BEXCO

𝗩𝗶𝘀𝘂𝗮𝗹 𝗳𝗶𝗲𝗹𝗱 𝗧𝗲𝘀𝘁

This is a measure of your central vision and is the most critical part of your vision. However, that is only one a measure of your visual function. Another aspect is your overall visual field, sometimes referred to as peripheral vision. Although many people mistake it as simply a peripheral vision test, a visual field test is actually designed to measure the overall field of vision as it is interpreted by the brain in four neurological quadrants. Different parts of your brain control different parts of your visual field. Results of a visual field test can sometimes help physicians made a diagnosis.

𝗠𝗲𝗮𝘀𝘂𝗿𝗶𝗻𝗴 𝗬𝗼𝘂𝗿 𝗩𝗶𝘀𝘂𝗮𝗹 𝗙𝗶𝗲𝗹𝗱

There are different ways to conduct a visual field examination. The most common way to measure the four quadrants of a visual field is to perform "confrontation neurologic" visual fields. This is the most common way to measure it. Both optometrists and ophthalmologist perform confrontation visual fields with this method during a comprehensive eye examination. It is performed by having the doctor or technician sit at eye level with the patient. One eye is covered. The other eye focuses directly on the technician's eye and either one, two or four fingers are held in each of the four quadrants. The patient is not allowed to move their eye or look at the fingers but must respond with how many fingers the technician is holding up. After all four quadrants are tested, the other eye is measured.

When a visual field deficit is discovered with the finger counting method or if the physician suspects visual field changes, a more formal method will be used called automated perimetry. An automated perimeter is a computerized instrument that measures the field with different lights of different sizes and brightness. An automated perimeter is able to conduct several different types of field tests in a standardized fashion. A threshold test measures an individuals "just barely detectable" vision and quantifies how sensitive a patient may or may not be of detecting points that are considered normal.

𝗪𝗵𝗮𝘁 𝗶𝘀 𝘃𝗶𝘀𝗶𝗼𝗻 𝘀𝗰𝗿𝗲𝗲𝗻𝗶𝗻𝗴?

A vision screening, also called an eye test, is a brief exam that looks for potential vision problems and eye disorders. Vision screenings are often done by primary care providers as part of a child's regular checkup.

𝗪𝗵𝗮𝘁 𝗶𝘀 𝗶𝘁 𝘂𝘀𝗲𝗱 𝗳𝗼𝗿?

Vision screening is most often used to check for possible vision problems in children. The most common eye disorders in children include:

𝗔𝗺𝗯𝗹𝘆𝗼𝗽𝗶𝗮, also known as lazy eye. Children with amblyopia have blurry or reduced vision in one eye.
𝗦𝘁𝗿𝗮𝗯𝗶𝘀𝗺𝘂𝘀, also known as crossed eyes. In this disorder, the eyes don't line up right and point in different directions.

𝗪𝗵𝘆 𝗱𝗼 𝗜 𝗻𝗲𝗲𝗱 𝘃𝗶𝘀𝗶𝗼𝗻 𝘀𝗰𝗿𝗲𝗲𝗻𝗶𝗻𝗴?

A routine vision screening is not recommended for most healthy adults. But most adults are encouraged to get eye exams from an eye care specialist on a regular basis. If you have questions about when to get an eye exam, talk to your primary care provider.

𝗣𝗔𝗦𝗖𝗔𝗟 𝗗𝘆𝗻𝗮𝗺𝗶𝗰 𝗖𝗼𝗻𝘁𝗼𝘂𝗿 𝗧𝗼𝗻𝗼𝗺𝗲𝘁𝗲𝗿

The PASCAL Dynamic Contour Tonometer is a digital contact tonometer that directly measures IOP continuously based on a numeric output of IOP and ocular pulse amplitude (OPA). Unlike applanation tonometry, which is influenced by corneal thickness and other characteristics of the cornea, the PASCAL Dynamic Contour Tonometer provides a direct measurement of IOP, independent of interindividual variations in corneal properties and biomechanics, and also measures pulsatile pressure fluctuations caused by the change in ocular blood flow during systole versus diastole.

𝗠𝗲𝘁𝗵𝗼𝗱

The study included 176 eyes of 126 subjects (39 eyes with open-angle glaucoma, 137 normal eyes) and consisted of 528 dynamic contour measurements and 352 Goldmann tonometry measurements. Corneal pachymetry measurements were additionally performed.

𝗖𝗼𝗻𝗰𝗹𝘂𝘀𝗶𝗼𝗻𝘀

For measurement of intraocular pressure, dynamic contour tonometry may offer a new technology, which, compared with applanation tonometry, may show a lower dependence on central corneal thickness.

𝗪𝗵𝗮𝘁 𝗶𝘀 𝗢𝗽𝗵𝘁𝗵𝗮𝗺𝗼𝘀𝗰𝗼𝗽𝗲

Ophthalmoscope, instrument for inspecting the interior of the eye. The ophthalmoscope generally is considered to have been invented in 1851 by the German physiologist Hermann von Helmholtz, though it is sometimes credited to English mathematician and inventor Charles Babbage, who in 1847 developed an instrument thought to resemble the ophthalmoscope. The device consists of a strong light that can be directed into the eye by a small mirror or prism. The light reflects off the retina and back through a small hole in the ophthalmoscope, through which the examiner sees a nonstereoscopic magnified image of the structures at the back of the eye, including the optic disk, retina, retinal blood vessels, macula, and choroid. The ophthalmoscope is particularly useful as a screening tool for various ocular diseases, such as diabetic retinopathy.

