Keratoconus

Keratoconus is an eye condition in which the normally round cornea (the clear front layer of the eye) becomes thinner and begins to bulge out into a cone shape. This causes vision problems due to changes in the refraction of light passing through the deformed cornea.

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Epidemiology

The epidemiology of keratoconus studies the prevalence, causes, and consequences of this disease in different population groups around the world. Despite differences in research methodology and diagnostic criteria, some aspects of the epidemiology of keratoconus can be distinguished:

1. Prevalence: Keratoconus occurs worldwide, but its prevalence varies by geographic region and ethnicity. Estimates of prevalence range from about 1 in 2,000 people to 1 in 500.
2. Age of onset: The disease usually begins in late childhood or adolescence and continues to progress until the 30s or 40s.
3. Gender: Some studies suggest that men may be more likely to develop keratoconus, although other data indicate no significant difference between the sexes.
4. Ethnic and genetic factors: Keratoconus has a higher prevalence among certain ethnic groups, such as people of Middle Eastern, Asian, and South Asian descent. There is also a genetic predisposition, and cases of keratoconus are more common in first-degree relatives.
5. Associated factors: Chronic eye rubbing and exposure to ultraviolet radiation are considered risk factors, as well as the presence of allergic diseases such as atopic dermatitis and bronchial asthma.
6. Seasonality: Studies have shown that some patients with keratoconus may have seasonal exacerbations, which is associated with the level of ultraviolet radiation and allergies.

Epidemiological data are important for understanding keratoconus because they can help identify risks and develop strategies to prevent and treat the disease.

Causes keratoconus

The causes of keratoconus are not fully understood, but there are several theories and factors that may contribute to its occurrence and progression:

1. Genetic predisposition: Keratoconus tends to be inherited, and people with a family history of the condition are more likely to develop it. Some genetic studies have identified mutations in certain genes that may be associated with keratoconus.
2. Enzymatic abnormalities: Research suggests that people with keratoconus may have increased activity of collagen-breaking enzymes (enzymatic abnormalities) in the cornea, leading to thinning and weakening of the corneal tissue.
3. Oxidative stress: The cornea is susceptible to oxidative stress due to its high content of unsaturated lipids and exposure to ultraviolet radiation. Decreased antioxidant levels can lead to damage to collagen fibers and the development of keratoconus.
4. Mechanical damage: Constant, intense rubbing of the eyes can lead to mechanical damage to the cornea, which worsens its thinning and bulging.
5. Hormonal changes: It has been suggested that hormonal changes during puberty may play a role in the development or progression of keratoconus.
6. Connective tissue disorders: Keratoconus may be associated with other disorders including Marfan syndrome, Ehlers-Danlos syndrome, and osteogenesis imperfecta.
7. Allergic diseases: A link has been established between allergic diseases and keratoconus. Chronic allergic reactions can lead to increased eye rubbing and inflammatory reactions, which can worsen the disease.
8. Inflammation: Some studies have suggested that chronic inflammation may play a role in the pathogenesis of keratoconus.

However, none of these factors alone is sufficient to cause keratoconus, and the disease is thought to be the result of the interaction of many conditions and factors. A comprehensive approach is usually required to understand and treat the condition.

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Risk factors

Risk factors for keratoconus are not fully understood, but research has identified several potential causes and conditions that may increase the likelihood of developing the condition:

1. Genetic predisposition:

• The presence of keratoconus in close relatives increases the risk of developing the disease.

2. Mechanical impact:

• Frequent eye fiddling or harsh eye rubbing may contribute to the development of keratoconus because these actions can cause microdamage to the corneal tissue.

3. Chronic allergic diseases:

• Allergic conditions such as atopic dermatitis or allergic conjunctivitis may be associated with keratoconus, especially due to rubbing of the eyes during allergic attacks.

4. Connective tissue syndromes:

• Some systemic connective tissue diseases, such as Marfan syndrome and Ehlers-Danlos syndrome, may be associated with keratoconus.

5. Endocrine factors:

• Hormonal changes during puberty may play a role in the development of keratoconus.

6. Inflammatory processes:

• Damage to corneal cells due to inflammation may also be a risk factor.

7. UV radiation:

• Long-term exposure to ultraviolet radiation may increase the risk of developing keratoconus, although the specific link is not fully established.

