Ocular health assessment

C. Lisa Prokopich, Patricia Hrynchak, David B. Elliott and John G. Flanagan

7.1 Differential diagnosis information from other assessments

During a problem-oriented examination, a list(s) of tentative diagnoses is made during the case history and this is used to determine which tests may be useful to help differential diagnosis. The list is then updated after consideration of the results from each test of the eye examination. A brief introduction to some of the relevant information regarding ocular health provided in the case history and assessments of other systems is provided here.

Optimal visual acuity measurements (section 3.2) that are different in the two eyes or are reduced compared to age-matched normal values or compared to a previous visit indicate some ocular abnormality. A pinhole visual acuity test can be used to make sure that the reduced visual acuity is not due to an incorrect determination of the refractive correction. Reductions in visual fields and contrast sensitivity and increases in disability glare (Chapter 3) can indicate ocular disease, even when visual acuity is normal.

7.1.5 Incomitant heterotropias

Recent-onset incomitant heterotropias can be the first sign of the underlying ocular or systemic disease including diabetes, hypertension, multiple sclerosis, thyrotoxicosis, and temporal arteritis and it is therefore essential to determine if the condition is of recent-onset or longstanding (section 6.15; Table 6.5). Missing the signs of these conditions, particularly in children, is a significant cause of malpractice claims in the US.¹

7.2 Examination of the anterior segment and ocular adnexa

An examination of the anterior segment of the eye and adnexa including the eyelids, eyelashes, conjunctiva, tear layer, cornea, anterior chamber, iris, crystalline lens and anterior vitreous is typically performed during most oculo-visual and contact lens assessments. It should also be performed before and after any procedure that touches the eye such as tonometry and gonioscopy to determine the presence and severity of any iatrogenic damage.

7.2.1 Comparison of tests

Slit-lamp biomicroscopy examination is greatly preferred over direct ophthalmoscopy, penlight and loupe or Burton lamp assessment as it provides much greater resolution, depth of field and control of illumination, as well as higher illumination and more variable and greater magnification (from about 10× to 40×). Involuntary eye movements reduce the clarity of highly magnified images and limit the value of increasing the magnification beyond 40×. The quality of the image is better in slit-lamp models that have higher optical quality lenses that use multi-aspheric lens designs and anti-reflection coatings. Disadvantages include that slit-lamp examination can produce discomfort in some patients who are photophobic due to the high illumination and obese patients or those that have neck or back problems may find positioning themselves in the slit lamp uncomfortable.

7.2.2 Procedure

See online video 7.1 for general slit-lamp examination. Familiarity with the adjustment controls of the slit lamp is required. The positions of the controls differ for different models but all slit lamps have similar features. It should be possible to change the width and height of the beam, rotate the beam, change the angle between the light source and viewing system, add filters over the light source (Table 7.1), change the magnification (this may involve changing the eyepieces to a stronger power), change illumination intensity, adjust the microscope height and focus the microscope with the joystick. With most instruments it is possible to break the linkage between the illumination and viewing systems (decoupling), which allows focus on a point other than that being illuminated.

Table 7.1

Filters available on most slit-lamp biomicroscopes

Filter	Typical symbol	Use
Cobalt blue	Blue filled circle	Enhances the view of fluorescein dye in the tear film of the eye. Typically used for fluorescein staining and Goldmann tonometry.
Red free	Green filled circle	Used to enhance the view of blood vessels and haemorrhages
Neutral density	Circle with hashed lines	Decreases maximum brightness for photosensitive patients
Heat absorbing	Built into most slit lamps	Decreases patient discomfort
Grey	Circle with thick line	Decreases maximum brightness for photosensitive patients
Yellow filter	Yellow filled circle Located in the observation system	For good contrast enhancement when using fluorescein and the cobalt blue filter
Diffuser	May be a flip-up filter placed on the illumination source	Used for general overall observations of the eye and adnexa

Brands of slit lamps differ in their illumination and their observation systems. The Haag-Streit type slit lamps have a tower illumination system with the bulb above a mirror. This system has the advantage of being able to be decoupled in the vertical meridian, which is helpful when the slit lamp is used for gonioscopy or fundus examination. Magnification is provided in one of three ways, a flip magnification system (the most basic with magnification typically provided at 10× and 16×), a rotating barrel or zoom continuous magnification (typically from 10× to 40×). Slit lamps also differ in the degree of convergence of the microscope and clinician preference seems to vary depending on their own convergence stability.

