What is Aphakia? What is the difference
between aphakia and pseudophakia? How do you manage a case of uniocular aphakia
after cataract operation due to trauma? (on a patient of 20years age)
Definition:-
Literally,
Aphakia means the absence of the
the crystalline lens in the eyeball. Optically it
means absence of the crystalline
lens from its
normal
anatomical position in the pupillary
area. Aphakia may be due to surgical removal, a perforating wound
or ulcer, or congenital anomaly. It causes a loss of accommodation, hyperopia,
and a deep anterior chamber. Complications include detachment of the vitreous
or retina and glaucoma.
Aphakia
|
Pseudophakia
|
|
What is it?
|
Aphakia means the absence of the
the crystalline lens in the eyeball. Optically it
means absence of the crystalline
lens from its
normal
anatomical position in the
pupillary
area.
|
An eye in which the natural lens is replaced with an
intraocular lens
|
Diagnosis
|
3rd and 4th Purkinje image
absent, iridodonesis present, increased anterior chamber depth, Black jet pupil
|
3rd
and 4th Purkinje image present bright glassy reflex present behind
the pupil, mild iridodonesis and slight increase in anterior chamber depth
present.
|
Conditions
where it happens
|
Congenital,Traumatic,As
a complication of cataract surgery(Nowadays IOL implantation is the
preferred method along with cataract surgery; excepting some conditions like
microphthalmos, recurrent uveitis, severe subluxated lens)
|
As a
cataract surgery procedure.
IOL maybe
present
(IOL maybe
used to correct refractive errors i.e.:-Phakic IOL, Ocular albinism)
|
Visual
Acuity
|
Hardly 1/60
without glass
|
Vision
improves, May be normal. Depends upon the implanted IOL
|
Refractive
Status
|
high
hypermetropia with astigmatism
|
Variable
refractive error(depends upon the implanted IOL)
|
Retinoscopy
|
Poor glow
|
Normal
|
Near vision
|
Requires
glass
|
Requires
glass; but in case of multifocal lens used, may not require
|
TREATMENT OF the case:-
The person In the question is a
20year old patient(Young) and he became aphakic after operation for traumatic
cataract. It is not known whether the person was previously suffering from any
refractive error or not. So there are three possibilities
a)
The non-traumatic eye may be emmetropic
b)
The non-traumatic eye may be myopic
c)
The non-traumatic eye may be hypermetropic.
These are important
in making a decision regarding treatment policy of the patient.
Uncorrected unilateral aphakia is one of the leading
causes of monocular visual impairment. The treatment options are as follows:-
A)Spectacles.
B)Contact lenses.
C)Surgery on the cornea – to change the shape of the cornea.
D) An intraocular lens(Secondary)
1)Posterior chamber intraocular lens implantation
2)Iris Claw lens
3) Anterior chamber Intraocular lens implantation
Before
starting the discussion regarding treatment options, let us consider the
optics and optical defects in Aphakia
Optics and Optical defects of Aphakia:-
1) The eye becomes highly
hypermetropic
2) Total power of the eye is
reduced to about +44 D from +60 D.
3) The anterior focal point
becomes 23.2 mm in front of the cornea
4) The posterior focal point
is about 31 mm behind the cornea,i.e about 7mm behind the eyeball. (The
anteroposterior length of the eyeball is about 24 mm)
5) The two principal points
are almost at the anterior surface of the cornea
6) The nodal points are very
near to each other and are located about 7.75mm behind the anterior surface of
cornea.
7) There is a total loss of
accommodation
8) Associated with high
astigmatism
A)Aphakic Spectacles:
To correct
the refractive error in aphakia about 10 dioptres of convex lenses are required
for distance vision and about 13 dioptres for near vision along with correction
for surgically induced astigmatism(Assuming that the patient was emmetropic).
Such high power lenses are associated with numerous physical and optical
problems. The most important of these problems are:
1.
Magnification:
Each dioptre of convex power leads to about 3 % magnification of the image and a
the difference of image size between the two eyes(aniseikonia) of about 5 % is
tolerable. Thus 10 dioptre aphakic spectacles lead to about 30 % magnification
of the image which gives rise to diplopia i.e., two images of one object are
seen one small (from the normal eye) and other larger (from the aphakic eye). Moreover,
when the objects appear larger they appear falsely closer than reality, and
this leads to physical in-coordination(spatial disorientation or disturbances
in-depth perception).
2.
Roving Ring Scotoma:
The edge of a convex lens acts as a prism and the higher the power of the
convex lens the greater is the prism angle. In aphakic spectacles, the prism
angle being large, the light falling at
the edge of the lens bends towards the centre of the lens (base of the prism) and
does not reach the pupil and is, therefore, not seen. This results in an area
of the visual field which is not visible to the patient, or scotoma. And
because the edge of the lens is present all around the lens like a ring, so it
gives rise to a ring-shaped scotoma. The position of this scotoma is not fixed
in the visual field because the eye keeps moving (or roving) in relation to the
aphakic spectacle. Hence, the result is a roving ring scotoma.