8. Ethnicity:

• Studies have shown that keratoconus may be more common in certain ethnic groups, such as people of Asian and Arab descent.

Understanding the risk factors helps in preventive measures and early diagnosis of keratoconus, which is important for effective management of the disease and preventing its progression.

Pathogenesis

Keratoconus disease begins at the age of 10-18 years, and sometimes earlier. Irregular astigmatism appears, which cannot be corrected. The patient often changes glasses because the degree and axis of astigmatism change. Changes in the axis of astigmatism can sometimes be noted even when changing the position of the head.

The process is usually bilateral, but does not always develop in the same way and simultaneously in both eyes. Observation of identical twins with keratoconus showed that they developed symptoms of the disease at the same age and recorded the same refraction data of the eye, cornea, as well as the degree and axis of astigmatism. Several years later, keratoconus also developed in both twins' paired eyes at the same time.

The weakness of the elastic framework of the cornea is observed mainly in the central section. The apex of the conical cornea is always lowered downwards and does not correspond to the projection of the pupil. This is associated with the appearance of irregular astigmatism. Upon careful examination in the light of a slit lamp, one can see barely noticeable thin stripes almost parallel to each other, localized in the central section of Descemet's membrane - cracks in the elastic membrane. The appearance of this symptom can be considered the first reliable sign of keratoconus. The thickness of the cornea in the center gradually decreases, the depth of the anterior chamber increases, the optical power reaches 56-62 diopters. When examining using the keratotopography method, characteristic symptoms of changes in the optical properties of the cornea are revealed - a downward shift of the optical center, the presence of irregular astigmatism, large differences in the refractive power between the opposite sections of the cornea.

When large cracks appear in Descemet's membrane, a condition called acute keratoconus suddenly occurs. The corneal stroma is saturated with intraocular fluid, becomes cloudy, and only the most peripheral sections remain transparent. In the acute stage of keratoconus, the central section of the cornea is significantly thickened; sometimes, during biomicroscopy, cracks and cavities filled with fluid can be seen. Visual acuity decreases sharply. Edema in the center of the cornea gradually resolves, sometimes even without treatment. This process always ends with the formation of a more or less coarse scar in the central section and thinning of the cornea.

Symptoms keratoconus

Symptoms of keratoconus can range from mild to severe and usually develop in adolescence or early adulthood.

The main symptoms of keratoconus include:

1. Change in refraction:

• Mild to moderate vision loss that cannot always be corrected with standard glasses.
• Progressive astigmatism, in which vision becomes distorted or blurred.

2. Decreased visual acuity:

• Difficulty focusing, especially when reading small print or in low light conditions.
• A gradual deterioration in vision that can change rapidly.

3. Photophobia and increased sensitivity to light:

• Unpleasant sensations from bright light or glare.
• Unpleasant sensations when looking at light sources, especially at night.

4. Polyopia:

• Observation of multiple images of an object (multiple reflections).

5. Visual instability:

• Inconsistent vision that may change throughout the day or from one day to the next.

6. Fleischer striae:

• Fine vertical lines that may form in the structure of the cornea and are only visible during certain types of medical examinations.

7. Corneal scarring:

• In later stages, scars may appear on the cornea, which further distort vision.

8. Difficulties with using contact lenses:

• Problems with the selection and wearing of contact lenses due to the non-standard shape of the cornea.

9. Pain in the eyes:

• In rare cases, especially with rapid progression (hydrops), pain may occur due to stretching of the cornea and intracorneal fluid leakage.

For an accurate diagnosis and assessment of the extent of the disease, an examination by an ophthalmologist is required, including computer topography of the cornea, which allows you to assess its shape and thickness, and other specialized tests.

Stages

1. Initial stage:

• Slight thinning and bulging of the cornea.
• Mild astigmatism and myopia.
• Vision can be corrected with glasses or soft contact lenses.

2. Progressive keratoconus:

• Astigmatism and myopia increase.
• Distortions and blurred vision appear, which are difficult to correct with glasses.
• Rigid gas permeable contact lenses may be needed to improve vision.

3. Late stage:

• Severe thinning of the cornea.
• Pronounced irregular astigmatism.
• Often, surgical intervention, such as corneal transplantation or implantation of intracorneal rings, is required.

