45 Comments

  1. Fadi Al Awad says:

    dear Sir,
    I need your help to get a 3 dimentions explaining about the meaning of Cylinder,Sphere and Axis.
    thank you for your interest
    Eng. Fadi Al Awad

  2. Did anyone spell check these?? Foropter?? PHROPTER correct spelling

    1. . . .or maybe PHOROPTER . . ?

  3. MUHAMMAD BILAL says:

    great pa ji cha gai ho tussiiii ki kawan twano hun pai jan

  4. Katherine says:

    Spelling mistakes to note:
    Phoropter has a letter o before and after the r!

    Re the Optics Flash Cards. Accommodation has two letter “c” and two letter “m” (have omitted the plural s as it looks silly however I type it) and as I don’t want to imply any possession, I can’t use an apostrophe! Obviously something one says rather than writes.

  5. Worderful topic i ever enjoy during this study
    Mark iga anthony ophthamology student in university of juba

  6. i am from Tajikistan. Good jod, Thank u.

  7. You should all be thanking Mr. Root for his amazing site, not nitpicking the spelling of terms. Great work!

  8. Actually, isn’t the engineer’s “football”‘s axis at 125 degrees, necessitating the plus cylinder at 35 degrees?

    Editors Note: Yep, but I didn’t write this out explicitly as it would sound confusing. My focus with that “example” was that astigmatism occurs at different angles than 90 and 180. I don’t find it useful for beginners to think about the shape of the eyeball “football” in too great detail, as this gets very confusing. You are technically correct, though, and I may reword this next edition.

  9. wonderfull book short review of ophthalmology really very nice book

  10. How accurate and specific is the calculation for intraocular lens implants?
    Can the patient expect to get specific results?

    My partner, after much discussion with his surgeon, opted for a lens “just off infinity” (the surgeon’s words)so that he would be able to see extremely well in the 20-50 foot range (he’s an athlete, plays basket ball, baseball)

    2 weeks following surgery, his focal length appears to be just about a meter and a half, fuzzy any further distant than 20-25 feet.

    Monovision with a distance lens implanted in the second eye is NOt a good option…he needs good acuity, and most important, good depth perception.

    ?thoughts?

  11. The website is very educative and i will like people from Nigeria to benefit for it.
    Thank you for ur good work of inform and educating world esp. the 3rd world countries.

  12. sir, this site is very nice n very special for learning and educating to people. nice nice nice ya its nice

  13. i´m from brazil, resident of oftalmology
    this site is very nice, learned so much, thing that i couldn´nt understand just on books ! THANKS!

  14. Francisca Gracia says:

    hi I am optometrist and I have been learning to do biometry.
    for the calculation of the IOL.
    I order to do this we need the prescription of the glasses of the patient, keratometry and then the axial lens. then, the calculation of IOL can be made.
    when patien has cataract usually the prescription changes and i have been reading that the appropiate prescription use for the calculation should be the one before cataract.
    I feel confused how to get that prescription. my manager at the hospital say that we should use the prescription available on the clinical notes that we have at the hospital. however I think that if we do this we will always consider precription of the glasses when the patient has develop cataract.
    As i have been working now in both in private practice at the community and the hospital I think that the prescription before the patient developed cataract could be requested at the practice and then have a more accurate information. what are the consequences of considering the prescription of glasses when the patient has develop cataract already?
    many thanks

  15. 1.IOL calculation formula do you use? ( please show me the
    equation)

    2.cataract can cause myopic shift.

    thanks.

  16. NITIN SAGAR says:

    dear Sir,
    I need your help to get a 3 dimentions explaining about the meaning of Cylinder,Sphere and Axis as requested else where.

    interested in learning optic basics

  17. hello! sir
    how we can get -1.0 D against the rule astigmatism post operatively? kindly request reply.

