Erum Zafar Malik,
Pakistan
Superb.... easy and cool illustrations...
thanks a lot!!!
great work man.......
thanks for such an easy way of describing things....:)
i would like to add something to the modalities to treat aphakia....:
it can also be done by keratophakia and epikeratophakia
Thanks a lot ....... I wish I could have explanation like this to every topic I read......I'm short of words to describe how grateful I m ......
Swati Chitkara
thanks a lot...
Thanks a lot !
Understood the concept
St. johns Medical college
Bangalore
great job & keep it up.
thank u sir...very very simple concept only bcoz of u...
simply explained and i got it all. Thanks. Final year DMC student.
Excellent, so simple explanation, thanx!
Dr. Irshad khan J&K India.
thanks a lot.explanation is very simple
Simply One word... SUPERB.
thanx a lot sir.
SUSHIL, Mangalore
THANX A LOT!!!!!!!
DR A SARKAR,KOLKATA
heartful thanks for u hav made me clear of such greek nd latin terms.THANK U VERY MUCH...
really superb explanation...:):)really superb explanation...:):)
wow wat a way 2 explain.....really i must say if dis s d way to explain den i must nw m ur fan..wow wat a way 2 explain.....really i must say if dis s d way to explain den i must say nw m ur fan
..
dr.om frm india..
thank u....
i had to make a presentation on aphakia and was going crazy trying to find an easy explanation for these phenomena, thank you so much!!! :D
3rd year AKU student
Outstanding..thank u very much..dr. Rajesh scbmc
awesome! hunted in parson's, couldnt get it. has helped me a lot a day before my practs! thanks a ton........
Christian medical college,Vellore, India
Good Work Dude...Keep it up.
SUPERB SIMPLE!!! Thanks a lot :)
there is visual field that is not visible 2 patient in periphery.......then u said there is more magnification at periphery...????please explain.....????
Thank You so much...understood it in just the first reading!!!
great work...........do you have some other confusing concepts to explain?
Beautiful explanation.i didnt understand when i read this in PArson.
Thanks. I love you
Excellent web site pg aspirent
Dr. Ajeet chamania
A wonderful explanation please continue the good job
Great explanation. Understood everything easily. Thanks a lot
bindaaas explanation....no where did i get such an interesting nd easy xplanation..sambhavam colour aayintundu ketaa !!!thnx a lot
Dr.Jassim Abdulla, calicut medical college,kerala.,india
Thank u so much
Dr Bhawna
thanx a lot! u made it seem so simple
JAZAKALLAHU KHAIRAN:) AYESHA NAZIR-4TH YEAR STUDENT FROM PAKISTAN
thank u very useful information
Thank you so much ! That was a concise :D
Brilliant is the word . Good explanation.
Seriously...its beautiful to understand it this way....thanks a tonnn
Such a wonderful explanation.. Thanks a lot..
Thank u.... thank u soooo much sir... love this explination... Even the professors who teach us never gave us such clear explination.. That was really awesome :) <3 Cherukuri.Vineela
I.M.Sc Optometry.
H.C.U
So crystal clear
Hats off professor
Vishnu
Mbbs
Jnmc
Thnq so much fr dis post...helped me a lot
Pearl
MBBS
India
explained in very good manner.Dr Azhar Mahmood, Pakistan
Thanks a lot for such a lucid explanation...
Thans a lot
G8 explanation thank u sooooo much for making it so easy
Really very explicitly said... Easy to understand
very good explanation..great job
Great explanation
Excellent description.....wid perfect diagrams
Amazed to get an clear overview ... Thnk u
Thanks for such an easy explanation!
...
Thank you very much doctor. You made it so easy to understand. Depicted pictures were of great help .
Can you clarify more on pin cushion effect.. In which lens does this effect take place and whats its difference with barrel shaped effect.
You really spelled out the concept to the reader!! Amazing! Thanks!
really u made me to understand this concept easily....thnq so much....from Mahesh R.M
You're freaking awesome
Very niceee
Very niceee
Woah! U the man. Thanks!
Thank you ,explained it in a very easy manner
Thank you!
Thank you!
Thankyou .. Smiplified ...
Thankyou .. Smiplified ...
Thanks a lot.. very easily understandable~~
Very gud and easy explanation.. . thnq
thank you for so easy explaination of complex concept.
I've worn very strong aphakic glasses (+20 about) my whole life and I finally understand some things about my vision, like why its hard to walk in crowds with people moving all about.
I've worn very strong aphakic glasses (+20 about) my whole life and I finally understand some things about my vision, like why its hard to walk in crowds with people moving all about.
Amazing! Made my concept crystal clear! Thank you so much.
This explanation is really easy to understand...... Thanku so much..... really awesome
Dude you nailed it
very nice explanation bro.............. great job...............
Thank you for this wonderful explanation
thank you...
Good explanation
Very well explained.IUnderstood the concept quickily and easily .Thank you so much.
Thanku soo much! Very helpful and eash to understand
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Great explanation !!!
Thanks alot .
Thank you, that was very easy to understand :)
hello, today as always your post is lovely that I liked it and I am waiting for your new works in future, good luck to all of you.
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Sir, I have searched a lot of textbooks and journals for an explanation to this effect. Not one of them has even come near the explanation given here.
Thank you so much. Hope you help more students in this manner.
Very nicely explained. Jack in the box phenomenon was so simply explained. Thnku sir
Thanks....it clears my concept about the topic
u deserve a hug . thank you so much
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