𝗪𝗵𝗮𝘁 𝗶𝘀 𝗢𝗽𝗵𝘁𝗵𝗮𝗹𝗺𝗼𝘀𝗰𝗼𝗽𝘆

Ophthalmoscopy, also called funduscopy, is a test that allows a health professional to see inside the fundus of the eye and other structures using an ophthalmoscope (or funduscope). It is done as part of an eye examination and may be done as part of a routine physical examination. It is crucial in determining the health of the retina, optic disc, and vitreous humor.

𝗨𝘀𝗲𝘀 𝗼𝗳 𝗢𝗽𝗵𝘁𝗵𝗮𝗹𝗺𝗼𝘀𝗰𝗼𝗽𝘆
It is used to detect and evaluate symptoms of various retinal vascular diseases or eye diseases such as glaucoma.

In patients with headaches, the finding of swollen optic discs, or papilledema, on ophthalmoscopy is a key sign, as this indicates raised intracranial pressure (ICP) which could be due to hydrocephalus, benign intracranial hypertension (aka pseudotumor cerebri) or brain tumor, amongst other conditions. Cupped optic discs are seen in glaucoma.

In patients with diabetes mellitus, regular ophthalmoscopic eye examinations (once every 6 months to 1 year) are important to screen for diabetic retinopathy as visual loss due to diabetes can be prevented by retinal laser treatment if retinopathy is spotted early.

In arterial hypertension, hypertensive changes of the retina closely mimic those in the brain, and may predict cerebrovascular accidents (strokes).

𝗜𝗺𝗮𝗴𝗲: 𝗼𝗽𝗵𝘁𝗵𝗮𝗺𝗼𝘀𝗰𝗼𝗽𝗲

𝗪𝗵𝗮𝘁 𝗶𝘀 𝗜𝘀𝗵𝗶𝗵𝗮𝗿𝗮 𝘁𝗲𝘀𝘁?

The Ishihara test is a color perception test for red-green color deficiencies, the first in a class of successful color vision tests called pseudo-isochromatic plates ("PIP"). It was named after its designer, Shinobu Ishihara, a professor at the University of Tokyo, who first published his tests in 1917.

𝗛𝗼𝘄 𝘁𝗼 𝗽𝗲𝗿𝗳𝗼𝗿𝗺 𝗶𝘀𝗵𝗶𝗵𝗮𝗿𝗮 𝘁𝗲𝘀𝘁

Being a printed plate, the accuracy of the test depends on using the proper lighting to illuminate the page. A "daylight" bulb illuminator is required to give the most accurate results, of around 6000–7000 K temperature, and is required for military color vision screening policy. Fluorescent bulbs are many times used in school testing, but the color of fluorescent bulbs and their CRI can vary widely. Incandescent bulbs should not be used, as their low temperature (yellow-color) give highly inaccurate results, allowing some color vision deficient persons to pass.

Proper testing technique is to give only three seconds per plate for an answer, and not allow coaching, touching or tracing of the numbers by the subject. The test is best given in random sequence, if possible, to reduce the effectiveness of prior memorization of the answers by subjects. Some pseudo-isochromatic plate books have the pages in binders, so the plates may be rearranged periodically to give a random order to the test.

Since its creation, the Ishihara Color Blindness Test has become commonly used worldwide because of its easy use and high accuracy. In recent years, the Ishihara test has become available online in addition to its original paper version. Though both media use the same plates, they require different methods for an accurate diagnosis.

𝗣𝗗𝗠 𝗗𝗶𝗴𝗶𝘁𝗮𝗹 𝗣𝘂𝗽𝗶𝗹𝗹𝗼𝗺𝗲𝘁𝗲𝗿

With the help of PDM obtaining accurate interpupillary measurements is easy. Operators simply align the measuring lines to the Purkinje images on the patient's corneas. Measurement data can be obtained for a single eye, or both eyes, and results are accurate within 0.5mm. Interpupillary distance for a range of focusing points can be obtained by selecting the appropriate focus distance on the circular dial. The PDM's LCD displays measurement data in clear, easy-to-read format.

https://drive.google.com/file/d/1NpaGxa-l-r8h7HPYedzRVJcoy09Fg9js/view?usp=sharing

OPHTHALMICPRICE LIST INDIAN.pdf

https://drive.google.com/file/d/1D-ZThdTITzxb1pEbIGtCzYnB5p-R7YfU/view?usp=sharing

Ophthalmic Equipment.pdf

𝗔𝘂𝘁𝗼𝗿𝗲𝗳𝗿𝗮𝗰𝘁𝗼𝗿

An autorefractor or automated refractor is a computer-controlled machine used during an eye examination to provide an objective measurement of a person's refractive error and prescription for glasses or contact lenses. This is achieved by measuring how light is changed as it enters a person's eye.

