Importance of Interpupillary Distance in Spectacles

Importance of Interpupillary Distance

Globally approximately 145 million people of the total population and approximately 40% of India’s population is having an uncorrected refractive error (means need a pair of glass/spectacle).

Refractive error is one of the most important ocular conditions that are affecting all age groups and a priority under the VISION2020 initiative. Most refractive errors can be easily corrected at the primary care level with the help of spectacles. Uncorrected refractive error is the second leading cause of vision impairment in developing countries (including India).

Interpupillary distance (IPD) is the distance between the centers of your two eyes (center of corneal reflex) which is measured in millimeter. IPD can be measured monocularly and binocularly. Monocular IPD is the distance between the center of each eye and the center bridge of the nose. Monocular IPD may be slightly different for each eye due to anatomical variation and is dependent on your eye placement. An adult IPD usually remains more than kids IPD. IPD measurement is required for all types of spectacles including buying spectacles for distance or near. The near IPD is usually smaller than distance IPD due to convergence of the eyes together to fuse an object at near.

Different ways to measure IPD:

•    Ruler and torchlight (old method)
•    Pupillometer
•    Essilor Visioffice (USA)
•    Eye-Ruler 2 (USA) 
•    Zeiss i-Terminal2

IPD Measurement with Ruler and torchlight

Examiner should be exactly in front of the patient maintaining the same eye level height and holding a ruler at arm's length distance. Examiner closes his right eye and the patient must be looking at the examiner’s left eye with his right eye and put the ruler at the patient’s nose bridge area (for better stability) while aligning ‘0’ at patient’s center of the right eye. And without moving off a ruler examiner should open his right eye (after closing his left eye) and the patient must be looking at the examiner’s right eye with his left eye. Now measure the distance between both eyes center with ruler – this is your distance IPD. Average distance IPD may fall in the range of 56-66mm. The drawback of this method is parallax may skew measurement, examiner PD and patient’s PD must be very similar and the patient’s pupil must have the same size.
Another way to measure IPD is the distance between the right eye’s outer limbus to left eye’s inner limbus. With this method, IPD measurement may be inaccurate.

IPD measurement with Pupillometer

IPD measurement with pupillometer is more convenient. A Pupillometer has forehead rest, nose bridge, dial to change the distance to focus, display for monocular and binocular PD. Putting dial at infinite while using pupillometer over patient nose and aligning forehead rest. Now patient must be looking at small light inside the pupillometer and the examiner should align the measuring slide (a line or bar) until vertical lines should coincide with the corneal reflex. And read the reading in the display for monocular and binocular IPD. 
This device is faster than using manual measurement and takes all necessary measurements for personalized progressive lens and provides numerous solutions to select the lenses and frames. This device assesses the different measurement centers of eye rotation, the distance between pupils, the dominance of eye, reading distance, pantoscopic tilt, the fitting height of the lens, and frame parameters ie. wrap angle, A, B, and DBL.

Zeiss i-Terminal2

Zeiss i-Terminal2 is faster than using manual measurement and captures and calculates the patient’s required parameters with the click of a button. This device enables the measurement of highly ametropic patients through vergence control technology.  Measurement can be taken for any type of frame including large-size sunglasses and sports frames. It can measurement all height persons (children, taller or wheelchair person) ranging from ~120-208cms.

IPD is used to align the center of eyeglass lenses with the center of your eyes, which will give you a comfortable and relaxed vision. If the centers of eyeglass lenses are not aligned properly as per your eyes centration, then you may experience eyestrain, headaches, distorted vision, double vision, blurred vision, and/or an inability to wear your eyeglasses for a longer duration.

There are so many spectacle users (patients) who complain of eye strain. Many spectacle users are unsatisfactory that is the result of incorrect estimation of the IPD for distance and near. So it is an important While making a pair of glasses the dispensing professional need to measure Interpupillary distance (IPD) of a person.