4. Acute keratoconus (hydrops):

• A sudden deterioration in vision due to a sudden accumulation of fluid within the cornea.
• Scarring and permanent vision loss may occur.

Forms

1. Nipple keratoconus:

   • The corneal cone is sharper and smaller in size.
   • Usually located in the center of the cornea.

2. Oval keratoconus:

   • The cone is wider and oval.
   • Often displaced downward from the center of the cornea.

3. Globe-keratoconus:

   • The most severe form, in which most of the cornea is pulled forward.
   • It is rare and often requires surgical intervention.

In addition, a distinction is made between primitive and secondary keratoconus. Primitive keratoconus develops on its own, without obvious causes or systemic diseases. Secondary keratoconus may be associated with other eye conditions (such as chronic eyelid rubbing) or be the result of eye surgery.

Specialized diagnostic tools are used to evaluate and classify keratoconus, including corneal topography and pachymetry, which measure the shape and thickness of the cornea, respectively.

Complications and consequences

In cases where keratoconus is not treated or progresses, the following complications may develop:

1. Progressive vision loss: Without treatment, keratoconus can lead to significant and ongoing vision loss.
2. Acute corneal hydrops: A sudden intracorneal fluid buildup that causes severe vision loss and pain. This condition may cause scarring and require surgery.
3. Scarring: Gradual thinning of the cornea can lead to scarring, which can further impair vision.
4. Contact lens intolerance: Due to corneal deformation, standard contact lenses may become uncomfortable or even impossible to wear.
5. Frequent change of glasses or contact lenses: Due to the progression of the disease, frequent correction of visual aids may be required.
6. Night vision problems: Patients may experience increased sensitivity to light, glare and halos around lights, making it difficult to drive at night.
7. Keratoglobus: An extreme form of keratoconus in which the cornea becomes spherically protruding.
8. Corneal transplant: In severe cases, a corneal transplant may be required, which has its own risks and potential complications, including rejection of the donor tissue.

It is important to note that with modern treatments, including corneal cross-linking, ICC, and custom-fitted contact lenses, many complications of keratoconus can be prevented or their progression significantly slowed.

Diagnostics keratoconus

Diagnosis of keratoconus includes a number of specialized ophthalmological studies:

1. History: The doctor will take a complete medical history, including family history, and will ask about symptoms such as blurred vision and astigmatism that is not corrected by conventional means.
2. Visometry: A standard test of visual acuity that can show a decrease in a person's ability to see detail.
3. Refractometry: Determining the refraction of the eye to determine the degree of myopia and astigmatism.
4. Corneal topography: A computerized test that maps the surface of the cornea and can show changes in its curvature typical of keratoconus.
5. Pachymetry: A measurement of corneal thickness, which can be useful because the cornea is often thinner in patients with keratoconus.
6. Optical coherence tomography (OCT): High-tech imaging that can produce detailed sections of the cornea and help determine its shape and thickness.
7. Corneal confocal microscopy: This test can examine in detail microscopic changes in the structure of the cornea.
8. Ophthalmoscopy: A high-resolution examination of the back of the eye, including the cornea, to detect any abnormalities.
9. Tear film and ocular surface examination: To detect any signs of dry eye or other conditions that may accompany keratoconus.

Early diagnosis of keratoconus is important to initiate treatment and prevent further progression of the disease. Depending on the stage of keratoconus and the degree of visual impairment, treatment may include glasses, contact lenses (soft or rigid gas permeable), collagen cross-linking (CXL), intrastromal corneal rings (ICR), or in extreme cases, keratoplasty (corneal transplant).

Differential diagnosis

Differential diagnosis of keratoconus is important to rule out other diseases and conditions that may mimic its clinical presentation or symptoms. Here are some conditions to consider when differentiating keratoconus:

