7.1.1 Symptoms

Blurred vision, asthenopia, headache and diplopia are most commonly caused by ametropia and decompensated heterophoria, but can be caused by diseases of the oculo-visual system. In particular, symptoms of sudden vision loss are suggestive of an ocular disease rather than ametropia, although such symptoms can also be due to gradual monocular vision loss that was suddenly noticed. Gradual vision loss in elderly patients can often indicate age-related cataract and/or maculopathy. A myriad of other symptoms can accompany ocular diseases and some are characteristic, such as the association of flashes and floaters with retinal and posterior vitreous detachment. Note that some diseases, such as primary open-angle glaucoma, are generally asymptomatic until the late stages.

7.1.2 Ocular history

A history of previous ocular disease and treatment can indicate what findings should be detected during your subsequent investigations (e.g., keratic precipitates after iritis, posterior capsular remnants after cataract surgery) and a detailed ocular history can save significant unnecessary investigation. In addition, a history of certain recurring diseases, such as trichiasis, corneal erosion and blepharitis, can make subsequent diagnoses easier. A positive family history often indicates that there is a greater chance that the patient will also have the particular hereditary condition. Common familial eye diseases include age-related cataract, age-related macular degeneration and both primary open-angle and primary closed angle glaucoma.

7.1.3 General health and medications

Some systemic diseases, such as diabetes mellitus and hypertension, are well known to cause complications in the eye. In addition, certain systemic medications have a higher risk of adverse ocular effects and these should be investigated, particularly if the patient has been taking the medication for a long period and/or at high dose. For example, it is well known that beta-blockers prescribed for systemic hypertension can cause dry eyes and oral corticosteroids can cause posterior subcapsular cataracts.

7.1.4 Visual function

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

7.2.1 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.

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.

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.

7.2.4 Recording

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

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

7.3.2 Procedure for corneal and conjunctival staining

The procedure for fluorescein instillation is provided here. The procedure for lissamine green is performed in exactly the same way, except that approximately twice the volume of the dye is required. You should wait 2–3 min before examining the eye and white light is used with the contrast enhanced using a red filter (Wratten 25).

7.3.3 Procedure for meibomian gland evaluation

7.3.4 Procedure for tear break-up time (TBUT)

See online video 7.3. TBUT is used to assess the stability of the tear film between blinks. Dry spots appear in the tear film that are thought to form by evaporation and retraction of the tear film after each blink and by diffusion of the superficial lipid through the aqueous layer to the mucin surface. Topical anaesthetics should not be used prior to TBUT measurement, as this may cause a further reduction in TBUT.

7.3.5 Procedure for non-invasive break-up time (NIBUT)

NIBUT or tear thinning time measurements involve projecting a pattern on to the tear film and observing the specular image. Keratometer mires are commonly used in clinical practice but grids are also available and the tearscope is a commercially available test for measuring NIBUT.14,20

7.3.6 Procedure for phenol red thread test

7.3.7 Procedure for Schirmer tear test

7.3.8 Procedure for diagnostic collagen plugs

See online video 7.4.

7.3.9 Recording

7.3.10 Interpretation

7.3.11 Most common errors

7.4.1 Comparison of tests

The dye disappearance test and/or the Jones 1 test help to determine whether there is a stenosis or blockage of the nasolacrimal system. If they suggest a stenosis or blockage, then dilation and irrigation of the system is indicated. Contraindications for dilation and irrigation include symptoms and signs of canaliculitis and dacryocystitis (including regurgitation of discharge from the punctum). Lacrimal sac palpation may help to determine if dilation and irrigation of the system is contraindicated. Dilation and irrigation itself may dislodge a concretion or mucous plug that has blocked the canaliculus. In this respect it is a therapeutic procedure. However, it is also a diagnostic procedure in that it helps to determine if the system is patent. Jones 2 testing, which attempts to determine the site of any blockage, is rarely used in primary eye care as if dilation and irrigation was unsuccessful the patient would likely be referred.