IPD measurement is not the part of an eye examination but the IPD measurement is the responsibility of the dispensing professional and it is an important part of a spectacle prescription. Other spectacle dispensing services includes selection of an appropriate frame, lens type, lens thickness and coatings, adjustment of the spectacle frame, and proper alignment of the bifocal or progressive lens height.
Sometimes being perfect IPD alignment and proper spectacle lens fitting still patient complain of eye strain or unsatisfied. What could be the next to find for eye strain or unsatisfactory? So it is very useful scientifically to check the front and back curvature of the lens, coating of the lens, design (aspheric or conventional) of the lens of old glasses as sometimes spectacle users may not very satisfy with new glasses because of this. Sometimes new spectacle lens may have different front and back curvature, different coating of the lens, and design (aspheric or conventional) of the lens.

There are some more factors including frame size (bigger or smaller size over face), pantoscopic tilt (the amount of tilt on the front of the frame), wrap angle (the amount the frame is curved towards your face) and frame alignment over the face which can lead eye strain or unsatisfactory.

There are some other measurements that your optician will take when fitting you for progressive or multifocal lenses. There are two important key measurements - the IPD and the segment height must be checked while fitting a multifocal lens. These two measurements will be providing a comfortable vision with lesser adaptation time.

Each spectacle lens manufacturer is having its version of customized progressives. Near-pupillary distance measurement is also important in progressive addition lenses as these lenses are having customization instead of being standard. There are few other measurements including the vertex distance (the distance between the frame and the cornea), the pantascopic tilt, and the wrap angle to be checked while making a selection of a frame. The latest progressive lenses are more user friendly, giving a wider area of the field of vision and are generally easier to adapt to, especially for those with higher power prescriptions.

In my practice, if any patient complains of eye strain, double vision (shadow feeling while watching TV, or reading text at near), headache after wearing new glasses then my first check would be refraction (repeat power) check-up, IPD measurement, vertex distance, pantoscopic tilt, etc. Most patients are satisfied with repeat refraction and IPD measurement and their comfort changes after reassuring these two checks.

Progressive Lenses vs Bifocal Lenses

 Progressive Lenses vs Bifocal Lenses

  Approximately at the age of 40 (+/-2 years) your eyes gradually lose the ability to see things for near. It is a normal part of aging. The term is called “presbyopia”, comes from a Greek word which means “old eye.” You will probably find that you hold reading materials farther away or stretch hands in order to see them clearly.
When you are young, the lens is soft and flexible, easily changing shape due to this you can focus both distance and near objects clearly. After 40 years of age, the lens becomes more rigid and cannot change shape easily. This makes you to read at near with efforts, thread a needle, or do other close-up tasks. There is no way to stop or reverse the normal aging process that loses the ability to see things at near. However, this can be corrected with eyeglasses, contact lenses or surgery but surgical choice may not be very good for everyone. If you do not correct presbyopia, you may experience eye stress, eyestrain, focus-defocus, headaches and sometimes you feel that your hands shorten.
Wearing eyeglasses is an easy way to correct presbyopia. Seeing clear vision with eyeglasses offers the opportunity to select from different types of lens options, frame designs and even lens coatings for various purposes.
There are different types of eyeglass lens designs: single vision lens – corrects only one distance vision, bifocal lens – corrects distance and near vision (does not has intermediate distance to see monitor), and multifocal or progressive lens – designed to correct all distances vision (the upper portion is focused for distance vision, middle portion focused for monitor, while the bottom portion is used for reading).
Bifocals have two zones to correct vision for reading on the bottom half of the lens and another for seeing at a distance on the top. Some special lenses may also have segments at the top for those who need to look upward at objects that are in the intermediate or near range these lenses are called double-D bifocals (but not used frequently).
Progressive or multifocal lenses function generally the same way as bifocals due to a smooth transition between distance and near focal areas instead visible dividing lines in bifocal.
If you don't want to use glasses for distance, you can use reading glasses only which can be purchased from any optical store. You will probably must change your eyeglass prescription from time to time (approx every 1-2 years) between the ages of 40 and 60 because your eye's natural lens will still lose flexibility and consequently focusing ability.