1. Keratoglobus is a condition in which the cornea is thin and convex, but, unlike keratoconus, the convexity is distributed more evenly.
2. Pellicide marginal degeneration - characterized by a thin band in the lower peripheral cornea, while the central cornea usually remains normal.
3. Post-LASIK ectasia is a condition that can develop after LASIK surgery and results in thinning and bulging of the cornea, similar to keratoconus.
4. Keratitis is an inflammatory disease of the cornea that can lead to changes in its shape and thinning.
5. Corneal dystrophies are hereditary diseases that affect the structure and transparency of the cornea.
6. Steroid induced ectasia - may occur in patients using steroid eye drops for long periods of time.
7. Contact lens-induced warpage is a corneal deformity that can occur as a result of long-term wear of rigid contact lenses. Contact lens-induced warpage is a change in the shape of the cornea that can occur as a result of long-term wear of contact lenses, especially rigid gas permeable (RGP) lenses.
8. Down syndrome - This syndrome may be associated with keratoconus, but can also cause corneal changes that may be mistaken for keratoconus.
9. Trichiasis - Ingrown eyelashes can cause constant friction against the cornea, which can lead to permanent trauma and changes to the cornea.

Diagnostic methods that help in differential diagnosis include corneal topography, pentacam, corneal optical coherence tomography (OCT) and ocular biomicroscopy. These methods allow visualization of the shape, thickness and structure of the cornea, which is critical for accurate diagnosis and exclusion of other possible pathologies.

Treatment keratoconus

Treatment of keratoconus depends on the stage and severity of the disease. Here are some modern methods of treating keratoconus:

1. Glasses or soft contact lenses:

In the early stages, when changes in corneal curvature are small, glasses or soft contact lenses can correct mild blurred vision and astigmatism.

2. Rigid gas permeable contact lenses:

As the disease progresses, rigid gas permeable contact lenses may be a better choice for vision correction because they maintain their shape on the eye and may provide clearer vision than soft lenses.

3. Hybrid contact lenses:

These lenses combine a hard center with a soft rim, which can provide the comfort of soft lenses with the clarity of vision of hard lenses.

4. Scleral and semi-scleral lenses:

These are large contact lenses that cover the entire cornea and part of the sclera (white of the eye). They can be effective in correcting vision in more severe forms of keratoconus.

5. Corneal crosslinking (CXL):

This corneal strengthening method involves the use of vitamin B2 (riboflavin) and UV light to create additional chemical bonds in the cornea's structure. The procedure can prevent further thinning and bulging of the cornea.

6. Intrastromal corneal rings (ICR):

These thin, translucent rings are inserted into the cornea to improve its shape and vision. They may be useful in certain stages of keratoconus.

7. Topography-guided photorefractive keratectomy (Topo-PRK):

This laser vision correction method can be used to slightly smooth the surface of the cornea and correct minor refractive errors.

8. Corneal transplant:

In more severe cases, when vision can no longer be corrected with contact lenses, a corneal transplant may be considered. This can be either a total corneal replacement (penetrating keratoplasty) or a partial one (lamellar keratoplasty).

9. Personalized options:

The development of customized lenses and surgical procedures continues to meet the unique needs of each keratoconus patient.

10. Mini-aspheric keratoplasty:

This is a new method in which special implants are implanted into the cornea, changing its curvature to improve vision.

A radical method of treating keratoconus is penetrating subtotal keratoplasty with excision of the entire altered cornea. Most patients (up to 95-98%) have high visual acuity after surgery - from 0.6 to 1.0. The high percentage of transparent engraftment of the corneal transplant is explained by a number of factors. With keratoconus, there is no inflammation in the cornea, no vessels, and, as a rule, there is no other eye pathology.

The indication for surgery is determined not by the degree of corneal stretching, but by the state of the eye function.

11. Collagen cross-linking with transepithelial approach:

This is a modification of standard corneal crosslinking that does not require removal of the corneal epithelium, which reduces recovery time and reduces the risk of complications.

12. Automated deep anterior lamellar keratoplasty (DALK):

This technique is an alternative to full-thickness corneal transplantation, in which only the anterior cornea is removed, leaving the posterior layer and endothelium intact. This reduces the risk of graft rejection.

13. Femtosecond laser in keratoconus surgery:

Femtosecond lasers can be used to precisely create tunnels in the cornea for implantation of intrastromal corneal rings and to refine corneal layers in DALK.

14. Personalized phototherapeutic keratectomy (PTK):

This laser technique can be used to remove irregularities and abnormalities on the front surface of the cornea caused by keratoconus.

15. Biomechanical strengthening of the cornea:

New approaches to enhance corneal biomechanics are being explored, including new types of cross-linking agents and modifications in procedural technique.

