Transient colour vision disturbance and increased light sensitivity

What acts on it

1. Early in development it was noted that besides its major inhibitory effect on the intended target, the vascular-associated PDE5, the drug also exerts a lesser but definite inhibitory effect on the closely related PDE6 located in the retina, and for this reason preclinical evaluation included electroretinography plus postmortem histology and an extended eye examination was incorporated into clinical protocols, with data on the incidence, duration and type of colour vision defects observed at different doses.

   Structural homology between phosphodiesterase type 5 and rod phosphodiesterase 6 → Transient colour vision disturbance and increased light sensitivity source_derived_draftungraded
   Experimental context and source evidence

   evidence_span

   {"source_cache": "artifacts/sildenafil-research/10703120.abstract.txt", "locator": "Indexed abstract; zero-based, end-exclusive Unicode character offsets", "file_sha256": "fc004205f7e036cf52e469c5f9941c4f69d216a012ccd8a588052b950c1077e6", "start_char": 0, "end_char": 2146, "text_sha256": "fc004205f7e036cf52e469c5f9941c4f69d216a012ccd8a588052b950c1077e6"}

   experimental_model

   Review of how the ocular safety profile was established from preclinical work through to post-marketing surveillance

   exposure

   Electroretinography and histology in preclinical evaluation, with extended eye examination in clinical protocols and registry surveillance

   limitations

   A methodological review of how the signal was tracked rather than a new measurement. It is useful because it records that the retinal effect was predicted before it was looked for.

   nutrient_topic

   Sildenafil research collection; topical membership is not evidence of a direct clinical effect, and the drug is recorded separately from its N-desmethyl metabolite and its target enzyme from the homologous retinal PDE6. · Sildenafil

   organism

   Human and animal

   plain_language

   The visual effect was not a surprise; the homology between the two enzymes predicted it and the trials were designed to look for it.

   primary_references

   [sil-p10703120] Ocular safety of Viagra, (sildenafil citrate). (1999). https://pubmed.ncbi.nlm.nih.gov/10703120/

   tissue_or_cell_type

   Retina

   Sildenafil: the enzyme it occupies instead of the substrate, why it cannot start a signal it can only preserve, the organic nitrate interaction that follows from that, the homologous retinal enzyme ten-fold away, and the pulmonary circulation where the same mechanism became a second indication (2026-09-22) · lines 496–507

   AI-assisted literature curation; primary study URLs and scope retained in the document and extraction. Not publisher full text. · supports · Review of how the ocular safety profile was established from preclinical work through to post-marketing surveillance · source_derived_draft · unverified_draft

   ### sil-the-off-target-was-predicted Early in development it was noted that besides its major inhibitory effect on the intended target, the vascular-associated PDE5, the drug also exerts a lesser but definite inhibitory effect on the closely related PDE6 located in the retina, and for this reason preclinical evaluation included electroretinography plus postmortem histology and an extended eye examination was incorporated into clinical protocols, with data on the incidence, duration and type of colour vision defects observed at different doses. Condition category: normal nutrient_topic: Sildenafil research collection; topical membership is not evidence of a direct clinical effect, and the drug is recorded separately from its N-desmethyl metabolite and its target enzyme from the homologous retinal PDE6. plain_language: The visual effect was not a surprise; the homology between the two enzymes predicted it and the trials were designed to look for it. organism: Human and animal tissue_or_cell_type: Retina experimental_model: Review of how the ocular safety profile was established from preclinical work through to post-marketing surveillance limitations: A methodological review of how the signal was tracked rather than a new measurement. It is useful because it records that the retinal effect was predicted before it was looked for. exposure: Electroretinography and histology in preclinical evaluation, with extended eye examination in clinical protocols and registry surveillance evidence_span: {"source_cache": "artifacts/sildenafil-research/10703120.abstract.txt", "locator": "Indexed abstract; zero-based, end-exclusive Unicode character offsets", "file_sha256": "fc004205f7e036cf52e469c5f9941c4f69d216a012ccd8a588052b950c1077e6", "start_char": 0, "end_char": 2146, "text_sha256": "fc004205f7e036cf52e469c5f9941c4f69d216a012ccd8a588052b950c1077e6"} [sil-p10703120] Ocular safety of Viagra, (sildenafil citrate). (1999). https://pubmed.ncbi.nlm.nih.gov/10703120/

   Complete structured claim and evidence

2. Sildenafil has a mild inhibitory effect on PDE6, which controls the level of cyclic guanosine monophosphate in the retina, and it may cause a perception of bluish haze or increased light sensitivity in some patients, with long-term retinal damage not reported although long-term electroretinographic studies have not been performed; the drug causes a mild lowering of blood pressure and is contraindicated in patients taking any form of nitrate medication.

