As we want to feature all the resources on Refractive Errors this month, you will find this part take you to the quick overview of all the products available on this topic.

To access all the resources on Refractive Errors, go to the homepage of the site (www.v2020eresource.org) and enter your user name and password on the boxes provided at the end of the page. This will take you to the Resource bank page where you will find the key areas and management processes. Or please click on the following link to go directly to the Resource Bank page:
www.v2020eresource.org

Click on the "Plus" mark of the "Disease Strategies" and checkmark "Refractive Error Services" box and click "Submit" button at the bottom of the page. The resources under this category of check will be listed down in 5 pages, with 27 products. You can find an Abstract, Guideline, Refer to friends, See Product, Write a Review and Place your vote for each product. Some of the most excellent products under this category are listed below:

1. Quality Assurance in Refraction
2. Outpatient Examination, Refraction and Glass Prescription procedure - Protocol
3. Magnitude of Refractive Errors Estimation tool
4. Frequently Asked questions on Eye Glasses
5. Frequently Asked Questions on Refractive Errors
6. Brochures and Posters for Patient Education
7. Articles addressing the management and clinical issues in Refractive Errors

Contact lenses are the smallest, least visible, the finest of all devices for correcting refractive errors of the eye. Prescribing and fitting contact lenses have become an integral part of today's comprehensive ophthalmology practice. Majority of the people are using contact lenses for cosmetic purposes. Other reasons for wearing contact lenses include occupational preferences, sports and therapeutic uses. Their growing importance makes it appropriate to inquire into the origins and development of these valuable ophthalmic resources. History

The idea of contact lens was first conceived by Leonardo da Vinci in 1508. He described a glass cup containing water which was placed over the eye, eliminating the cornea as a refractive surface. After, so many attempts made by different scientists, in 1920, zeiss produced, a fitting set used to correct Keratoconus. This was the first set of trial contact lens. In 1929 Heine described a method of fitting Contact Lens by means of a trial set consisting of large number of contact lenses.

Later in 1937, there was a break through, William Feinbloom, an American used plastic in the construction of Contact Lens. A year earlier in 1936 the Rohm and Hass company introduced transparent Methyl Methacrylate. The first plastic corneal contact lens was introduced in 1947 by Kelvin touhy. Then in 1960, wichetrle discovered the soft contact lens which is made up of hydrophilic material.

Advantages of contact lenses
There are several advantages of contact lenses over spectacles. Some of them are:

1. Fewer magnification effects
2. Decreased peripheral and chromatic aberrations
3. Increase in the size of visual fields4. Marked decrease in aniseikonia in monocular aphakia and Anisometropia.
4. Good Cosmetic appearance.
5. Permits better correction for refractive errors that occur with keratoconus and irregular astigmatism.

1. Optical: Myopia, Hypermetropia, Astigmatism, Presbyopia, Aphakia, Post Keratoplasty, Keratoconus .
2. Orthoptic uses: Aniesokonia, Anisometropia, Amblyopia (Occlusion).
3. Special Uses: Albinism, Aniridia, Nystagmus with Refractive error, coloboma, symblepharon.
4. Therapeutic uses: Bullous Keratopathy, corneal ulcers, Glaucoma therapy (for Drug Delivery)
5. Prosthetic uses: Pthisical eye, corneal opacity, leukoma , corneal scars.
6. Surgical Uses: Corneal protection at surgery

1. There are several contra indications especially Dry eyes, lid problems such as active Blepharitis, stye, chalazion, entropion
2. Acute and chronic conjunctivitis, corneal abrasions, hyphema, Vth nerve paralysis, hypopyon, Uveitis and iritis
3. Some Rare contra indications are allergies, Uncontrolled diabetes, pregnancy period and Pterygium

1. Soft
2. Semi soft and
3. Hard contact lens

1. More comfortable because the lens fits under the eyelid margins, flexes with each blink and the softness permits more oxygen to reach the cornea
2. Spectacle blur is uncommon.
3. Less chances of lens loss, because of larger size and minimal movement.
4. Minimal over wear reaction, because of its soft nature and to create oxygen tear pump mechanism by flexing with each blink.
5. Less glare and photophobia.
6. Ideal for children because of comfort and less chances of lens loss factor.

1. Record the 'K' reading and convert it to millimeters (mm).
2. Measure the corneal diameter in mm
3. Diameter: The initial lens diameter selected should be 1.0 - 2.0 mm larger than the corneal diameter.
4. Power: Determine the spherical power first, convert the refraction prescription into minus cylinder and use spherical equivalent method. Add to the sphere to determine the lens power and compensate this for vertex distance.
5. Base curve: Select the base curve which is 0.4 - 0.6 mm flatter than the flattest 'K' for smaller lenses and 0.6 - 1.0 mm flatter for larger lenses.
6. Fit the contact lens to the respected eye and leave the patient to wait for 15-20 minutes to settle the lens well.