1. Wash your hands thoroughly and clean the slit-lamp contact surfaces with a sterile wipe in front of the patient.

2. If one is available, place the focusing rod in the appropriate holder, with the flat surface towards the viewing system. Normally, you will perform the biomicroscope examination without glasses, as the field of view is greater the closer your eyes are to the slit-lamp eyepieces. If you have a high cylinder in your glasses, you may need to wear your correction to obtain adequate resolution. To focus the eyepieces, first switch on the illumination system to produce a slit-image on the focusing rod. Look through one eyepiece and turn it fully counter clockwise (plus direction) then, while viewing the focusing rod, turn the eyepiece clockwise until the slit-image on the rod is first in sharp focus. Repeat the procedure for the other eyepiece. The eyepiece should be set at approximately zero if you are an emmetrope or wearing your correction and set to your mean sphere correction (sphere + half of cylinder) if you are not wearing your glasses. More minus might be required in younger practitioners due to proximal accommodation. Once you have each eyepiece focused, adjust the distance between the eyepieces so that the image is centred in the field of view of each eye. You should see a single clear image.

3. Seat the patient comfortably on a stable chair without rollers, and ask the patient to remove any glasses. Explain the procedure in lay terms to your patient: ‘I am going to use this special microscope to carefully examine the front of your eyes.’

4. Adjust the height of the biomicroscope table so that the patient may lean forward comfortably and place their chin in the chin rest and forehead against the forehead rest. Adjust the chin rest so that the patient’s eyes are at an appropriate height to provide a large enough vertical range to allow adequate examination of the adnexa. Many biomicroscopes have an eye alignment marker on a supporting beam of the headrest that should be level with the patient’s outer canthus. If your patient is obese, an exaggerated bend at their waist will often allow satisfactory positioning. Having the patient hold onto the handles if available can also be helpful.

5. Dim the room lights and ask the patient to look at your ear (your right ear for the patient’s right eye and your left ear for the patient’s left eye) or the instrument’s fixation device so that the patient’s gaze is in the primary position.

6. Use one hand to control the joystick (focusing and lateral/vertical movement) and the other to control the magnification and illumination and to manipulate the patient’s eyelids. A useful tip is to have a low rheostat setting for a wide, diffuse beam (for patient comfort) and a high rheostat setting for a narrower beam, or when filters are used, to give sufficient image contrast.

7. There are several types of illumination that with experience you will use alternately or in combination to thoroughly examine the anterior segment and adnexa. A general procedure is to use diffuse illumination followed by a parallelepiped and is described below. This is followed by descriptions of additional techniques with examples of when they might be used.

8. Diffuse illumination: Provides an overall assessment under low magnification (~10×). Adjust the illumination to a wide beam and place a diffusing filter in front of it to systematically examine the components of the anterior segment and adnexa as described below.

9. Direct illumination using a parallelepiped: Use low to moderate magnification (~10×) as magnification that is too high will result in missing obvious, moderately sized abnormalities. Set the illumination system at approximately 45° from the microscope position on the temporal side and use a beam width of approximately 2 mm. An illuminated block of corneal tissue in the shape of a parallelogram should be visible (Figure 7.1). A beam that is too narrow will make it difficult to detect abnormalities. Assess each of the structures described below in a systematic manner using the following procedure: Focus on the temporal tissue first with the illumination coming from the temporal side. Move the slit lamp laterally across the tissue until the centre is reached, maintaining good focus at all times. Then sweep the illumination system across to the nasal side, taking care not to bump into the patient’s nose, and examine the nasal tissue. This scanning procedure may be repeated several times to examine all areas of the tissue concerned and may require more than one level of magnification. Being able to keep a parallelepiped sharply in focus as you scan from temporal limbus to central cornea and then nasal limbus to central cornea, is the foundation for good slit-lamp technique.