Progressive Lens Designs

 Progressive Lens Designs

 Population age than 40 years having confusion that which type of glasses they should use! As they find discomfort while seeing ingredient/price tag on product or teaching their child(ren).
Glasses with distance and near vision correction are called bifocal. This comes with 'D shape' or 'Circle shape' or 'straight line' bifocal. This type of lens can give confusion in vision while walking, climbing up & down on stairs, when vision falls at the junction of distance and near segment. It is difficult to see monitor with this type of glasses. And person may experience back and neck pain.
Progressive lens provides clear vision in vertically (distance to near) without image jump but creates distortion in peripheral vision (side vision). But this distortion may depend on the design of progressive lens. Progressive lens comes in different field of vision ie. Narrow (hard design), medium and wider (soft design) field of vision progressive lens.
Wider field of vision progressive lenses are the best choice to use where user may have very less distortion in side vision, better comfort while adaptation, lesser adaptation time.
Progressive lenses are available with top brands like Essilor, Zeiss etc.

Online teaching could make kids vulnerable to Corona Virus

Online teaching could make kids vulnerable to Corona Virus

 In olden time kids were usually read books and was spending lesser time to screen (includes TV,  computer, etc). In the past few years teaching kids is not remaining same as earlier.

In the recent past, online education is rapidly increased due to competition among children. Most children take online classes due to nuclear-family as both parents go to work and parents can’t take them to coaching classes. Kids are spending lesser time in outdoor activities (lesser exposure in sunlight) as both parents are not having sufficient time to spend with them. Teachers also give them more creative activity as homework so kids use computers or mobile to search mostly.

Eye experts are informing parents of the dangers of increased digital screen-time on their children’s eyes due to online classes. Due to which children are at the risk of myopia (near-sightedness), dryness and redness of the eyes and disrupted sleep patterns. Dryness of the eyes can damage to the ocular surface (front surface of cornea) and could even make patients more susceptible to contracting COVID-19.

If someone use digital screen (including mobile, tablet, computer, laptop etc) and spending average 6-12 hours per day then their blink rate reduces along with that they could have symptoms of gritty sensation, itching, redness and dryness in the eyes. “When a person blinks, tears are liberated through tiny pores which lubricate the eye.

So kids also have lesser blink rate, pink eyes, and dryness of eyes while using screen and sometimes they are not expressing in front of parents. Most families may not have laptop or computer with them so mostly kids are taking classes in mobile phone.

“The patient can become vulnerable to catching an infection when their ocular defence mechanisms are down. Conjunctivitis is a common presentation among Covid-19 patients, indicating that people with dryness issues in their eyes are at risk of contracting the infection. As they touch their eyes due to dryness and irritation, and eyes are at risk of contracting the infection.

Why we are more sensitive to smart phone or tablet screen? Why we should restrict small screen usage?

1. Smart phone and tablet screen size is smaller than laptop or computer screen.
2. Smaller screen size means smaller font size in mobile and tablet screen.
3. Digital screen (mobile and tablet) is having sensors due to which screen brightness keep fluctuating with lighting conditions.
4. Mobiles, tablets and laptops screen usually have glossy screen where light reflection may occur but computer monitors are not having glossy screen.
5. Laptop and computer monitors do not have sensors to change the brightness and contrast automatically.
6. Good thing: mobile and tablets are more handy - whenever or wherever you want to use them, press the button and screen get on within a second.
7. Laptops are bulky; relatively screen size is bigger than a tablet but takes time to boot. A laptop has a glossy screen due to that reflection occurs.
8. Computers need more space and computer screen size is definitely bigger in all screens and takes time to boot. There are no sensors to change the brightness and contrast automatically and there is no glossy screen in monitor.

 Eye specialists advise parents to exercise caution by restricting screen time for children and incorporate regular breaks during class work.

Children who aren’t getting enough sunlight or change of scenery were at high risk of developing myopia or progression of myopia (worsening of nearsightedness). “Increased screen time will also lead to disruptions in their sleep patterns.” Eye specialist recommends an age-bracket approach to restricting screen time for children. “It is important that the number of teaching hours should be reduced greatly. If a child used to have eight hours of classes at school, the number of online hours cannot be of the same length.”