7.4.2 Initial procedures

7.4.3 Procedure for fluorescein dye disappearance test

7.4.4 Procedure for Jones 1 or primary dye test

7.4.5 Procedure for dilation and irrigation

Dilation and irrigation is generally undertaken if no fluorescein is recovered with the Jones 1 test.

7.4.6 Recording

7.4.7 Interpretation

7.4.8 Most common errors

7.5.1 Comparison of tests

The van Herick anterior angle assessment is a relatively quick and simple procedure and can be part of a routine assessment of the anterior eye using the slit-lamp biomicroscope. The superior angle is the narrowest and most likely to close. Although the van Herick angle assessment is unable to assess the superior angle, in most cases the technique is sufficient to indicate whether there is a danger of angle closure.²⁶ Only if the angle appears narrow using this assessment is gonioscopy required to determine whether dilation is safe. The van Herick assessment is a conservative one in that many patients with a narrow angle as determined by the test can be safely dilated.²⁷

The simple shadow test is very quick and simple and is useful when a biomicroscope is not available or when a van Herick assessment is not possible, such as with a patient in a wheelchair or a young child. Most young children are very unlikely to have a narrow angle unless they are a high hyperope and the shadow test is ideal to use as a safety check prior to the use of a cycloplegic drug. It is not as accurate as van Herick’s grading system with the biomicroscope.

7.5.2 Procedure: van Herick assessment

See online video 7.5.

7.5.3 Procedure: Shadow test angle estimation

7.5.4 Recording

7.5.5 Interpretation

The angle should normally be grade III or grade IV (Figure 7.18). The prevalence of narrow angles of grade I and II is about 2%. If the angle is grade II or narrower, there is a risk of angle closure and the pupil should be dilated only if a gonioscopy examination indicates that it is safe to do so. Hyperopic eyes, being relatively small, tend to have smaller anterior angles while the larger, myopic eye tends to have larger anterior angles. The growth of the crystalline lens throughout life (before cataract surgery) means that elderly patients are much more likely to have a small anterior angle and children typically have large anterior angles. Note that early age-related cataract, particularly anterior and posterior subcapsular cataracts, typically lead to a thinner lens and a wider anterior angle.²⁸

7.5.6 Most common errors

• Narrow anterior chamber angles suggested by van Herick to assess the relative risks for pupillary dilation. Gonioscopy is the gold standard technique against which screening tests for narrow angles are compared.²⁹

• Narrow (or closed) angle glaucoma including evaluation and documentation of peripheral anterior synechiae if present.²⁹

• Primary open angle glaucoma (POAG) and risk factors for POAG (e.g. elevated intraocular pressure) to confirm ‘primary’ diagnosis.

• Secondary open angle glaucoma and risk factors (e.g. pseudoexfoliation, pigment dispersion, chronic uveitis) to contribute to determination of disease severity.

• Risk of angle neovascularisation (e.g. confirmed rubeosis iridis, and ischaemic posterior segment conditions including vein or artery occlusions and diabetic retinopathy).³⁰

• Risk of angle recession post blunt trauma.

• Risk of intraocular foreign body.

• Congenital or acquired structural irregularities of the iris and anomalies of the anterior chamber (e.g. iris cysts or tumours, ectopic pupil).

• Post laser peripheral iridotomy to assess effect on angle depth.

• Recent ocular trauma especially in the presence of hyphaema or microhyphaema.

• Recent intraocular surgery, including cataract surgery.

7.6.1 Comparison of different gonioscope lenses

Scleral-type lenses such as the Goldmann 3-mirror lens (Figure 7.21) provide excellent optics and mirror placement allowing for the detection of subtle angle findings (e.g. early angle neovascularisation), which can be more difficult with the poorer image quality of corneal-type lenses. Scleral-type lenses also provide excellent lens stability on the eye once inserted and good eyelid control even with a patient with blepharospasm. This allows a better view in patients with significant loss of corneal transparency. The image may be more transient with corneal-type lenses as the tear film seal is disrupted easily if the lens is not maintained on the central cornea. The Universal lens also contains two additional mirrors angled for evaluation of the peripheral and midperipheral fundus as well as a central lens for evaluation of the vitreous and posterior pole (section 7.12).