3.
Jack-in-the-box Phenomenon:
The presence of the above scotoma leads to another interesting phenomenon. If
an interesting object appears in the periphery of the patients visual field, it
appears blurred (because the light is passing from the side of the spectacle
frame). The person tends to move his head towards the object in order to see it
clearly. But as he turns the head the object comes to lie in the area of
scotoma and thus disappears. As he turns his head further so that the object
comes to lie in front of the spectacle in the visible area and so reappears
again clear and sharp. This sudden disappearance and sharp reappearance of the
objects is called jack-in-the-box
phenomenon.
4.
Pin Cushion Effect:
The magnification of image is more at the periphery of the lens due to prism
effect. Therefore, all the objects appear stretched out at the corners like apin-cushion.
5.
Spherical Aberrations: The light
converges more near the edge of the lens than at the center so the rays of
light falling near the edge are brought to focus in front of the rays falling
at the center. This results poor quality of image despite appropriate
correction of refractive error.
6.
Chromatic Aberrations:
The shorter the wave-length the more is the refraction a ray of light
undergoes. Therefore, in VIBGYOR the violet end undergoes greater refraction
than the red end of the spectrum. This causes diffraction of light and makes
the edges of white object appear rain-bow colored.
7.
Restricted field of vision
8.
Coloured vision:- Occurs due to
the absence of natural filter of a crystalline lens and due to chromatic
aberration
9.
Cosmetic blemish:-Due to thick
glasses
10.
Cumbersome to use:- as the glass
is very thick and heavy
11.
Problem in near vision:-Thick
bifocal glasses are specially difficult to adjust with.
As our patient in the question is a young patient with uniocular
high hypermetropia,spectacle correction is not possible in this patient due
to above stated problems with aphakic glass correction.
Contact Lens:-
Contact lens use is an
alternative for young patient with unilateral high hypermetropia because of the
following reasons:-
Advantages Of contact
lens:-
Less magnification
of image
Elimination of aberrations and prismatic effect of thick
glasses
Wider and better field of vision
Cosmetiaclly more acceptable
Better suited for uniocular aphakia.
Though contact lens is
having some disadvantages as described below,till it is a good option for the
patient described in the question:-
Disadvantages of contact
Lens:-
·
Take time to become accustomed to
·
Easily lost
·
Fragile and prone to tearing
·
Fiddly to handle
·
Can be more expensive than glasses
·
Require ongoing maintenance
·
Build up of dust and debris
·
Degrade in quality over time
·
Risk of eye infections(Corneal ulcer)
·
Risk of scratches
Secondary intra-ocular lens implantation:-
Surgical correction of
uniocular Aphakia(Implantation of Intra-ocular lens i.e.making the patient
pseudophakic):-
It is best option for the patient in the question because of
the following reasons:-
1) Rapid
improvement of quality & quantity of vision in IOL implantation.
2)
No spherical aberration & prismatic effect in IOL.
3)
IOL is cosmetically well accepted.
4)
Image magnification in IOL is only 0-2%
5)
No alteration of visual field in IOL.
6)
Binocular vision is possible.
Site of IOL
Implantation:-
Ideallly it
should be implanted in the capsular bag;but the patient in question had
undergone surgery due to traumatic cataract and also kept aphakic following
first surgery;So it can be concluded that the capsular bag was compromised in
this patient.The reason may be due to trauma(e.g:- traumatic
subluxation,traumatic posterior capsular tear) or may be surgically induced.
If sufficient
capsular support is not there, anterior chamber intra-ocular lens(IOL)
implantation can be done;but the anterior chamber IOL is notorious for damaging
corneal endothelium.So, in this young patient it is better to avoid anterior
chamber IOL. The same is true for anterior chamber iris claw lens.
However few
studies have shown better results with implantation of posterior chamber iris claw lens in young
patients.
Another alternative
is implantation of Scleral-Fixated posterior chamber intra-ocular lens(Suture
or glue fixed SFIOL).Hoever no surgical procedure is free of complications.It
is associated with uveitis(immediate), IOL tilt(in future) and astigmatism.
Surgery on the cornea(Refractive
corneal surgery):-
a)Keratophakia:-
In
this procedure,a lenticule prepared from the donor cornea is placed between the
lamellae of the patient’s cornea.
b)EpiKeratophakia:-In this procedure,a lenticule prepared from
the donor cornea is stitched over the surface of cornea after removing the
epithelium.
C)Hyperopic Laser in –situ Keratomileusis(LASIK):-It is a better
alternative to treat such type of patients.
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