Over the last few months Optician has published a number of case studies from UK practitioners using the Optomap retinal exam. Here, US optometrist William Jones describes the system and offers some hints on image interpretation.
The main advantage of the Optomap retinal exam is that it is able to capture a 200º fundus image with or without dilation. The instrument is operator-friendly and only requires a practice assistant to operate it. The 200º imaging (80 per cent of the fundus) allows for detection of most lesions. The ora serrata is 240º and eye steering increases the field of view to around 230º in most cases.
The instrument has been used to image approximately seven million patients and has found thousands of intraocular lesions. Examples would be tumours, retinal detachments, retinal breaks, diabetic and hypertensive retinopathy, leukaemic retinopathy, retinoschises, macular degeneration, and so on. There have been many incidences where a lesion was found on the Optomap retinal image and not recorded in the patient's chart over the past many years.
The Optomap imaging system has simultaneous dual colour images (red and green), which allow for additional diagnostic ability not found in most standard fundus camera systems.
A strong benefit, therefore, in diagnosing with Optomap is that there is a pure red and green laser used to capture an image. The green laser obtains most of the information from the sensory retina to the pigment epithelium and the red from the pigment epithelium down through the choroid. The image obtained is like having a colour transparency of the retina overlaying a transparency of the choroid. This is not the same image captured by a standard fundus camera, which captures most of the image from the retinal layers.
Thus, the instrument is able to display either the red or green images (like separating the colour transparencies), and therefore a view of most of the sensory retina or choroid is made available. By noting if the fundus lesion is better in the red or green laser image, the lesion may be localised to the sensory retina or the choroid.
This can be used in the differential diagnosis. For example, a lesion may appear to be a choroidal naevus, but since it was also seen in the green laser image, it may be a congenital hypertrophy of the pigment epithelium (CHRPE). Or if a retinal lesion was observed and if you wanted to know if there was deeper involvement down to the pigment epithelium and choroid, the simultaneous dual colour laser images could be able to determine this possibility.
Since other systems don't have simultaneous dual colour images, this type of colour image diagnostic capability is not possible.
When viewing in the green laser separation, retinal vessel detail and retinal haemorrhages are readily seen and often can enhance the discovery of haemorrhagic retinopathies - for example, diabetes and systemic hypertension. Since it is now known that diabetic retinopathy can appear first in the periphery, the instrument has detected the first signs of this disease by imaging peripheral haemorrhages.
Since the captured image is digital, the image can be magnified or minimised in order to gain additional information. Also, post-image software enhancement programs are available to add or subtract colour, brightness, or contrast in order to enhance the image. Additional software allows for adding arrows or circles or annotations on the image to direct a reviewer to areas of interest. There are measuring devices in the software to allow for determining the linear length and area of a lesion in pixels.
Pixels are used because they are not affected by changing the magnification of the image. There is software used to determine the cup-to-disc ratio. Again, since the image is digital, it can be emailed to a local or distant expert for consultative purposes.
Examples of Fundus Lesions with Optomap Retinal Exam
Congenital retinal pigment epithelium hypertrophy
Congenital hypertrophy of the retinal pigment epithelium may be either unifocal or multifocal in nature. Unifocal congenital hypertrophy of the retinal pigment epithelium (CHRPE) presents as pigmented, flat, round lesions with distinct margins.
Areas of congenital hypertrophy range in colour from light brown to jet-black, depending on the amount of melanin in the epithelial cells. These areas are not to be confused with a choroidal naevus, which is usually flat, slate grey in colour, and with indistinct margin. They are almost always stable in size but may change in colouration due to chorioretinal atrophy. Areas of pigment mottling and chorioretinal atrophy often occur; the areas of chorioretinal atrophy produce window-like defects that are known as 'lacunae' and they allow a clear view 'window-view' of the underlying choroid. There may be a single lacuna or many lacunae present within the boundary of the lesion (see Chorioretinal atrophy). The lacunae can enlarge or increase in size over time. There may be a thin clear halo around all or part of the lesion, which is pathognomonic for a CHRPE. The prevalence of these lesions is quite common, although it seems an estimated percentage for the general population has not been reported.
