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Why Scleral Lenses
Scleral lenses have two basic
features that are commonly perceived as disadvantages, these being
their large size and sclera bearing
surface. However, these features should actually be recognised as
providing the following positive benefits :
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Because scleral lenses bear on the sclera, they
do not depend on precise alignment to the corneal surface. Therefore
even highly irregular corneal topography can be fitted with
some kind of scleral lens
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They are almost never dislodged because they
fit under the eyelids
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They are dimensionally stable, robust and not
subject to much deterioration
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Insertion and removal is easier for clumsy
patients, eg elderly aphakics who do not have an implant for
some reason
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Powers in excess of ± 40.00 D are possible
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Lid sensation is minimal and foreign bodies
under lenses are rare
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Since the introduction of gas permeable material
for scleral lenses, the fitting processes have become straightforward
and predictable, so many more people can successfully use them
The Disadvantages of Scleral
Lenses
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Clinical Indications
The most frequent indication for scleral lenses is keratoconus,
but they have applications for post corneal transplant, high myopia,
aphakia and high astigmatism. They retain a fluid reservoir behind
the lens while they are in the eye, so may assist in the management
of dry eye conditions.
Before the introduction of rigid gas permeable materials, scleral
lenses were only considered for the most advanced eye conditions,
but now they can be available for lower grades of keratoconus where
there are problems with corneal lens tolerance or to give an alternative
to corneal lens wear.
Irregular or abnormal corneal topography
High astigmatism
Keratoconus or other primary corneal ectasia
Corneal transplant
Traumatized eye
Post-refractive surgery
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Keratoconus
Downwardly displaced and protrusive ectasia. A scleral lens
is seen in situ with a glancing apical contact. |
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Corneal transplant
25.00DC post-op astigmatism with a ridge in the inferior sector.
A non-ventilated RGP scleral
lens gave a VA of 6/9 with all day wear. |
High refractive errors
High powers leading to centration difficulties with high-power corneal
lenses.
Intolerance to corneal or hydrogel lens wear in myopia or hypermetropia
Significant non-pathological corneal astigmatism
Iris encapsulation
Intractable diplopia.
Cosmetic shells.
Unsightly blind eyes.
Aniridia. Microphthalmos.
Therapeutic or protective applications
Corneal hydration in serious dry eye conditions such as
Stevens Johnson syndrome and cicatricising pemphigoid
Potential for corneal healing
Prevention of tear film evaporation with poor lid closure or lid
absence
Corneal protection against trichiasis or lid margin keratinisation
Preventing mucus filaments adhering to the cornea
Ptosis
The main role of scleral lenses is to augment the options when
contact lenses are clinically necessary for satisfactory vision
or as a therapeutic appliance. However, there is also a role across
the whole range of contact lens usage.
Recreational or occupational applications
Intermittent use where short-term adaptation may be
easier than with corneal lenses
Contact sports
Water sports
Work in dusty environments
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Who Would Benefit
Sclerals have retained a unique
role in contact lens practice, but clinical practice techniques
feature only minimally in the current training programme for optometrists
and ophthalmologists. As a consequence, there is poor recognition
of the occasions when sclerals are indicated, and difficulty finding
suitably experienced practitioners. Traditional methods are perceived
to be cumbersome, but the introduction of RGP
materials has reduced sequelae, and has enabled simple and predictable
fitting process. The application of sclerals can now be considered
as a feasible option for a range of visual and therapeutic conditions,
and for lower grades of pathology, rather than only at a stage which
would be described as end point pathology.
There is a substantial role for sclerals in keratoconus
management, which in recent years has accounted for just over 50%
of the total requirement for sclerals.
Given reasonable contact lens visual potential, RGP
sclerals offer a valuable alternative to corneal transplantation.
There are also many applications following corneal transplantation.
High myopes or aphakes
may find sclerals the lens of choice, and the retention of a pre-corneal
liquid reservoir offers unique therapeutic potential for some
dry eye conditions.
We estimate that there are about 2,000 patients using our RGP lenses
for a variety of corneal conditions, and many report their quality
of life has been significantly improved
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Disadvantages of
Scleral Lenses
- Even if skilfully fitted, the full corneal coverage considerably
reduces oxygen available to the cornea for PMMA sclerals
- They are labour intensive to produce compared to most other
lens types
- Their physical size can intimidate some patients
- Some patients are conscious of the feeling of bulk
- The scleral zone substance may cause a pseudo-proptosis appearance
during wear
- Fenestrations in scleral lenses admit air bubbles to the pre-corneal
reservoir causing visual disturbances and localised dehydration
- Fenestrations also cause settling back on the globe with consequent
tightness of the fit, especially at the limbus
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Rigid Gas Permable Lenses
(RGP)
RGP materials enabled a major shift away from both traditional
preformed fitting methods and from impression methods as mainstream
scleral lens clinical practice.
