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Scleral contact lenses: indications<br />

and current clinical methods<br />

Ken Pullum, Senior Optometrist, Moorfields Eye<br />

Hospital, London and Oxford Eye Hospital<br />



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OT CET points awarded will be<br />

uploaded to its website by us. All<br />

participants must confirm <strong>the</strong>se<br />

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so that <strong>the</strong>y can move <strong>the</strong>ir<br />

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record” into <strong>the</strong>ir “Final CET<br />

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Scleral contact lenses (ScCLs) predate rigid corneal and hydrogel lenses by<br />

seven decades, but still have a unique clinical role. The general perception is<br />

that <strong>the</strong>y are only useful in <strong>the</strong> most advanced cases of ectatic corneal disease,<br />

<strong>the</strong> fitting process is cumbersome, <strong>the</strong>y are uncomfortable to wear and <strong>the</strong>y<br />

are <strong>the</strong> cause of hypoxic corneal changes. Professional instruction has become<br />

a low priority in recent years, hence relatively few practitioners have an<br />

understanding of sclerals’ unique advantages or <strong>the</strong> transformation in clinical<br />

methods and manufacturing techniques enabled by <strong>the</strong> introduction of rigid<br />

gas permeable (RGP) materials 1 . Contrary to popular belief, most RGP ScCL fitting<br />

is a straightforward and predictable process, so consequently, <strong>the</strong>y are<br />

also a feasible option for very much lower levels of pathology, ra<strong>the</strong>r than at<br />

a stage which would be described as end point. For example, <strong>the</strong>y may be<br />

offered when patients can still be fitted with corneal lenses, but are<br />

experiencing discomfort and excessive lens mobility.<br />

2 standard CET points<br />

1 CET point<br />

Module 5 Part 4<br />

Specialist contact lens<br />

fitting<br />

About <strong>the</strong> author<br />

Ken Pullum is a Senior<br />

Optometrist at Moorfields<br />

Eye Hospital with a special<br />

interest in medical indications<br />

for contact lenses and<br />

developments in modern<br />

scleral lens practice.<br />

Lens types: fenestrated or<br />

non-ventilated<br />

A ventilated ScCL includes a design feature<br />

which enables fresh oxygenated tears to<br />

access <strong>the</strong> cornea. The expression sealed<br />

has two conflicting meanings in ScCL practice.<br />

In reference to scleral lens categorisation,<br />

it is used to indicate a lens with no<br />

intended means of ventilation incorporated<br />

into <strong>the</strong> design. In a clinical context, its use<br />

describes <strong>the</strong> appearance in situ of a lens<br />

which beds down on <strong>the</strong> sclera so <strong>the</strong>re is<br />

no or only an insignificant tear exchange.<br />

A fenestration 2 is <strong>the</strong> most widely used of<br />

ventilation and can be used for both preformed<br />

and impression lenses. Channels<br />

and slots are alternatives for impression<br />

lenses, but do not function well for preformed<br />

lenses as <strong>the</strong> improved scleral zone<br />

apposition and centration of impression<br />

lenses is required for ei<strong>the</strong>r to function<br />

properly.<br />

It is quite possible that a non-ventilated<br />

coaxial ScCL may have a functional tear<br />

exchange if <strong>the</strong> underlying sclera is irregular,<br />

<strong>the</strong>refore is not sealed. Conversely, if an<br />

intended ventilation feature is non-functional<br />

for some reason, say if a fenestration<br />

is blocked, <strong>the</strong> lens may effectively be<br />

sealed. For clarification, use of <strong>the</strong> term<br />

sealed in <strong>the</strong> remainder of this text refers to<br />

a lens which bears on <strong>the</strong> sclera so that<br />

<strong>the</strong>re is no or insignificant tear exchange,<br />

and non-ventilated to a lens constructed<br />

without a fenestration or o<strong>the</strong>r intentional<br />

means of ventilation.<br />

Lens types: impression or<br />

preformed<br />

ScCLs can be specified after preformed trial<br />

diagnostic lenses of known parameters<br />

have been evaluated in situ, or an individually<br />

bespoke lens may be produced on <strong>the</strong><br />

basis of an eye impression. Impression lenses<br />

can be used virtually irrespective of irregular<br />

topography. Prior to <strong>the</strong> introduction of<br />

RGP materials this was <strong>the</strong> more versatile<br />

system as <strong>the</strong> great majority of <strong>the</strong> cases<br />

were fitted with ScCLs because of irregular<br />

corneal topography.<br />

The introduction of RGP materials shifted<br />

<strong>the</strong> emphasis back to preformed for two<br />

reasons. Firstly, RGP materials are not sufficiently<br />

<strong>the</strong>rmoplastic to be pressed over a<br />

cast, which is <strong>the</strong> simple traditional method<br />

used for PMMA. It is possible to make RGP<br />

impression lenses, but <strong>the</strong> process is much<br />

more cumbersome requiring precision<br />

milling or moulding. Secondly, corneal<br />

swelling studies show that nonventilated<br />

high Dk RGP ScCLs reduce<br />

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corneal swelling to a level comparable to<br />

normal overnight swelling, thus<br />

reintroducing <strong>the</strong> option of fitting ScCLs<br />

without <strong>the</strong> complicating impact of<br />

incorporating a fenestration 3,4,5 .<br />

Advantages and<br />

disadvantages of ScCLs<br />

Advantages<br />

The large size creates a scleral bearing surface<br />

and retains a pre-corneal fluid reservoir<br />

providing optical neutralisation of an astigmatic<br />

or irregular corneal surface and<br />

corneal hydration. Very high powers, up to<br />

+/- 40.00D, are possible because <strong>the</strong>re are<br />

minimal lid traction and centre of gravity<br />

effects. They cannot be dislodged by <strong>the</strong> lids<br />

and are often relatively comfortable even<br />

for <strong>the</strong> unadapted eye because <strong>the</strong> lid<br />

margin is in contact with <strong>the</strong> surface of <strong>the</strong><br />

lens ra<strong>the</strong>r than <strong>the</strong> edge. If RGP non-ventilated<br />