Fig. 7.1 (a) Diagram illustrating the position of the illuminating and viewing systems when using direct illumination. (b) A parallelepiped section of the cornea showing an irregularity above the corneal apex.

(a) Eyelids and lashes: Examine the superior eyelid and lashes first using the scanning procedure described above. This can be easier with the patient’s eyes closed. Examine the inferior lid and lashes in the same manner, while also examining lid apposition to the eye and meibomian gland appearance (section 7.3.3). Assess the lid for anomalies including an abnormal lid position (e.g., ptosis, entropion, ectropion), redness, inflammation, ulcers and growths. Inspect the lashes for colour (e.g., white), areas where the lashes are missing or misdirected and the presence of scales.

(b) Conjunctiva: Ask the patient to look upwards while you pull the lower eyelid gently downward to expose the lower fornix for examination. Examine both the bulbar and palpebral conjunctiva using a scanning process. Next ask the patient to look downwards and gently pull up the upper eyelid, thereby exposing the superior bulbar conjunctiva for examination. Finally ask the patient to look in right and then left gaze to allow examination of the entire conjunctiva, plica and the caruncle.

(c) Cornea and tear film: Use the scanning process to examine the cornea in three sweeps: inferior, central and superior. Examine the inferior cornea by having the patient look up and the superior cornea by having the patient look down while holding up the upper eyelid. With increasing experience you will be able to look at both the area illuminated (direct illumination, Figure 7.1) and the area just outside the area of illumination (indirect illumination, Figure 7.2, examples in Figures 8.12, 8.16). It can be useful to assess the tear film after a blink and note the quantity and type of debris if any. You can increase the width of the section of stroma seen by increasing the angle between the microscope and illumination system. You can obtain greater detail by increasing the magnification.

Fig. 7.2 (a) Diagram illustrating the position of the illuminating and viewing systems when using indirect illumination. (b) Corneal nerve fibres seen in indirect illumination.

(d) Assessment of the tear meniscus: The height of the tear meniscus can be estimated by decreasing the height of the slit-lamp beam to one millimetre and then judging the relative height of the meniscus at the lower lid margin as a proportion of the beam height.

(e) Iris: Examine the iris with direct illumination by moving the joystick towards the patient. Take note of the depth of the anterior chamber and the shape of the pupil.

(f) Lens: For a non-dilated pupil the illumination angle must be reduced until an optic section of the lens is just seen. This may be as small as 15° for an elderly patient with a small pupil. Further discussion of slit-lamp assessment of cataract under mydriasis is provided in section 8.4.

(g) Anterior vitreous: Moving the joystick further towards the patient allows viewing of the anterior vitreous with a parallelepiped when the pupil is dilated. To look for anterior vitreous floaters (Figure 7.3), it can be useful to ask the patient to look up, look down and then straight ahead, so that the opacities become visible as they float through the field of view (see online video 8.1).

Fig. 7.3 Vitreous floaters seen in the anterior vitreous by direct illumination.

7.2.3 ‘Specialised’ slit-lamp techniques

See online video 7.2. If an abnormality/anomaly is suspected from the case history or detected during a routine slit-lamp examination, one or more of the following illumination techniques may be used. With experience many or all techniques are used in fast succession. The slit-lamp magnification can be varied to examine the anomaly more carefully noting its size, shape, appearance, depth and location.

1 Optic section

This is a type of direct illumination in which the illumination beam is narrowed to allow a judgement of depth of any abnormalities within the cornea or lens (Figure 7.4). For example, it can be used to judge the depth of a foreign body in the cornea, whether an opacity is anterior or posterior cortical or subcapsular and is the technique used to grade nuclear lens opacity (section 8.4).

Fig. 7.4 A corneal section indicating that the corneal abrasion shown in Figure 7.1 is in the corneal epithelium.

1. Set the illumination system at approximately 45° from the microscope using low to moderate magnification (~10×).

2. If the area of the cornea/lens you wish to view is temporal, place the illumination on the temporal side and if it is nasal, place it on the nasal side.