   Sildenafil → Transient colour vision disturbance and increased light sensitivity source_derived_draftungraded
   Experimental context and source evidence

   evidence_span

   {"source_cache": "artifacts/sildenafil-research/10541153.abstract.txt", "locator": "Indexed abstract; zero-based, end-exclusive Unicode character offsets", "file_sha256": "8c5d3c6e9d606690e6cc997086ded515a4e9f785561a7fc58fdbfb75b3f0a79a", "start_char": 0, "end_char": 1024, "text_sha256": "8c5d3c6e9d606690e6cc997086ded515a4e9f785561a7fc58fdbfb75b3f0a79a"}

   experimental_model

   Review of the ophthalmic profile shortly after marketing approval

   exposure

   Reported visual effects at therapeutic doses

   limitations

   A short review written in the first year of marketing. It records explicitly that long-term electroretinographic studies had not been performed, which is the limitation that matters for the claim.

   nutrient_topic

   Sildenafil research collection; topical membership is not evidence of a direct clinical effect, and the drug is recorded separately from its N-desmethyl metabolite and its target enzyme from the homologous retinal PDE6. · Sildenafil

   organism

   Human

   plain_language

   The colour disturbance some people notice is the same drug reaching the retinal version of the enzyme.

   primary_references

   [sil-p10541153] Sildenafil (Viagra) and ophthalmology. (1999). https://pubmed.ncbi.nlm.nih.gov/10541153/ DOI: 10.1016/s0039-6257(99)00079-x

   tissue_or_cell_type

   Retina

   Sildenafil: the enzyme it occupies instead of the substrate, why it cannot start a signal it can only preserve, the organic nitrate interaction that follows from that, the homologous retinal enzyme ten-fold away, and the pulmonary circulation where the same mechanism became a second indication (2026-09-22) · lines 483–494

   AI-assisted literature curation; primary study URLs and scope retained in the document and extraction. Not publisher full text. · supports · Review of the ophthalmic profile shortly after marketing approval · source_derived_draft · unverified_draft

   ### sil-transient-visual-disturbance Sildenafil has a mild inhibitory effect on PDE6, which controls the level of cyclic guanosine monophosphate in the retina, and it may cause a perception of bluish haze or increased light sensitivity in some patients, with long-term retinal damage not reported although long-term electroretinographic studies have not been performed; the drug causes a mild lowering of blood pressure and is contraindicated in patients taking any form of nitrate medication. Condition category: normal nutrient_topic: Sildenafil research collection; topical membership is not evidence of a direct clinical effect, and the drug is recorded separately from its N-desmethyl metabolite and its target enzyme from the homologous retinal PDE6. plain_language: The colour disturbance some people notice is the same drug reaching the retinal version of the enzyme. organism: Human tissue_or_cell_type: Retina experimental_model: Review of the ophthalmic profile shortly after marketing approval limitations: A short review written in the first year of marketing. It records explicitly that long-term electroretinographic studies had not been performed, which is the limitation that matters for the claim. exposure: Reported visual effects at therapeutic doses evidence_span: {"source_cache": "artifacts/sildenafil-research/10541153.abstract.txt", "locator": "Indexed abstract; zero-based, end-exclusive Unicode character offsets", "file_sha256": "8c5d3c6e9d606690e6cc997086ded515a4e9f785561a7fc58fdbfb75b3f0a79a", "start_char": 0, "end_char": 1024, "text_sha256": "8c5d3c6e9d606690e6cc997086ded515a4e9f785561a7fc58fdbfb75b3f0a79a"} [sil-p10541153] Sildenafil (Viagra) and ophthalmology. (1999). https://pubmed.ncbi.nlm.nih.gov/10541153/ DOI: 10.1016/s0039-6257(99)00079-x

   Complete structured claim and evidence