ScCLs are used, corneal contact can be<br />

minimal.<br />

ScCLs, including RGP lenses, can be kept<br />

dry when not being worn. There is no risk of<br />

contaminated storage solutions since none<br />

is used, so <strong>the</strong> risk of infections is reduced.<br />

They are robust, <strong>the</strong> surface can be polished<br />

or resurfaced periodically, and <strong>the</strong>y are not<br />

easily lost. Less dextrous patients may<br />

find <strong>the</strong>m easier to handle because <strong>the</strong>y do<br />

not need to be precariously balanced<br />

on a fingertip.<br />

Disadvantages<br />

While not producing any lid sensation, <strong>the</strong>re<br />

is a feeling and an appearance of bulk, and<br />

some people are intimidated by <strong>the</strong>ir large<br />

size. They cover a large area of <strong>the</strong> anterior<br />

globe, considerably reducing <strong>the</strong> oxygen<br />

available to <strong>the</strong> cornea, although <strong>the</strong> introduction<br />

of RGP materials has led to a major<br />

improvement. Because <strong>the</strong>y are fitted with<br />

corneal clearance, <strong>the</strong> VA and <strong>the</strong> ability of<br />

<strong>the</strong> lens to reduce distortions in ectatic<br />

corneal conditions may be reduced compared<br />

to rigid corneal lenses. However, if an<br />

RGP ScCL can be worn when a corneal lens<br />

cannot, <strong>the</strong> comparison is not valid.<br />

Indications<br />

ScCLs are indicated simply when <strong>the</strong> unique<br />

advantages of ScCLs can be applied. They<br />

can be considered to manage any eye condition<br />

if <strong>the</strong>re is a strong enough reason for<br />

contact lens correction, and in <strong>the</strong> management<br />

of some ocular surface disease. There<br />

have been a number of publications in<br />

recent years describing ScCL applications.<br />

6,7,8,9,10,11,12,13,14,15,16,17,18<br />

Irregular or abnormal<br />

corneal topography<br />

Corneal ectasia<br />

Keratoconus or o<strong>the</strong>r primary corneal<br />

ectasias (PCE) form <strong>the</strong> majority of current<br />

indications for ScCLs. RGP corneal lenses<br />

Figure 2 Irregular corneal topography<br />

as a consequence of a transplant that has<br />

unexpectedly sprung forward. There is a<br />

clear depression in <strong>the</strong> superior<br />

mid-periphery which would be a major<br />

problem for corneal lens fitting. A nonventilated<br />

RGP ScCL is unaffected by a<br />

localised irregularity like this provided it is<br />

sealed on <strong>the</strong> sclera<br />

may be simply impossible to fit in very<br />

advanced cases, for example, as shown in<br />

Figure 1, but <strong>the</strong>re is also an application for<br />

ScCLs when corneal lenses persistently<br />

dislodge, or are not well tolerated due to<br />

excessive mobility or <strong>the</strong> formation of<br />

epi<strong>the</strong>lial erosions.<br />

Corneal transplant<br />

The second largest group for which ScCLs<br />

are indicated are post-corneal transplants if<br />

<strong>the</strong>re is a residual refractive error, or if <strong>the</strong><br />

surface remains irregular, illustrated in<br />

Figure 2. Even if <strong>the</strong> astigmatism is very<br />

high, which still happens sometimes even<br />

with <strong>the</strong> most expert surgery, non-ventilated<br />

RGP ScCL fitting post-transplant is usually<br />

a comparatively straightforward exercise.<br />

The lenses are fitted with full corneal<br />

clearance irrespective of corneal topography,<br />

<strong>the</strong>refore <strong>the</strong> appearance is much <strong>the</strong><br />

same whe<strong>the</strong>r <strong>the</strong> cylinder is 2.00D or in<br />

excess of 20.00D.<br />

Figure 1 Downwardly displaced apex in an advanced keratoconus. Many corneal<br />

lenses were tried, but all dislodged almost immediately. ScCL fitting was a straightforward<br />

process with only two lenses necessary to establish corneal clearance<br />

Corneal trauma or postsurgery<br />

The vision in traumatised eyes with corneal<br />

scarring may be improved with ScCLs if <strong>the</strong><br />

injury has caused irregularities, but has left<br />

some areas of reasonably transparent<br />

cornea in <strong>the</strong> pupillary region. Some cases<br />

of unsuccessful refractive surgery may benefit<br />

if supplementary correction with rigid<br />

contact lenses is helpful in reducing visual<br />

disturbances such as starbursting and<br />

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ghosting. Grossly abnormal topography<br />

would not be expected after refractive surgery,<br />

but some patients remain intolerant of<br />

corneal lenses, in which cases ScCLs<br />

could be tried.<br />

Normal topography with high<br />

refractive errors<br />

ScCLs may be indicated when high power<br />

rigid corneal lenses cause intractable problems<br />

of excessive mobility or poor centration.<br />

They may be used whatever <strong>the</strong><br />

ametropia if <strong>the</strong>re is intolerance to corneal<br />

or hydrogel lens wear in high myopia, or<br />

hypermetropia or significant non-pathological<br />

corneal astigmatism.<br />

Therapeutic or protective<br />

applications<br />

ScCLs uniquely retain a pre-corneal fluid<br />

reservoir providing corneal hydration in serious<br />

dry eye conditions, such as Stevens<br />

Johnson Syndrome or ocular cicatricising<br />

pemphigoid. A ScCL in situ may give an<br />

improved environment for corneal healing<br />

where newly formed epi<strong>the</strong>lium is continually<br />

sloughed away by <strong>the</strong> action of <strong>the</strong> lids,<br />

or may prevent tear film evaporation with<br />

poor lid closure or lid absence. The lens<br />

retains a fluid reservoir which maintains<br />

some degree of corneal hydration and<br />

protects <strong>the</strong> cornea from trichiasis and lid<br />

margin keratinisation, and <strong>the</strong> front surface<br />

provides hugely improved refracting surface,<br />

giving a considerable visual benefit.<br />

There is also an application in less severe<br />

dry eye or tears dysfunction pathology.<br />

Sometimes <strong>the</strong> patient may describe very distressing<br />

and disproportionate ocular discomfort<br />

with very little visible corneal disruption.<br />

Mucus filaments adherent to <strong>the</strong> cornea are<br />

very painful when <strong>the</strong>y pull on <strong>the</strong> epi<strong>the</strong>lium<br />