Computer use for children should be as follows (if needed):

-First standard classes should not be conducted online at all.
-Second to fifth class online classes should be 2-3 hours per day with the break of 30 minutes and parents should be involved for homework through email or Whatsapp.
-Sixth to eighth class online classes should be 3-4 hours per day with the break of 30 minutes and parents should be involved for homework through email or Whatsapp.
-Ninth to twelfth class online classes should be 4-6 hours per day with the break of 30 minutes and parents and teachers should be involved for homework through email or Whatsapp.

 Parents should be counseled that the kid should have some snacks, drink water and focus far objects during the break time. Room illumination should not be very bright or dull (semi dark) at the time of screen usage. Kids should not use screen in sleepy position and close to face. Parents should insist on kids to make book-reading habits. Book reading should always be in good illuminating room and sitting position. Books, mobile, and tablet should be kept at 30-35 cms distance from eyes. Computer monitor should be at least one hand’s-distance (50 cms) from eyes.

 If kids are getting any kind of discomfort in their eyes; they should:

1. Avoid excessive screen usage and eye rub.
2. Take water wet cloth and put it over closed eyes.
3. Frequent blinking during screen usage time.
4. After online classes kids should close their eyes and give rest to their eyes for one hour.

Children should follow computer vision syndrome (CVS) rules means take a 20 second-long break after every 20 minutes of screen time, and focus at something located 20 feet away.

Lubricating eye drops could be administered during the day to facilitate moisture on eye surface.

If kids rub their eyes then there is a risk to change the eyeball shape and glasses power may increase. Eye rubbing could sometimes lead as an eye allergy.

How to take care Contact lens related allergies?

Contact lenses (CLs) provide safe and effective vision correction if adequate lenses’ care is ensured as recommended. However, CLs’ wearers may have risk of eye infections if they fail to clean, disinfect, and store their CLs as instructions given.

    Contacts are composed of hypoallergenic materials. This means the materials themselves do not usually cause an allergic reaction. Instead, what causes it is a buildup of contaminants on the contacts. However, in rare cases, people can develop allergies to the actual lenses.
    Your eyes produce a protein that is deposited on your contact lenses while being worn. The protein is broken down when the lenses are stored in the contact lens solution. Over time, from daily usage of contact lens, the proteins can end up in your bloodstream via eyelids. Your immune system identifies these proteins as foreign invaders, similar to an allergen.
    Your body then begins creating antibodies and once these antibodies are enough in your bloodstream, the contact lenses become uncomfortable. This leads to an allergic sensation through a condition called giant papillary conjunctivitis or GPC.
    Sometimes contact lens user may find discomfort with CLs due to improper fitting of CL, uncorrected astigmatism, CL induced dry eyes, excessive digital screen usage and other allergies. Discomfort with contact lens can be identified by irritation, redness, bright light, pain in the eyes every time while lenses are worn.
    Sometimes contact lens solution could be the next cause of eye allergy because these solutions contains preservatives. Even proper cleaning of contact lenses may still leave traces of preservative. Thimersol is one of the main preservative in contact lens solutions - better to use Thimersol-free or presarvative-free contact lens solution.
    If still you have any kind of discomfort in your eyes, firstly to stop using contact lens. Prolong CL wear will increase discomfort, aggravate pain and eye infection.
    Better to consult with eye doctor for your eye discomfort, pain and infection.

Pterygium - Prevention, cause, symptoms and treatment


Pterygium is fleshy conjunctival membrane growth (has blood vessels) that cover the white area of the eye and slowly spread over the cornea. This growth is a kind of triangular shape. It may occur in one eye or both eyes. If it develops in both eyes called bilateral pterygium. Early-stage of pterygium is looked like pingecula, so sometimes it is difficult to differentiate between pterygium and pingecula.