3. Narrow the beam to the narrowest possible width and sharply focus on the cornea/lens using the joystick. As you have greatly narrowed the beam, you need to increase the slit-lamp illumination using the rheostat.

4. A slice of the cornea/lens should now be visible (cornea, Figure 7.4; lens, Figure 7.5; nuclear cataract, Figure 8.22). If the illumination system is temporal to the viewing system, the corneal epithelium or anterior lens will be on the temporal side of the image with the corneal endothelium or blurred posterior lens on the nasal side.

Fig. 7.5 An optical section of the lens anterior cortex (on the left side within the pupil) and lens nucleus (central). The posterior cortex is blurred and on the right side of the pupil. The blurred arc to the left is the out-of-focus cornea.

5. To view the posterior lens, the joystick needs to be moved further forward and the angle of the illumination system may need to be reduced further, depending on the pupil size.

6. The section of corneal stroma can be broadened by increasing the angle between the microscope and illumination system. The focusing should be precise enough to allow the graininess of the stroma to be visualised.

7. Once the object of interest is identified, increase the magnification to obtain greater detail.

2 Indirect illumination

This technique (Figure 7.6) is used to view areas that become bleached with excessive light using direct illumination, such as fine blood vessels at the limbus and microcysts. It is also used to look for iris features such as the outer rim of the iris sphincter.

Fig. 7.6 A pinguecula seen in indirect illumination by viewing outside the illuminated area.

1. Use a 1–2 mm parallelepiped, low to moderate magnification (~10×) and set the illumination system at ~45° from the microscope.

2. Rather than focus on the illuminated area (direct illumination), simply direct your gaze just outside the area that is illuminated (indirect illumination). Subtle abnormalities can be seen using light scattered by the cornea away from the main area of illumination.

3. Increase the magnification as required.

4. The technique can also be used after decoupling the illumination and viewing systems.

3 Specular reflection

This technique is used to examine the endothelium (for polymegethism and pleomorphism), the precorneal tear film and variations in contour of the epithelium.

When learning this technique, it is best to start by attempting to obtain an image of the anterior lens surface by specular reflection (Figure 7.7).

Fig. 7.7 (a) Diagram illustrating the position of the illuminating and viewing systems when using specular reflection to view the corneal endothelium. (b) Specular reflection from the anterior surface of the lens showing its orange peel appearance.

1. Set the illumination system at approximately 30° to 45° from the microscope, using a moderately wide 2–3 mm parallelepiped. Look through the eyepieces and focus the parallelepiped on the anterior lens.

2. Change the angle of illumination until the reflection of the instrument lamp is seen from the lens surface. This occurs when the angle of incidence equals the angle of reflection from the lens (Figure 7.7a).

3. View the orange peel textural appearance of the anterior lens (Figure 7.7b) to the side of the bright reflex.

4. To examine the tear film and epithelium, set the illumination system at approximately 45° to 60° from the microscope, using a moderately wide 2–3 mm parallelepiped. Look through the eyepieces and focus the parallelepiped on the cornea. Ask the patient to blink and use the particles floating in the tear film to help you focus.

5. Change the angle of illumination until a bright reflection is seen from the precorneal tear film. This occurs when the angle of incidence equals the angle of reflection from the cornea. This can also be obtained by moving the illumination/microscope system laterally until the two angles are equal.

6. To examine the endothelium, set the magnification to about 16× with a fairly wide 2–3 mm parallelepiped and initially focus on the tear film.

7. Alter the illumination angle and/or lateral position of the slit lamp until the bright corneal reflexes (Purkinje images) fall on top of the corneal section. There should be two reflexes: On the epithelial side of the corneal section there should be a bright white reflex from the tear film (conjugate with the epithelium) and on the endothelial side a less bright, slightly yellowed reflex from the endothelium. You may need to alter the angle of illumination very slightly to separate the two reflections.

8. Increase the magnification to about 40× and move the joystick slightly forward to focus on the endothelium. If you then look to the side of the dull endothelial slightly yellowed reflex (nasal or temporal to the reflex depending on the position of the illumination system) the duller picture of the endothelial hexagonal cells will be in view.

