A cycloplegic refraction is a procedure whereby a refractive error is determined while the ciliary muscles that control accommodation (focusing) are temporarily paralysed with cycloplegic eyedrops. This procedure is commonly used in children especially those below 10 years of age, who have immense accommodative powers.

During the refractive process these patients may “over-use” their accommodative ability while trying to read a line of letters. This must be controlled in order in order to properly determine the refractive error and prescribe the appropriate correction. This is especially so in cases of high hypermetropia, convergent strabismus and unstable refractions due to fluctuations of accommodation. This procedure is also used in adults prior to refractive surgery to insure the manifest refraction is correct. It is useful in cases where for some reason are uncooperative such as those with Down’s syndrome.

There are disadvantages of cycloplegic refraction. Occasional toxic and allergic side effects have been reported. The procedure is time consuming and the effect of cycloplegia. It may last a long time inconveniencing the person. The refractive power obtained on cycloplegia may not be what the patient needs. The associated dilation of the pupil makes the retinoscopy diffi cult because of confusing refl exes seen at the edge due to peripheral scattering of light.

When performing cycloplegic refraction, be aware that occasionally the patient may not refract to the same visual acuity as during manifest refraction. This is due to the fact that a dilated pupil lacks the benefi t of the pinhole effect of the small pupil.

The perfect cycloplegic agent is yet to be invented. Its desired qualities will include fast action, fast recovery time and no adverse reactions. There is a difference between cycloplegia and mydriasis (dilation of the pupil). However, cycloplegics also paralyse the sphincter muscle of the iris causing dilation of the pupil. Commonly used cycloplegic agents include atropine, homatropine, cyclopentolate and tropicamide.

Atropine and homatropine are too long acting and can be toxic. Fever, fl ushing of the face and hallucinations have been reported with atropine. The preferred agent is cyclopentolate eyedrops. It is rapid acting and fairly potent. It is available in 0.5%, 1% and 2% concentrations. The full cycloplegic effect takes 20 to 30 minutes. Tropicamide is a weak cycloplegic agent, used primarily for dilation of the pupil. Phenylephrine eyedrops have no cycloplegic action.

In Malaysia, because of dark irises, more and stronger concentrations of cycloplegic eyedrops may have to be used due to pigment binding. However, the drug may be more toxic in very young children due to smaller body size, so caution is necessary. In adults there is always the possibility of precipitating an acute attack of closed angle glaucoma. Accommodation can also be controlled by fogging technique which needs to be mastered.

Discomfort and dryness are reported to be the greatest causes of contact lens dropoutsi. This matters to us both as clinicians and business people because it is highly likely that some patients will not just drop out from contact lens wear, but also from our practices. To stay in business we need to retain our existing patients as well as to attract new ones.Dry eye is a problem which is likely to stay with us for a long time. It is more likely to become significant as people get older, and in modern practice we see many more patients new to contact lens wear who are in the 45+ age group.

These together with existing contact lens wearers getting older will represent a substantial part of many contact lens practices. The widespread use of VDUs further impacts on the problem. It has been shown that a decreased blink rate may increase tear evaporation when working at a VDUii.Symptoms of dryness, however, are not unique to those who wear contact lenses. The majority of people who work with computers in air-conditioned offices will have experienced the itchy, gritty, tired eyes.

These people may benefit from the use of tear supplements described later in this article even though they do not wear contact lenses.Dry eye may be due to a reduction in the overall volume of the tear fluid, or rapid evaporation of the available tears, or a combination of these two factors. The evaporation may be due to imbalances in the constituents of the tear fluid.

PRODUCTION AND DRAINAGE OF TEARS

Tear fluid is defined as the fluid structure which covers the ocular structures within the palpebral aperture. From the frontal aspect it consists of :

• The thin pre-corneal film
• The tear prism (tear meniscus)
• 75% to 95% of the total volume of the tear fluid is contained within the tear prism.

The pre-corneal tear film is a three-layer structure consisting of :

• Mucous layer
• Watery (Aqueous) layer
• Oily (Lipid) layer

A tear volume which is less than normal or an imbalance in any of the constituents can lead to discomfort, damage to the corneal epithelium and a consequent increase in the risks of infection.

MUCOUS LAYER

The mucous layer is situated next to the cornea, and is derived from the conjunctival goblet cells. Its functions are :

• Removal of tear film contaminants
• To act as a surfactant
• To make the corneal surface wettable

AQUEOUS LAYER

This is derived from the main lachrymal gland, and the accessory lachrymal glands of the conjunctiva. It represents more than 99% of the thickness of the pre-ocular tear film thickness. It is 98.2% water and 1.2% solids.