With Optomap technology - because lesions are in the RPE layer, they are usually seen well on the red and poorly on the green separation. The halo is best seen on the red laser separation.
Choroidal naevus
A choroidal naevus appears as a pigmented area of the fundus, which can display a varied appearance. The shape of these lesions is generally round to oval but more irregular configurations may be seen.
These lesions usually vary in size from 0.5mm to 10mm, with a majority ranging from 1.5mm to 5mm in diameter. These lesions are usually flat but they can be elevated from one to two dioptres (this elevation is usually barely perceptible during ophthalmoscopy) and sometimes they can be 2mm or more. They are usually found as a single lesion but occasionally, multiple naevi may be found in one eye. Also, they generally present as a unilateral entity but bilateral presentations are not uncommon. Histological studies have shown that 90 per cent of choroidal naevi are found posterior to the equator. There are no proven risk factors for developing these lesions; however, they seem to be more common in lightly pigmented people.
The choroidal naevus is probably the most common intraocular tumour found in the ophthalmic practice. The incidence of choroidal naevi ranges from 1 per cent to 2 per cent in clinical studies and 6.5 per cent in autopsy eyes. One study found the incidence of choroidal naevi in patients over 30 years of age to be 3.1 per cent. The time of onset of these lesions is uncertain but it is an extremely rare finding in infants and young children and they become more prominent at about puberty. It may well be that the potential cells are present in the choroid at birth but do not become very pigmented until puberty.
With Optomap technology - because lesions are in the choroidal layer, they are usually seen well on the red and not on the green separation.
Malignant choroidal melanoma
A melanoma, although rare, is the most frequently occurring malignant intraocular tumour in the adult population. Incidence in the white population over the age of 50 years is approximately one in 50,000 a year and another study found that they occur in about one in 150,000 Caucasian adults per year. The chance of developing bilateral melanomas of the choroid has been estimated to be around 1 in 5x107 patients in a lifetime. The tumour is almost always benign in African-Americans and it is less common in Asians and Hispanics.
The appearance of a choroidal melanoma can be very variable but it is usually a mottled, oval to round, elevated mass in the fundus and often has a brown to greenish grey colour. Sometimes the tumour may be a nodular mass, which is bi-lobed or even multi-lobed. The mottled appearance is the result of drusen and degeneration of the pigment epithelium above the tumour.
Melanomas of the choroid are often asymptomatic but sometimes they cause blurred vision when fluid from the tumour extends into the macula. Other less common symptoms are: visual field defect, floaters, or photopsia and these are symptoms similar to that of a rhegmatogenous retinal detachment.
With Optomap technology - because the melanoma is likely to be growing in an anterior direction, it will be seen both on the red and green laser separations (better on the red).
White-with- or white-without-pressure
White-with-pressure is an optical phenomenon in which the fundus changes from its usually orange-red colour to a translucent white or greyish-white upon scleral depression. This condition can occur in a small isolated area or be seen as a circumferential band that travels the entire perimeter of the retina. The circumferential band can have smooth or scalloped margins.
The area of white-with- or white-without-pressure can be migratory in nature and therefore its shape can be different on subsequent examinations. The posterior margin of this condition tends to be very sharp and the anterior margin gently fades into the peripheral retina. It is not unusual to see just posterior to an area of white-without-pressure a small zone where the retina appears to be darker red.
This condition is generally found from the ora serrata to approximately three disc diameters posteriorly. However, it can occur as far posterior as the equator and rarely, as far as the temporal arcades. White-with- or white-without-pressure is presumed to be an optical phenomenon associated with the vitreo-retinal interface. It is believed that continued mild vitreal traction is responsible for changes in the transparency of this interface.
With Optomap technology - because white-with-pressure is caused by traction on the surface of the retina, it is seen much better on the green laser separation and poorly on the red.
