Specular microscopy examines the cornea, a transparent tissue at the front of the eye, located just in front of the iris. The cornea acts as a very powerful lens whose job is to focus light onto the retina. It has 5 layers, one of which is called the endothelium. This lies on the inner side of the cornea and consists of a single layer of cells that do not regenerate during our lifetime. This test measures these cells, whose number decreases in some cases.
Page contents
- Which conditions is this test useful for?
- How long does the test take?
- Is the test painful?
- Is any special preparation needed for this test?
- When is specular microscopy needed?
- How is specular microscopy performed and how long does it take?
- Why the endothelium is so important
- What exactly specular microscopy measures
- Normal values and how to read them
- Fuchs dystrophy: the most common endothelial disease
- Specular microscopy before cataract surgery
- ICL lenses and endothelial monitoring
- Contact lenses and the endothelium
- After a corneal transplant
- Specular microscopy and other corneal tests
- Other conditions that affect the endothelium
- How often the test is repeated
- Can we protect the endothelium?
- Questions worth asking about your result
- How the specular microscope works
- Symptoms that may be related to the endothelium
- Specular microscopy before refractive surgery
- Who interprets the test
- In summary: when to consider specular microscopy
- Frequently Asked Questions about Specular Microscopy
Which conditions is this test useful for?
The most common and most important condition that leads us to request this test is Fuchs dystrophy.
In this inherited condition, the number of cells in the endothelial layer decreases, so they can no longer do their job. This dysfunction makes the cornea less transparent.
How long does the test take?
A few seconds. All we need to do is focus on the endothelial cells so that we can image them clearly. Our specialised software automatically calculates the density of these cells.
Is the test painful?
Not at all. It is as simple as having an ordinary photograph taken
Is any special preparation needed for this test?
None. As mentioned above, it is a very simple test, just like having an ordinary photograph taken.
When is specular microscopy needed?
The endothelial cells keep the cornea clear, but they do not regenerate. This is why counting them is particularly valuable in certain situations:
- Before cataract surgery, especially when there are signs of a weakened endothelium. The operation causes some loss of cells and the surgeon needs to know the cornea’s reserves, as we explain on our page about cataracts.
- Fuchs dystrophy, where the cells decrease gradually. The test helps plan when, and with which technique, any surgery should be carried out.
- Many years of contact lens wear, mainly lenses with low oxygen permeability, which can alter the shape and size of the cells.
- Before implanting a phakic intraocular lens for high myopia, and for monitoring it in the following years.
- After a corneal transplant, glaucoma surgery or an eye injury.
Specular microscopy is also recommended when the cornea shows oedema, or when vision is blurred in the morning and improves during the day, a symptom that may indicate a weakened endothelium.
How is specular microscopy performed and how long does it take?
The test is carried out in the clinic with a special microscope (specular microscope), without touching the eye. You sit down, rest your chin and forehead on the support and look at a light. The device focuses automatically and photographs the endothelium in a few seconds for each eye.
The images are used to calculate:
- cell density per square millimetre,
- the variation in cell size (polymegethism),
- the percentage of cells with a normal hexagonal shape,
- often, the thickness of the cornea as well.
The whole procedure takes about 5-10 minutes. No dilating drops or anaesthetic are needed, it is painless and you can drive straight afterwards. If you wear contact lenses, ask the clinic whether you need to remove them beforehand. The results are assessed together with the rest of the examination, for example during the assessment before cataract surgery.
Why the endothelium is so important
The cornea must be completely transparent for us to see clearly. To stay transparent, it must contain the right amount of water: no more and no less. The fluid inside the eye constantly pushes its way into the cornea, and the endothelial cells act like tiny pumps that remove it again.
In humans, these cells do not multiply. When some are lost, because of age, disease or surgery, the neighbouring cells enlarge and spread out to fill the gap. As long as their number remains sufficient, the cornea stays transparent. However, when it falls below a critical threshold, the pump can no longer keep up, the cornea “swells” with water, becomes cloudy and vision deteriorates. Specular microscopy shows us how large a reserve of cells the eye has, before we reach that point.
What exactly specular microscopy measures
The specular microscope photographs the inner surface of the cornea at high magnification. The software analyses the cells and gives a series of values:
- Cell density (CD): How many cells there are per square millimetre. This is the best-known and most important value.
- Polymegethism (CV): How much the cells differ in size from one another. A healthy endothelium has cells of similar size.
- Hexagonality (HEX): The percentage of cells with the normal hexagonal shape. The lower it is, the more “stressed” the endothelium.
- Corneal thickness (pachymetry): Many devices also measure thickness at the same time. A cornea that is getting thicker may indicate that the endothelium is starting to struggle.