𝗛𝗼𝘄 𝗔𝘂𝘁𝗼𝗿𝗲𝗳𝗿𝗮𝗰𝘁𝗼𝗿 𝗪𝗼𝗿𝗸?

The majority of autorefractors calculate the vision correction a patient needs (refraction) by using sensors that detect the reflections from a cone of infrared light. These reflections are used to determine the size and shape of a ring in the retina which is located in the posterior part of the eye. By measuring this zone, the autorefractor can determine when a patient’s eye properly focuses an image. The instrument changes its magnification until the image comes into focus. The process is repeated in at least three meridians of the eye and the autorefractor calculates the refraction of the eye, sphere, cylinder and axis. Modern autorefractors are based on the idea patented by Medina.

𝗨𝘀𝗲𝘀 𝗼𝗳 𝗔𝘂𝘁𝗼𝗿𝗲𝗳𝗿𝗮𝗰𝘁𝗼𝗿

In some offices, this process is used to provide the starting point for the ophthalmologist or optometrist in subjective refraction tests. Here, lenses are switched in and out of a phoropter and the patient is asked "which looks better" while looking at a chart. This feedback refines the prescription to one which provides the patient with the best vision.

Automated refraction is particularly useful when dealing with non-communicative people such as young children or those with disabilities.

𝗜𝗺𝗮𝗴𝗲: 𝗔𝘂𝘁𝗼𝗿𝗲𝗳𝗿𝗮𝗰𝘁𝗼𝗿

𝗧𝗮𝗻𝗴𝗲𝘁 𝗦𝗰𝗿𝗲𝗲𝗻 𝗧𝗲𝘀𝘁𝗶𝗻𝗴

The tangent screen is a relatively simple and easy test to run and is much more sensitive than confrontation fields. The tangent screen has a black felt background with circular stitching every five degrees and will test out to thirty(30) degrees at one meter. It usually also has radial stitching that starts at the 180 meridian running through the fixation point every 22.5 degrees The tangent screen targets are pigments. Therefore, the test is more sensitive the dimmer the lighting is on the screen (more difficult to see). The light falling on the tangent screen should be 7 foot candles.

𝗛𝗼𝘄 𝗧𝗮𝗻𝗴𝗲𝘁 𝗦𝗰𝗿𝗲𝗲𝗻 𝗧𝗲𝘀𝘁𝗶𝗻𝗴 𝗪𝗼𝗿𝗸

This test can be conducted in your eye doctor’s office. You will be seated about 3 feet away from a computer screen. This screen will have a target in the center for you to focus on throughout the test.

The computer will generate images on different areas of the screen. Without moving your eyes, you will tell your doctor when you are able to see objects in your side vision. Your doctor will be able to use the information collected to form a map of your visual field. This will help them determine if there are certain areas in your visual field that you are not able to see. The location of these areas can help your doctor diagnose the cause of the visual field problems.

𝗜𝗺𝗮𝗴𝗲: 𝗧𝗮𝗻𝗴𝗲𝘁 𝗦𝗰𝗿𝗲𝗲𝗻

𝗧𝗿𝗶𝗮𝗹 𝗟𝗲𝗻𝘀 𝗦𝗲𝘁𝘀

Trial Lens set or Trial Lens Kit Mainly consists of positive and negative sphere lens, positive and negative cylinder lens, prism lens and accessory lens etc. According to different usage, there're basically 68 lens set, 90 lens set, 104 lens set, 158 lens set, 232 lens set and 266 lens set. The trial lens set normally come with a trial frame.

𝗨𝘀𝗲𝘀 𝗼𝗳 𝘁𝗿𝗮𝗶𝗹 𝘀𝗲𝘁 𝗮𝗻𝗱 𝗳𝗿𝗮𝗺𝗲

1. To find out axis of cylinder + or –
2. Emsley fincham test
3. To find out whether patient is having astigmatism
4. Vertex distance also measure.
5. For the measurement and correction of the angle of
deviation.
* It is also used in instruments like Gonioscopy , Keratometer ,
slit lamp and applanation tonometer.

𝗜𝗺𝗮𝗴𝗲: 𝗧𝗿𝗶𝗮𝗹 𝗟𝗲𝗻𝘀 𝗦𝗲𝘁

𝗪𝗵𝗮𝘁 𝗶𝘀 𝗕𝗶𝗻𝗼𝗰𝘂𝗹𝗮𝗿 𝗜𝗻𝗱𝗶𝗿𝗲𝗰𝘁 𝗢𝗽𝗵𝘁𝗵𝗮𝗹𝗺𝗼𝘀𝗰𝗼𝗽𝗲?

The BIO device consists of a headband, binocular lens with mirrors, and a light source (see diagram). The examiner wears the device by positioning the headband around his or her head so that the binocular lenses sit directly in front of their eyes. Mirrors in the device split the light reflecting back toward the examiner so the image may be presented to each of the examiner’s eyes. The light is between the doctor's eyes just above the bridge of their nose.