4 Eyelid eversion

This technique is used to examine the superior and inferior palpebral conjunctivae, particularly in contact lens wearers and when looking for allergic conjunctival changes, papillae, and foreign bodies.

1. Ask the patient to look down and grasp the superior eyelashes and pull them slightly away from the eye. It can be useful to press a cotton bud onto the superior lid to lift it away from the inferior lid, making it easier to grab just the superior lashes.

2. Gently press down on the superior margin of the tarsal plate at the crease using a cotton swab (or the index finger or thumb of the other hand), and at the same time pull the eyelashes up and over the cotton bud. This technique will evert the eyelid to permit viewing of the superior palpebral conjunctiva (Figure 7.8) using a parallelepiped.

Fig. 7.8 The superior palpebral conjunctiva viewed after lid eversion.

3. To re-evert the eyelid, hold the eyelashes and ask the patient to look up and gently pull the eyelashes away from the eye.

4. To evert the lower eyelid, pull the eyelid down and press under the eyelid margin while moving your finger upwards. The eyelid will evert over your finger.

5 Retro-illumination from the iris

This technique (Figure 7.9) is used in the examination of corneal vessels, epithelial oedema, pigment deposits or keratic precipitate on the endothelium and small scars on the cornea using light reflected from the iris. Opaque features appear dark against a light background.

Fig. 7.9 Diagram illustrating the position of the illuminating and viewing systems when using retro-illumination from the iris.

1. Use a 1–2 mm parallelepiped with low magnification and set the illumination system to an angle of about 45°.

2. If it is possible to view the abnormality in direct illumination, bring it into focus and then lock the joystick position.

3. Decouple the illumination and viewing systems, direct the light onto the iris and view the structure against the light reflected from the iris. The magnification can be varied as necessary.

6 Retro-illumination from the fundus

This is a commonly used technique to examine iris disorders and cataracts using light reflected from the fundus. Cataracts are seen as dark opacities against the red background glow from the fundus (Figures 7.10, 8.20–8.24) and it is a particularly useful for examination of cortical and posterior subcapsular cataracts (section 8.4). Retro-illumination can also be used to detect iris abnormalities such as peripheral iridotomies and loss of pigment (iris transillumination, Figure 7.11). In this case, the red glow of the fundus is seen through the iris. The shape and location of the defects can help in identifying the cause of the transillumination.

Fig. 7.10 A cortical cataract seen in retro-illumination from the fundus.

Fig. 7.11 Iris transillumination. Loss of localised iris pigment is shown by the red fundal glow appearing through parts of the iris when light is shone through the pupil. (Courtesy of Dr David Williams, University of Waterloo.)

1. Use a 1–2 mm parallelepiped with low magnification and set the illumination system to an angle of 0°. Adjust the beam height to the height of the pupil.

2. Focus on the iris or lens as appropriate.

3. You will only be able to focus the anterior or posterior part of the lens at any one time. You can gain an approximate focus on the anterior lens by focusing the iris. To focus the posterior lens you will need to push the joystick forwards (towards the patient). To gain a retro-illumination image of the lens with an undilated small pupil, you may need to decouple the instrument slightly and alter the angle of illumination by a small amount.

4. Observe any illumination coming through the iris. While lens opacities are best observed with the pupil dilated, iris transillumination is best observed before dilation.

7 Sclerotic scatter

Sclerotic scatter involves observing the cornea while the illumination is directed at the limbus. The light is totally internally reflected in a healthy cornea and creates a glowing halo of light where it escapes from the opposite limbus (Figure 7.12).

Fig. 7.12 (a) Diagram illustrating the position of the illuminating and viewing systems when using the sclerotic scatter technique. (b) Sclerotic scatter showing an S-shape of contact lens deposits.

1. Turn off the room lights to keep the surrounding light levels as low as possible so you can observe subtle amounts of light scatter.