or finally detach, but wave freely in <strong>the</strong> precorneal<br />

fluid reservoir behind a ScCL, and<br />

appear to float off into <strong>the</strong> fluid pool with little<br />

discomfort. ScCLs may be used as a prop<br />

for some cases of ptosis.<br />

Cosmetic shells<br />

A realistic iris can be encapsulated into<br />

PMMA scleral shells to mask unsightly blind<br />

eyes, or to relieve intractable diplopia or<br />

glare in cases of aniridia.<br />

Recreational or occupational<br />

applications<br />

Particles behind rigid corneal lenses in dusty<br />

work place environments are very troublesome.<br />

ScCLs eliminate this problem almost<br />

entirely. Most recreational activities are satisfactorily<br />

managed with <strong>the</strong> use of hydrogel<br />

lenses, but ScCLs are still indicated on<br />

occasions for contact or water sports.<br />

ScCL fitting options<br />

Ventilation by some means is a prerequisite<br />

for PMMA lenses whe<strong>the</strong>r impression or preformed,<br />

but non-ventilated designs are <strong>the</strong><br />

preferred option for RGP. Some limitations<br />

still remain for irregular ocular topography<br />

with RGP preformed sclerals, but considerably<br />

more irregular eyes can be fitted using<br />

preformed RGP sclerals because of <strong>the</strong> tear<br />

reservoir compared to fenestrated PMMA.<br />

Impression lenses of some kind can be used<br />

virtually irrespective of irregular topography.<br />

All <strong>the</strong> following alternatives are possible,<br />

and have different applications.<br />

RGP<br />

RGP sclerals should now be considered <strong>the</strong><br />

first choice for <strong>the</strong> great majority of ScCL<br />

cases. Some long-term wearers have worn<br />

<strong>the</strong> lenses for over 50 years, so <strong>the</strong>se should<br />

be considered a long-term option for most<br />

new referrals. As <strong>the</strong> great majority of ScCL<br />

referrals are for PCE or corneal transplant, it is<br />

crucial to minimise <strong>the</strong> risk of corneal hypoxia.<br />

A transplant may have to be a future management<br />

option for any PCE referred for ScCL<br />

fitting. If so, corneal neovascularisation, while<br />

not necessarily sight-threatening in its own<br />

right in <strong>the</strong> early stages, may increase <strong>the</strong> risk<br />

of transplant rejection.<br />

Preformed non-ventilated RGP can be<br />

used for <strong>the</strong> great majority of cases, irrespective<br />

of corneal topography. There are more<br />

potential problems with <strong>the</strong> scleral topography,<br />

but if <strong>the</strong> scleral zone is well enough<br />

sealed, a pre-corneal fluid reservoir is<br />

retained without bubbles and with minimal<br />

settling on <strong>the</strong> globe. The optimum clearance<br />

at <strong>the</strong> visual axis is approximately 0.25mm,<br />

but can be more than twice that value at <strong>the</strong><br />

limbus in some sectors without causing any<br />

problems provided it remains air free.<br />

The principal problem with preformed<br />

non-ventilated RGP ScCLs is that <strong>the</strong>y have<br />

to be inserted filled with saline. This requires<br />

keeping <strong>the</strong> lens horizontal at <strong>the</strong> moment<br />

of insertion, so it is necessary also to have<br />

<strong>the</strong> patient’s head horizontal and facing <strong>the</strong><br />

floor. This is a more difficult task for<br />

patients, and sometimes for <strong>the</strong> practitioner<br />

as well, compared to <strong>the</strong> relatively simple<br />

procedure for inserting a fenestrated lens,<br />

which can be inserted with <strong>the</strong> head in <strong>the</strong><br />

normal upright posture.<br />

Preformed fenestrated RGP is indicated<br />

if a fenestration is beneficial, for<br />

example, if retention of <strong>the</strong> pre-corneal fluid<br />

reservoir at <strong>the</strong> moment of insertion is<br />

impossible. However, <strong>the</strong>re is a serious limitation<br />

because air bubbles are admitted into<br />

<strong>the</strong> pre-corneal fluid reservoir and cross <strong>the</strong><br />

visual axis if <strong>the</strong> pre-corneal fluid reservoir<br />

depth is greater than 0.1mm. It is unlikely<br />

that a tear pool of uniformly shallow depth<br />

can be maintained with even just a moderately<br />

irregular corneal topography.<br />

Impression non-ventilated RGP is an<br />

option if <strong>the</strong>re is an intractable problem<br />

retaining an air free pre-corneal fluid reservoir<br />

with a non-ventilated preformed<br />

design. The ultimate fitting target is a flush<br />

back surface for <strong>the</strong> scleral zone and an<br />

optic zone clearance similar to that for a<br />

non-ventilated preformed RGP. As <strong>the</strong> scleral<br />

zone is fabricated from an eye impression,<br />

a very good alignment can be expected with<br />

effective sealing on <strong>the</strong> scleral zone, hence<br />

<strong>the</strong>re is scope for increasing <strong>the</strong> optic zone<br />