𝐏𝐫𝐨𝐜𝐞𝐝𝐮𝐫𝐞

𝐓𝐞𝐜𝐡𝐧𝐢𝐪𝐮𝐞 𝐭𝐨 𝐏𝐞𝐫𝐟𝐨𝐫𝐦 𝐁𝐈𝐎
1. Adjustment of the ophthalmoscope
2. Adjust headband crown
3. Adjust the pupillary distance
4. Check illumination intensity. Usually start with lower i5. 5. 5.
llumination and slowly increase illumination as needed and
as tolerated by the patient. Check for a proper
elevation/position. Check can be done by extending arm or
by looking at a wall.
5. Apply filter if desired
6. Positioning the patient - Patient should be in a supine
position
7. Patient should be looking directly up, initially (primary
position)
8. Examiner should initially stand to the side of the patient,
leaning over the patient
9. Keep handheld lens approximately 2 inches away from
patient's eye, moving it closer or farther away to focus and
refine the view
10. Examiner swivels his view around to view different parts of
the retina, by tilting the head and walking around the patient
The doctor instructs the patient to look at various extremes
of their vision
11.The macula is examined at the last, as the light is bright
and patient cooperation for BIO may reduce drastically if
macula is examined at the initiation of BIO.

𝗜𝗺𝗮𝗴𝗲: 𝗕𝗶𝗻𝗼𝗰𝘂𝗹𝗮𝗿 𝗜𝗻𝗱𝗶𝗿𝗲𝗰𝘁 𝗢𝗽𝗵𝘁𝗵𝗮𝗹𝗺𝗼𝘀𝗰𝗼𝗽𝗲

𝐖𝐡𝐚𝐭 𝐢𝐬 𝐩𝐡𝐨𝐫𝐨𝐩𝐭𝐞𝐫?

A phoropter is an instrument used to test individual lenses on each eye during an exam. If, during an eye examination, your doctor has discovered a vision problem like nearsightedness, farsightedness or astigmatism, it's likely that one of the next steps you'll take will involve a phoropter.

𝐔𝐬𝐞 𝐨𝐟 𝐩𝐡𝐨𝐫𝐨𝐩𝐭𝐞𝐫

The purpose of the device is to test individual lenses on each eye during an exam. Whether you’re nearsighted, farsighted or astigmatic, you’ll likely spend some time behind this machine. Using the phoropter, your optometrist can quickly switch multiple lenses in front of your eyes, trying to find the right combination for the best vision possible.

𝐇𝐨𝐰 𝐝𝐨𝐞𝐬 𝐚 𝐩𝐡𝐨𝐫𝐨𝐩𝐭𝐞𝐫 𝐰𝐨𝐫𝐤?

The process of switching lenses in front of your eyes is less involved than it may look, given the imposing nature of the device. A phoropter is used to manually determine “refraction” – exactly how a lens must be shaped and curved to correct your vision to a normal state, nothing more.

𝗜𝗺𝗮𝗴𝗲: 𝗣𝗛𝗢𝗥𝗢𝗣𝗧𝗘𝗥

𝐖𝐡𝐚𝐭 𝐢𝐬 𝐚 𝐒𝐥𝐢𝐭 𝐋𝐚𝐦𝐩?

A slit lamp is a microscope with a bright light used during an eye exam. It gives your ophthalmologist a closer look at the different structures at the front of the eye and inside the eye. It’s a key tool in determining the health of your eyes and detecting eye disease.

𝐒𝐥𝐢𝐭 𝐥𝐚𝐦𝐩 𝐮𝐬𝐞𝐝 𝐟𝐨𝐫

Doctors use the slit lamp as part of a complete eye exam to get a better look at the structures within a person's eyes. These include the following:
*𝐂𝐨𝐧𝐣𝐮𝐧𝐜𝐭𝐢𝐯𝐚
*𝐂𝐨𝐫𝐧𝐞𝐚
*𝐄𝐲𝐞𝐥𝐢𝐝𝐬:
*𝐈𝐫𝐢𝐬
*𝐏𝐮𝐩𝐢𝐥
*𝐋𝐞𝐧𝐬
*𝐒𝐜𝐥𝐞𝐫𝐚
*𝐑𝐞𝐭𝐢𝐧𝐚

𝐏𝐫𝐨𝐜𝐞𝐝𝐮𝐫𝐞

1. After an initial look at the eyes, the doctor may apply a special dye called fluorescein to them to make the exam easier. They will administer this as an eye drop or on a small, thin paper strip that touches the white of the eye.

2. The doctor will then administer a series of eye drops that will dilate the pupils. The dilation will make it easier for the doctor to see the other structures in the eye. It takes about 20 minutes for the drops to work.

3. Once the individual has dilated pupils, the doctor will repeat the eye exam. This time they will hold a particular lens close to the eye.

4. The procedure does not hurt, although there may be some brief stinging during the application of the eye drops.

5. Dilated pupils become very large, which can make the eyes sensitive to light. This can make driving or spending time outside uncomfortable. However, the eye drops should wear off within a couple of hours, and wearing sunglasses should help during this period.

𝐈𝐦𝐚𝐠𝐞: 𝐒𝐥𝐢𝐭 𝐋𝐚𝐦𝐩 𝐭𝐞𝐬𝐭

𝗪𝗵𝗮𝘁 𝗶𝘀 𝗚𝗼𝗻𝗶𝗼𝘀𝗰𝗼𝗽𝘆?