Normal values and how to read them
Endothelial cell density naturally decreases with age. In children it is very high, while in middle-aged adults it is usually around 2,500 cells per square millimetre, and slightly lower in older people. The cornea stays transparent even with considerably fewer cells, but when density approaches very low values, the risk of clouding increases significantly.
A number on its own does not tell the whole story. The ophthalmologist assesses density together with polymegethism, hexagonality, corneal thickness, the patient’s age and the slit lamp findings. Comparing the two eyes, and comparing with previous measurements, is also important, as it shows how fast cells are being lost.
Fuchs dystrophy: the most common endothelial disease
Fuchs endothelial dystrophy is an inherited, slowly progressing condition that usually appears after the age of 50 and is more common in women. Small deposits, called guttae, form on the surface of the endothelium, and the cells gradually decrease.
The typical symptom is blurred vision in the morning that improves during the day. During sleep, with the eyes closed, water does not evaporate from the surface and the cornea “swells” more. As the disease progresses, the blurring lasts for more and more hours, glare from lights appears and, in advanced stages, there is pain from small blisters on the surface.
Specular microscopy confirms the diagnosis, records its severity and helps decide the right time for treatment. In the early stages, hypertonic drops that draw water out of the cornea help. In advanced stages, the solution is an endothelial transplant.
Do you need specular microscopy?
The test is done in the clinic in a few minutes, without touching the eye. Book an appointment with Dr. Skouteris.
Specular microscopy before cataract surgery
Every intraocular operation, even the most careful, causes a small loss of endothelial cells. In a healthy eye this has no consequences. In an eye that already has a low reserve, however, it may be the last straw and the cornea may become cloudy after surgery.
This is why, before cataract surgery, specular microscopy is particularly recommended for people with Fuchs dystrophy or suspicious slit lamp findings, previous eye surgery, a history of injury, glaucoma or uveitis, as well as for very hard, advanced cataracts. If the endothelium is borderline, the surgeon adapts the technique and materials used to protect it, and informs the patient about the risk. In some cases, combined cataract surgery and endothelial transplantation is planned.
ICL lenses and endothelial monitoring
Phakic intraocular lenses, such as the ICL, are placed inside the eye to correct high myopia in patients who are not suitable for laser. Specular microscopy is required before implantation to confirm that the number of cells is sufficient for the patient’s age. After the operation, the test is usually repeated every year to make sure the rate of cell loss remains normal.
Contact lenses and the endothelium
Many years of contact lens wear, especially older types with low oxygen permeability or lenses worn during sleep, can cause changes in the shape and size of the endothelial cells. Density does not usually drop significantly, but polymegethism increases and hexagonality decreases. In long-term wearers, especially if they are planning laser or other refractive surgery, specular microscopy gives a useful picture of the health of the cornea. The advice is simple: high-permeability lenses, no sleeping in lenses and regular check-ups.
After a corneal transplant
Today, in many endothelial diseases, the whole cornea is not transplanted, only the thin endothelial layer. These techniques offer faster recovery and better vision than the older full-thickness transplant. After the transplant, specular microscopy is used to monitor the number of cells in the graft over time, so that any rejection or failure can be detected early.
Specular microscopy and other corneal tests
Specular microscopy only examines the innermost layer of the cornea. For the shape of the cornea, which is crucial in keratoconus and before laser eye surgery, corneal topography or tomography is used. For thickness, pachymetry is used. These tests are often carried out at the same visit and combined, to give a complete picture of the cornea.
Other conditions that affect the endothelium
Apart from Fuchs dystrophy and surgery, the endothelium can be affected by:
- Acute angle-closure glaucoma: A sudden, very high pressure can destroy a significant number of cells within a few hours.
- Herpetic endotheliitis: Inflammation of the endothelium caused by the herpes virus, with corneal oedema and clouding.
- Injuries: A blow to the eye or a penetrating injury can reduce the cells locally.
- Diabetes mellitus: Endothelial cells in people with diabetes are often more vulnerable to surgical stress.
- Rare dystrophies and syndromes, such as posterior polymorphous dystrophy and iridocorneal endothelial syndrome, where the specular microscopy appearance is characteristic and helps with the diagnosis.
How often the test is repeated
In a healthy eye with no planned surgery, specular microscopy does not need to be done regularly. In other cases, the schedule is:
- Fuchs dystrophy: Usually every 6 to 12 months, depending on the stage and symptoms.
- ICL lenses: Every year, for as long as the lens remains in the eye.
- After a transplant: According to the graft follow-up schedule.
- Before any intraocular surgery in an eye with a suspected or known endothelial problem.