clearance with a good prospect of retaining<br />

a pre-corneal fluid reservoir.<br />

Impression fenestrated RGP is a major<br />

undertaking because it is a departure from<br />

mainstream manufacturing and, in<br />

addition, requires very precise fabrication of<br />

<strong>the</strong> back surface to keep a uniform depth of<br />

<strong>the</strong> pre-corneal fluid reservoir. However,<br />

<strong>the</strong>re may be a better chance than with a<br />

fenestrated preformed RGP lens because<br />

<strong>the</strong> optic zone is individually fabricated from<br />

<strong>the</strong> exact shape of <strong>the</strong> eye.<br />

PMMA<br />

PMMA ScCLs still have a role to play but<br />

<strong>the</strong>re is an acknowledged long-term threat of<br />

hypoxic corneal changes, so <strong>the</strong>se would not<br />

normally be <strong>the</strong> first choice for new ScCL<br />

wearers. However, if a PMMA lens has been<br />

worn successfully for some years without significant<br />

sequelae, <strong>the</strong>re is no reason for a<br />

change is to be made. Most impression<br />

PMMA lenses for moderate or advanced<br />

corneal ectasias were ventilated, hence <strong>the</strong><br />

initial clearance at <strong>the</strong> visual axis could not be<br />

much more than 0.1mm. After a period of<br />

settling on <strong>the</strong> globe, an almost universal<br />

occurrence with a ventilated lens, <strong>the</strong> result<br />

was apical contact. The author’s observation<br />

is that contact is better tolerated in PMMA<br />

than with RGP materials. The probable explanation<br />

is <strong>the</strong> increased co-efficient of friction<br />

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for RGP materials compared to PMMA.<br />

For <strong>the</strong> same reason, <strong>the</strong>re may be more<br />

surface/tarsal plate interaction with RGP<br />

compared to PMMA. Fur<strong>the</strong>rmore, <strong>the</strong> visual<br />

performance in terms of visual acuity,<br />

contrast and reduction of distortions or<br />

ghosting is reduced when <strong>the</strong>re is a visual<br />

axis contact zone.<br />

Impression ventilated PMMA proved to<br />

be a successful option in many cases before<br />

RGP materials were available. A ventilated<br />

impression PMMA lens is easier to produce<br />

than RGP due to its superior <strong>the</strong>rmoplasticity,<br />

and because it can be cut and polished<br />

with minimum risk of irreparable damage.<br />

Impression ventilated ScCLs very often have<br />

central corneal contact zones after settling<br />

back, irrespective of <strong>the</strong> material. If so, PMMA<br />

is more likely to be tolerated. Impression<br />

PMMA is arguably <strong>the</strong> method of choice for<br />

elderly aphakes. Centration is optimised with<br />

<strong>the</strong> impression method of fitting as <strong>the</strong>re is a<br />

near glove fit on <strong>the</strong> sclera. Thus <strong>the</strong> front<br />

optic can be sited over <strong>the</strong> visual axis to<br />

minimise aberrations.<br />

Preformed fenestrated PMMA may be<br />

a preferable option to RGP fenestrated<br />

because it may be fitted with less initial<br />

clearance so that apical contact following<br />

any settling on <strong>the</strong> globe is better tolerated<br />

than if an RGP lens is similarly fitted.<br />

However, <strong>the</strong> chances of a successful outcome<br />

with a moderately or advanced ectasia<br />

and irregular topography remain limited<br />

for <strong>the</strong> reasons discussed previously.<br />

Impression or preformed nonventilated<br />

PMMA has no place for long<br />

term wear as <strong>the</strong> onset of hypoxia is very<br />

rapid. However, it is worth remembering that<br />

advanced keratoconus causes extremely poor<br />

unaided vision and spectacles may do next to<br />

nothing by way of correction.<br />

Therefore, all contact lens options should<br />

be borne in mind. If good vision to deal with<br />

a particular task is urgently required for a<br />

few minutes, a non-ventilated PMMA lens<br />

provides just that.<br />

The fitting and production are <strong>the</strong> simplest<br />

for all scleral lens types provided <strong>the</strong><br />

scleral zone seals adequately on <strong>the</strong> sclera,<br />

which should be <strong>the</strong> case following an<br />

impression lens if not with a preformed lens.<br />

Preformed non-ventilated RGP<br />

ScCL fitting<br />

PMMA ScCLs, whe<strong>the</strong>r preformed or<br />

impression of preformed, are comparatively<br />

infrequently required nowadays. The fitting<br />

Figure 3 Optimum preformed lens fitting with scleral alignment and optic zone clearance<br />

Figure 4 Steep fitting scleral zone<br />

illustrating fluorescein encroaching almost<br />

to <strong>the</strong> periphery of <strong>the</strong> lens. There is also a<br />

small amount of blanching at <strong>the</strong> edge<br />

Figure 5 Flat fitting scleral zone on <strong>the</strong><br />

same eye as seen in Figure 4. The<br />

fluorescein is only seen just beyond <strong>the</strong><br />

limbus, and <strong>the</strong>re is obvious blanching in<br />

<strong>the</strong> mid-periphery<br />

systems for both have been well documented<br />

in previous textbooks and summarised<br />

recently 19 , so it is not appropriate to expand<br />

fur<strong>the</strong>r on <strong>the</strong> preceding discussion which<br />

outlines <strong>the</strong>ir role.<br />

However, <strong>the</strong> fitting processes for RGP<br />

ScCLs have been more recently developed,<br />

hence <strong>the</strong> principles are outlined in <strong>the</strong> following<br />

text.<br />

Lens diameter<br />

The diameter is chosen according to <strong>the</strong><br />

appearance at <strong>the</strong> assessment and fitting<br />

process, and can be between 16mm and<br />

25mm. In fact, 18mm to 23mm is a more<br />

usual range for preformed lenses. Indeed,<br />

16mm is very small for a lens to be defined<br />

as a ScCL, that is, having a scleral bearing<br />

surface and essentially with corneal clearance.<br />

If <strong>the</strong> corneal diameter is taken to be<br />

12mm, and it is deemed desirable to allow<br />

an extra 1mm all round for limbal clearance,<br />

a 16mm total diameter only allows a 1mm<br />

scleral bearing annulus. The author<br />

acknowledges <strong>the</strong> valuable role for lenses<br />

with a diameter smaller than 16mm, but<br />

<strong>the</strong>y do not conform to this definition of a<br />

ScCL and are fitted according to a different<br />

rationale.<br />

A small variation in <strong>the</strong> diameter may not<br />

make much difference, but if a lens were to<br />

be made progressively smaller <strong>the</strong> original<br />

bearing surface would eventually be eliminated.<br />

The new bearing surface would <strong>the</strong>n<br />

be <strong>the</strong> sector of <strong>the</strong> sclera which was previously<br />