Gonioscopy is performed during the eye exam to evaluate the internal drainage system of the eye, also referred to as the anterior chamber angle. The "angle" is where the cornea and the iris meet. This is the location where fluid inside the eye (aqueous humor) drains out of the eye and into the venous system. Under normal circumstances, the angle cannot be seen on exam. A special contact lens prism placed on the surface of the eye allows visualization of the angle and drainage system.

𝐖𝐡𝐚𝐭 𝐢𝐬 𝐆𝐨𝐧𝐢𝐨𝐬𝐜𝐨𝐩𝐞?

Gonioscopy describes the use of a goniolens (also known as a gonioscope) in conjunction with a slit lamp or operating microscope to gain a view of the iridocorneal angle, or the anatomical angle formed between the eye's cornea and iris.

𝗛𝗼𝘄 𝘁𝗼 𝘂𝘀𝗲 𝐆𝐨𝐧𝐢𝐨𝐬𝐜𝐨𝐩𝐞?

*briefly explaining the procedure to the patient
*cleaning and sterilising the front (curved) surface of the
goniolens
*applying lubricating fluid to the front surface if appropriate
*anaesthetising the patient's cornea with topical anaesthetic
*preparing the slit lamp for viewing through the goniolens
*gently moving the patient's eyelids away from the cornea
*slowly applying the goniolens to the ocular surface, forming
suction
*fine-tuning the slit lamp to optimise the view
*interpreting the gonioscopic image
*swivelling the goniolens to view each section of the
iridocorneal angle
*when satisfied, very carefully breaking suction via the eyelids
*cleaning the instruments and irrigating the patient's eyes.

𝗜𝗺𝗮𝗴𝗲: 𝟰 𝗠𝗶𝗿𝗿𝗼𝗿 𝗚𝗼𝗻𝗶𝗼𝘀𝗰𝗼𝗽𝗲 𝗟𝗲𝗻𝘀 𝘄𝗶𝘁𝗵 𝗛𝗮𝗻𝗱𝗹𝗲

𝗪𝗵𝗮𝘁 𝗶𝘀 𝗹𝗲𝗻𝘀𝗼𝗺𝗲𝘁𝗲𝗿?

A lensmeter or lensometer, also known as a focimeter or vertometer, is an ophthalmic instrument. It is mainly used by optometrists and opticians to verify the correct prescription in a pair of eyeglasses, to properly orient and mark uncut lenses, and to confirm the correct mounting of lenses in spectacle frames.

𝗛𝗼𝘄 𝘁𝗼 𝗨𝘀𝗲 𝗮 𝗟𝗲𝗻𝘀𝗼𝗺𝗲𝘁𝗲𝗿?

*Mount one of the eyeglass lenses on the manual lensometer’s viewing platform. Both lenses should be flush with the bottom of the platform, and the lensometer’s viewing lens should be centered on the lens's optical center. Fix the lens in place with the lensometer’s brace.

*Determine the spherical value of the lens. Turn the axis and focus k***s until the thin lines in the viewfinder are both parallel and in focus. Read the measurement on the focus k**b to get the spherical value for the lens. Manual lensometers typically measure values to the nearest quarter diopter.

*Measure the cylinder value of the lens. Rotate the focus k**b to bring the fat lines that are perpendicular to the thin lines into focus. Subtract the current measurement on the focus k**b from the previous reading obtained in step

*Record this difference as the cylinder value of the lens, being sure to include the sign.

*Record the axis value of the lens. This is the current measurement of the axis dial. The spherical, cylindrical, and axis values provide the complete curvature of the primary part of the lens.

*Calculate the add value for bifocal lenses. Center the viewing lens of the lensometer on the bifocal portion of the lens. Adjust the focus k**b once again to bring the fat lines back into focus and subtract the current reading from the previous reading. This difference is the add value for the bifocal lens.

𝗪𝗵𝗮𝘁 𝗶𝘀 𝗗𝗶𝗮𝗴𝗻𝗼𝘀𝘁𝗶𝗰 𝗟𝗲𝗻𝘀𝗲𝘀?

These diagnostic lenses are all use in ophthalmology for viewing the posterior segment of the eye. Depending on which model you choose, lenses can be either contact or non-contact, and available in a variety of magnifications and view fields. Additionally, some lenses may be reusable multi-use lenses or single use lenses.

T𝗿𝗶𝗮𝗹 𝗳𝗿𝗮𝗺𝗲?

Trial frame is a type of spectacle frame with variable adjustments, for holding trial lenses during refraction.

𝗨𝘀𝗲𝘀 𝗼𝗳 𝗧𝗿𝗮𝗶𝗹 𝗙𝗿𝗮𝗺𝗲 𝗼𝗿 𝗧𝗿𝗮𝗶𝗹 𝗕𝗼𝘅?

Trial frame an eyeglass frame designed to permit insertion of different lenses used in correcting refractive errors of vision.

• OBJECTIVE REFRACTION
• SUBJECTIVE REFRACTION
• DIPLOPIA CHARTING
• DIAGNOSIS OF SQUINT
• ASSESS BINOCULAR VISION

𝗪𝗵𝗮𝘁 𝗶𝘀 𝗧𝗼𝗻𝗼𝗺𝗲𝘁𝗲𝗿?

