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"Invention" of spectacles was a great achievement
at a time when patients with refractive error were severely handicapped or practically
blind. Spectacles enjoyed high degree of popularity for a long time, but now their
disadvantages viz., cosmetic blemish, restricted field of clear vision, aberrations,
obstruction in sports and physical discomfort, are apparent. However, this should not mean
that spectacles are to be condemned. There are still many situations where spectacles are
not just the only alternative available for restoration of vision but a respectable visual
device.
A question that always haunts the mind of the
ophthalmologists and patients: why depend on prosthesis when it is possible to restore
natural vision with all its inherent advantages (not just cosmetic) finds no answer.
Extensive research and technical advancements have produced
following alternatives:
- Contact Lenses
- LASIK (Laser Assisted In-situ Keratomileusis)
- Customised Ablation LASIK or Wavefront Guided Lasik
- Phakic IOLs
- Intra-corneal Rings (Intaacs)
Contact Lenses
These are small polymer lenses, which are placed directly
over the cornea. They are of two main types - soft and semi soft. Soft contact lenses are
pliable and therefore very comfortable, but require utmost meticulous care and
maintenance. Infections and allergy (GPC: giant papillary conjunctivitis) are the likely
complications. Semi soft lenses (or Rigid Gas Permeable) are rigid and thus, initially,
slightly uncomfortable to wear, but they do not require too much care. Complications like
infection and allergy are uncommon with these lenses. However, in the Indian context
infection, GPC, mishandling, dust and pollution associated conjunctivitis continue to be
major causes of contact lens intolerance. Patient compliance is generally not satisfactory
relating to the lens care and maintenance schedules. However, they do give us a reversible
alternative for vision correction especially in circumstances where other modalities are
either not advisable (young individuals with unstable error) or not possible (scarred or
irregular cornea).
- High degree of astigmatism can not be corrected by contact
lenses.
- Extended wear lenses are not as suitable for Indian
conditions as in the west.
- Hard lenses are obsolete and should never be used as they
prevent oxygen supply to the cornea.
LASIK (Laser Assisted In-situ Keratomileusis)
Lasik is currently the best method of correction of
refractive errors. It is accurate, effective and safe.
In LASIK an ultra-thin (130 to 180 micron)
flap of cornea is raised and then using a computer controlled Excimer
Laser (mostly Argon Fluoride 193nm) is delivered to reshape the corneal
stroma into predetermined curvature. The flap is repositioned back. This
leads to correction of both myopia and hypermetropia, and also moderate
amount of astigmatism. The procedure is short and simple and being
computer controlled is highly accurate.
The steps are detailed below.
Patient Selection for Lasik
Case selection is an extremely important determinant of
the result of Lasik surgery:
- Refractive error: 1 to 12 diopter of myopia or up to
8
diopter hypermetropia
- Astigmatism of up to 6 diopter
- Minimum age 18 to 21 years (preferably 21 years)
- Refraction should have been stable for 2 years.
- Contraindications: keratoconus, thin
corneas, corneal inflammatory
diseases, herpetic keratitis and autoimmune diseases.
Preoperative Preparation for Lasik
- Refraction under cycloplegia
- Corneal Topography
- Pachymetry for corneal thickness
- Detailed Retina Examination
- Informed consent
Lasik Procedure
LASIK is performed under topical anesthesia (lignocaine 4%
or Proparacaine) and the only cooperation required of the patient is to fixate at a
blinking (red) light. Newer LASIK machines have an eye tracker device which realigns the Laser
to any changes in the position of the eye thereby ensuring proper centration of ablation.
The steps are:
- After the anesthesia the face of the patient is covered with
a drape just exposing the eye and an eyelid speculum is applied to retract the eyelids
(patient feels a stretch on the lids).
The patient fixates his gaze at a blinking light.
- A suction ring is placed around the cornea and serves to
stabilize the eyeball and act as a platform for the microkeratome.
When suction is activated vision be comes hazy and a pressure on the eye
is felt.
- The automated microkeratome dissects through the superficial
layers of the cornea and the corneal flap is folded back. During this step the
patient hears the sound of a motor in front of the eye.