<strong>the</strong> transition zone with <strong>the</strong> larger<br />

diameter lens. The result is likely to be<br />

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Figure 6 The optic zone sagitta, and consequently, <strong>the</strong> apical clearance, is increased<br />

by steepening <strong>the</strong> BOZR<br />

Figure 7 The optic zone parameters<br />

can be defined according to <strong>the</strong> projection<br />

of <strong>the</strong> optic zone from <strong>the</strong> continuation of<br />

<strong>the</strong> scleral curve measured axially at <strong>the</strong><br />

apex and at <strong>the</strong> limbus<br />

increased settling back with reduction of<br />

<strong>the</strong> optic zone clearance.<br />

There are some comparative advantages<br />

and disadvantages of smaller and larger<br />

lenses. The author’s observation is that <strong>the</strong><br />

scleral topography just outside <strong>the</strong> limbus is<br />

more regular and symmetrical than <strong>the</strong><br />

more peripheral sclera. Smaller diameter<br />

ScCLs may be indicated when a tighter fitting<br />

is necessary. For example, <strong>the</strong>y should<br />

be tried when a non-ventilated 23mm diameter<br />

lens fails to seal well enough on <strong>the</strong><br />

sclera to prevent admission of an air bubble<br />

into <strong>the</strong> pre-corneal reservoir. Bearing on<br />

<strong>the</strong> most symmetrical region of <strong>the</strong> sclera<br />

leads to noticeably less decentration, which<br />

may reduce any prismatic effects.<br />

Smaller lenses can be made thinner than<br />

larger lenses because <strong>the</strong> rigidity is greater<br />

with smaller diameter lenses. The reduced<br />

mass, and less movement on <strong>the</strong> eye compared<br />

to larger lenses, may render a contact<br />

zone more tolerable. Hence <strong>the</strong>y can be fitted<br />

with less corneal clearance, which may<br />

prove to be advantageous if <strong>the</strong> vision is<br />

improved with a visual axis contact zone. A<br />

final advantage of <strong>the</strong> improved centration<br />

and closer proximity to <strong>the</strong> cornea is a more<br />

even depth of <strong>the</strong> pre-corneal fluid reservoir,<br />

this increases <strong>the</strong> possibility that a fenestration<br />

can be more successful than with larger<br />

diameter lenses. However, on <strong>the</strong> downside,<br />

<strong>the</strong> increased tightness of <strong>the</strong> fitting on <strong>the</strong><br />

eye and <strong>the</strong> reduced limbal clearance are significant<br />

drawbacks at times. Although such<br />

lenses are more likely to retain an air-free<br />

pre-corneal reservoir <strong>the</strong>y are more difficult<br />

to insert without a bubble in <strong>the</strong> first place,<br />

and because <strong>the</strong>y fit tighter on <strong>the</strong> eye, <strong>the</strong>y<br />

are distinctly more difficult to remove than<br />

larger diameter lenses.<br />

Optimal scleral zone alignment<br />

The bearing surface should be spread as<br />

evenly as possible over <strong>the</strong> sclera, but with<br />

optic zone clearance. In fact, 13.50mm to<br />

14.50mm is a usual back scleral radius (BSR)<br />

range for most preformed ScCLs. The bearing<br />

surface is displaced away from <strong>the</strong> limbus<br />

if <strong>the</strong> scleral zone is too steep, and may<br />

cause <strong>the</strong> lens to vault as it rests only at <strong>the</strong><br />

periphery, giving an appearance of excessive<br />

apical clearance. A flat fitting scleral zone<br />

shifts <strong>the</strong> bearing surface nearer to <strong>the</strong> limbus,<br />

but does not appreciably affect <strong>the</strong> apical<br />

clearance. Figure 3 diagrammatically<br />

illustrates scleral zone alignment and<br />

corneal clearance. Figures 4 and 5 are fluorescein<br />

photographs showing a steep and<br />

flat fitting scleral zone respectively.<br />

A glove fit on <strong>the</strong> sclera is not possible,<br />

nor essential, but <strong>the</strong> scleral zone needs to<br />

be sufficiently sealed to prevent <strong>the</strong> introduction<br />

of air bubbles into <strong>the</strong> pre-corneal<br />

fluid reservoir. An overall view of <strong>the</strong> scleral<br />

zone with a hand-held low magnification<br />

lamp is sufficient to see <strong>the</strong> extent of <strong>the</strong><br />

clearance beyond <strong>the</strong> limbus. Any areas of<br />

conjunctival blood vessel blanching, which<br />

are due to localised compression while <strong>the</strong><br />

lens is in situ, can be seen simultaneously<br />

with a white light source.<br />

Corneal and limbal clearance<br />

Achieving optimal clearance at <strong>the</strong> limbus<br />

and at <strong>the</strong> apex is determined by varying <strong>the</strong><br />

back optic zone radius (BOZR) and <strong>the</strong> back<br />

optic zone diameter (BOZD) in combination<br />

to give <strong>the</strong> optic zone sagitta (OZS). Varying<br />

<strong>the</strong> BOZR with a constant BOZD gives rise to<br />

a precisely calculable change to <strong>the</strong> central<br />

corneal clearance, as in Figure 6, but varying<br />

<strong>the</strong> BOZD with a constant BOZR does not<br />

because <strong>the</strong> curvature of <strong>the</strong> scleral bearing<br />