Tonometer is an instrument used to measure intraocular pressure (IOP). Non contact tonometers use a puff of air to measure IOP. It doesn't hurt but there may be a loud click as the puff of air is delivered.

𝗪𝗵𝗮𝘁 𝗶𝘀 𝗧𝗼𝗻𝗼𝗺𝗲𝘁𝗿𝘆?

Tonometry is a quick and simple test that checks the pressure inside your eyes. The results can help your doctor see if you’re at risk for glaucoma.

𝗪𝗵𝘆 𝗗𝗼 𝗜 𝗡𝗲𝗲𝗱 𝗧𝗵𝗶𝘀 𝗧𝗲𝘀𝘁?

Your eyes are filled with different fluids that keep them healthy. New fluid is constantly being made and old fluid drained out. But if this drainage system gets plugged, the fluids build up. That causes the pressure inside your eyes to rise.

Sometimes the pressure is caused by an eye injury or trauma. Once your eye heals, everything may go back to normal. But some people have a drainage system that doesn’t work like it should.

Over time, high pressure inside your eye can damage your optic nerve, which sends images from your eyes to your brain. Left untreated, it can cause glaucoma.

𝗛𝗼𝘄 𝘁𝗼 𝘂𝘀𝗲 𝗧𝗼𝗻𝗼𝗺𝗲𝘁𝗲𝗿?
Method to use

*Instil the local anaesthetic drops and then the fuorescein. Only a very small amount of fuorescein is needed

*For measuring the IOP in the right eye, make sure the slit beam is shining onto the tonometer head from the patient's right side; for the left eye, the beam should come from the patient's left side

*Move the filters so that the blue filter is used to produce a blue beam

*Make sure the beam of light is as wide as possible, and that the light is as bright as possible. This makes visualising the fluorescein rings easier (with the slit diaphragm fully open)

*Ask the patient to look straight ahead, open both eyes wide, fix his or her gaze and keep perfectly still

*With the thumb, gently hold up the patient's top eyelid, taking care not to put any pressure on the eye

*Direct the blue light from the slit lamp or the Perkins tonometer onto the prism head

*Make sure that the tonometer head is perpendicular to the eye

*Move the tonometer forward slowly until the prism rests gently on the centre of the patient's cornea

*With the other hand, turn the calibrated dial on the tonometer clockwise until the two fluorescein semi-circles in the prism head are seen to meet and form a horizontal ‘S’ shape. (Note: the correct end point is when the inner edges of the two fluorescein semi-circle images just touch)

*Note the reading on the dial and record it in the notes

*Withdraw the prism from the corneal surface and wipe its tip

*Repeat the procedure for the other eye

*Wipe the prism with a clean, dry swab and replace it in the receptacle containing the disinfectant.

𝐏𝐑𝐈𝐒𝐌 𝐁𝐀𝐑 - 𝐄𝐱𝐚𝐦𝐢𝐧𝐚𝐭𝐢𝐨𝐧

𝐈𝐧𝐭𝐫𝐨𝐝𝐮𝐜𝐭𝐢𝐨𝐧 𝐓𝐨 𝐂𝐥𝐢𝐧𝐢𝐜𝐚𝐥 𝐏𝐫𝐢𝐬𝐦𝐬

Prisms, like double vision, seem to be pretty dreaded by most people (aside from strabismus specialists and optics fans). For testing purposes and clinical applications, we thankfully don't have to know a ton of things about prisms apart from the essential applications within our clinics. Hopefully this will help you understand the principles of prisms better so that you can use them effectively in clinic as well as answer any test questions that might pop up!

𝐓𝐡𝐞 𝐏𝐫𝐢𝐬𝐦 𝐃𝐢𝐨𝐩𝐭𝐞𝐫

Prisms bend light (i.e., change the direction of a light ray). We use the unit prism diopter (Δ) to quantify how much a prism will bend light. This is different from the diopters used to describe the refractive power of a lens (D) - don't get these two things confused!

A prism diopter is the distance an image is shifted by the prism (in cm) at a distance of 1 m (or 100 cm) away from the prism.

(Illustration developed by Edmond H. Thall, MD, and Kevin M. Miller, MD, and rendered by C. H. Wooley.)

Image credit: American Academy of Ophthalmology. Used with permission.

𝐄𝐗𝐀𝐌𝐏𝐋𝐄 𝐐𝐔𝐄𝐒𝐓𝐈𝐎𝐍

A prism is placed in front of an object. The resulting image is displaced 10 cm at 2 m. What is the power of the prism, in prism diopters?

A. 5 Δ
B. 10 Δ
C. 15 Δ
D. 20 Δ

Answer: A. The prism displaces the image 10 cm at 2 m, or 5 cm at 1 m (10 cm/2).

𝐇𝐨𝐰 𝐓𝐨 𝐇𝐨𝐥𝐝 𝐏𝐫𝐢𝐬𝐦𝐬 𝐈𝐧 𝐂𝐥𝐢𝐧𝐢𝐜

When you're using prisms, it matters if the prism you're holding is made of glass or plastic. Glass prisms, like the ones in a trial lens set, should be held parallel to the iris regardless of what direction the eye is moving. Plastic prisms, like the ones in prism bars or loose lens sets. should be held parallel to the face.