All corneal-type lenses (e.g. Posner, Zeiss, Sussman; Figure 7.22) have a smaller (9 mm) and flatter area of contact on the cornea as compared to the scleral-type lenses and have four mirrors, all of which are angled to allow examination of the anterior chamber angle. The smaller, less concave surface enables gonioscopy without the need for a viscous coupling solution and essentially no lens rotation is required as all four mirrors are angled for gonioscopic assessment. The lens is easily inserted onto the cornea of a cooperative patient thus facilitating a relatively quick assessment, unlike the more challenging lens insertion and required coupling solution with scleral-type lenses. Corneal compressions can only be undertaken with corneal-type lenses and allows differentiation between appositional and synechial angle closure. Disadvantages of corneal-type lenses include the identification of an artificially wider angle if too much pressure on the cornea causes the angle to appear to widen. Corneal epithelial disruption may also occur if significant lens movement occurs on the corneal surface.

7.6.2 Goldmann 3-mirror (Universal) gonioscopy procedure (see summary in Box 7.1)

See online video 7.6.

7.6.3 Additional examination technique: The convex iris technique

The convex iris technique involves changing the angle of the gonioscopy lens relative to the angle being viewed in order to visualise the otherwise obscured angle details in an eye with a shallow anterior chamber and narrow angle. This involves tilting the lens into the quadrant to be examined and/or having the patient look toward the position of the thumbnail mirror. The light from the angle can then vault over the anteriorly bowed iris to the mirror and allow the more posterior structures of the angle to be visualised. With a scleral-type lens, it is generally best to have the patient look towards the mirror (i.e., for examining the inferior angle with the mirror placed at 12 o’clock, ask the patient to look up while maintaining the seal of the lens on the eye). However, the view may still not be optimal and the lens may also need to be tilted away from the mirror being used. For corneal-type lenses, less movement is needed to facilitate the view into the angle as the mirrors are placed closer to the apex of the cornea. Less eye movement by the patient and more lens manipulation is generally better. However, when observing very narrow angles, it may be necessary to both tilt the lens away from the mirror and have the patient look towards the mirror.

7.6.4 Corneal-type gonioscopy procedure

7.6.5 Additional examination technique: The corneal compression technique

The corneal compression technique is also termed compression, pressure or indentation gonioscopy. This technique can be used to differentiate if an observed angle closure is appositional (i.e. iris is in contact with the angle structures but is not adherent) or synechial (i.e. the iris is physically and irreversibly adherent to the angle). Pressure is applied with the four-mirror gonioscopic lens directly on the centre of the cornea forcing aqueous into the peripheral chamber and forcing the iris posteriorly. Pressure on an eye with an appositionally closed angle will cause the iris to pull away from the angle to reveal some angle structures, while a synechial angle closure will remain closed.

7.6.6 Recording

The most common reason for a gonioscopic assessment is to determine the relative openness of the anterior chamber angle. There are several published grading systems but the suggested method is to use an anatomically descriptive recording system, thus eliminating the discrepancies and controversies that exist between grading systems. The anterior chamber angle is widest inferiorly and is most narrow superiorly, with the nasal and temporal quadrants in between. All quadrants should be inspected and graded independently. Recording of observations should include the following:

Other characteristics and pertinent negatives include:

Common alternate grading systems include that of Shaffer which grades the angle by the estimate of the geometrical angle between the iris and angle wall at the recess. This system most closely correlates with the van Herick angle estimation method. Grades III to IV are widely open angles of 30–40°. In both the van Herick and Shaffer systems, angles designated grade II (20°) or less are considered capable of closure. Grade 0 angles are considered closed. The Spaeth grading system uses three criteria to describe the angle. The angle is initially described in a similar way to the Shaffer system but in degrees. The peripheral iris contour is then described as being either regular (r), steep (s), or concave (q for queer). Finally the site of iris insertion is described anatomically (see further reading for details).