16. Proteinase inhibitors:

Research suggests that the corneas of keratoconus patients have increased proteinase activity, which may contribute to corneal thinning. Inhibitors of these enzymes may be a potential target for treatment.

17. Hormonal therapy:

Some studies suggest that hormonal factors may play a role in the progression of keratoconus, opening up possibilities for hormonal therapy.

18. Combined methods:

Sometimes a combination of the above mentioned methods may give better results, such as using CXL in combination with intrastromal corneal ring implantation or photorefractive keratectomy to stabilize the cornea and correct vision.

The choice of treatment method depends on many factors, including the stage of the disease, the degree of visual impairment, and the patient's lifestyle.

19. Gene therapy:

Although still in the research stage, gene therapy has the potential to treat keratoconus by correcting genetic defects that may contribute to the development and progression of the disease.

20. Antioxidant therapy:

Since oxidative stress is considered one of the pathogenetic factors of keratoconus, the use of antioxidants can help protect corneal collagen fibers from damage.

21. Regenerative medicine and tissue engineering:

Innovations in the fields of regenerative medicine and tissue engineering are opening up new possibilities for creating biocompatible corneal implants that can be used to replace damaged corneal tissue.

22. Adaptive optics:

Adaptive optics systems can improve vision quality in patients with keratoconus by compensating for optical distortions caused by an uneven cornea.

23. Behavioural therapy and visual rehabilitation:

In addition to medical treatment, patients with keratoconus may be recommended special eye training and visual rehabilitation to make the most of their remaining vision.

24. Supporting technologies:

The development and use of various assistive technologies, including text magnification software and audio books, may help people with keratoconus better adapt to their vision limitations.

25. Psychological support and social adaptation:

The importance of psychological support and assistance in social adaptation for patients with keratoconus should not be underestimated, as the disease can significantly affect the quality of life.

26. Investigational drugs and clinical trials:

New drugs and treatments are regularly studied in clinical trials. Participation in such studies can offer patients access to new treatments that are not yet available to the general public.

Keratoconus treatment is an evolving field, and new, more effective treatments may become available in the future. It is important to consult with your ophthalmologist regularly to monitor your condition and adjust your treatment plan to the latest scientific advances and your individual needs.

Prevention

Prevention of keratoconus in the traditional sense, as prevention of the disease itself, is not yet possible, because the exact causes of the development of keratoconus have not been fully studied and it is assumed that the disease has a multifactorial nature, including genetic predisposition.

However, there are several general recommendations that can help slow down the progression of the disease or prevent it from getting worse:

Recommendations for preventing worsening of keratoconus:

1. Avoiding eye injury: Avoid situations that may result in eye injury, as damage may accelerate the progression of the disease.
2. Allergy Control: If you have any allergies, you should carefully control them to avoid excessive eye rubbing.
3. Eye Care: Avoid vigorous or frequent eye rubbing, as this may contribute to the progression of keratoconus.
4. Regular medical monitoring: Early management of keratoconus under the supervision of an ophthalmologist can help optimize vision and slow progression.
5. Use UV protection: Wear sunglasses with UV protection, especially if you spend a lot of time in the sun.
6. Balanced Diet: Maintain a healthy lifestyle and a balanced diet rich in antioxidants and vitamins that are important for eye health.
7. Avoiding bad habits: Smoking can negatively affect eye health and potentially worsen keratoconus symptoms.
8. Early treatment: Modern treatments such as corneal crosslinking can prevent further deterioration of the condition in some patients.

Preventive studies:

Currently, research into keratoconus prevention focuses on early detection and treatment. Regular eye exams, especially in adolescents and young adults with a family history of keratoconus, can help in early detection and prompt treatment, which in turn can prevent or slow its progression.

Forecast

The prognosis for keratoconus depends on several factors, including the extent and rate of progression of the disease, the age at diagnosis, and the overall health of the patient's eyes.

Key aspects of prognosis in keratoconus:

1. Stage at diagnosis: Early detection and treatment can help slow the progression of the disease.
2. Disease progression: In some people, keratoconus progresses rapidly, while in others it may remain relatively stable for many years.
3. Treatment options: Newer treatment options such as sclerotic contact lenses, crosslinking (a stabilizing procedure that links collagen fibers in the cornea), and sometimes surgery (such as keratoplasty) can improve vision and quality of life.
4. Comorbidities: In patients with allergic diseases such as atopic dermatitis or asthma, keratoconus may progress more rapidly.
5. Genetic predisposition: Sometimes keratoconus is hereditary, and family history can influence the prognosis.

