1. Normal physiology of vision and visual pathway
2. Physiological basis of image formation on retina
3. Changes taking place with age in normal lenses
4. Physiological basis of refractive errors and principals of their correction
5. Optics of vision
 Disturbed Vision:
Acute Pesticide poisoning — xylene .
Drug side effect causes of Disturbed vision
The following drugs, medications, substances or toxins may possibly cause Disturbed vision as a side effect.
 Difficulty in driving and reading:
General causes include:
1: abnormality in refrective surfaces of eye.
2:change in eye ball diameter
3: abnormality in the focusing apparatus of the eye( change in the length,curvature and tension of lens… abnormality in pupils controling mechanisms, change in the elasticity of lens etc..)
4: trauma/depression/damage to the visual pathways.
5:abnormality in cornea.
 Decreased vision:
This is the differtional diagnostic step, keeping in mind the patient’s difficulty in driving (indication of near sightedness), reading(indication of far sightedness) +age factor+duration from onset of disease, provided no other acute trauma/damage to the eye.
The goal of treatment is to compensate for the inability of your eyes to focus on nearby objects. Treatment options include wearing corrective lenses, undergoing refractive surgery or getting lens implants.
If you had good, uncorrected vision before developing presbyopia, you may be able to use nonprescription over-the-counter reading glasses. Ask your eye doctor if nonprescription glasses are OK for you.
Reading glasses sold over-the-counter are labeled on a scale that corresponds to the degree of magnification (power). The least powerful are labeled +1.00, and the more powerful are labeled in increasing increments up to +4.00. When purchasing reading glasses:
- Try different powers until you find the magnification that allows you to read comfortably.
- Test each pair on printed material held about 14 to 16 inches (about 35 to 40 centimeters) in front of your face.
You’ll need prescription lenses for presbyopia if over-the-counter glasses are inadequate or if you already require prescription corrective lenses for nearsightedness, farsightedness or astigmatism. Your choices include:
- Prescription reading glasses. If you have no other vision problems, you can have prescription lenses for reading only.
- Bifocals. These glasses come in two styles — those with a visible horizontal line and those without a line (progressive bifocals). When you look through progressive bifocals at eye level, the lenses correct your distance vision. This correction gradually changes to reading correction at the bottom.
- Trifocals. These glasses have corrections for close work, middle-distance vision — such as for computer screens — and distance vision. Trifocals come with visible lines or progressive lenses.
- Bifocal contact lenses. Bifocal contact lenses, like bifocal glasses, provide distance and close-up correction on each contact. The bottom, reading portion of the lens is weighted to keep the lens correctly positioned on your eye. These are frequently difficult to fit and often do not provide altogether satisfactory visual results.
- Monovision contact lenses. With monovision contacts, you wear a contact lens for distance vision in your dominant eye and a contact lens for close-up vision in your nondominant eye. Your dominant eye is generally the one you use when you’re aiming a camera to take a picture.
- Modified monovision. With this option, you wear a bifocal contact lens in your nondominant eye and a contact lens set for distance in your dominant eye. You use both eyes for distance and one eye for reading. Your brain learns which lens to favor — depending on whether you’re viewing things close up or far away — so you don’t have to consciously make the choice of which eye to use.
Refractive surgery changes the shape of your cornea. For presbyopia, this treatment — equivalent to wearing monovision contact lenses — may be used to improve close-up vision in your nondominant eye. The American Academy of Ophthalmology recommends that people try monovision contacts to determine if they can adjust to this kind of correction before considering refractive surgery.
Refractive surgical procedures include:
- Conductive keratoplasty (CK). This procedure uses radiofrequency energy to apply heat to very tiny spots around the cornea. The degree of change in the cornea’s curvature depends on the number and spacing of the spots, as well as the way in which the corneal tissue heals after the treatment. The results of CK are variable and unstable in many people.