In addition to grading and describing the angle, the trabecular meshwork can be graded with respect to the degree of pigmentation. The scale is somewhat arbitrary but convention describes 0 as no pigment, 1 as trace, 2 as mild, 3 as moderate, and 4 as dense pigment deposition. The absence of pigment (grade 0) makes the angle assessment difficult as the various structures are highlighted with pigment. The focal line technique helps to delineate the faint Schwalbe’s line and therefore to help determine the most posterior structure.

7.6.7 Interpretation

With the mirror in the 12 o’clock position and when examining the angle in the right aspect of the mirror (i.e. 1 o’clock), the view is of the 5 o’clock position of the angle (not the 7 o’clock position). Examination of the wider inferior angle first facilitates the identification of the various structures. It is useful to approach the angle evaluation from an anterior to posterior direction as all structures are not always present:

7.6.8 Other gonioscopic findings

Peripheral anterior synechiae (PAS) are adhesions formed between the iris tissue and the trabecular meshwork or even Schwalbe’s line. Their appearance is dependent on the aetiology of the adhesion. Angle closure PAS are usually found where the angle is narrowest, whereas inflammatory PAS are often located inferiorly due to the settling of inflammatory debris. PAS may be seen adjacent to surgical incisions, such as for cataract or glaucoma surgery or in association with posteriorly located laser burns following laser trabeculoplasty.

Neovascular growth may be preceded by rubeosis iridis at the pupillary ruff; however, neovascularisation of the angle may occur without neovascularisation of the iris. Early neovascular bridging vessels across the angle can be very difficult to detect. The risk of missing neovascularisation by not performing gonioscopy in patients with central retinal vein occlusion is about 10%.³⁰

7.6.9 Most common errors

7.7.1 Comparison of tonometers

Goldmann applanation tonometry (GAT) has long been the gold standard for IOP measurements and its accuracy is such that it is used to determine the validity of other tonometers. The Perkins tonometer uses the same principal as the GAT, but is a hand-held tonometer and does not require a slit-lamp biomicroscope (Figure 7.25). Its advantages are that it is portable, can be used on domiciliary (home) visits and being hand-held may be used with the patient either sitting up or lying down (note that the IOP will likely be higher when the patient is lying down). In addition, some patients are less apprehensive with this technique. Its disadvantages include that it is less stable than the biomicroscope-mounted instrument, has a fixed low magnification for viewing the mires and does not allow for efficiently examining the cornea before and after the test as the patient is not already at the biomicroscope.

Both GAT and Perkins have the disadvantage that they only provide valid measurements for corneas with near average thickness. For a very thick corneas, GAT tends to overestimate IOP, and for very thin corneas it underestimates IOP. For example, Johnson et al. reported details of a 17-year old patient with GAT readings between 30 and 40 mmHg due to extremely thick corneas of 0.90 mm (compared to a normal average of 0.54 mm) whose ‘real’ IOP was 11 mmHg.33,34 This inaccuracy of GAT has been known for some time, but has come to the fore since the findings of significant IOP reductions due to the corneal thinning induced for refractive surgery.^34,35 The influence of central corneal thickness on applanation IOP may lead to the classification of some normal subjects with thick corneas as ocular hypertensives and several reports have suggested that central corneal thickness should be measured in ocular hypertensives,^33,34,36 making the measurement of central corneal thickness the standard of care in the assessment of those at risk of glaucoma. Some reports have suggested that non-contact tonometry provides even higher IOP values than Goldmann tonometry in patients with thick corneas.^37,38 In addition, this effect could also mean that some patients diagnosed as having normal tension glaucoma using GAT may actually be patients with high IOP but a thin cornea.³⁹ In this regard, a clinical note reports two cases of post-LASIK patients with steroid response progressing to end-stage glaucoma, and that the late detection may have been partly caused by unreliably low IOP after surgery.⁴⁰ Attempts have been made to determine the relationship between corneal thickness and GAT to provide a validated correction factor, but there is wide disagreement among investigators.⁴¹