LIPID LAYER

This is the outermost layer of the tear film. It derives from the tarsal meibomian glands. It differs from the lipid secretions produced by the skin, and does not mix with them. Sebum skin lipids can cause instability and breakdown of the tear film. Its functions are :

• To prevent (delay) lachrymal evaporation
• To maintain a homogenous tear film surface

DRAINAGE

Normal drainage of the tear fluid is achieved by way of the punctae situated nasally on the eyelids.

TEAR EXAMINATION OF A NEW PATIENT

A detailed history will include questioning about symptoms relating to dry eye and possible problems with working environment such as computer use and air conditioning. Some practitioners recommend the use of a questionnaire similar to the one recommended by McMonniesiii (fig.1).

Tear evaluation should take place as early as possible in a slit lamp routine because photophobia will trigger reflex tearing and the heat of the slit beam can cause evaporation. Neutral density and heat absorbing slit lamp filters may be used to minimise these effects.

We can assess both the quantity and the quality of the tears. In each case both invasive and non-invasive methods are available :

QUANTITY Invasive

• Schirmer stripsiv
• Phenol red thread testv

In the Schirmer test a strip of filter paper 5 mm by 35 mm is folded 5 mm from one end. The short end is inserted under the lower lid on the temporal side about one third of the way in from the temporal edge. Care should be exercised to avoid causing a corneal abrasion, especially with patients whose eyes are quite small. The filter paper absorbs tear fluid rather like a wick. After 5 minutes the paper is removed and the length of moistened paper is measured. A value of 5 mm or less is considered to indicate severe deficiency, 5 to 10 mm a moderate deficiency and an average is considered to be 17 mm.

Schirmer is a very invasive test, which is found to be moderately uncomfortable by most people. Its validity has been questioned on the basis that it is likely to stimulate an abnormal quantity of tears.

The Phenol Red Thread Test may be considered to be less invasive than the Schirmer. A thread impregnated with phenol red dye is inserted in a similar manner to the Schirmer paper. The phenol red is a pH indicator, and the tear fluid causes a change in colour from red to yellow. The thread is left in place for 15 seconds and then removed and measured. A normal measurement is in the region of 15 mm with 7 mm being a dry eye. While this may be considered to be a much less invasive test then the Schirmer it is still invasive, and some excess tearing is likely to be caused by the introduction of a foreign body.

Non-invasive

• Tear prism heightvi

Tear meniscus height may be measured with a slit lamp. An eyepiece incorporating a measuring graticule may be fitted, or an estimate may be made by selecting a 0.2 mm spot beam and focussing that on the tear prism. While this is a non-invasive measurement care should be exercised not to use a wide, bright beam which may stimulate reflex tearing due to photophobia. A normal measurement would be 0.25 ®C 0.3mm, with less than 0.2mm being unlikely to be suitable for CL wear and may even cause symptoms in a non contact lens wearer.

QUALITY Invasive

• Fluorescein break up timeFluorescein is instilled and the green reflex is inspected using a cobalt blue filter on the slit lamp. The tear break up time (TBUT) is measured in seconds. The patient is instructed to blink, and then to keep the eyes open and stare. Timing stops when a blue break is observed in the green reflex. Values of 10 to 12 seconds or more are considered normal, or good. Values as low as 5 seconds would indicate a very dry eye.

Non-invasive

• Regularity of tear prismIrregularity or scalloping of the tear meniscus indicates a poor secretion form the meibomian glands or meibomian gland dysfunction.
• Non invasive break up time (NIBUT) – one position keratometer or Loveridge Grid

These methods are non-invasive because fluorescein is not used. An observation is made of the time lapsed, following a blink, until an image reflected from the tear film distorts. In practice the NIBUT is most often recorded using a one-position keratometer. NIBUT values tend to be longer than those obtained with fluorescein because instilling Fluorescein changes the make of the tears. A NIBUT of less than 15 seconds would be considered abnormal 15 to 20 seconds possibly problematical, and 20 seconds or more normal.The Loveridge Gridvii is a very useful instrument for observing and recording tear break-up. It offers a much greater coverage of the corneal surface than the keratometer and has an integral timer (available from Evans Instruments).