- Laser-assisted in-situ keratomileusis (LASIK). With this procedure, your eye surgeon uses either a special laser or an instrument called a keratome to make a thin, hinged flap in your cornea. Your surgeon then uses an excimer laser to remove inner layers of your cornea to steepen its domed shape. An excimer laser differs from other lasers in that it doesn’t produce heat. A newer procedure, known as epithelial laser in situ keratomileusis (epi-LASIK), is believed to avoid some of the risks associated with LASIK.
- Laser epithelial keratomileusis (LASEK). Instead of creating a flap in the cornea, the surgeon creates a flap only in the cornea’s thin protective cover (epithelium). Your surgeon will use an excimer laser to reshape the cornea’s outer layers and steepen its curvature and then reposition the epithelial flap.
- Photorefractive keratectomy (PRK). This procedure is similar to LASEK, except the surgeon removes the epithelium. It will grow back naturally, conforming to your cornea’s new shape.
Another procedure used by some ophthalmologists involves removal of your clear natural lens and replacement with a synthetic lens inside your eye (intraocular lens implant). Some newer lens implants are designed to allow your eye to see things both near and at a distance. However, these special lens implants haven’t been entirely satisfactory — some people have experienced problems with glare and blurring.
In addition, this surgery carries with it the same risks associated with conventional cataract surgery, such as inflammation, infection, bleeding, glaucoma and retinal detachment. However, development of newer technologies may make these implants more satisfactory in the future.
ADDITIONAL READING ABOUT PRESBYOPIA:
Presbyopia, which means “old eye” in Greek, is the gradual loss of the eye’s ability to see things up close. Around the age of 40, many people start complaining that “their arms are not long enough” to read a menu or a telephone book. This familiar event is often the first sign of Presbyopia, which can, if uncorrected, cause eye fatigue and headaches.
What causes Presbyopia?
To see both near and distant objects clearly, the lens of the eye changes shape, getting thicker and thinner as you focus on an object.
When we are young, the lens of the eye is soft and flexible. To see something up close, like print, the ciliary muscle inside the eye contracts. This causes the lens to thicken, which adds focusing power to the eye. To look at something far away, the ciliary muscle relaxes, which causes the lens to flatten. When the lens is soft and flexible, it can easily respond to the movement of the ciliary muscle. As we age, the lens loses its flexibility or the power to accommodate. When this happens, most people begin to have difficulty reading and performing other close-up tasks.
No medications, supplemental vitamins, or exercises can stop or reverse the normal aging process responsible for Presbyopia.
To see something up close the ciliary muscle contracts, to focus on something at a distance it relaxes. As we age, our lens loses the ability to accommodate the movement of the ciliary muscle, resulting in Presbyopia.
Some of the signs and symptoms of myopia include:
- Hard time reading small print
- Having to hold reading material farther than arm’s distance
- Problems seeing objects that are close to you
Common misconceptions about presbyopia:
1. With the right eye exercise, presbyopia can be cured without the use of reading glasses. Not true…Presbyopia is caused by the loss of pliability of the crystalline lens. This is aging of tissue and cannot be fixed by eye exercises.
2. The use of reading glasses will speed up the loss of focus. Not true…Aging is the only thing that causes further loss.
3. Doing lots of reading will cause presbyopia to occur at an earlier age. Not true…Again, the only thing that causes presbyopia is the loss of lens pliability with increasing age. Because of genetic differences, presbyopia will develop at different rates. For example, you may need bifocals at age 43 and your spouse may need them at age 41 and a friend may need them at age 45. This is due to genetics and not because one person used his eyes more or less.
4. Using over-the-counter reading glasses will harm your eyes. Not true… Glasses will not cause harm to your eyes. Even if the prescription is wrong, the worst that can happen is headache or eyestrain that will go away after taking off the glasses. Over-the-counter reading glasses cannot be used by each person, but if your prescription is compatible with them, they can be an easy and cheaper alternative to prescription glasses