This is important because the effective deviation of the prism changes based on how you hold it in front of the eye; the BCSC gives an example of a glass prism that is held parallel to the face that has a reduced prismatic effect.

Correct positions for holding glass and plastic prisms.

Illustration developed by Edmond H. Thall, M.D., and Kevin M. Miller, M.D., and rendered by C. H. Wooley.

Image credit: American Academy of Ophthalmology. Used with permission.

𝐑𝐞𝐚𝐥 𝐚𝐧𝐝 𝐕𝐢𝐫𝐭𝐮𝐚𝐥 𝐎𝐛𝐣𝐞𝐜𝐭𝐬 𝐯𝐬. 𝐈𝐦𝐚𝐠𝐞𝐬

One of those pesky optics questions is talking about the differences between something real vs. virtual, and the differences between objects and images. With prisms, this is important for the sake of understanding how to use prisms to measure strabismus using various techniques.

I spent about 15 minutes reading and re-reading the 2 paragraphs in the BCSC discussing this concept, and basically came to the following conclusion:

When talking about real images (i.e., a projected light source or laser focused through a prism), the image is shifted toward the base. When talking about virtual images (i.e., our perception of an object through a prism lens), the image is shifted toward the apex.

In a patient with normal alignment (orthophoria), the patient will report seeing only one circle/light (red or white, depending on which eye is dominant).

𝐂𝐋𝐈𝐍𝐈𝐂𝐀𝐋 𝐄𝐗𝐀𝐌𝐏𝐋𝐄

An example of this concept that I commonly use in my neuro-ophthalmology clinic is the the red glass test for measuring strabismus. In the red glass test, a red glass is placed over the right eye while the patient is looking at a white circle or light source. If the eyes are aligned or there is suppression, the patient will only see 1 circle/light (red or white). However, if there is some misalignment, the red glass dissociates the images (1 red circle/light and 1 white circle/light). To measure the misalignment, prisms are then placed in front of the right eye to "move" the circles/lights together.

I typically ask the patient, "where is the red circle/light compared to the white?" As long as the patient is able to accurately tell you if the red circle/light is to the right, left, above, or below the white circle/light, you can neutralize the deviation using loose prisms or a prism bar.

𝐄𝐗𝐀𝐌𝐏𝐋𝐄 𝐂𝐀𝐒𝐄: 𝐓𝐇𝐄 𝐑𝐄𝐃 𝐂𝐈𝐑𝐂𝐋𝐄/𝐋𝐈𝐆𝐇𝐓 𝐈𝐒 𝐓𝐎 𝐓𝐇𝐄 𝐑𝐈𝐆𝐇𝐓 𝐎𝐅 𝐓𝐇𝐄 𝐋𝐄𝐅𝐓 𝐂𝐈𝐑𝐂𝐋𝐄/𝐋𝐈𝐆𝐇𝐓 (𝐄𝐒𝐎𝐓𝐑𝐎𝐏𝐈𝐀)

In esotropia, the image that is being projected onto the retina is a real image and, in the esotropic eye, will be focused nasal to the fovea (left figure). Because the area of the nasal retina corresponds to the temporal visual field, the perceived image (the virtual image) appears temporal to its real location.

By placing a base out prism in front of the eye (which is the treatment for esotropia), the real image is shifted towards the base of the prism and will focus on the fovea. This results in the merging of the two images. The patient would then, in essence, perceive the image moving towards the apex of the prism (or, the virtual image moves towards the apex of the prism).

I do want to note that when I am in clinic, I never think about this principle to this degree. I just point the apex of the prism in the direction I want the perceived image to go - in this example, because the red circle/light is to the right of the white, I point the apex to the left so that I "push" the perceived image to the left. This is essentially the same explanation as before, but intuitively it makes my prism measurements much faster.

𝐄𝐗𝐀𝐌𝐏𝐋𝐄 𝐐𝐔𝐄𝐒𝐓𝐈𝐎𝐍

A patient presents with 20 Δ of exotropia and a fixation preference of the left eye. Where is the real image on the retina after the placement of a base-in, 10 Δ prism in front of the right eye?

A. Nasal to the optic nerve
B. Between the fovea and optic nerve
C. On the fovea
D. Temporal to the fovea

Answer: D. A patient with exotropia will have a real image projected temporal to the fovea. After placement of a base-in, 10 Δ prism over the right eye, the exotropia will be partially corrected but not completely corrected - as such, the real image will still be temporal to the fovea

𝐒𝐋𝐈𝐓 𝐋𝐀𝐌𝐏 𝐌𝐈𝐂𝐑𝐎𝐒𝐂𝐎𝐏𝐄

𝐇𝐨𝐰 𝐭𝐨 𝐔𝐬𝐞 𝐚 𝐒𝐥𝐢𝐭 𝐋𝐚𝐦𝐩

You can’t diagnose or treat a problem if you can’t identify it. Here’s a quick guide on how to navigate the slit-lamp biomicroscope ahead of time to avoid fumbling in front of an anxious patient.