- Excimer Laser ablates the stromal bed to resurface it into
desired curvature. What makes the Excimer laser so well suited for corneal ablation is its
ability to remove tissue with accuracy up to 0.25 micron with each pulse. Often, only 50
microns of tissue are removed to achieve the proper amount of correction. The Excimer
produces a non-thermal light beam that eliminates the possibility of thermal damage to
surrounding tissues. In current Lasers employing flying spot technology a 2 mm spot ablates
the tissue to correct the refractive error and then a 1 mm spot blends this area with
surrounding cornea by creating smooth transition zones.
During this step a clicking sound is heard and an odor of ablating tissue (similar to
charring hair) is smelt and a light flashing close to the eye is seen.
All this while patient needs to concentrate on the center of the
blinking red spot of light.
- The corneal flap is then repositioned and allowed to dry for
a few minutes. The flap self-seals without the need of sutures.
- The eye may be patched after instilling antibiotic drops for 1-2
hours and the patient is advised to report back the next day. Eye
drops are prescribed to be started on the same day. Analgesics are prescribed
for 2-3 days.
Precautions to be taken after Lasik
- Avoid swimming and splashing of water on the eyes for
a month.
- Avoid rubbing the eyes for a month.
- Use sunglasses to avoid bright sun, dust, wind and
air pollution.
- Avoid excessive viewing of TV or computers for a
week.
- Use medicines regularly as advised.
- Consult your eye surgeon in case of any problem
Complications of Lasik
No surgical procedure is without any complications. However, LASIK
is a relatively safe technique of correction of refractive errors. The possible
complications can be:
- Under or over correction
- Reduced contrast sensitivity
- Glare
- Decentration of ablation
- Astigmatism
- Flap damage
- Button holing of flap
- Corneal perforation
- Central Island
- Infection
- Corneal infiltration
- Corneal Ulceration
- Diffuse Lamellar Keratitis (DLK or Sands
of Sahara)
Results of
Lasik
Results are generally very satisfactory and it has been reported
that in carefully selected cases more than 90 % achieve unaided visual acuity of
6/12 or better (i.e., 6/12 6/9 6/6 6/5).
There is a subjective difference in degree of satisfaction among the
patients. Some patients with a vision of 6/12 may feel very happy while other may be
dissatisfied even with a vision of 6/5.
Wavefront Guided or Custom Lasik
Standard Lasik involves assessment of only refractive
errors (myopia, hypermetropia or astigmatism) and correction of the same.
But human eye may have some finer degrees of optical imperfections called
aberrations. Standard Lasik does not correct these aberrations and may
actually induce some aberrations leading to decrease in contrast and
problems with low light conditions and night vision.
Wavefront guided or custom Lasik measures aberrations
present in the eye (aberrometry) and attempts to correct them. Moreover,
the treatment maps generated are customized to the individual eye and
maintain the natural prolate profile of the cornea. This prevents
induction of any aberrations. All this leads to better contrast and night
vision.
Epi-Lasik or Lasek
In patients with thin corneas it may help to lift just a
thin epithelial flap as in Epi-Lasik or remove epithelium using alcohol as
in Lasek. This leaves behind greater amount of tissue in the coneal bed to
achieve higher refractive correction.
Although it possible to correct greater amount of
refractive error in these procedures but the recovery is rather slow and
more uncomfortable than in Lasik and there are greater chances of haze
developing in the cornea.
Conclusion
LASIK is major advance in the field of refractive surgery,
which combines efficacy, safety, precision and accuracy. This technique is taking us on
the path that, in the past, ophthalmologists feared to tread, towards the goal of unaided
natural clear vision.
The future is here
today ... Wave-front Guided Lasik promises to correct all optical
aberrations of the eye resulting in much better quality vision ...
Expenses
Indicative charges for Lasik Surgery are:
1. Standard Lasik INR 25,000
2. Wavefront Guided Custom Lasik INR 35,000
Please note that actual expenses incurred may vary and subject to
change.
Time Involved
An optimal time schedule is as follows:
Day 1 - Detailed eye examination (2-3 hours)
Day 2 or 3 - Lasik Surgery (3-4 hours in the center)
Day 3 or 4 - First post-Lasik examination (1 hour)
Day 7-10 - Second post-Lasik examination (1 hour)
Patient may return after the second examination and follow-up with
local eye care practitioner every 2-4 weeks for 3 months.
Author -
Dr. Sanjay Dhawan
Last
Update -
30 June, 2007
New Delhi,
India
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