surface is an unknown quantity. This is <strong>the</strong><br />

same principle as traditional style PMMA<br />

ScCL fitting, but most modern fitting<br />

systems utilising <strong>the</strong> OZS principle calculate<br />

<strong>the</strong> combined specifications to give significant<br />

variations in apical and limbal<br />

clearance, <strong>the</strong>refore it is not necessary for<br />

<strong>the</strong> practitioner to try combinations of<br />

BOZRs and BOZDs.<br />

The corneal clearance can also be varied<br />

by changing <strong>the</strong> optic zone projection (OZP)<br />

in progressive increments but without reference<br />

to <strong>the</strong> BOZR or BOZD. Figure 7 illustrates<br />

OZP diagrammatically. The optic zone<br />

Figure 8 Off-axis apical contact zone in<br />

an advanced keratoconus wearing a nonventilated<br />

RGP scleral lens. This amount of<br />

contact was tolerated by <strong>the</strong> wearer and<br />

did not lead to any corneal erosion<br />

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Figure 9 The same eye as seen in<br />

Figure 8 with a significant increment in <strong>the</strong><br />

optic zone projection illustrating full<br />

corneal clearance.<br />

comparison to <strong>the</strong> corneal thickness, as<br />

shown in Figure 10. The fluorescence can<br />

be seen perfectly well with white light;<br />

cobalt blue filters reduce <strong>the</strong> brightness too<br />

much for <strong>the</strong> corneal thickness to be seen<br />

well.<br />

Apical clearance between 0.2mm and<br />

0.3mm is a satisfactory target for a nonventilated<br />

ScCL, approximately half a normal<br />

corneal thickness, with <strong>the</strong> pre-corneal<br />

fluid reservoir extending just beyond <strong>the</strong><br />

limbus. The exact measurement of corneal<br />

clearance is not critical, although if excessive<br />

it is more difficult to maintain an<br />

air-free pre-corneal fluid reservoir or for <strong>the</strong><br />

patient to insert <strong>the</strong> lens without an air<br />

methods consequent to <strong>the</strong> introduction of<br />

RGP materials. There are many fitting<br />

nuances which could not be covered, and<br />

<strong>the</strong>re are significant problem areas which<br />

have only briefly been touched upon.<br />

However, it is emphasised that <strong>the</strong> fitting<br />

processes have become straightforward and<br />

predictable in most cases, with a rapid<br />

arrival at <strong>the</strong> end-point mostly using nonventilated<br />

preformed RGP designs.<br />

ScCLs may be lens-of-choice when a<br />

result is needed more than at any o<strong>the</strong>r<br />

time. There are no conditions for which <strong>the</strong>y<br />

cannot be considered, so it is clearly necessary<br />

to preserve <strong>the</strong> clinical and manufacturing<br />

skills required . Since <strong>the</strong> introduction of<br />

is defined according to two axially measured<br />

parameters: <strong>the</strong> OZP from <strong>the</strong> extrapolation<br />

of <strong>the</strong> scleral curve measured at <strong>the</strong> apex<br />

and at <strong>the</strong> limbus. These increments are just<br />

clinically significant enough to keep <strong>the</strong><br />

number of lenses in <strong>the</strong> fitting system<br />

manageable. OZP is a function of <strong>the</strong> BSR,<br />

hence if <strong>the</strong> BSR is flattened, <strong>the</strong> OZP needs<br />

to be increased to compensate.<br />

The OZS or OZP for an initial trial lens is<br />

selected from an assessment of <strong>the</strong> overall<br />

corneal profile with <strong>the</strong> naked eye. If inaccurately<br />

estimated, <strong>the</strong>re is no major loss as<br />

<strong>the</strong> first lens inspected in situ gives a clear<br />

indication for subsequent lens selection.<br />

Keratometry and corneal topography are of<br />

limited value as nei<strong>the</strong>r provides any information<br />

about <strong>the</strong> peripheral cornea or <strong>the</strong><br />

projection from <strong>the</strong> sclera.<br />

The parameters are assessed simultaneously<br />

with <strong>the</strong> lens in situ, but <strong>the</strong> initial decision<br />

must be to determine <strong>the</strong> optimum<br />

scleral zone specifications as <strong>the</strong> scleral zone<br />

has an impact on <strong>the</strong> optic zone clearance.<br />

The lens is inserted filled with saline and fluorescein<br />

so that areas where <strong>the</strong> lens is clear<br />

of <strong>the</strong> surface can be easily distinguished<br />

from areas where <strong>the</strong> lens is in contact.<br />

Figures 8 and 9 demonstrate <strong>the</strong> effect of<br />

increasing <strong>the</strong> OZP to reduce corneal contact.<br />

Slit lamp biomicroscopy<br />

assessment of <strong>the</strong> optic zone<br />

If fluorescein is added to <strong>the</strong> saline prior to<br />

insertion, inspection of <strong>the</strong> optic zone using<br />

a cobalt blue filter shows any corneal<br />

contact zones. A slit lamp optical section<br />

can be used to measure <strong>the</strong> optic zone<br />

clearance. A pachometer is not necessary<br />

but <strong>the</strong> depth of <strong>the</strong> pre-corneal reservoir<br />

can be estimated with sufficient accuracy by<br />

Figure 10 Slit lamp optical cross section demonstrating <strong>the</strong> pre-corneal fluid reservoir.<br />

The lens, <strong>the</strong> reservoir and <strong>the</strong> cornea are all clearly seen in cross section. The depth of<br />