OTHER OBSERVATIONS

Other observations which are helpful warning signs of possible dry eye problems are the presence of inferior corneal staining “smile stain” and wrinkles in the inferior bulbar conjunctiva.

ACTIONS

It is good practice to explain the tests that are being performed with the patient. It is usually best, however to delay discussing the results until the examination has been completed. In severe cases it may be necessary to advise against contact lens wear. In other cases the patient may be safely fitted under certain conditions with careful monitoring.

AFTERCARE

The act of putting a contact lens in the eye itself disrupts the tear layer to some extent. The patient who had relatively poor tears, but was asymptomatic may now have symptoms.

HISTORY

The patient should be questioned for possible dry eye symptoms :

• Discomfort towards the end of the wearing time
• Lenses tend to stick to the eye on removal
• Damaged lenses
• Discomfort in particular environments

It has been shown that the volume of tear production decreases towards the end of the day. If patients are questioned about how the lenses feel on removal some will reveal that it feels like the lenses have to be peeled off the eye. If this has caused considerable damage to the corneal epithelium they may report stinging on insertion the next day. In some cases the use of a rewetting solution 5 minutes before removal may deal with the problem, leaving the patient not only more comfortable, but also at less risk of corneal infection. As soft lenses are more fragile when partially dehydrated this may provide the answer to the elusive problem of opening the lens case in the morning to find a damaged lens.

EXAMINATION WITH LENSES IN SITU

Tear prism height may be assessed and pre-lens tear film may be inspected by specular reflection. Pre-lens break up time (PLBUT) may be measured with instruments like the Loveridge Grid. A PLBUT for soft lens patients of less than 5 seconds indicates poor on-eye wettability, 5 to 10 seconds probably acceptable wettability, and greater than 10 seconds good on-eye wettability.

A soft lens which is drying out will appear to fit tighter, so any decease in movement from that recorded previously may be significant. Poor pre lens tear film and partial lens dehydration may cause unstable over refraction, particularly with toric lenses.

EXAMINATION AFTER LENSES HAVE BEEN REMOVED

Corneas should be inspected for staining, and break up time can be measured.

STRATEGIES FOR THE MARGINAL DRY EYE

CHANGE LENSES

• Lens thickness and water content. Studies have indicated that very thin, high water content lenses are the worst option for marginal dry eye.
• Lens ionicity. Ionic lenses attract protein, which is hydrophobic.
• Lens material. “Biomimetic” materials such as Proclear or Benz tend to suffer less from dehydration. Silicone hydrogels (on a daily wear schedule) may be an option because very little tears are required to keep these lenses hydrated
• Some lenses are now impregnated with wetting agents e.g. Acuvue “Moist” and Ciba Dailies with “Aqua Comfort Plus”

CHANGE THE SOLUTIONS

• Many one-bottle solutions now contain a wetting agent
• Consider change to peroxide based system if a low level solution sensitivity is suspected

TEAR SUPPLEMENTS

• Rewetting drops may prove helpful. Preparations containing sodium hyuralanate (e.g. “Blink Contacts”) are often successful as they improve the effectiveness of the lipid layer as well as increasing the tear volume.. Again if sensitivity to preservatives is suspected single dose units are to be preferred. A new product recently introduced in the UK is “Clarymist”. This is an aerosol spry which is applied with the eyes closed. Unlikely as this may sound it is very effective in reinforcing the lipid layer, and is unaffected by make up. For further information see www.clarymist.co.uk.

Rewetting drops should be used as prevention rather than cure, especially if corneal staining is present.

WEARING TIME

• Limit total hours
• Remove earlier in the evening
• Restrict to certain activities

DIET

Some studies show a dietary link with dry eyeviii. Zinc supplements may be helpful in some cases. It is also worth considering that few people actually drink the recommended quantity of water in a day.

CONSIDER PUNCTAL PLUGS

In this procedure plugs of either silicone or collagen are inserted to prevent the drainage of tears from the eyelid punctae. This option should only be considered under medical advice.

CONCLUSION

The safe fitting of marginal dry eye patient with soft contact lenses is a challenge. With the increasing contact lens market, the widening of the age range of contact lens patients, and modern working conditions that challenge is likely to increase.

Careful screening can help to avoid problems and a wide variety of products and modalities are available for us to offer our patients. In practice a combination of various measures may be necessary to achieve our objectives as well as those who wear contact lenses.possible dry eye problems in our spectacle wearing patients Perhaps we should all be more proactive in enquiring about.