2. Set the magnification at about 10× and use a 1–2 mm slit at about 45°. Focus the central cornea by ensuring the particles in the tear film are focused. Asking the patient to blink will move the tear film debris making them easier to find. Lock the slit-lamp position to ensure the viewing system remains focused on the central cornea.

3. Decouple the illumination and viewing systems and from 45–60° on the temporal side, move the 1–2 mm slit onto the temporal limbus. Ideally, shorten the length of the slit so that it enters at the limbus. Any extra slit length can produce light scatter from the sclera that may reduce the visibility of subtle defects.

4. Although you can scan the cornea for areas of light scatter with the naked eye, it is preferable to view it using the decoupled slit-lamp viewing system. Iatrogenic damage due to novice contact tonometry or gonioscopy use, foreign bodies, scars and central corneal clouding due to rigid contact lens wear can all be observed with this technique.

8 Anterior chamber assessment

This technique is used to look for flare (i.e., protein) or floating cells in the anterior chamber (by using more magnification and a longer beam). The following procedure has been recommended by the Standardization of Uveitis Nomenclature Working Group.²

1. Turn off all the room lights and close your own eyes for a few minutes to start to dark-adapt.

2. Set the illumination system at approximately 45° from the microscope using moderate magnification (~16×).

3. Narrow the height and width of the beam to obtain a beam 1 mm by 1 mm in size. Move the beam to the centre of the pupil and focus in the anterior chamber midway between the anterior surface of the crystalline lens and the posterior surface of the cornea. Focusing forward and back within the anterior chamber will facilitate the viewing of cells.

4. Cells are a sign of active inflammation and should be counted in the grading process. Aqueous flare is the result of leakage of protein through damaged iris blood vessels and is graded by the degree of obscuration of the iris details.

9 Double eyelid eversion

This technique is used to find small foreign bodies in the superior fornix. Care should be taken to minimally irritate the palpebral conjunctiva. The eyelid is not actually everted twice.

1. Sterilise Desmarres Lid Retractor using an alcohol wipe.

2. Instil anaesthetic and fluorescein into the eye.

3. With the patient at the slit lamp, single-evert the upper eyelid. Use the Desmarres lid retractor to hook under the everted tarsus with the blade placed between tarsus and bulbar conjunctiva.

4. Gently pull up and out to expose the fornix.

5. Observe for any small foreign bodies using fluorescein and the cobalt blue filter on the slit lamp or irrigate the fornix in free space to try to dislodge any foreign bodies.

7.2.4 Recording

Normal appearance: If no abnormalities are detected, record ‘clear’ if the tissue is transparent, such as the cornea and lens. Otherwise record ‘No abnormalities detected’ (NAD) or ‘Within normal limits’ (WNL) or equivalent.

Anomalies/abnormalities: Record the size, shape, appearance and location of any abnormalities/anomalies using a diagram and a written description as well as digital imaging if available. In addition, observations such as fluorescein staining, corneal oedema, conjunctival anomalies (papillae, follicles), injection and vascularisation may be graded on a scale of 0 to 4+ with 0 being absence of a response, 1+ being trace response, 2+ being mild response, 3+ being moderate response and 4+ being severe response.

Cataracts: Unless digital imaging is available, record cortical and subcapsular cataracts by drawing them (Figure 7.13). The undilated pupil can be recorded as a dashed line on this diagram. If there are cortical opacities in both the anterior and posterior cortex, both should be recorded. Nuclear yellowing and opacification can be graded on a scale of 0 to 4+ with 0 being absence of opacity and 4+ being the most severe form of opacity. For more precise grading, a cataract grading system such as the LOCS III system may be used.³ In this type of system the cataract is graded on a decimal scale against standardised colour photographs.

Fig. 7.13 Recording of cataract.

Cells and flare: Cells in the anterior chamber are graded according to the number observed with grade 0 being <1 cell, 0.5+ being 1–5 cells, 1+ being 6–15 cells, 2+ being 16–25 cells, 3+ being 26–50 cells, and 4+ being >50 cells.² Aqueous flare is graded from 0–4+ depending upon the visibility of the iris detail; with grade 0 being no flare, grade 1+ being faint flare, 2+ being moderate (iris and lens details remain clear), 3+ being marked (iris and lens details are hazy), and 4+ being intense (fibrous or plastic aqueous).