Retinoschisis
'Cystoid degeneration of the retina', 'retinocoele' and 'retinal cyst' are previously used terms to describe this entity. Retinoschisis results from the splitting of the sensory retina into two layers and often this results in an elevated bullous lesion (like a 'blister' of the retina). Therefore, it has been defined as a splitting of the retina that is large enough to be a 'clinically visible cavity' and histopathologically it is defined as an intraretinal cavity that is at least 2mm (1.3DD) in size. It may be congenital or acquired and although the physical appearance is essentially the same, the pathogenesis of the two forms is different.
Retinoschisis is typically seen as an elevated bullous lesion in the peripheral fundus. A retinoschisis has a smooth, taut surface that does not undulate on eye movements, as commonly occurs with retinal detachments. On the Panoramic 200 it is seen as a semicircular transparent lesion that is convex to the posterior pole. Underlying choroidal detail is mildly hazy. There may be inner or outer layer breaks present and rarely both at the same time.
With Optomap technology - if the retinoschisis is bullous and the retinal vessels are in the inner layer, they will go from red in colour in the normal retina to black appearing in the area of the retinoschisis. This occurs because the vessels are far enough anterior to cause a blocking shadow in the image. Underlying choroidal detail is mildly obscured due to the scattering of the laser light.
Retinal detachment
A retinal detachment is characterised by a separation of the sensory retina from the retinal pigment epithelium (RPE).
The clinical appearance of a retinal detachment is that of a bullous elevation of whitish, diaphanous (transparent to translucent) retina into the vitreous cavity.
Detection of the detached retina is made easier by noting the retinal vessels, which are sometimes more obvious than the semi-transparent retina. A fresh retinal detachment appears whitish due to the scattering of the white light by the irregular posterior surface of the detached retina. The retinal blood vessels appear dark and tortuous on the whitish detached retina.
Another hint that the retina is detached is the loss of detail in the underlying choroid pattern. This again is caused by the scattering of light by the detached retina. The detached retina forms folds - small folds for a shallow detachment and a bullous detachment often displays large retinal folds.
With Optomap technology - because the shorter wavelength light is scattered more, a bullous fresh detachment will appear green on the image. Underlying choroidal detail is much obscured due to the scattering of the laser light. Sometimes the retinal vessels will be dark on the detachment but usually not to the same extent as seen on a retinoschisis. Folds in the detached retina are best seen on the green laser separation. The underlying choroid often appears dark on the red separation. Shallow detachments are rather transparent.
Vitreous floaters
A vitreous floater is any area of vitreous that is sufficiently dense enough to either be detected by the patient (symptom) or be seen during fundoscopy by the clinician (sign).
Floaters are generally derived from material naturally found within the eye but sometimes they may come from external sources such as intra-vitreal foreign bodies.
Vitreous floaters can be the result of vitreous degeneration such as found in the natural synchysis, syneresis, and PVD due to age; from hereditary vitreoretinal degenerations; secondary to vitreous inflammation, such as seen in cases of vitritis, pars planitis and retinochoroiditis, scarring due to inflammation and trauma (such as vitreous foreign bodies). Floaters are the most common entopic phenomenon reported by patients.
Vitreous floaters come in many different sizes, varying from many disc diameters to being very tiny and just perceptible. There are multiple shapes of floaters, they may appear as spherical, disc-shaped, thin linear or curvilinear strands, broken pieces of strands, ring-shaped, cystic and many other presentations.
In young eyes the vitreous is more gelatin-like and floaters will tend to move very little on eye movements but in older eyes with PVD, their motion can be considerable. Floaters can be found in any area of the vitreous cavity, but generally they are more likely to be found above the posterior pole and above the far peripheral retina.
The most common colour appearance is transparent to greyish but they may appear whitish secondary to post-inflammatory scarring, reddish in red blood cells, brown in melanocytes and melanin granules and occasionally blackish.
With Optomap technology - typical vitreous floaters that are dense and close to the retinal surface may look white to grey in colour and cast a shadow on the underlying retina. Floaters that are anterior (not close to the retinal surface) are seen as black objects on the image due to the blocking shadow effect. They are much better seen on the red laser separation than on the green (even though faintly seen on the green, overlying retinal vessels detail is obscured). The floaters almost always change positions on eye movements; therefore, on re-imaging, they will be seen at a different location.
William L Jones is an optometrist and consultant for Optos