Corneal swelling studies and clinical experience gained so far,
indicates that sealed scleral lens designs provide sufficient oxygenation
to alleviate significant corneal hypoxia. This crucial development
has transformed scleral lens practice. Air bubbles are largely excluded
from the pre-corneal fluid reservoir, and its positive pressure
is retained, thereby significantly reducing settling back and enabling
controlled corneal clearance.
Complex and unpredictable fitting processes are now only necessary
in a minority of cases encountered. Virtually any corneal topography
can be easily fitted with sealed RGP scleral lenses, provided that
the sclera is regular enough to be fitted with a preformed design.
If this is not the case, an impression may have to be taken, from
which a PMMA scleral lens can be made in the traditional way, or
the final fitted PMMA scleral lens can be duplicated in an RGP material.
However, it should be pointed out that this duplication exercise
is a cumbersome manufacturing exercise compared to any other scleral
lens manufacturing process.
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Case Studies
For more extensive case study information see A
study of 530 patients referred for rigid gas permeable scleral contact
lens assessment by KW Pullum and RJ Buckley published in the
Cornea (1997) 16(6), 612 - 622.
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Female,
age 30. Teenage onset keratoconus
A corneal lens had been worn successfully in the early stages
after diagnosis, but gave increasing discomfort as it aggravated
a proud epithelial nebula, seen here at the apex of the cornea.
A corneal transplant was offered, but the patient declined,
preferring to try further contact lens options.
A sealed RGP scleral lens was
an uncomplicated fitting exercise. The final lens had full
corneal clearance, totally relieving the discomfort. After
three years of alternating between corneal and scleral lenses,
the patient has switched entirely to use of the scleral lens
only.
Return to Case Study List
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Female age
55. Teenage onset keratoconus
Corneal lens fitting was impossible with such a protrusive
profile.
Scleral lenses offered
an opportunity for a conservative management option irrespective
of the highly protrusive corneal topography. A large donor
for a transplant would have been required, bringing the junction
into proximity to the limbal arcades, thereby increasing the
risk of rejection.
Sealed RGP scleral lens leaving
a glancing contact zone was a straightforward process, giving
a satisfactory 6/18 VA with comfortable full day wear.
Return to Case Study List
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Female age
55. Exposure Keratitis
This patient suffered an acoustic neuroma at age 52. The
tumour was successfully excised, but leaving a residual facial
nerve palsy with consequent poor lid closure on the right
side.
The continuous exposure led to gross scarring and vacularisation,
and unaided vision of counting fingers. A sealed RGP
scleral lens was fitted, retaining a full and constant pre-corneal
liquid reservoir. The visual acuity improved to 6/36 and
the progress of the veovascularisation was held in status
quo.
Return to Case Study List
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Female, age
50. Acute Stevens Johnson sensitivity to routinely prescribed
sulphonamides at age 25.
linical History:
Spectacle VA: <6/60
Rigid lens potential VA: 6/24
Fellow eye: nil L/P, wears cosmetic shell.
Contact lens history:
1981. An impression PMMA scleral lens was issued after recovery
from the acute phase. This was worn successfully for 23 years.
1998. Tolerance to the PMMA lens began to be more difficult,
so a preformed RGP sealed scleral
lens, fitted with corneal clearance, was issued. Her tolerance
improved, but the VA was inferior. A second lens with central
corneal contact gave a significant improvement in VA and,
surprisingly, was more comfortable.
2000. The RGP scleral lens has been worn for 24 months with
improved tolerance compared to the PMMA lens. The patient
also reported an improvement in clarity of vision. The recorded
VA was much the same as before, at 6/24, although 6/18 has
been recorded on some occasions.
Return to Case Study List
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Male, age
55. Late onset keratoconus
diagnosed age 45.
There was a rapid development of a very protrusive globic
type corneal profile lead to significant visual loss over
a four year period leaving no worthwhile improvement with
spectacles. Rigid corneal lens fitting was unsuccessful due
to discomfort and instability of the lens in situ. The other
eye had developed hydrops, which had more or less resolved,
but refitting with contact lenses had been postponed. The
profile was much the same as the right eye, having a similar
outcome with corneal lenses prior to the hydrops episode.
A scleral lens was suggested as a final option before a transplant.
The idea was immediately taken up by the patient who did not
want an eye operation if there was a feasible alternative.
A sealed RGP scleral lens was
fitted clear of the cornea at the visual axis and a glancing
contact at the cone apex. Following issue, he built up to
all day wear within one week. Visual acuity was 6/9. To date,
the lens has been worn trouble free for 24 months.
Return to Case Study List
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Female age
15. Congential cataract and ptosis.
The congenital cataract was removed but following post surgical
complications, the eye was left with counting fingers only.
Approaching her mid teens, she became more appearance conscious
and asked if any non surgical option was available to improve
the appearance.
A sealed RGP scleral lens was
a starightforward fitting exercise and made a significant
raise in the level of the upper lid from just at the upper
pupil margin by a further 2 to 3mm
Return to Case Study List |
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Created by Michael W North IT Services. Copyright Ken
Pullum 2003. Last updated 9/10/2005
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