𝐁𝐚𝐬𝐢𝐜 𝐀𝐩𝐩𝐫𝐨𝐚𝐜𝐡

First, take a quick second to observe the patient as a whole. Once under the microscope, macropathology such as iris heterochromia, periorbital neoplasms and heterotropias can be surprisingly easy (and embarrassing) to miss. Begin with a lower magnification — and fight the urge to jump to obvious lesions. Then figure out your exam algorithm, beginning with external features and working towards deeper structures. Stick to that order so you don’t neglect other important, but more subtle, findings.

𝐋𝐢𝐠𝐡𝐭𝐢𝐧𝐠 𝐓𝐞𝐜𝐡𝐧𝐢𝐪𝐮𝐞𝐬

Remember that there is a human on the other end of the scope. Cranking up the light intensity may improve your view, but it’s uncomfortable for the patient. If you must do so, give a courtesy heads-up and keep it short. The rule of thumb is to decrease the beam width and/or height as you increase brightness.

Here are a few of the more common and useful lighting techniques that you’ll need to employ:

𝐃𝐢𝐟𝐟𝐮𝐬𝐞 𝐢𝐥𝐥𝐮𝐦𝐢𝐧𝐚𝐭𝐢𝐨𝐧

10x magnification

With this technique, an open beam is directed on the eye at 45°. This is useful for conducting an overall survey of the eye, lids, lashes, caruncle, sclera, surface vessels and media opacities.

Vascularized iris cysts viewed with diffuse illumination.1

𝐒𝐜𝐥𝐞𝐫𝐨𝐭𝐢𝐜 𝐬𝐜𝐚𝐭𝐭𝐞𝐫
10x magnification

With this technique, a tall, wide beam is directed straight at the limbus. The light is scattered through the cornea to reveal a general pattern of opacities.

Map-dot-fingerprint dystrophy viewed with sclerotic scatter.2

𝐑𝐞𝐭𝐫𝐨𝐢𝐥𝐥𝐮𝐦𝐢𝐧𝐚𝐭𝐢𝐨𝐧
10x–16x magnification

𝐈𝐫𝐢𝐬 𝐫𝐞𝐭𝐫𝐨𝐢𝐥𝐥𝐮𝐦𝐢𝐧𝐚𝐭𝐢𝐨𝐧: Light is reflected anteriorly off of the deeper iris to study corneal opacities and guttata.

𝐑𝐞𝐝 𝐫𝐞𝐟𝐥𝐞𝐱 𝐭𝐞𝐬𝐭: A short light beam is directed through the pupil and reflects off the retina to reveal lens opacities (best with dilated pupil) and iris transillumination (best with undilated pupil).

𝐎𝐩𝐭𝐢𝐜𝐚𝐥 𝐒𝐞𝐜𝐭𝐢𝐨𝐧
𝐕𝐚𝐧 𝐇𝐞𝐫𝐢𝐜𝐤’𝐬 𝐭𝐞𝐜𝐡𝐧𝐢𝐪𝐮𝐞
6x–10x magnification

A narrow slit beam is angled at 60° onto the limbus to estimate the depth of the peripheral anterior chamber. The angle is considered open if the ratio of aqueous to cornea is greater than 1:2 and narrow when this ratio is no greater than 1:4. Note: This method is not appropriate for plateau iris syndrome.

𝐂𝐨𝐧𝐢𝐜𝐚𝐥 𝐛𝐞𝐚𝐦
16x–20x magnification

Using the pupil as a dark background, a bright conical beam of light is angled 45° to 60° onto the aqueous to assess cells and flare. This technique also works with a small rectangular beam.

𝐂𝐨𝐫𝐧𝐞𝐚𝐥 𝐜𝐫𝐨𝐬𝐬-𝐬𝐞𝐜𝐭𝐢𝐨𝐧
16x–20x magnification

A thin, bright beam is angled at 45° to 60° for a detailed view of the corneal layers. This technique is used to gauge the depth of lesions and any areas of thinning (ulcers and ectasias).

𝐋𝐢𝐠𝐡𝐭 𝐅𝐢𝐥𝐭𝐞𝐫𝐬
Neutral density: This colorless, gray filter reduces illumination for photosensitive patients.

𝐂𝐨𝐛𝐚𝐥𝐭 𝐛𝐥𝐮𝐞: This filter is utilized with fluorescein for applanation and to assess the tear lake, tear breakup time, contact lens fit and corneal lesions and defects. It’s also employed in Seidel testing to evaluate aqueous leakage from penetrating/perforating injuries, surgical wounds or thin filtering blebs.

𝐑𝐞𝐝 𝐟𝐫𝐞𝐞: This filter obscures red light to enhance the observation of retinal nerve fiber layer wedge defects. It also helps differentiate pigmented lesions (which appear dark before the filter is applied) from blood vessels and hemorrhages (which appear dark after the filter is applied).

𝐘𝐞𝐥𝐥𝐨𝐰 𝐛𝐚𝐫𝐫𝐢𝐞𝐫: This filter enhances contrast when using fluorescein and the cobalt blue filter.
Fluorescein stain highlighting dendritiform lesions in herpetic keratitis.6