<strong>the</strong> reservoir is just less than <strong>the</strong> corneal thickness at <strong>the</strong> visual axis, <strong>the</strong>refore<br />

approximately 0.35mm to 0.4mm. By comparison, <strong>the</strong> cornea is 0.5mm to 0.6mm in<br />

thickness. The reservoir is thinner superiorly, and thicker inferiorly, indicating a degree of<br />

downward displacement of <strong>the</strong> lens. This is a normal feature with non-ventilated RGP<br />

ScCL fitting and does not usually have any detrimental effect (Courtesy of Scott Hau)<br />

bubble. If <strong>the</strong>re is insufficient clearance,<br />

corneal contact zones may reduce comfort<br />

and tolerance. Increasing <strong>the</strong> OZS or OZP by<br />

0.25mm alleviates a compressive central<br />

contact zone to give corneal clearance.<br />

Conclusion<br />

This is paper intended to provide an introduction<br />

to modern scleral contact lens practice,<br />

principally to outline changes in fitting<br />

RGP materials <strong>the</strong>ir application can be made<br />

at all grades of pathology where benefits<br />

can be seen. There remain some problems,<br />

and commitment to clinical practice is a<br />

prime requirement. The pathology may be<br />

active or progressive, so close liaison with<br />

ophthalmology is essential. A small number<br />

of practitioners are needed to maintain a<br />

functional service, but those who are not<br />

directly involved should also be aware of <strong>the</strong><br />

significant developments in recent years.<br />

31 | October 20 | 2006 | OT


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References<br />

1) Ezekiel D. Gas permeable haptic lenses.<br />

J Br Contact Lens Ass, (1983), 6(4),<br />

158 - 161.<br />

2) Bier N (1948). The practice of ventilated<br />

contact lenses. Optician 116, 497-501.<br />

3) Pullum KW, Hobley AJ and Parker JH.<br />

Dallos Award Lecture part two. Hypoxic<br />

corneal changes following sealed gas<br />

permeable impression scleral lens wear.<br />

J Br Contact Lens Assoc 1990; 13(1):<br />

83 - 87.<br />

4) Pullum KW, Hobley AJ and Davison C.<br />

100 + Dk: Does thickness make much<br />

difference? J Br Contact Lens Assoc<br />

1991; 6: 158 - 161.<br />

5) Pullum KW and Stapleton FJ (1997).<br />

Scleral lens induced corneal swelling:<br />

what is <strong>the</strong> effect of varying Dk and<br />

lens thickness? The CLAO Journal.<br />

23(4), 259 – 263.<br />

6) Pullum KW, Parker J H and Hobley AJ.<br />

Development of gas permeable<br />

impression scleral lenses. The Josef<br />

Dallos Award Lecture, part one. Trans<br />

BCLA Conf J. Br. Contact Lens Ass.<br />

1989; 77-81.<br />

7) Schein OD, Rosenthal P and Ducharme<br />

C. A gas-permeable scleral contact lens<br />

for visual rehabilitation. Am J<br />

Ophthalmol, (1990), 109, 318 - 322.<br />

8) Kok JHC, and Visser R. Treatment of<br />

ocular surface disorders and dry eyes<br />

with high gas-permeable scleral lenses.<br />

Cornea, (1992), 11, 518 - 522.<br />

9) Tan DTH, Pullum KW and Buckley RJ.<br />

Medical Applications of Scleral Contact<br />

Lenses: 2. Gas-Permeable Scleral<br />

Contact Lenses. Cornea, (1995), 14(2),<br />

130 – 137.<br />

10) Pullum KW and Buckley RJ. A study of<br />

530 patients referred for rigid gas<br />

permeable scleral contact lens<br />

assessment. Cornea, (1997), 16(6),<br />

612 – 622.<br />

11) Cotter J and Rosenthal P. Scleral contact<br />

lenses. J Am Optom Ass, (1998), 69,<br />

33 - 40.<br />

12) Swann PG and Mountford J. Facial<br />

nerve palsy and scleral contact lenses.<br />

Br J Optom and dispensing, (1999), 7,<br />

85-87.<br />

13) Ramero-Rangel T, Stavrou P, Cotter JM,<br />

Rosenthal P, Baltatzis S, Foster CS.<br />

Gas-permeable scleral contact lens<br />

<strong>the</strong>rapy in ocular surface disease. Am J<br />

Ophthalmology, (2000), 130, 25 - 32.<br />

14) Rosenthal P, Cotter JM, Baum J.<br />

Treatment of persistent corneal<br />

epi<strong>the</strong>lial defect with extended wear of<br />

a fluid-ventilated gas-permeable scleral<br />

contact lens. Am J Ophthalmology,<br />

(2000), 130, 33 - 41.<br />

15) Tappin MJ, Pullum KW, and Buckley RJ.<br />

Scleral contact lenses for overnight<br />

wear in <strong>the</strong> management of ocular sur<br />

face disorders. Eye, (2001). 15,<br />

168-172.<br />

16) Rosenthal P, Cotter J. The Boston<br />

scleral lens in <strong>the</strong> management of<br />

severe ocular surface disease.<br />

Ophthalmol Clin North Am<br />

(2003);16:89-93<br />

17) Fine P, Savrinski G, Millodot M. Contact<br />

lens management of a case of Stevens-<br />

Johnson syndrome: a case report.<br />

Optometry (2003) Oct; 74:659-64<br />

18) Looi AL, Lim L, Tan DT. Visual rehabili<br />

tation with new-age rigid gas-perme<br />

able scleral contact lenses - a case<br />

series. Ann Acad Med Singapore<br />

(2002);31:234-7<br />

19) Contact Lenses, edited by Anthony<br />

J Phillips and Lynne Speedwell,<br />

Publishers Elsevier, Chapter 15, Scleral<br />

Contact Lenses, by KW Pullum,<br />

pp 333 - 353.<br />

Acknowledgements<br />

The author is grateful for <strong>the</strong> assistance of<br />

<strong>the</strong> cornea consultants at Moorfields and<br />

Oxford Eye Hospitals, and for <strong>the</strong>ir support<br />

over many years in a long-term project<br />

modernising scleral lens practice and developing<br />

new clinical and manufacturing techniques.<br />

Figure 10 is courtesy of Scott Hau,<br />

senior optometrist, Moorfields Eye Hospital.<br />