  18. Great info., I now know what the Prescription means! Thanks!

  19. DR.EHIKPENMI says:

    this site is quite awesome.’tis a good site for the populace to know more about their eyes and eyes condition. DR.ROOT,you have done a great job. more power to your elbow.
    DR.EHIKPENMI O.D. (Nigeria)

  20. this site is awesome,two thumbs up.i would like to find out what is binocular vision,what tests would one perform if the px has no binocular vision.how to perform streak retinoscopy,highlight mix astigamatism,high myopic astigmatism and aphakia.
    PAUL NENANI BANDA(optometry student,zambia)

  21. llongoria says:

    can severe astigmatism be corrected by the Intralase and Ziemer systems?

  22. Am wondering … how much spherical power does the cylindrical portion of an Rx have? If have been told 50%.
    If that’s true, then -1.00 +1.00 would be a net spherical power of -.50.

    So, I’m wondering 1) if that is actually true, and 2) if the 50% would change depending on where the axis is … ?

  23. First, Spherical Equivalent of a cylinder component is always equal to half of its value in addition to the spherical component. For example: -0.50 -4.00 x 165 will give us a Spherical Equivalent of -2.50D.

    Second, it doesn’t matter what’s the axis, the value of the Spherical Equivalent won’t be affected.

  24. Dr. Root this is a wonderful training tool you have provided for students in all fields of Optometry, I am an Optician and your break down of phoria and tropia for example made it so easy to understand and absorb the topic. Thank you for your help in guiding us to become better providers to all our patients.

  25. Hello Dr. Root ,

    I am a 4th year medical student and your website helps a lot in studying the basics .
    I was wondering if you could tell us something about the different angles in the eye –
    The alpha , kappa , gamma and lambda angles , its too confusing .

    Thankyou – your follower .

  26. This website was of great help sir, it’s so hard to find detailed information such as yours that doesn’t make me want to sleep. This truly helped a lot, thank you sooo much! 🙂

  27. hi there i am a resident in opthalmology
    how are you?
    thank you so much for sharing all of this information with us.
    i am from Recife-Pe,
    brazil in south america. and i love this channel.
    this website i meant to say.
    well
    don’t ever change anything in here.
    this website is wonderful. and i am about to buy your book at amazon.
    when are you coming to south america to visit us down here?
    look me up
    Facebook
    claudioagmfilho
    best of luck.
    and come to brazil to visit.

  28. I have a question about hyperopia. 40 yr. old uncorrected Va distance OD 20/100 OS 20/60 but his Uncorrected near Va is
    OD 20/40 OS 20/30

    M OU +5.50 range Wavescan shows him +8.00 range OU

    How can his near VA be this good?

  29. I AM AN OPTOMETRIST FROM NIGERIA I MUST COMMEND THE AUTHOR. WHAT A WONDERFUL BOOK. WRITTEN WITH ALL SIMPLICITY YET INCISIVE. THANKS DOC

  30. dr sarita says:

    hello,I am final year MS student ,you make ophthal very easy.

  31. Awesome explanation…Just got what I needed. Thanks!

  32. Thx for the great job but I need to learn the steps of refraction , any suggested books or websites that might help?

  33. Thank you so much for such a simple explanation for a difficult subject. You have truly helped me so much.

  34. Kathleen Harrell says:

    Thank you so much, I have been looking for a site that explains all of this in much simpler terms. I feel I have a much better understanding!!!

  35. Hi Dr. Root,

    I’ve heard of the term “spherical equivalent” and I know how it’s calculated. However, I don’t know what it is and I have a vague understanding that it’s used to calculate soft lens power and spherical glasses power. Please clarify. Thanks!

  36. I’ve heard of the term “spherical equivalent” and I know how it’s calculated. However, I don’t know what it is and I have a vague understanding that it’s used to calculate soft lens power and spherical glasses power. Please clarify. Thanks!

  37. I simply love it all! Thanks a lot 🙂

  38. Julissa Rodriguez says:

    Hi, Dr. Timothy Root

    My name is Julissa and I am an Ophthalmic Technician here in Orlando. I am from Puerto Rico and got a job as Oph Tech and I am having some problems with the refractions. Can you do a video lecture of How to Recract as the ones of Tropias vs. Phorias, Retinoscopy, and Slit lamp? There where awesome.

    Thanks

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