Pterygium is a non-cancerous growth; sometimes this may disconfigure the eye cosmetically. Due to moderate to advanced pterygium growth person may experience redness, irritation, discomfort, and blurry vision. Pterygium grows very slowly but in very few cases it may grow rapidly.
Reason for occurrence - cause for pterygium occurrence is unclear. It could be due to overexposure to Ultraviolet rays, excessive exposure to dust and pollution. In case of dry eyes pterygium may increase. In case of injury or burn near black eyeball or its adnexa will also cause pterygium occurrence.

Stages of Pterygium

Stage 0: In this stage very small elevation appears near the black eyeball over the sclera. In this stage there is no vascularisation and conjunctival and corneal ectasia are seen.
Stage 1: In this stage small bump like mass touches the limbus.
Stage 2: In this stage bump flatten a little just on the limbus with minimal vascularisation.
Stage 3: In this stage the fleshy layer covers the area between the limbus and pupillary margin with minimal congestion and vascularisation. This stage is associated with mild to moderate astigmatism.
Stage 4: In this stage the fleshy layer reaches to central to the pupillary margin with severe congestion and dilation. This stage is associated with an increase in astigmatism and rarely leads to the limitation of eye movement.

Signs and Symptoms

Pterygium causes redness, itching, irritation, foreign body sensation, sometimes dryness in the eyes. Redness may increase when someone is exposed to air, dust, and pollution or drives without protective glass. Contact lens users may find discomfort due to poor fitting of contact lens in moderate to advanced pterygium conditions. The cosmetic appearance of the eye may not look good in the case of pterygium. Pterygium is stretching the front surface of the eye (cornea), which leads to astigmatism and higher-order aberrations which affects the quality of vision.

Treatment and prevention

  • Avoid eye rubbing excessively.
  • To wear protective glasses (covering full eyes).
  • UV light protected glasses.
  • Lubricants (eye moisten drops).
  • Surgically (in case of moderation or advanced pterygium) - But recurrence rate is 2-5% after pterygium surgery. 
There are different techniques to remove pterygium surgically:
a. Pterygium excision with autologous conjunctival autografting
b. Pterygium excision with mitomycin C,
c. Pterygium excision with conjunctival limbal autograft
d. Pterygium excision with amniotic membrane transplantation

During the pterygium surgery fleshy mass is removed and replaced with a graft of associated membrane tissue to prevent recurrent pterygium growths. And this graft is attached either with sutures or fibrin glue, post pterygium surgery eye experienced lesser discomfort, and recovery time reduces with fibrin glue. But fibrin glue is having its own risk of transmitting infection (viral) and more inflammation.

Recovery time

Post pterygium surgery redness, irritation, foreign body sensation, and graft dissolving usually takes 6-8 weeks but this healing time may change due to the type of technique used during surgery.

Top Eye Hospitals in India | Eye Hospitals

1. L V Prasad Eye Institute (LVPEI), Hyderabad
   Address: Kallam Anji Reddy (KAR) campus, Banjara Hills Road no. 2, Hyderabad - 500034
Phone: +91 6810 2020
Email (Hyderabad):,

    L V Prasad Eye Institute jointly founded by Dr Gullapalli Nageshwar Rao and Mr Ramesh Prasad, son of Mr. Akkineni Lakshmi Vara Prasada Rao (L V Prasad) in 1987.

    LVPEI is a World Health Organization Collaborating Centre for Prevention of Blindness. The Institute offers comprehensive patient care, sight enhancement and rehabilitation services and high-impact rural eye health programs and ocular Tissue Engineering research center.

    It's main campus Centre of Excellence is located in Hyderabad, India.
    The LVPEI network includes a Centre of Excellence in Hyderabad, 3 tertiary centres in Bhubaneswar, Visakhapatnam and Vijayawada, 11 secondary and 95 primary care centres that cover the remotest rural areas in the state of Telangana, Andhra Pradesh and Odisha, India.

L V Prasad Eye Institute receives patients from all over India and internationally.