Of the non-Goldmann tonometers, a systematic review of the literature suggested that the NCT seems the most accurate, with two-thirds of readings within 2 mmHg of GAT.⁴² Most non-contact tonometers (NCTs) are now highly automated and simply involve lining up the instrument in the correct position when it will automatically take measurements. They are easier to perform than Goldmann or Perkins tonometry, do not require corneal anaesthesia, and can be performed by trained clinical assistants. However, results are typically less reliable than GAT with slight differences that are model dependent.⁴² You should check the literature for information regarding the model type you have. At least three readings are required to average the effects of the arterial pulse, which varies IOP by over 4 mmHg. However, averaging four measurements appears to provide the best sensitivity and specificity of results and is recommended.⁴³ If an NCT is used, a useful protocol can be to screen patients who do not have risk factors for glaucoma using NCT measurements taken by a clinical assistant and to repeat any measurements which are high, unequal or increased from previous visits using GAT or Perkins. Any patient with glaucoma or any risk factors for glaucoma should have pressures measured by contact tonometry.

7.7.2 Procedure for GAT

See online video 7.7.

7.7.3 Alternative procedure: Perkins tonometry

7.7.4 Recording

Record the tonometer readings for the right and left eyes on the right and left side respectively of a capital letter ‘T’. Also indicate that you used a Goldmann or Perkins tonometer and the time of day (IOP varies diurnally). For example:

With NCTs, it is best to record all 3–4 tonometer readings. For example:

7.7.5 Interpretation

The range of normal Goldmann IOPs is from 7 to 20 mmHg (mean of about 13 mmHg). However, note that Goldmann readings are influenced by central corneal thickness and provide a significant underestimation with corneal epithelial oedema.34,44 Various systemic drugs can alter IOP, including systemic and topical steroid use that can significantly raise IOP in steroid ‘responders’ and beta-adrenergic blockers that can lower IOP. IOPs below 7 mmHg may suggest conditions such as retinal detachment, uveitis or wound leak. IOPs above 20 mmHg indicate ocular hypertension and may suggest glaucoma. However, note that patients can have primary open-angle glaucoma and have a normal IOP below 21 mmHg. The difference in IOP between the two eyes should not exceed 4 mmHg. IOPs vary diurnally, with the highest IOP generally measured in the mornings. If a suspected glaucoma patient has a normal IOP in the afternoon, ask the patient to return on another day in the early morning, so that IOPs can be remeasured at that time.

7.7.6 Most common errors

7.8.1 What are the risks with diagnostic drugs?

Diagnostic drugs are available to the majority of optometrists and other primary eye care practitioners throughout the world. The three major types of diagnostic drugs available are anaesthetics, cycloplegics and mydriatics. Staining agents are discussed in section 7.3. The advantages to be gained by using these drugs far outweigh the possible adverse ocular and systemic effects that rarely occur. For example, in a systematic review of published research between 1933–1999, Pandit and Taylor concluded that the risk of inducing acute glaucoma following mydriasis with tropicamide alone is close to zero, and the risk with long-acting or combined agents is between 1 in 3380 and 1 in 20,000.²⁷ Mydriasis with tropicamide alone is safe even in patients with primary open angle glaucoma. Note that the most common cause of malpractice claims in the US is misdiagnosis of intraocular disease, principally retinal detachment, open-angle glaucoma, and tumours. The great majority of claims alleging misdiagnosis involve optometrists who have failed to use diagnostic drugs for dilation of the pupil with very few claims being due to adverse responses to ophthalmic drugs.⁴⁵ Of course, precautions must always be taken when using any of these drugs to ensure that the patient is at minimal risk.

7.8.2 Obtaining informed consent

7.8.3 Safety checks

7.8.4 Choosing the appropriate drug and dosage

7.8.5 Checks prior to instillation

7.8.6 Drug instillation procedure

See online video 7.8.

7.8.7 Post drug instillation procedure

7.8.8 Recording

Record the time, the number of drops instilled into each eye and the drug and its concentration.