Long term forecast:

• In most patients: The disease may progress over 10 to 20 years, after which its progression slows or stops.
• In some patients: Corneal transplantation (keratoplasty) may be needed, especially if scarring develops or significant visual impairment occurs that cannot be corrected by other methods.
• Preserving vision: Most patients with keratoconus maintain functional vision throughout their lives with the help of glasses, contact lenses, or surgery.

It is important to remember:

Keratoconus is a condition that requires ongoing monitoring and management. Following the recommendations of an eye doctor and visiting specialists regularly to monitor the condition can help patients lead active and fulfilling lives.

Keratoconus and the army

The question of whether people with keratoconus are called up for military service depends on the severity of the disease and the legislation of a particular country. In many countries, such as Russia, the presence of keratoconus can be grounds for a deferment from military service or recognition of unfitness for military service due to health reasons.

If keratoconus does not affect vision and does not require correction, the conscript is more likely to be considered fit for service. However, in cases where the disease causes a significant decrease in vision and cannot be corrected with regular glasses or contact lenses, the conscript may be exempted from service.

As a rule, to determine suitability for military service, a conscript undergoes a medical examination, during which the state of his vision is assessed. Important indicators are visual acuity, refraction stability, the presence of dystrophic changes in the cornea, as well as the possibility of vision correction.

Each case is considered individually and the final decision on fitness for service is made on the basis of a medical opinion. If keratoconus progresses or is accompanied by other ophthalmological problems, treatment or surgery may be recommended.

It is worth noting that military personnel who develop keratoconus during their service may be transferred to other work that does not involve eye strain, or dismissed early for medical reasons.

For accurate information and recommendations, please contact the appropriate military medical authorities or qualified ophthalmologists.

Disability in keratoconus

Whether you qualify for disability status for keratoconus depends on the degree of visual impairment and how it affects your daily life and ability to work. The criteria for qualifying for disability can vary significantly from country to country, but the main factors are usually:

1. Visual acuity: If keratoconus results in a significant reduction in visual acuity even after correction, and this reduction cannot be restored either by surgery or with contact lenses or glasses, disability may be considered.
2. Disability: If visual function is so reduced that a person cannot perform normal work or requires special accommodations for work or education, this may also be grounds for recognition of disability.
3. Stability of the condition: If the condition is progressive and unstable, making it impossible or very difficult to find permanent employment, this may also be grounds for obtaining disability.
4. Need for constant external care: If a person requires constant assistance or care due to decreased vision, this may also be grounds for receiving disability.

In the case of keratoconus, patients are usually prescribed special vision correction with rigid gas permeable contact lenses, which can significantly improve vision. Surgical treatments such as intrastromal corneal ring implantation, corneal transplantation, or crosslinking procedures can also slow the progression of the disease or improve vision.

To assess the condition and the possibility of receiving disability, the patient should undergo a medical examination by an ophthalmologist, who will be able to give an opinion on the severity of the disease and its impact on the quality of life.

References

"Incidence and Severity of Keratoconus in Asir Province, Saudi Arabia"

• Year: 2005
• Authors: Y. Al-Rajhi, A. Wagoner, et al.
• Journal: British Journal of Ophthalmology

"Prevalence of keratoconus in a community sample of young adults in Israel"

• Year: 2004
• Authors: E. Shneor, R. Millodot, et al.
• Journal: International Journal of Keratoconus and Ectatic Corneal Diseases

"Update on the molecular genetics of keratoconus"

• Year: 2013
• Authors: F. Karinia, C. J. McGhee, et al.
• Journal: Experimental Eye Research

"The genetics of keratoconus: a review"

• Year: 2007
• Authors: AJ Rabinowitz
• Journal: Survey of Ophthalmology

"A Comprehensive Study on the Occurrence and Profile of Keratoconus in a Sample of Egyptian Population"

• Year: 2011
• Authors: A.H. Hafez, M. El Omda, et al.
• Magazine: Cornea

These studies represent only a small part of the extensive literature on keratoconus, and scientific databases and resources should be consulted for complete information.