Contact lens complications: Contact lens complications can be graded by using the Centre for Contact Lens Research Unit (CCLRU) or the Efron grading scales (Section 5.6).⁴

7.2.5 Interpretation

A good understanding of the normal anatomy and physiology of the anterior segment and adnexa as well as the normal changes with age is required. Variations in normal appearance of the anterior segment and changes with age are discussed in Chapter 8.

7.2.6 Most common errors

1. Not positioning the slit lamp so that the patient is leaning forward into the chin rest. This often results in the patient not being able to maintain their forehead against the headrest, resulting in the image going in and out of focus.

2. Not focusing the eyepieces to compensate for your refractive error.

3. Not increasing the brightness when narrowing the beam or using a filter.

4. Not maintaining a sharp focus as the beam is swept across the eye.

5. Not developing a smooth, logical routine that can be repeated.

7.3 Tear film and ocular surface assessment

The tear film is usually assessed during the slit-lamp examination of the anterior segment, and is specifically indicated in those wearing or wishing to wear contact lenses (Chapter 5), patients who have undergone or wish to undergo refractive surgery and patients with any symptoms of dry eye or a history that might suggest susceptibility (e.g. patients taking medications that include beta-blockers, antihistamines, oral contraceptives and acne medications, and smokers).⁵ The incidence of dry eye is increased following laser refractive surgery and nearly half of contact lens wearers report symptoms of dryness.^6,7 Dry eye is a multifactorial disease that results in symptoms of discomfort, visual disturbance and tear film instability with potential damage to the ocular surface and is accompanied by increased osmolarity of the tear film and inflammation of the ocular surface.⁸ It is classified based upon aetiology as either aqueous tear-deficient or evaporative. Aqueous deficient dry eye includes Sjögren syndrome (autoimmune) and non-Sjögren syndrome dry eye and evaporative types are classified according to intrinsic causes (e.g., meibomian gland dysfunction) and extrinsic causes (topical drug preservatives, contact lens wear and ocular surface disease such as allergy).⁸ Symptoms commonly include irritation, dryness, foreign body sensation, burning, gritty sensation, transient blurring of vision, stinging pain, epiphora and contact lens intolerance. Less commonly mentioned symptoms include haloes around lights (especially at night), excessive tearing, stringy mucus discharge, redness, photophobia, itching and asthenopia. Patients often report closing their eyes to obtain some relief.

In primary eye care, practitioners are most commonly trying to diagnose and manage marginal rather than severe cases of dry eye. A patient with marginal dry eye is likely to exhibit signs and symptoms when the relationship between the tear film and the ocular surface is under stress, such as when fitted with a contact lens, or when undertaking concentrated tasks that reduce the blink rate, such as reading, using display screen equipment or driving. Environmental factors such as wind, air conditioning, airline travel and low humidity indoors in winter months can produce similar effects. Those with more serious dry eye disease will have an exacerbation of their symptoms under such conditions.

The international standard criteria for dry eye diagnosis is symptom assessment, interpalpebral surface damage, tear instability and tear hyperosmolarity. Although tear hyperosmolarity is mentioned as part of the criteria for diagnosis, it is currently impractical to measure in the clinical setting.⁹ Assessments appropriate for primary care would include symptom recording, including by standardised questionnaire, lower tear meniscus height, tear break-up time, tear volume by Schirmer or phenol red thread test, grading of conjunctival and corneal fluorescein staining and meibomian gland expression.⁷

Lacrimal occlusion can also be useful for the patient with marginal dry eye who wishes to continue wearing contact lenses, as well as for short-term occlusion during the healing process after ocular surgeries such as LASIK.6,10 Patients must be evaluated for the suitability for use of punctal or intracanalicular plugs as they are relatively expensive and reversal of the occlusion may be difficult in some cases if patient selection was inappropriate and excess tearing or complications occur. Temporary occlusion with dissolvable collagen plugs is a relatively inexpensive diagnostic test which allows the determination of suitability for therapeutic occlusion options.