For fur<strong>the</strong>r information<br />

contact address:<br />

Ken Pullum, 73 Railway Street, Hertford,<br />

Hertfordshire, United Kingdom, SG14 1RP,<br />

(kenpullum@btinternet.com,<br />

kenpullum@tiscali.co.uk)<br />

Continuing<br />

education and<br />

training initiative<br />

For all CET<br />

Queries please<br />

contact:<br />

Jessica<br />

Buckingham<br />

CET,<br />

McMillan-Scott,<br />

9 Savoy Street<br />

London,<br />

WC2E 7HR<br />

Telephone:<br />

0207 878 2412<br />

Fax:<br />

0207 379 7118<br />

E-mail:<br />

jessica@mcms<br />

london.co.uk<br />

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Module questions<br />

Course code: c-4090<br />

Please note, <strong>the</strong>re is only one correct answer. Enter online or by form provided.<br />

1. For a highly irregular corneal topography would you<br />

try as first choice...<br />

a. Non-ventilated impression RGP scleral lens?<br />

b. Preformed fenestrated RGP scleral lens?<br />

c. Fenestrated impression PMMA scleral lens?<br />

d. Non-ventilated preformed RGP scleral lens?<br />

2. What is <strong>the</strong> optimum corneal clearance for a<br />

non-ventilated RGP scleral lens?<br />

a. Not more than 0.1mm<br />

b. Not less than 1.0mm<br />

c. Between 0.2mm and 0.3mm<br />

d. Between 0.4mm and 0.9mm<br />

3. If <strong>the</strong> BSR is changed from 13.50mm to 14.50mm<br />

without altering <strong>the</strong> OZP, would you expect...<br />

a. Increased apical clearance<br />

b. Reduced apical clearance<br />

c. There would be no difference<br />

d. There would be increased vaulting from <strong>the</strong> scleral zone<br />

4. What is <strong>the</strong> most probable objective when<br />

fenestrating an RGP scleral lens?<br />

a. To enable easier handling<br />

b. To increase apical clearance<br />

c. To create corneal contact<br />

d. To give a crescent-shaped bubble under <strong>the</strong> lens<br />

5. What is <strong>the</strong> usual objective when fenestrating a<br />

PMMA scleral lens?<br />

a. To give a crescent shaped bubble<br />

b. To increase apical clearance<br />

c. To facilitate oxygenated tear exchange<br />

d. To create corneal contact<br />

6. What would be <strong>the</strong> reason for considering a scleral<br />

lens in moderate keratoconus?<br />

a. To improve on vision achieved with a corneal lens<br />

b. To give increased oxygenation<br />

c. To alleviate corneal contact<br />

d. To create corneal contact<br />

7. Comparing small and large diameter non-ventilated<br />

scleral lenses, would you expect...<br />

a. More limbal clearance with <strong>the</strong> smaller lens?<br />

b. More apical clearance with <strong>the</strong> smaller lens?<br />

c. Better tear pool retention with <strong>the</strong> larger lens?<br />

d. The smaller lens to be more stable on <strong>the</strong> eye?<br />

8. What is <strong>the</strong> most common modern indication for<br />

scleral lenses?<br />

a. Aphakia<br />

b. High myopia<br />

c. Keratoconus<br />

d. Corneal transplant fitted post-operatively<br />

9. What is meant by <strong>the</strong> term sealed in <strong>the</strong> context of<br />

scleral lens practice?<br />

a. Near perfect alignment to <strong>the</strong> cornea<br />

b. Near perfect alignment to <strong>the</strong> sclera<br />

c. A lens retaining an air bubble-free tear pool<br />

d. A lens which is very difficult to remove<br />

10. Under what circumstances could a PMMA scleral be<br />

arguably preferable to an RGP scleral?<br />

a. For keratoconus<br />

b. Never<br />

c. For aphakia<br />

d. For work in dusty environments<br />

11. If <strong>the</strong> BSR is changed from 14.50mm to 13.50mm, & <strong>the</strong> OZP<br />

is increased one clinically significant step, would you expect...<br />

a. An 0.25mm increase in <strong>the</strong> apical clearance?<br />

b. A 0.50mm or greater increase in <strong>the</strong> apical clearance?<br />

c. No change in <strong>the</strong> apical clearance?<br />

d. A reduction in apical clearance of 0.25mm?<br />

12. What would be <strong>the</strong> probable outcome of reducing <strong>the</strong> diameter<br />

of a non-ventilated RGP scleral lens from 23mm to 18mm?<br />

a. Increased apical clearance<br />

b. More decentration of <strong>the</strong> lens<br />

c. An apical contact zone<br />

d. More chance of <strong>the</strong> lens falling out<br />

An answer return form is included in this issue.<br />

It should be completed and returned to:<br />

CET initiatives (c-4090), OT, McMillan Scott, 9 Savoy Street, London, WC2E 7HR by November 15. Under no circumstances will forms received after this date be<br />

marked – <strong>the</strong> answers to <strong>the</strong> module will be published in our December 15 issue.<br />

OT Book Shop<br />

Why not purchase your educational books through <strong>the</strong> OT Bookshop.<br />

You can do this by calling our customer services team on 020 7878 2300 and ask for <strong>the</strong> Angela or Louise in <strong>the</strong> OT Bookshop.<br />

Also you can log on to www.optometry.co.uk and select OT Bookshop.<br />

We do our best to deliver usually within 7 working days, however some titles may take up to 28 days depending on stock availability. If <strong>the</strong>re<br />

are any o<strong>the</strong>r titles that you are interested in but cannot see <strong>the</strong>m on our site, please contact us as we will do our best to make available all<br />

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33 | October 20 | 2006 | OT

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