For example:

7.8.9 Most common errors

7.9.1 Pupillary function

Evaluation of pupillary function provides valuable information about the integrity and function of the iris, optic nerve, posterior visual pathways and the third and sympathetic nerves to the eye, and some of the conditions that cause pupil reflex abnormalities are life threatening. Afferent pupillary defects are caused by lesions in the ‘front end’ of the pupillary light reflex pathway and most commonly by lesions in the retina and optic nerve. The afferent pupillary pathways leave the visual pathways in the last third of the optic tracts to reach the pretectal nuclei (Figure 7.27). Afferent pupillary defects do not cause anisocoria (different pupil sizes), but may produce abnormal pupillary light reflexes. Efferent pupillary defects produce anisocoria and are caused by lesions to the motor neurone system, which carries signals from the central nervous system to the iris via the 3rd cranial nerve.

7.9.2 Comparison of tests

Pupil size should be assessed in both bright and dim illumination to investigate any anisocoria. The swinging flashlight test provides a sensitive assessment of any unilateral or asymmetric afferent defects, and has been shown to be superior to the Marcus Gunn test (redilation under sustained illumination) for detecting relative afferent pupillary defects.52,53 There is no condition in which the near reflex is defective or lost when the light reflex is normal. Therefore the near reflex need only be checked if the light reflex is abnormal. Patients can show an abnormal light and near pupil reflex or an abnormal light reflex with a normal near reflex (light-near dissociation).

7.9.3 Procedure for pupil assessment

See online video 7.9.

7.9.4 Recording

Pupil shape and size: Record any irregularity in pupil shape and any anisocoria.

Pupil reflexes: A 0 to 4+ grading system can be used for direct (D) and consensual (C) reflexes where 0 indicates no pupil response, 1+ (or +) indicates a very small, just visible response, 2+ (++) indicates a small, slow response, 3+ (+++) indicates a moderate response and 4+ (++++) indicates a brisk, large response typical of a healthy young patient. An alternative is to use acronym PERRL (Pupils Equal Round and Respond to Light), but this does not differentiate between a just visible response and a large, brisk one. If the light reflex is abnormal, the near reflex must be checked. Some disorders produce an absent light reflex with a normal near reflex (light-near dissociation).

Also record the result of the swinging flashlight test as +ve RAPD (if an RAPD is indicated) or –ve RAPD (this indicates that there is no problem). If +ve RAPD is found, record which side was defective. If the defect is quantified using a neutral density filter, indicate the filter density in log units.

Examples:

7.9.5 Interpretation

Pupils are normally equal in size and typically vary from 3 to 6 mm in diameter in bright light to about 4 to 8 mm in dim light and show slight physiological fluctuations in size or hippus. The pupil gets smaller with age. Physiological anisocoria is seen in about 20% of normal patients and is generally the same in dim and bright illumination, usually small (<1 mm), shows normal pupil reflexes and has been present for years. If the diagnosis is in any doubt, this can be checked by asking the patient to bring in some old close-up photographs of themselves looking straight ahead. Pathological anisocoria is due to an abnormality in the efferent or motor pupil pathway. Anisocoria that is greatest in bright light will generally show an abnormal direct and consensual light reflex. This indicates a problem in the motor leg of the light reflex pathway, such as in the third nerve, ciliary ganglion (including Adie’s tonic pupil) or iris, or could be drug induced.

An abnormal direct light response in a pupil capable of a normal consensual response indicates an afferent (visual pathway) defect. There is generally no anisocoria. The swinging flashlight provides a more sensitive assessment of any unilateral or asymmetric afferent defects. It compares each eye’s direct response (reflecting the normality of its visual pathway) with its consensual response (reflecting the normality of the other eye’s visual pathway). Symmetrical afferent defects do not show a positive RAPD. Some normal subjects may show a persistent but small RAPD in the absence of detectable pathologic disease. Therefore, an isolated RAPD in the range of 0.3 log unit that is not associated with any other significant historical or clinical finding should probably be considered benign.⁵⁴ Similarly, patients with unilateral cataract may show an RAPD in the non-cataractous eye that is not reflective of visual pathway disease.⁵⁵

7.9.6 Most common errors