Can we protect the endothelium?
Because the cells do not regenerate, protecting them is essential. This means using contact lenses correctly, treating glaucoma and eye inflammation promptly, protecting the eyes from injury with safety glasses in high-risk work or sports, and carefully planning every operation on the basis of specular microscopy. In cataract surgery, modern techniques and special substances that protect the endothelium during the operation significantly reduce cell loss.
In Fuchs dystrophy, small daily habits help in the early stages: a warm stream of air from a hairdryer, held at arm’s length from the face for a few minutes in the morning, speeds up the evaporation of water from the cornea and helps vision clear. Hypertonic drops are only used on the ophthalmologist’s advice.
Questions worth asking about your result
- Is my cell density normal for my age?
- Is there a difference between my two eyes?
- Does the result affect future cataract or laser surgery?
- Do I need to repeat the test, and when?
- Is there anything I can do to protect my cornea?
How the specular microscope works
Modern specular microscopes are non-contact: the device does not touch the eye and no anaesthetic drop is needed. The patient rests their chin and forehead on a special support and looks at a small light. The device focuses automatically, emits a short flash of light and records the reflection from the inner surface of the cornea, as if photographing a mosaic of tiny tiles.
Several images are usually taken from the centre and, when needed, from peripheral points of the cornea, because in some conditions the changes are not uniform. The software recognises the borders of each cell and calculates the values. The ophthalmologist always checks the quality of the images and, if needed, corrects the analysis so that the result is reliable. If the cornea is very cloudy, imaging may be difficult, and it is then combined with other tests.
Symptoms that may be related to the endothelium
- Blurred vision in the morning that gradually improves during the day
- Halos and glare around lights, mainly at night
- Vision that becomes blurred in a humid environment or after keeping the eyes closed for many hours
- Blurring that persists for weeks after cataract surgery
- A foreign body sensation or pain in advanced endothelial failure
If you have any of these, especially blurring in the morning, an examination with a slit lamp and specular microscopy will clarify whether the cornea is responsible or another condition, such as cataract or dry eye.
Specular microscopy before refractive surgery
Before laser eye surgery, the main test is corneal tomography. However, in some candidates, such as long-term contact lens wearers, people with suspicious slit lamp findings or those considering an intraocular lens instead of laser, specular microscopy is added to the pre-operative assessment. This rules out early dystrophy that could change the treatment plan, and records a baseline value for the future.
Who interprets the test
The test is carried out in the clinic and assessed by the ophthalmologist who examines you, together with all the other clinical findings. You receive the result with the images and values, and we explain what they mean in your case. Keep it, as it will be valuable for comparison at future check-ups or before any operation, even if this is carried out at another centre.
In summary: when to consider specular microscopy
Specular microscopy is a quick, painless and harmless test that provides information no other test can give with such accuracy. It is essential if you have blurred vision in the morning, if you have been told you have Fuchs dystrophy or guttae, if you are going to have cataract surgery and have other eye problems, if you are considering an ICL lens or if you have had a corneal transplant. Your ophthalmologist will tell you whether you need it after the clinical examination. Because it does not require pupil dilation, you can drive and return to your activities straight away. When you need it, it can be scheduled together with your eye examination, so that everything is completed in a single visit. Let us know when booking your appointment if another doctor has asked you to have specular microscopy, and bring the referral or your previous measurements with you so that the comparison can be made straight away.
To book a specular microscopy appointment, call 210 677 0007.
Frequently Asked Questions about Specular Microscopy
When is specular microscopy needed?
Specular microscopy is recommended before cataract surgery when a weakened endothelium is suspected, in Fuchs dystrophy, after many years of contact lens wear and before a phakic intraocular lens is implanted. It is also used for monitoring after a corneal transplant or glaucoma surgery. Your ophthalmologist will decide when it is necessary.
Is specular microscopy painful?
No. The test is carried out with a special microscope that photographs the cornea without touching the eye. No anaesthetic drops or pupil dilation are needed, and all you notice is a bright flash. You can drive and return to your activities straight after the test.
How long does specular microscopy take?
Photographing the endothelium takes a few seconds for each eye, and the whole test is completed in about 5-10 minutes. The results, such as cell density and cell shape, are calculated automatically and are available immediately, so they can be discussed with the ophthalmologist at the same visit, together with the rest of the examination.
What does a low endothelial cell count mean?
The number of endothelial cells naturally decreases with age. When it drops below a certain threshold, the cornea struggles to stay clear and may swell, especially after surgery. A low result does not necessarily rule out an operation, but it helps the surgeon adapt the technique and inform the patient properly.
Medically reviewed by: Dr. Vasileios Skouteris MD, FEBO