7.3.1 Comparison of tests

Ocular surface damage caused by dry eye can be assessed using various vital dyes such as fluorescein, lissamine green and rose bengal. Fluorescein, which can pool in an indentation and is taken up by damaged cells and adheres to the surface of cells is the standard assessment for ocular surface damage.11,12 Lissamine green exhibits staining properties that are similar to rose bengal, but with significantly less toxicity and discomfort.¹³ Indeed, now that lissamine green is in widespread use, rose bengal tends to be rarely used in primary eyecare and is reserved for assessing more severe dry eye cases. Lissamine green stains dead and devitalised cells along with mucin but is not toxic to healthy cells. It is particularly useful for viewing more subtle conjunctival damage, in suspected marginal dry eye, patients with ocular allergies and current or potential contact lens wearers.

Tear break-up time (TBUT) is fast, easy to perform and comfortable for the patient. It requires equipment that is standard to optometric practice such as a biomicroscope with a cobalt blue filter and sodium fluorescein. The main disadvantage of the technique is that it is intrinsically invasive. In addition, a localised corneal surface abnormality will typically produce a break-up of the tear-film in that location and can suggest a falsely low TBUT. However, although a wide variability of the TBUT is present in normal individuals, a TBUT shorter than 10 sec has sufficient specificity to screen patients for evidence of tear film instability.¹⁴

Evaporative dry eye can be assessed with meibomian gland evaluation, the evaluation of lid and blink dynamics and lid anomalies causing poor lid closure. Aqueous deficient dry eye can be detected using tear flow/volume tests, such as the assessment of the tear meniscus and the Schirmer and phenol red thread tests.⁷ Note that these conditions are not mutually exclusive as meibomian gland dysfunction is present in 70% of patients with aqueous-deficient dry eye.¹⁴ The phenol red thread test is very easy to perform and patients generally tolerate it well as only a soft thread is touched to the lid and the results are obtained in 15 seconds per eye. Due to the relatively quick assessment, it is useful for examining the tear volume before and after insertion of lacrimal occlusive devices. The Schirmer tear test uses a 5 by 35 mm strip of filter paper to measure basic and reflex tear secretion when used without anaesthetic. The Schirmer test is used in severe dry eye patients and as part of the definition of Sjögren syndrome, although research has suggested that it has limited reliability and validity.^14–16

Short-term dissolvable collagen plugs are the only diagnostic test that determines whether more permanent punctal and intracanalicular plugs are suitable for the patient. They imbibe water and expand in the canaliculus to approximately two times their diameter, then proceed to dissolve in 4–7 days. After approximately one week, the patient is asked to return and subjective and objective assessments of dry eye are compared pre- and post-insertion of the plugs. The only decisions to be made are the number of implants required and which canaliculi to occlude. More than one trial of collagen implants may be required to prove to you and/or the patient that (semi-)permanent plugs will be a useful therapeutic option for their particular case. For example, patients with poor corneal sensitivity from nerve damage or chronic ocular surface disease may be unable to detect an improvement in comfort during the course of the collagen trial, and therefore may feel that long-term occlusion options will not be helpful for them. In those cases, the objective signs are more helpful in determining suitability and therefore repeated trials may be considered to monitor the corneal and conjunctival health to determine if occlusion is advisable. It is also generally true that a single collagen plug (even the largest size that can fit into the punctal opening) is often insufficient to appropriately occlude a canaliculus and therefore may generate a false negative trial. This is because the diameter of the canaliculus may be unrelated to the size of the punctum and a single plug may migrate out of the system before it has had the opportunity to imbibe water and occlude the drainage. Similarly, some clinicians occlude only the inferior canaliculi for the diagnostic test. While this may be appropriate in some circumstances, it is also more likely to generate a false negative diagnostic test. Full occlusion, even if it generates some degree of epiphora, is generally preferred and is short-lived. Measurement of tear thinning time suggests that superior plug insertion may not be necessary and that occlusion of the lower punctum is sufficient, although occlusion of both prolonged the preservation of tear volume.¹⁷