 Hospital Services:
1. Emergency services
2. Cornea and Anterior Segment
3. Retina
4. Oculoplasty
5. Center for sight enhancement and rehabilitation services
6. Pediatric
7. Refractive surgery
8. Ocular Oncology
9. Squint
10. Orthoptics
11. Eye Bank
12. Microbiology and pathology
13. Cataract services
14. Contact lens
15. Aesthetic Facial Plastic Surgery, Cosmetic Dermatology
16. Glaucoma services

2. Dr R P Centre for ophthalmic sciences AIIMS 

New Delhi

Dr. R.P.Centre for ophthalmic sciences A.I.I.M.S - New Delhi

 Address: Sri Aurobindo Marg, Ansari Nagar, New Delhi - 110029
 Phone: +91-11-26588500 / 26588700         Fax: +91-11-26588663 / 26588641
Email address: ""
Appointment: "" (new patients) and  "" (follow up patient)

Dr. Rajendra Prasad Centre for Ophthalmic Sciences, named after the first President of India, Dr. Rajendra Prasad, was established on the 10th of March, 1967 as a National centre for ophthalmic science, to provide state of the art patient care, expand human resources for medical education and undertake research to find solutions to eye health problems of national importance. 

Hospital Services:
1. Clinical Units and Allied Departments
2. Out Patient Services
3. Emergency Services
4. Clinical Laboratories
5. National Eye Bank
6. Investigative Laboratories
7. Day Care Surgery
8. Community Ophthalmology
9. In Patient Services

3. Sankar Netralaya - Chennai (Tamil Nadu).
No. 41 (old 18), College Road, Chennai 600 006, Tamil Nadu, India.
Telephone: +91-44-4227 1500, +91-44-2827 1616
e-mail (Chennai) :,,

It was in 1976 when addressing a group of doctors, His Holiness Sri Jayendra Saraswathi, the Sankaracharya of the Kanchi Kamakoti Peetam spoke of the need to create a hospital with a missionary spirit.

Sankara Netralaya (SN) FIRST ISO 9002 certified Eye Hospital in Asia.

SN is a not-for-profit missionary institution for ophthalmic care (i.e., an eye hospital) in Chennai, India. In "Sankara Nethralaya" Sankara is a reference to Shiva and Nethralaya means "The Temple of the Eye".

Sankara Netralaya receives patients from India and internationally. Nani A. Palkivala, former Indian ambassador to United States, described Sankara Netralaya as the "Best managed charitable organization in India".

4. Aravind Eye Hospital - Madurai (Tamil Nadu).

1, Anna Nagar, Madurai - 625020 Tamil Nadu, India

Phone: +91 452 435 6100
Email :,

It was founded by Dr. Govindappa Venkataswamy in 1976.
Since then it has grown into a network of eye hospitals that have seen a total of nearly 32 million patients in 36 years and performed nearly 4 million eye surgeries, majority of them being very cheap or free.

Dr. Venkataswamy's vision was to eradicate needless blindness in India. Dr. Venkataswamy. wanted to emulate the service efficiency of McDonald's fast food and sought to adapt it to the eye care system to cope with increasing the numbers of patients treated.

The model of Aravind Eye Care hospitals has been applauded all over the world and has become a subject for numerous case studies.

5. Center for Sight (CFS)

Established in 1996, by Dr. Mahipal Sachdev, eminent ophthalmologist and a Padmashree awardee, Centre for Sight is instrumental in changing the face and service standards of eye care in the country.
Since its inception, Centre for Sight has been guided by patient centric values of efficiency, precision, compassion and integrity. In 2010, Centre for Sight was awarded the prestigious Frost & Sullivan award as the Eye care provider company of the year, an affirmation of its values.
In 2012, Centre for Sight won the prestigious FICCI Healthcare Excellence award for Operational Excellence. The award is a recognition of our efforts to make eye care a super speciality in India.

Hospital Services:
1. ReLEx Smile
3. Cataract Services
4. Retina & Uvea Services
5. Glaucoma Services
6. Cornea Services
7. Keratoconus Clinic
8. Neuro- Ophthalmology
9. Pediatric Ophthalmology
10. Oculoplasty & Facial Aesthetics
11. Ocular Oncology
12. Eye Bank
13. Contact Lens & Low Vision Aids

Updating some more hospital soon...