1. Acceptable fitting should show about 0.5 - 1 mm lag as the eye is turned upon to the side. Movements have best been detected by asking the patient to look up and blink. When the lens moves more than 1 mm with each blink, then it is fitted as too flat. If it moves less than 0.5 mm it is steeper and will limit the tear exchange.
2. The other factors that should be considered while looking the fitting are:
3. Good centration
4. Adequate movement
5. Stable vision
6. Crisp retinoscopic reflex
7. Clear undistored Keratometry mires

1. Wash the hands thoroughly with soap and dry.
2. Take the lens out, clean and rinse it well
3. Place the lens on the tip of the index finger
4. Look up, and retract the lower lid with the middle finger and while looking upward, gently apply the lens to the lower part of the eye.
5. Remove the finger and then slowly release the lid.

   

6. Close the eye and gently massage the lids.
7. Cover the other eye and focus it to make the correct centration.
8. Repeat the same procedure to the next eye.
9. While removing, Look upward and retract the lower lid with middle finger and place the index finger tip on the lower edge of the lens.
10. Slide the lens down to the white of the eye.
11. Compress the lens between the thumb and the index finger, so that the air breaks the suction under the lens. Remove the lens for cleaning and sterilizing.

1. CAB (Cellulose Acetyl Butyrate) lenses
2. Silicon Acrylate
3. Butylstyrene

1. Increased comfort
2. Longer wearing time
3. Reduced corneal edema, spectacle blur and over wear syndrome.
4. Rapid adaptation
5. Permeability of more oxygen than other lenses
6. Larger optic zone consequently offers increased visual field and less glare.
7. Gas permeable lenses in a spheric form can cover upto five diopters of astigmatism.

• Record the Keratometry readings
• Select the initial lens based on base curve.
• The base curve of the initial lens should be slightly steeper than the flattest meridian.
• Diameter selection is directly related to base curve. The flatter the cornea the larger the lens.
• The following table describes the selection of diameter:
• While fitting the trial, leave the patient for 20 - 30 minutes to attain good centration and settlement of the lens.
• However for best results fit the lens according to its best position and comfort.

1. Wash your hands thoroughly with oil free soap
2. Take out the lens from the container.
3. Keep at your palm, clean it well with the prescribed solution.
4. Depress the lower lid by the middle finger while the index finger carrying the lens is gently applied on the cornea.
5. Slowly release the lids to avoid accident ejection of the lens. Release the lower lid first and then the upper.

1. Look downward, open the lids wide so that the edge of the lid will engage the edge of the lens
2. Draw the lid tight by a lateral pull of the index finger and blink.
3. The lid should dislodge the lens slowly
4. Cup the other hand under the eye to catch the lens

1. Normal fit: There is a slight vault over the apical zone of the cornea with slight central pooling with an absence of stain in the intermediate area. The peripheral portion of the lens should have a pooling of stain indicating that the edge is standing off from the cornea.
2. Flatter fit: Typically with a flat lens, there is a apical touch with little fluoresceine in the area of contact.
3. Steeper Fit: Tight lens fitting will have a central pooling with an intermediate or peripheral zone of touch.
4. Astigmatic Cornea: There is a band shaped area of touch on the flattest meridian.

• Record the Keratometry readings
• Select the initial lens based on base curve.
• The base curve of the initial lens should be slightly steeper than the flattest meridian
• Diameter selection is directly related to base curve. The flatter the cornea the larger the lens.
• While fitting the trial, leave the patient for 20-30 minutes to attain good centration and settlement of the lens.
• However for best results fit the lens according to its best position and comfort.

1. Wash your hands thoroughly.
2. Take out the lens from the container.
3. Keep at your palm, clean it well with the prescribed solution.
4. Depress the lower lid by the middle finger while the index finger carrying the lens is gently applied on the cornea.
5. Slowly release the lids to avoid accident ejection of the lens. Release the lower lid first and then the upper.

1. Look downward, open the lids wide so that the edge of the lid will engage the edge of the lens
2. Draw the lid tight by a lateral pull of the index finger and blink.
3. The lid should dislodge the lens slowly
4. Cup the other hand under the eye to catch the lens.

• Hypoxic related problems such as corneal edema, Superficial punctuate keratitis, decreased sensation, superficial and deep infiltrates, vascularisation, superior limbal kerato conjunctivitis, epithelial microcysts.
• Allergic related problems include hyperemia, sterile infiltrates, Giant papillary conjunctivitis.

1. Fitting Guide for Rigid and Soft Contact lens by Harold A. Stein, Bernard J. Slat .
2. Text book of contact lenses by V.K. Dada.
3. Contemporary contact lens practice by Jack Hartstein, V. swamson, Charles R.Harris.
4. The IACLE contact lens course.
5. Duke - elder's practice of refraction.
6. Contact lens theory and practice by Theodore P. Grosvenor.